FXUS63 KLOT 202309 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 609 PM CDT WED MAR 20 2013 .DISCUSSION... 609 PM CDT HAVE SENT OUT SOME UPDATED GRIDS AND NEW TEXT FORECAST TO BACK OFF ON POPS THIS EVENING AND JUST GO WITH SOME FLURRIES. ACARS SOUNDINGS FROM THIS AFTERNOON SHOW A MORE SHALLOWLY MIXED BOUNDARY LAYER THAN INDICATED IN MODEL FORECAST SOUNDINGS. IN ADDITION...BOUNDARY LAYER MOISTURE IS VERY LIMITED WITH SURFACE DEWPOINTS IN THE SINGLE DIGITS...RESULTING IN LFC'S AROUND 3800FT RESULTING IN CONVECTIVE CLOUD DEPTHS ONLY AROUND 1000FT BASED ON ACARS SOUNDINGS. WHILE IT IS COLD ENOUGH FOR ICE TO BE PRESENT IN THE CLOUDS...THE VERY SHALLOW DEPTH OF THE CONVECTION MEANS IT IS UNLIKELY THAT MORE THAN FLURRIES WILL FALL. POLL OF OUR OFFICE FACEBOOK FANS REVEALS A SMATTERING OF LIGHT FLURRY REPORTS ACROSS THE METRO AREA AND HAVE EXPANDED THE FLURRY MENTION A BIT FARTHER SOUTH IN THE GRIDS BASED ON A FACEBOOK REPORT OF FLURRIES AS FAR SOUTH AS MANTENO. SHORTWAVE RESPONSIBLE FOR THESE FLURRIES STILL LOOKS LIKELY TO SWING BY EARLY THIS EVENING RESULTING IN A RAMPING DOWN OF FLURRY THREAT LATER THIS EVENING. ONE EXCEPTION MAY BE NORTHEAST PORTER COUNTY WHERE SHORT FETCH OVER LAKE MICHIGAN COULD BE SUFFICIENT TO MAINTAIN FLURRIES AND POSSIBLY EVEN SOME LIGHT SNOW SHOWERS THOUGH THE BETTER CHANCES OF ACCUMULATING SNOW LOOK TO REMAIN EAST OF OUR CWA. IZZI && .PREV DISCUSSION... 300 PM CDT MAIN FORECAST CONCERNS CENTER AROUND POTENTIALLY SIGNIFICANT LATE SEASON STORM TO IMPACT THE REGION LATE IN THE WEEKEND. TODAY AND TONIGHT... AREA OF HIGH PRESSURE SPANS THE NORTHERN AND CENTRAL PLAINS THIS AFTERNOON WITH A MODERATE NORTHWESTERLY GRADIENT IN PLACE ACROSS THE GREAT LAKES REGION. COLD ADVECTION HAS ALLOWED H85 TEMPERATURES TO FALL FROM AROUND -14C EARLY THIS MORNING TO AROUND -18C THIS AFTERNOON PER LOCAL AMDAR SOUNDINGS. NAM/GFS SOUNDINGS WHICH HAVE INITIALIZED WELL SHOW ADDITIONAL COOLING ALOFT OVER THE NEXT FEW HOURS AS A BROAD H85 TROUGH BEHIND UPPER LOW OVER EASTERN GREAT LAKES PUSHES SOUTH ACROSS LAKE MICHIGAN. THIS SHOULD ALLOW THE ALREADY EXPANDING COLD AIR CU DECK TO CONTINUE TO DEEPEN WITH SCATTERED SNOW SHOWERS DEVELOPING. LOCALIZED ACCUMULATIONS OF A FEW TENTHS POSSIBLE BUT OTHERWISE DO NOT ANTICIPATE SNOW TO AMOUNT TO MUCH MORE THAN A LIGHT DUSTING ACROSS THE AREA. HIGH PRESSURE WEAKENS SLIGHTLY AS IT SHIFTS SLOWLY EAST TONIGHT...BUT A MODEST GRADIENT IS EXPECTED TO PERSIST OVERNIGHT KEEPING NORTHWEST WINDS PROPPED UP. SKIES SHOULD BEGIN TO CLEAR AFTER SUNSET THIS EVENING AND TEMPERATURES FALLING INTO THE SINGLE DIGITS IN AREAS WITH SNOW...LOW TO MID TEENS ELSEWHERE WILL COMBINE WITH THE BREEZY CONDITIONS LEADING TO WIND CHILL VALUES BELOW ZERO WEST OF THE FOX RIVER VALLEY...AND LOW SINGLE DIGITS ELSEWHERE. THURSDAY THROUGH SATURDAY... NO SIGNIFICANT WEATHER EXPECTED THROUGH THIS PERIOD. UPPER LOW OVER THE EASTERN LAKES TODAY WILL MOVE NORTHEAST INTO NEW ENGLAND WHILE H5 RIDGING BUILDS INTO THE MIDWEST. TEMPERATURES SHOULD GRADUALLY MODERATE THROUGH THE PERIOD. SATURDAY...WINDS BEGIN TO TURN SOUTHERLY AS THE SURFACE RIDGE AXIS FINALLY PUSHES ACROSS THE AREA. MEANWHILE...LOW PRESSURE BEGINS TO TAKE SHAPE OVER THE SOUTHERN PLAINS. SUNDAY THROUGH MONDAY... NO BIG CHANGES IN THE LATEST MODEL SUITE...THERE IS STILL CONSIDERABLE SPREAD AMONGST SOLUTIONS PARTICULARLY WITH RESPECT TIMING OF THE LOW THAT IS TO IMPACT THE REGION LATE IN THE WEEKEND OR EARLY NEXT WEEK. THERE IS GENERAL CONSENSUS IN A TRACK THAT TAKES THE LOW FROM THE LOWER MISSISSIPPI VALLEY INTO THE UPPER OHIO VALLEY. OPERATIONAL GFS/ECMWF/GEM ALL SHARE A SIMILAR TRACK AS DO MANY MEMBERS OF THE GEFS. GFS/GEFS IS ABOUT 12 HOURS FASTER THAN THE ECMWF AND 18 HOURS FASTER THAN THE GEM THOUGH. SHOULD THIS TRACK PAN OUT...THEN NORTHERN ILLINOIS WOULD LIKELY BE NORTH OF THE AXIS OF HEAVIEST SNOW...THOUGH PORTIONS OF EAST CENTRAL ILLINOIS MAY SEE DECENT SNOW ACCUMULATIONS. CONTINUE TO FOCUS POPS SOUTH OF THE I-80 CORRIDOR...BUT WITH THE UPPER WAVE STILL IN THE NORTH PACIFIC...EXPECT MODELS TO CONTINUE TO MAKE ADJUSTMENTS. THERMALLY...THIS SYSTEM LOOKS INTERESTING OVER PORTIONS OF THE CWA WITH POTENTIALLY DEEP DENDRITIC LAYER LEADING TO EFFICIENT SNOW PRODUCTION. INITIALLY THIS SYSTEM HAS OPEN ACCESS TO GULF MOISTURE BUT A SECOND LOW FORMING OVER THE SOUTHEAST WILL EVENTUALLY CUT OFF MOISTURE TRANSPORT AS THE SYSTEM CONTINUES TO EVOLVE. STILL THE GFS SPITS OVER AN INCH OF QPF OVER OUR SOUTHEASTERN COUNTIES. WHILE THE EUROPEAN HAS SIMILAR QPF AMOUNTS...IT FOCUSES IT MUCH FARTHER DOWNSTATE. TUESDAY THROUGH WEDNESDAY... BACK INTO NORTHWEST FLOW DURING THIS PERIOD LEADING TO LOW CONFIDENCE FORECAST AS MODELS ALWAYS STRUGGLE TO HANDLE WEAK SHORTWAVES IN THIS REGIME. REGARDLESS...STILL EXPECT THE JETSTREAM TO BE WELL TO OUR SOUTH WITH US ENTRENCHED IN THE UNSEASONABLY COOL AIRMASS. TEMPERATURES WILL RUN BELOW NORMAL WITH LOW CHANCE POPS THROUGH THE PERIOD...MAINLY DURING THE DAYTIME HOURS AS EXPECT THE DIURNALLY DRIVEN LOW LEVEL LAPSE RATES TO PLAY A ROLE IN THE BETTER CHANCES FOR PRECIP. BMD && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 22Z... * GUSTY WESTERLY WINDS SLOWLY DIMINISHING THIS EVENING INTO THE EARLY MORNING HOURS. * ISOLATED/SCATTERED SNOW SHOWERS POSSIBLE THROUGH EARLY/MID EVENING WITH ASSOCIATED BRIEF MVFR CIGS/VIS. CMS //DISCUSSION...UPDATED 22Z... CONFIDENCE CONTINUES TO DECREASE REGARDING POTENTIAL SNOW SHOWERS LATE THIS AFTERNOON INTO EARLY/MID EVENING. EVEN IF MORE MODERATE TO HEAVIER SNOW SHOWERS DO DEVELOP...THEIR DURATION AT ANY ONE POINT WILL PROBABLY END UP BEING FAIRLY SHORT AND WHILE THEY COULD STILL PRODUCE BRIEF PERIODS OF MVFR CIGS/VIS...OPTED TO REMOVE THE TEMPOS AND MAINTAIN PREVAILING LIGHT SNOW SHOWERS FOR NOW. CMS PREVIOUS DISCUSSION FROM 20Z... THERE STILL APPEARS TO BE A CHANCE OF SOME SCT SNOW SHOWERS LATE THIS AFTERNOON AT THE TERMINALS. A DECK OF STRATO CU CONTINUES TO DEVELOP ACROSS THE REGION AS COLDER AIR CONTINUES TO STREAM IN ACROSS THE AREA LEADING A DEEPER UNSTABLE LAYER. SURFACE ANALYSIS INDICATES A WEAK LOW LEVEL AREA OF CONVERGENCE ACROSS SOUTHERN WISCONSIN EARLY THIS AFTERNOON. THIS CONVERGENT AREA IS EXPECTED TO SHIFT SOUTHWARD ACROSS NORTHERN ILLINOIS OVER THE NEXT FEW HOURS AS A MID LEVEL DISTURBANCE DROPS SOUTH ACROSS WISCONSIN. THEREFORE...SOME WIDELY SCT SNOW SHOWERS ARE STILL EXPECTED. IT APPEARS THE BETTER CHANCES MAY BE ACROSS THE EASTERN TERMINALS AND KGYY INTO THIS EVENING. KJB PREVIOUS DISCUSSION FROM 18Z... A LARGE AREA OF LOW PRESSURE ACROSS SOUTHERN QUEBEC...AND A RIDGE OF HIGH PRESSURE ACROSS THE PLAINS ARE COMBINING TO PRODUCE GUSTY WEST-NORTHWESTERLY WINDS ACROSS THE TERMINALS AGAIN TODAY. WINDS ARE EXPECTED TO GUST UP AROUND 25 KT AT TIMES THROUGH THE EARLY EVENING HOURS BEFORE ABATING. THE ONLY OTHER WEATHER CONCERN TODAY IS THE CHANCES FOR SOME SNOW SHOWERS LATER THIS AFTERNOON AND EARLY THIS EVENING. THE PRESENCE OF AN UNSEASONABLY COLD AIRMASS IS RESULTING IN SOME STEEP LOW LEVEL LAPSE RATES ACROSS THE AREA...AND AS A WEAK MID LEVEL DISTURBANCE APPROACHES THE AREA LATER TODAY THIS WILL LIKELY SPARK OFF SOME STRATOCU AND SCATTERED SNOW SHOWERS. IT APPEARS THAT THERE COULD BE SOME LOWER VISIBILITY IN THE SNOW SHOWERS. HOWEVER...DUE TO THE SHOWERY NATURE OF THE PRECIP...I CONFINED THE LOWER VIS TO A TEMPO GROUP. ANY SNOW SHOWER ACTIVITY SHOULD END EARLY THIS EVENING...WITH QUIET VFR CONDITIONS EXPECTED INTO THURSDAY. KJB //ORD AND MDW CONFIDENCE...UPDATED 22Z... * HIGH CONFIDENCE GUSTY WESTERLY WINDS WILL DIMINISH LATER THIS EVENING AND OVERNIGHT...MEDIUM CONFIDENCE ON TIMING. * LOW CONFIDENCE REGARDING SNOW SHOWERS INTO THIS EVENING... INCLUDING LOW CONFIDENCE WITH ASSOCIATED VIS/CIGS. CMS //OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z... THURSDAY NIGHT...VFR. FRIDAY...VFR. SATURDAY...SLIGHT CHANCE OF LIGHT SNOW LATE WITH POSSIBLE MVFR. SUNDAY...CHANCE OF RAIN OR SNOW WITH POSSIBLE MVFR. MONDAY...CHANCE OF RAIN OR SNOW WITH POSSIBLE MVFR. TUESDAY...SLIGHT CHANCE OF RAIN OR SNOW WITH POSSIBLE MVFR. RODRIGUEZ && .MARINE... 201 PM CDT A STUBBORN AREA OF LOW PRESSURE CENTERED OVER WESTCENTRAL QUEBEC WILL DRIFT EAST...MEANWHILE A STRONG RIDGE OF HIGH PRESSURE CENTERED OVER THE CENTRAL PLAINS SLIDES EAST. BETWEEN THE TWO SYSTEMS A STRONG GRADIENT HAS CONTINUED...ALLOWING GUSTS UP TO 30 KT TO LINGER INTO THIS AFTERNOON. AS THE LOW DRIFTS FURTHER NORTHEAST AWAY FROM LAKE MICHIGAN THURSDAY MORNING...NORTHWEST WINDS WILL SLOWLY DIMINISH TO 15 TO 25 KT THURSDAY. HIGH PRESSURE WILL STRETCH AND BECOME ORIENTED FROM NORTH TO SOUTH ACROSS CENTRAL CANADA SOUTH THROUGH THE PLAINS INTO THE TENNESSEE VALLEY...HOWEVER THIS APPEARS TO KEEP LAKE MICHIGAN IN A PROLONGED NORTHWEST FLOW SETUP. SPEEDS WILL GENERALLY REMAIN BREEZY AT TIMES OR IN THE 15 TO 25 KT RANGE...HOWEVER THE GRADIENT DOES APPEAR TO RELAX FURTHER FRIDAY INTO SATURDAY. THEN THE FOCUS IS ON A SOUTHERN PLAINS/TEXAS LOW PRESSURE SYSTEM THAT IS EXPECTED TO SLIDE NORTHEAST SUNDAY MORNING TOWARD THE OHIO VALLEY. THE GRADIENT IS EXPECTED TO INCREASE ALONG THE NORTHERN PERIPHERY OF THIS LOW PRESSURE...ALLOWING WIND SPEEDS FROM THE NORTHEAST/EAST TO INCREASE SUNDAY FOR THE CENTRAL/SOUTHERN PORTIONS OF LAKE MICHIGAN. AT THIS TIME IT APPEARS THE GRADIENT WILL BE UNDER GALES. THE LATEST GUIDANCE HAS CONTINUED TO KEEP A SLIGHTLY FURTHER SOUTH TREND IN THIS SYSTEM...WHICH COULD PULL THE STRONGEST WINDS FURTHER SOUTH/SOUTHEAST OF LAKE MICHIGAN. CONFIDENCE...MEDIUM/HIGH. BEACHLER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 PM THURSDAY. SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 AM THURSDAY. && $$  FXUS63 KLOT 211408 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 908 AM CDT THU MAR 21 2013 .DISCUSSION... 904 AM CDT HAVE DROPPED LAKE EFFECT SNOW SHOWERS FROM NORTHWEST INDIANA. COMBINATION OF UNFAVORABLE WNW LOW LEVEL WINDS...DRY AIR...AND SHALLOW CLOUD DEPTH ARE WORKING AGAINST ANY SNOW SHOWER DEVELOPMENT. VIS SATELLITE SHOWS MOSTLY CLEAR SKIES LAKE AND PORTER. ELSEWHERE/OTHERWISE FORECAST SEEMS TO BE ON TRACK SO NO OTHER CHANGES. ALLSOPP && .PREV DISCUSSION... 256 AM CDT FOCUS REMAINS ON BELOW NORMAL TEMPS AND NEXT CHANCE FOR PRECIP LATE IN THE WEEKEND. EARLY MORNING WATER VAPOR IMAGERY CONTINUES TO SHOW MASSIVE UPPER LEVEL LOW SPINNING OVER EASTERN NORTH AMERICA WITH ONE CLOSED CIRCULATION OVER THE GULF OF ST. LAWRENCE AND ANOTHER WEAKER CIRCULATION OVER THE GREAT LAKES. UPPER RIDGING HAS SHARPENED ACROSS THE ROCKIES IN RESPONSE TO A LONG WAVE TROUGH PUSHING ONSHORE OVER THE WEST COAST. A CLOSED LOW IS EMBEDDED WITHIN THE TROUGH AXIS SPINNING OVER SOUTHERN BRITISH COLUMBIA. AT THE SURFACE...LOW PRESSURE IS OVER THE GULF OF ST. LAWRENCE WITH AN ELONGATED AREA OF HIGH PRESSURE EXTENDING FROM CENTRAL CANADA TO THE GULF COAST STATES. TODAY THROUGH SATURDAY...THE UPPER LOW WILL BEGIN TO SHIFT EAST TODAY WHILE THE AMPLITUDE OF THE UPPER RIDGE TO THE WEST DECREASES. THIS WILL LEAVE THE LOCAL AREA UNDER A WEAKENING UPPER FLOW. AT THE SAME TIME...THE SURFACE HIGH WILL SLOWLY MOVE EASTWARD WITH THE AXIS OVERHEAD FRIDAY. SOME LIGHT LAKE EFFECT SNOW SHOWERS ARE LINGERING ACROSS PORTER COUNTY EARLY THIS MORNING BUT WILL TAPER OFF/SHIFT TO THE EAST BY MID MORNING IF NOT SOONER AS LOW LEVEL FLOW TURNS NORTHWESTERLY. THE CORE OF COLDEST AIR...OVER THE AREA NOW...WILL SHIFT TO THE EAST WHICH WILL ALLOW FOR WARMER TEMPS THAN WEDNESDAY WITH THE WARMING TREND CONTINUING FRIDAY AS THE UPPER RIDGE REBUILDS SOMEWHAT PUSHING MILDER AIR IN ALOFT. EXPECT HIGHS FROM THE UPPER 20S NORTH TO THE LOWER 30S SOUTH WITH MID 30S NORTH TO AROUND 40 SOUTH FOR FRIDAY. IT APPEARS THERE IS SOME CHANCE FOR A LAKE BREEZE FRIDAY WITH LIGHT LOW LEVEL FLOW AND LAND TEMPERATURES AT LEAST TRYING TO WARM CLOSE TO THOSE OVER THE LAKE. SATURDAY LOOKS TO BE THE WARMEST DAY OF THE PERIOD AT THIS POINT...WITH H85 TEMPS ABOUT AS WARM AS THEY MAY BE THROUGH THE END OF NEXT WEEK AT -5 TO -6C. A SYNOPTIC NORTHEASTERLY FLOW WILL BE IN PLACE SO WILL KEEP TEMPS SLIGHTLY COOLER NEAR THE LAKE. SATURDAY NIGHT THROUGH MONDAY...CONCERNS FOR SNOW INCREASE SATURDAY NIGHT AND SUNDAY AS ENERGY MOVES DOWN THE WESTERN FLANK OF THE WESTERN UPPER TROUGH HELPING IT TO AMPLIFY INTO THE FOUR CORNERS REGION. GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE TROUGH THEN SWINGING EASTWARD ACROSS SOUTHERN MISSOURI AND ARKANSAS SOME TIME SUNDAY. SURFACE LOW PRESSURE WILL DEVELOP ACROSS TEXAS AND INTENSIFY AS IT MOVES ACROSS TENNESSEE. THE LATEST MODEL CONSENSUS BETWEEN THE ECMWF/GEM/GFS IS TO KEEP THE BULK OF THE SYSTEM TO THE SOUTH OF THE FORECAST AREA WITH EVEN THE PREVIOUSLY BULLISH GFS NOW SHOWING LITTLE IN THE WAY OF PRECIP FOR MOST OF THE AREA. THE MAIN JET ENERGY THAT WILL AID THE ENHANCEMENT OF THE UPPER TROUGH IS STILL OUT OVER THE PACIFIC SO TRACK ADJUSTMENTS ARE LIKELY. OVERALL THE SOUTHERN CWA REMAINS FAVORED FOR BETTER PRECIP CHANCES SUNDAY AND SUNDAY NIGHT WITH SNOW BEING THE PRECIP TYPE. TUESDAY AND BEYOND...A LESS AMPLIFIED FLOW IS EXPECTED FOR EARLY AND MID NEXT WEEK BUT THE UPPER TROUGH CURRENTLY OVER THE EASTERN U.S. WILL HAVE MOVED TO THE EAST OVER THE WEEKEND BUT MAY BEGIN TO RETROGRADE WESTWARD ACROSS EASTERN CANADA EARLY NEXT WEEK. PHASING BETWEEN THIS TROUGH AND A TROUGH OVER THE ROCKIES MAY OCCUR LEADING TO A COMPLEX FLOW PATTERN OVER THE REGION. AT THE LEAST THIS LOOKS TO BE CONDUCIVE TO THE PASSAGE OF WEAK WAVES IN THE GENERALLY NORTHWEST FLOW BUT HAVE LITTLE CONFIDENCE IN ANY SPECIFIC WAVES OR INTERACTION BETWEEN THE TWO TROUGHS AT THIS RANGE. THE OVERALL PATTERN STILL LOOKS COLD WITH GUIDANCE AGREEING ON H85 TEMPS REMAINING BELOW ZERO THROUGH THE PERIOD SO BELOW NORMAL TEMPS WILL CONTINUE. MDB && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 14Z... * NO CONCERNS THIS FORECAST PERIOD. PAW //DISCUSSION...UPDATED 12Z... A RATHER QUIET START TO THE FORECAST PERIOD AS SKC CONDITIONS PRESENT WITH A LIGHT WEST/NORTHWEST WIND. IN THE NEAR TERM EXPECT A SLOW RISE IN THESE NORTHWEST WINDS WITH SPEEDS REACHING AROUND 11KT TODAY...AS WELL AS SOME SCATTERED HIGH LEVEL CLOUD COVER PASSING OVER THE TERMINALS. SCATTERED CU WILL BE POSSIBLE BY MID DAY AND PERSISTING INTO THE AFTERNOON. THERE IS AN OUTSIDE POSSIBILITY FOR THE LAKE TO INFLUENCE THE WIND DIRECTION LATER THIS AFTERNOON. ALTHOUGH...THINK ANY INFLUENCE WILL BE LIMITED TO GYY WHERE THE WINDS COULD GO MORE NORTHERLY THAN THE CURRENT NORTHWEST DIRECTION. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 14Z... * HIGH CONFIDENCE IN ALL FORECAST ELEMENTS. PAW //OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z... FRIDAY NIGHT...VFR. SATURDAY...VFR. SUNDAY...CHANCE OF SNOW AND MVFR CONDITIONS. MONDAY...CHANCE OF SNOW AND MVFR CONDITIONS. TUESDAY...SLIGHT CHANCE OF SNOW AND MVFR CONDITIONS. WEDNESDAY...SLIGHT CHANCE OF SNOW AND MVFR CONDITIONS. RODRIGUEZ && .MARINE... 651 AM CDT A TROUGH OF LOW PRESSURE WILL CONTINUE TO SHIFT EAST OVER THE EASTERN GREAT LAKES TODAY AS HIGH PRESSURE REMAINS SITUATED ACROSS THE CENTRAL PLAINS. THE PRESSURE GRADIENT BETWEEN THE TWO WILL PROVIDE FOR SOME LINGERING NORTHWEST WINDS TO 30 KT HERE EARLY THIS MORNING...BUT MAINLY FOR THE NORTH HALF OF THE LAKE. EXPECT NORTHWEST WINDS TO PREVAIL WHILE REMAINING AT 15 TO 25 KT THROUGH TONIGHT. THEN EXPECT WINDS TO FURTHER DIMINISH FRIDAY AS HIGH PRESSURE SITUATES ITSELF OVERHEAD. OF MAIN CONCERN THIS FORECAST PERIOD WILL BE LATER THIS WEEKEND WHEN A DEVELOPING LOW OVER THE SOUTHERN PLAINS COULD TRACK NORTHEAST TOWARDS THE LAKE. CURRENTLY...IT IS ANTICIPATED TO TAKE A MORE SOUTHERLY TRACK LIMITING THE OVERAL SPEEDS OF THE NORTHEAST WINDS IN PLACE. ONCE AGAIN...IF A FURTHER NORTHWARD TRACK WERE TO OCCUR...THEN STRONGER WINDS TOWARDS 30KT OR EVEN POSSIBLE GALES COULD OCCUR BY LATE SATURDAY NIGHT INTO SUNDAY. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 PM THURSDAY. && $$  FXUS63 KLOT 221026 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 526 AM CDT FRI MAR 22 2013 .DISCUSSION... 524 AM CDT POTENTIAL FOR SIGNIFICANT SNOWFALL SUNDAY AND SUNDAY NIGHT...ESPECIALLY S OF I-80 AND NEAR THE IL AND IN LAKE SHORE. ATTENTION FOCUSED ON POTENTIAL OF SPRING SNOW STORM TO AFFECT THE LOCAL FORECAST AREA BEGINNING OVERNIGHT SATURDAY NIGHT ACROSS THE SW HALF OF THE FA AND THEN ACROSS THE ENTIRE FA SUNDAY AND SUNDAY NIGHT. ALSO POTENTIAL FOR LAKE ENHANCED SNOWFALL ALONG THE IL AND IN SHORES DURING SUNDAY AND SUNDAY NIGHT AS STRONG COLD NE LOW LEVEL FLOW BACKS TO OUT OF THE N WITH TIME AS THE SURFACE LOW OF THE STORM SYSTEM PASSES S AND SE OF THE REGION...POTENTIALLY CONTRIBUTING ENHANCED CONVECTIVE SNOWFALL TOO THE WIDESPREAD SYSTEM SNOW. THIS STORM HAS BEEN TOUGH TO NAIL DOWN AS MODELS HAVE BEEN OFFERING VARIOUS SOLUTIONS TO THE PATH OF THE STORM ACROSS THE CENTRAL U.S. OVER THE LAST SEVERAL RUNS. LATEST MODEL OUTPUT SEEMS TO HAVE CONVERGED SIGNIFICANTLY OVER PAST 24 HOURS AND CONTINUITY OF EACH MODEL FROM PREVIOUS MODEL RUN TO THE LATEST RUN...WITH ONE EXCEPTION...LENDS CREDENCE AND MORE CONFIDENCE IN A MORE SOUTHERLY TRACK OF THE UPPER LOW. A JET MAX CURRENTLY DIVING SSE OVER NV AND NORTHERN CA IS TO TURN SE OVER THE DESERT SW AND THE SOUTHERN ROCKIES TONIGHT AND SATURDAY MORNING THEN HEAD E OVER THE SOUTHERN PLAINS SATURDAY AFTERNOON AND EVENING BEFORE TURNING ENE OVERNIGHT CROSSING THE SOUTHERN MS VALLEY AND REACHING THE TN VALLEY BY SUNDAY EVENING. LOOP OF SATELLITE WATER VAPOR IMAGERY ALREADY REVEALS A DEVELOPING UPPER LOW CIRCULATION OVER THE INTERIOR PACIFIC NW. IN RESPONSE TO THE JET THIS LOW IS PROGGED TO STRENGHTEN AS IT CURVES SE AND E OVER THE CENTRAL ROCKIES AND THE CENTRAL PLAINS DURING SATURDAY AND THEN E OVER THE MID MS VALLEY. BESIDES THE OUTLIER OPERATIONAL 00Z GFS...MODEL CONSENSUS INCLUDING GFS ENSEMBLE MEMBERS...GFS ENSEMBLE MEAN...AND SREF MEAN IS FOR THE UPPER LOW TO TRACK ACROSS SOUTHERN MO OR ALONG THE MO-AR BORDER TO THE LOWER OH VALLEY DURING SUNDAY. WITH THIS SOUTHERN TRACK THE ASSOCIATED 850HPA AND SURFACE LOWS ARE PROGGED TO MOVE E ACROSS SOUTHERN MO SATURDAY NIGHT AND THEN TO THE FA LOWER OH VALLEY BY 18Z SUNDAY. BEST FORCING FROM ISENTROPIC UPGLIDE AND FRONTOGENESIS IS PROGGED TO STRETCH FROM NORTHERN MO ACROSS CENTRAL IL AND CENTRAL IN DURING THE SATURDAY NIGHT TO SUNDAY NIGHT PERIOD. WHILE FEEL FAIRLY CONFIDENT IN THE SOUTHERN TRACK OF THE SYSTEM A BIT MORE NORTHERLY TRACK...WHILE A VERY MINOR SHIFT FOR A HEMISPHERIC MODEL...WOULD BRING THE THREAT OF A HEAVY SPRING SNOWFALL TO THE SOUTHERN HALF OF THE LOCAL FORECAST AREA. BASED ON LATEST GUIDANCE HAVE A RANCE OF SNOWFALL FROM 1 INCH ALONG THE WI BORDER TO 6 TO 7 INCHES ACROSS FAR SOUTHERN LASALLE...SOUTHERN FORD...SOUTHERN IROQUOIS AND BENTON COUNTIES WITH THE 3 INCH TOTAL GENERALLY ALONG THE I-80 CORRIDOR. A WILD CARD THROWN INTO THE MIX IS THE POTENTIAL FOR LAKE EFFECT/ENHANCED SNOW TO OCCUR. DURING SUNDAY AND SUNDAY NIGHT THE COLD AIR IN PLACE ACROSS CANADA...THE GREAT LAKES AND THE NE U.S. WILL TRAVEL ACROSS LAKE MI ON NE TO NNE FLOW. FORECAST TEMPERATURE PROFILES INDICATE A CLOUD DEPTH OVER THE LAKE OF 5 TO 7K FT WITH TOPS 7-9K FT. EXPECT ENHANCED SNOWFALL NEAR THE IL AND IN SHORES ESPECIALLY SUN AFTERNOON AND EVENING AS THE BACKING OF THE FLOW DRAMATICALLY INCREASES THE FETCH OVER THE LAKE. THE LAKE EFFECT COULD LOCALLY DOUBLE SNOW AMOUNTS ALONG THE IL SHORE AND TRIPP LE THEM IN NW IN. ONCE ANY LINGER SNOW OR LAKE EFFECT SNOW SHOWERS END MONDAY AFTER AN UPPER TROUGH TRAILING W AND NW FROM THE UPPER LOW PROGGED TO BE WEAKENING AS IT MOVES FROM THE UPPER OH VALLEY ACROSS THE NORTHEASTERN U.S. THE REST OF THE WEAK LOOKS TO BE TRANQUIL OUTSIDE OF A SLIGHT CHANCE OF LIGHT SNOW TUESDAY AS ANOTHER UPPER TROUGH DROPS S FROM THE SOUTHERN GREAT LAKES. WHILE THE AMPLITUDE OF THE UPPER PATTERN ACROSS THE CONUS DECREASES WITH TIME DURING MID AND LATE WEEK TEMPERATURES ARE EXPECTED TO MODERATE SLIGHTLY AND REMAIN WELL BELOW NORMAL FOR LATE MARCH AS AN UPPER TROUGH REMAINS OVER EASTERN NOAM AND THE WESTERLIES STAY WELL SOUTH. TRS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * POSSIBLE LAKE BREEZE/NORTHEAST WIND SHIFT THIS AFTERNOON. //DISCUSSION...UPDATED 06Z... HIGH PRESSURE CENTERED OVER THE AREA WILL MOVE LITTLE THROUGH TODAY AND THIS EVENING. THURSDAY SAW A LAKE BREEZE WORK PARTIALLY INLAND AND EXPECTING SIMILAR TODAY. BECAUSE THIS DID NOT REACH THE ORD AND MDW YESTERDAY...CONFIDENCE IS MAINLY LOW ON IT REACHING THEM TODAY. HOWEVER...A WEAK AND SUBTLE BACKDOOR COLD FRONT MAY JUST OFFER A SYNOPTIC TURN TO NNE WINDS DURING THE LATE AFTERNOON/EARLY EVE. SPEEDS WILL LIKELY REMAIN BELOW 10 KT...UNLESS IT IS A TRUE LAKE BREEZE PUSH THEN THERE COULD BE AN HOUR OR TWO OF WINDS NEAR THAT MAGNITUDE. OTHERWISE...CIRRUS THICKENING LATER IN THE TAF PERIOD AND AN ATMOSPHERE TOO DRY TO SUPPORT MUCH BESIDES WIDELY PATCHY MVFR FOG. //ORD AND MDW CONFIDENCE...UPDATED 09Z... * LOW CONFIDENCE REGARDING LAKE BREEZE/WIND SHIFT THIS AFTERNOON AT ORD AND MEDIUM CONFIDENCE AT MDW. MEDIUM CONFIDENCE THAT IF IT OCCURS SPEEDS WILL REMAIN BELOW 10 KT. //OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z... * SATURDAY...DRY. VFR. * SUNDAY...CHANCE OF SNOW. MVFR POSSIBLE. GUSTY NORTHEAST WINDS. * MONDAY...CHANCE OF SNOW. MVFR POSSIBLE. * TUESDAY...SLIGHT CHANCE OF SNOW SHOWERS. MVFR POSSIBLE. * WEDNESDAY...DRY. VFR. MTF/CMS && .MARINE... 159 AM CDT PERSISTENT LOW PRESSURE OVER SOUTHERN QUEBEC WILL BEGIN TO FINALLY MOVE EAST LATER TODAY INTO TONIGHT EASING WIND SPEEDS ACROSS THE NORTHERN PART OF THE LAKE. THIS SYSTEM DEPARTURE WILL ALLOW FOR THE HIGH PRESSURE OVER THE MISSISSIPPI RIVER VALLEY TO SHIFT EAST OVER LAKE MI INTO THE DAY SATURDAY. THE MOST PRONOUNCED SYSTEM IMPACTS FOR THE LAKE WILL COME LATER SUNDAY...SUNDAY NIGHT...INTO THE DAY MONDAY AS LOW PRESSURE MOVES FROM THE OZARKS REGION UP THE OHIO RIVER VALLEY. SUCH A PATH WILL TIGHTEN THE PRESSURE GRADIENT ACROSS LAKE MI...ESPECIALLY THE SOUTH. WINDS TO 30 KT LOOK VERY LIKELY OVER THE SOUTHERN HALF INCLUDING NEARSHORE AREAS ON THE SOUTH...WITH GALE FORCE WINDS POSSIBLE DEPENDING ON SYSTEM STRENGTH AND PRECISE PATH. CIPS ANALOG GUIDANCE FOR SIMILAR REGIME MATCHES INDICATE A 50 PERCENT CHANCE OF WIND GUSTS EXCEEDING 30 KT ON NEARBY LAND AREAS FOR THIS TIME...SO OVER WATER THE LIKELIHOOD IS HIGHER. SO BEYOND THIS SYSTEM...GRADUALLY DIMINISHING NORTHERLY FLOW WILL CONTINUE FOR A WHILE WITH PERSISTENT RIDGING BUILDING ONCE AGAIN OVER THE MISSISSIPPI RIVER VALLEY. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$  FXUS63 KLOT 270757 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 257 AM CDT WED MAR 27 2013 .DISCUSSION... 255 AM CDT TEMPERATURES ARE THE PRIMARY INTRIGUE WITH THIS FORECAST ISSUANCE AS THE WARM-UP FROM A LONG DURATION COOL SPELL ENSUES. CONTINUED NORTHERLY FLOW THROUGH THE TROPOSPHERE PERSISTS OVER THE FORECAST AREA THIS MORNING THOUGH WESTERLY FLOW IS ADVANCING ACROSS THE PLAINS...WITH A FEW WEAK EMBEDDED IMPULSES ACROSS IA TO KS. CONFLUENT FLOW ALOFT BETWEEN THE CYCLONIC FLOW TO THE EAST AND THIS IMPEDING WESTERLY FLOW WILL KEEP IMPULSES SHEARED AS WELL AS OFFER SOME SUPPRESSION TO WORK AGAINST THE CLOUDS. LAST EVES RAOBS AND A COUPLE EARLY MORNING AMDAR SOUNDINGS INDICATE THE MOIST LAYER OF THE CLOUD DEPTH IS VERY SHALLOW...LESS THAN 700 FT...AND HOLES CONTINUE TO SHOW UP IN SATELLITE. THE ANOMALOUSLY COLD AIR AT 800-850MB HOWEVER SHOULD LEAD TO A FLARE UP IN DIURNAL CU/STRATOCU GIVEN STEEP LOW-LEVEL LAPSE RATES. SO A SYNOPTIC REGIME NOT THAT MUCH DIFFERENT FROM YESTERDAY IS EXPECTED...ALTHOUGH LIKELY WITH A LITTLE MORE SUN. TEMPERATURES WERE A FEW DEGREES WARMER THAN GUIDANCE YESTERDAY IN MULTIPLE COMMUNITIES...AND HAVE CONTINUED THAT TREND WITH TODAYS FORECAST HIGHS. A LAKE BREEZE DEVELOPED YESTERDAY INTO SOUTHEAST COOK COUNTY AND NORTHWEST INDIANA AND GIVEN A LITTLE WARMER TEMPERATURES FORECAST TODAY SEE NO REASON THAT A BREEZE WILL NOT AGAIN OCCUR. HAVE CONTINUED KEEPING NEAR-LAKE AREAS MAINLY IN THE UPPER 30S. IT IS ANTICIPATED THAT MUCH OF THE CLOUD COVER SHOULD DIMINISH THIS EVENING AS THE HEART OF THE COLD AIR POCKET AND THE CHANNELED VORTICITY ALOFT BOTH SHIFT EAST OF THE REGION. THE SURFACE RIDGE WILL ALSO BE ENVELOPING THE AREA AND THAT SHOULD ALLOW FOR THE COOLEST MINS THUS FAR THIS WEEK...WITH READINGS IN THE MID 20S IN MOST OUTLYING AREAS. THURSDAY AND FRIDAY WILL CONTINUE TO SEE MODERATING TEMPERATURES AS THICKNESSES RISES AND MORE SUNSHINE IS PREVALENT. BOTH DAYS SHOULD SEE A LAKE BREEZE DEVELOP AND LIKELY EARLIER THAN TODAY OR YESTERDAY. SO HIGHS ALONG THE LAKE SHORE ARE LIKELY TO HUG 40 WHILE RISING THROUGH THE 40S ELSEWHERE...WITH EVEN 50 EXPECTED IN FAR WESTERN PARTS OF THE FORECAST AREA FRIDAY. FOR AREAS SOUTH OF THE KANKAKEE RIVER THAT HAVE A FAIRLY DEEP SNOW PACK...WITH RISING TEMPERATURES AND DEW POINTS...ALL THIS SNOW COVER SHOULD BE GONE OR NEAR GONE BY SATURDAY. SO HAVE CONTINUED THE TREND OF SUPPRESSING HIGHS SOMEWHAT BEFORE THEN...BUT NOT BEYOND FRIDAY. BY THE START OF THE WEEKEND THE PRESSURE GRADIENT IS FORECAST TO TIGHTEN AND RETURN FLOW INCREASES AS A TROUGH DEVELOPS SOUTHEAST INTO THE CENTRAL PART OF THE COUNTRY. WHILE THERE IS STILL SOME SPLIT IN THIS TROUGH AS IT MOVES EAST...GUIDANCE AGREES ON A SURFACE LOW DEVELOPING ALONG THE BOUNDARY SATURDAY NIGHT ACROSS THE WESTERN/SOUTHERN GREAT LAKES. WHILE THE STRENGTH DIFFERS THE IDEA OF A DEEPER CONVERGENCE WITHIN THE PRE-FRONTAL MOIST PLUME IS NOW ADVERTISED. SO DO HAVE SOME LIKELY POPS FOR RAIN ON SATURDAY NIGHT. ONLY A COUPLE MEMBERS OF THE 00Z GFS ENSEMBLE PRODUCE A QUARTER OF AN INCH AT CHICAGO...SO THIS IS NOT EXPECTED TO BE A BIG PRECIP MAKER...NAMELY BECAUSE OF DURATION AS THE FRONT IS FORECAST TO MOVE FAIRLY QUICKLY. THAT ALSO RESULTS IN SUNDAY POPS HAVING BEEN TRENDED LOWER. THE PRE-FRONTAL AIR MASS ON SATURDAY WILL VERY LIKELY OFFER LOW TO MID 50S EVERYWHERE AND A MILD NIGHT FOR THIS MARCH. SUNDAY TEMPERATURES ARE A BIT MORE OF A CHALLENGE. WHILE COOLER AIR IS PROJECTED ALOFT FOR SUNDAY SO IS DRYING AND POTENTIAL SUNSHINE...AND THE SECONDARY COLD FRONT IS FORECAST TO NOT ARRIVE UNTIL SUNDAY NIGHT WITHIN THE GUIDANCE MEAN. SO UPPER 40S TO LOWER 50S ARE RIGHT NOW THE FAVORED FORECAST FOR SUNDAY...BUT IT COULD TURN OUT COOLER. FOR NEXT WEEK...THE UPPER TROUGH THAT BRINGS THE PRECIP CHANCES THIS WEEKEND DEEPENS ACROSS THE CENTRAL TO EASTERN GREAT LAKES...ALLOWING FOR A NORTHERLY WIND PERIOD AND AGAIN COOLER THAN NORMAL TEMPERATURES TO START APRIL. HAVE GONE AWAY FROM MOS FORECASTS AND MORE TOWARD THE RAW OUTPUT...WHICH AT TIMES WORKED WELL DURING THIS COOL MONTH WITH THE MOST BIAS TOWARD WARMER CLIMO IN THE EXTENDED. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * POTENTIAL FOR LAKE BREEZE DEVELOPMENT AND PUSH INLAND DURING THE AFTERNOON. TRS //DISCUSSION...UPDATED 06Z... AN UPPER TROUGH EXTENDS FROM THE N ATLANTIC WSW OVER THE CANADIAN MARITIMES...NEW ENGLAND...THE ST. LAWRENCE VALLEY AND THE LOWER GREAT LAKES WITH THE WESTERN EXTEND ACROSS FAR SOUTHERN LOWER MI...SOUTHERN LAKE MI AND FAR NORTHERN IL. BY THIS EVENING THE UPPER TROUGH WILL HAVE SLOWLY MOVE FURTHER TO THE E WHILE HEIGHTS ALOFT START TO RISE AS A RIDGE MOVES SLOWLY MOVES E OVER THE WESTERN U.S. A SURFACE RIDGE FROM MANITOBA SE OVER THE UPPER AND MS VALLEY IS PROGGED TO DRIFT FURTHER TO THE E THOUGH REMAINING W OF THE LOCAL FORECAST AREA THROUGH WED NIGHT. THIS WILL KEEP A DEEP BUT WEAK CYCLONIC FLOW OVER THE AREA WHICH WILL ENCOURAGE CONTINUED VFR STRATOCUMULUS CEILINGS WITH MOISTURE BEING TRAPPED UNDER AN INVERSION WHOSE BASE IT PROGGED TO GRADUALLY DROP FROM 775 TO 825 HPA DURING THE DAY. WHILE A LAKE BREEZE DID FORM TUESDAY AFTERNOON AND MADE SOME PROGRESS INLAND MODELS SHOW THE LOW LEVEL FLOW TAKING ON A SLIGHTLY MORE WESTERN COMPONENT FOR TODAY AND NO INDICATION OF A WELL DEFINED LAKE BREEZE DEVELOPING AND MOVING INLAND TODAY THOUGH HIGHER RESOLUTION REGIONAL MODELS SHOWING SOME HINTS OF SURFACE WINDS TURNING IN OFF OF THE LAKE MIDDAY. THE POSSIBILITY OF A LAKE BREEZE MOVING INLAND AND REACHING MDW MID AFTERNOON AND ORD MID-LATE AFTERNOON EXISTS BUT CONFIDENCE IS LOW AT THIS TIME SO HAVE NOT MADE MENTION OF ANY WIND SHIFT ASSOCIATED WITH A LAKE BREEZE IN THE LATEST TAFS. THE SURFACE RIDGE LINGERING TO THE W OF THE LOCAL TERMINALS WILL GRADUALLY CREEP TO THE E TONIGHT AND REACH WESTERN WI IL BY THU MORNING. NNW WINDS WILL BE LIGHT AND SKIES GENERALLY CLEAR OVERNIGHT BUT FORECAST DEW POINT DEPRESSIONS OF 5 DEG C SUGGEST THAT ANY SIGNIFICANT FOG THREAT IS LOW. WOULD EXPECT MORE LOCALIZED GROUND FOG THAT WILL OCCASIONAL REACH ABOVE EYE LEVEL AND TECHNICALLY BY CLASSIFIED AS BR /MIST/ BUT AGAIN WITH LOW PROBABILITY OF OCCURRENCE AT ORD AND/OR MDW HAVE LEFT OUT ANY MENTION OF BR OR MIFG FOR THE TONIGHT PORTION OF THEIR TAFS. TRS //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH CONFIDENCE MVFR THROUGH FORECAST PERIOD. * MODERATE CONFIDENCE IN LAKE BREEZE NOT REACHING AS FAR INLAND AS MDW AND/OR ORD DURING THE AFTERNOON. TRS //OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z... THURSDAY AND FRIDAY...VFR WITH AFTERNOON LAKE BREEZE LIKELY EACH DAY. SATURDAY...VFR BECOMING MVFR WITH CHANCE OF RAIN SATURDAY NIGHT. SUNDAY...MVFR WITH CHANCE OF RAIN. MONDAY...VFR. MDB && .MARINE... 307 PM CDT A WEAK TROUGH OF LOW PRESSURE EXTENDING ACROSS THE GREAT LAKES REGION WILL SLOWLY SHIFT EAST TONIGHT INTO WEDNESDAY WHILE A RIDGE OF HIGH PRESSURE EXTENDING FROM THE NORTHERN PLAINS SOUTH TO THE SOUTHERN PLAINS SLOWLY SHIFTS EAST. AS THIS OCCURS...WILL CONTINUE TO OBSERVE A NORTHWEST WIND ACROSS THE LAKE WHILE THE WINDS SLOWLY DIMINISH. THE HIGH WILL SHIFT ACROSS THE WESTERN GREAT LAKES LATE WEDNESDAY AND THEN CONTINUE TO MOVE ACROSS THE CENTRAL GREAT LAKES ON THURSDAY...REMAINING OVERHEAD THROUGH FRIDAY NIGHT. WITH THIS HIGH SHIFTING ACROSS THE AREA...A PERIOD OF LIGHTER WINDS WILL BE OBSERVED ACROSS THE ENTIRE LAKE. EXPECT THIS LIGHTER FLOW INTO THE START OF THE WEEKEND BUT WITH WINDS BEGINNING TO INCREASE THROUGH THE WEEKEND AS A TROUGH OF LOW PRESSURE AND ASSOCIATED COLD FRONT SHIFT EAST ACROSS THE GREAT LAKES REGION THROUGH THE WEEKEND. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$  FXUS63 KLOT 061142 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 642 AM CDT SAT APR 6 2013 .DISCUSSION... 328 AM...MULTIPLE FORECAST CONCERNS/CHALLENGES THROUGH THE MIDDLE OF NEXT WEEK. LOW PRESSURE OVER THE CENTRAL PLAINS WILL MOVE NORTHEAST ACROSS NORTH CENTRAL LAKE MICHIGAN THIS EVENING. THE GRADIENT WILL TIGHTEN QUICKLY THIS MORNING WITH SOUTHERLY WINDS GUSTING AS HIGH AS 40 MPH BY LATE MORNING. STRONGEST WINDS APPEAR TO BE MOST LIKELY DURING THE EARLY/MID AFTERNOON. EXTENSIVE MID/HIGH LEVEL CLOUD COVER SHOULD KEEP SKIES MOSTLY CLOUDY/CLOUDY BUT PRESSURE FALLS SHOULD BE SUFFICIENT TO OVERCOME LOSS OF SUNSHINE/MIXING. IN ADDITION...WARM AIR ADVECTION IS IMPRESSIVE BY ITSELF SO EVEN WITHOUT EVEN PARTLY SUNNY SKIES...APPEARS HIGHS TODAY SHOULD MAKE LOWER/MID 60S. BUT CONFIDENCE ONLY REMAINS MEDIUM FOR TODAY GIVEN THESE VARIABLES. ITS POSSIBLE THAT WIND GUSTS COULD BECOME A BIT STRONGER...BUT NOT CONFIDENT ENOUGH TO GO HIGHER ON CURRENT WIND SPEEDS/GUSTS. THUS WILL HOLD OFF ON A WIND ADVISORY AND CONTINUE WITH THE SPS FOR STRONG/GUSTY WINDS TODAY. A TRAILING COLD FRONT WILL MOVE ACROSS THE AREA THIS EVENING AND THIS APPEARS TO BRING THE BEST CHANCE FOR SHOWERS AND A FEW THUNDERSTORMS. THE LOW LEVELS REMAIN QUITE DRY INTO THIS AFTERNOON AND EXPECT ANY PRECIP TO BE LIGHT SHOWERS OR PERHAPS SPRINKLES WITH MOST AREAS REMAINING DRY. EXPECT SHOWERS TO DEVELOP AHEAD OF THE FRONT OVER EASTERN IA/WESTERN IL THEN QUICKLY MOVE EAST DURING THE EARLY/MID EVENING HOURS. INSTABILITY SUPPORTS MENTION OF THUNDERSTORMS BUT EVEN WITH OUT THUNDER...SHOWERS WILL LIKELY BE CONVECTIVE. STILL QUITE A BIT OF WIND IN THE LOW LEVELS INTO THE EVENING HOURS. SO IN ADDITION TO EXPECTING WINDY/BREEZY CONDITIONS TO CONTINUE INTO THE EVENING...SOME OF THE STRONGER SHOWERS/STORMS COULD MIX DOWN LOCALLY HIGHER WINDS THOUGH DOESN/T APPEAR THESE WOULD REACH SEVERE LIMITS. LINGERING SHOWERS WILL END FROM WEST TO EAST OVERNIGHT WITH WINDS DIMINISHING SIGNIFICANTLY OVERNIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL MOVE ACROSS THE WESTERN LAKES ON SUNDAY. NO SIGNIFICANT TEMP CHANGE BEHIND THE COLD FRONT SO WITH SOME SUNSHINE...TEMPS SHOULD REBOUND NICELY SUNDAY BUT A LAKE BREEZE SHOULD FORM BY EARLY AFTERNOON...WHICH WILL LOWER TEMPS SEVERAL DEGREES NEAR THE LAKE. FURTHER INLAND...HIGHS COULD EASILY REACH THE LOWER/MID 60S. MODELS ARE COMING INTO BETTER AGREEMENT WITH ANOTHER AREA OF LOW PRESSURE MOVING NORTHEAST ACROSS THE REGION LATE SUNDAY NIGHT INTO MONDAY MORNING. SHOWERS AND THUNDERSTORMS WILL SPREAD NORTH ACROSS THE AREA OVERNIGHT AND CONTINUE INTO MONDAY MORNING. PRECIPITABLE WATER VALUES REACH AN INCH DURING THIS TIME AND SOME HEAVY RAIN IS CERTAINLY POSSIBLE WITH SOME OF THE STORMS. THIS LOW QUICKLY MOVES NORTHEAST MONDAY AFTERNOON WITH PRECIP LIKELY ENDING MIDDAY OR EARLY AFTERNOON. HAVE LIKELY POPS GOING IN THE MORNING BUT DROPPED DOWN TO LOW CHANCE MONDAY AFTERNOON AND ITS POSSIBLE MONDAY AFTERNOON MAY END UP BEING DRY. APPEARS SOUTHERLY FLOW WILL REACH INTO NORTHERN IL AND HAVE BUMPED TEMPS UP...GENERALLY INTO THE 60S BUT KEPT LAKE SHORE AREAS A LITTLE COOLER...DUE THE UNCERTAINTY OF JUST HOW STRONG THE SOUTHERLY FLOW BECOMES AS WELL AS WHETHER IT CAN REACH AS FAR NORTH AS THE LAKE. FROM MONDAY NIGHT THROUGH THURSDAY...CONFIDENCE IS RATHER LOW WITH A FRONT BOUNDARY EXPECTED TO BE SOMEWHERE NEARBY. LOW PRESSURE OVER THE SOUTH CENTRAL PLAINS TUESDAY MORNING IS PROGGED TO LIFT ACROSS NORTHERN WI BY THE GEM...SOUTHERN WI BY THE GFS AND ACROSS THE OHIO VALLEY BY THE ECMWF...ALONG WITH TIMING DIFFERENCES. THIS RANGE OF SOLUTIONS WILL LEAD TO BIG BUST POTENTIAL REGARDING TEMPS. HAVE TRENDED TOWARD THE COLDER/FURTHER SOUTH ECMWF WHICH SETS UP SOMEWHAT STRONGER NORTHEAST FLOW AND THUS COLDER TEMPS ESPECIALLY NEAR THE LAKE. DEPENDING ON THE TRACK OF THE LOW... COULD BE PERIODS OF SHOWERS AND THUNDERSTORMS...PERHAPS WITH SOME PERIODS OF HEAVY RAIN BUT TOO EARLY TO GET SPECIFIC GIVEN THE HIGHER THAN USUAL UNCERTAINTY. CMS && .FIRE WEATHER... 328 AM...EASTERLY FLOW HAS MAINTAINED MUCH DRIER AIR ACROSS THE REGION AND EXPECT A SLOW RETURN OF LOW LEVEL MOISTURE ACROSS THE AREA TODAY. IT APPEARS DEWPOINTS WILL INCREASE BACK INTO THE 40S...BUT PROBABLY NOT UNTIL LATE AFTERNOON ACROSS WESTERN IL AND THE REST OF THE AREA THIS EVENING. THUS MINIMUM RH VALUES TODAY WILL LIKELY BE IN THE 35-40 PERCENT RANGE AND COULD POSSIBLY DIP INTO THE 30-35 PERCENT RANGE. WHILE THESE EXPECTED VALUES WILL REMAIN ABOVE RED FLAG CRITERIA OF 25 PERCENT...SOUTHERLY WINDS ARE EXPECTED TO QUICKLY INCREASE THIS MORNING WITH GUSTS AS HIGH AS 40 MPH FROM LATE MORNING THROUGH SUNSET WITH THE POTENTIAL FOR HIGHER GUSTS. WHILE THERE COULD BE A FEW LIGHT SHOWERS OR SPRINKLES TODAY...THE BEST TIMING FOR SHOWERS AND A FEW THUNDERSTORMS WILL BE FROM LATE AFTERNOON THROUGH MID/LATE EVENING. TEN HOUR FUEL MOISTURE DIPPED TO 8-9 PERCENT ON FRIDAY AND SIMILAR VALUES ARE POSSIBLE TODAY. AS A RESULT...THERE WILL BE AN INCREASED FIRE DANGER AND WHILE MEETING RED FLAG CRITERIA IS NOT EXPECTED... CONDITIONS WILL NEED TO BE MONITORED THROUGH DAY. CMS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * SOUTHEAST WINDS INCREASE AND BECOME GUSTY THIS MORNING * WINDS BECOME MORE SOUTHERLY (180-200) THIS AFTERNOON GUSTS INCREASE TO 30-40KT * SCT'D SHRA LIKELY THIS EVENING WITH ISOLD TSRA POSSIBLE IN AREA * SLIGHT CHANCE OF SOME MVFR CIGS LATE TONIGHT/EARLY SUNDAY MORNING IZZI //DISCUSSION...UPDATED 12Z... STRONG LOW PRESSURE OVER SOUTH DAKOTA WILL MOVE EAST TO WISCONSIN TODAY AND INTENSIFY A BIT FURTHER. EXPECT OVC VFR DECK TO REMAIN IN PLACE THROUGH THIS EVENING WITH ISOLD SPRINKLES OR VIRGA (-SHRA ALOFT) POSSIBLE TODAY WITH THE IMPRESSIVE WARM AIR ADVECTION...BUT DRY AIR DOWN LOW SHOULD KEEP ANY RAIN THAT MAY OCCUR FROM FROM BEING OPERATIONALLY SIGNIFICANT THROUGH MUCH OF TODAY. BIGGER CONCERN WILL BE STRENGTHENING SE WINDS THIS MORNING...LIKELY GUSTING TO BETWEEN 20-30KT BY MID MORNING. BY LATE MORNING INTO THE AFTERNOON WINDS SHOULD TURN MORE SOUTHERLY 170-200 AND INCREASE TO SUSTAINED 22-30KT WITH GUSTS OF 30-40KT LIKELY. WINDS SHOULD SUBSIDE VERY SLOWLY THIS EVENING BUT REMAIN STRONG UNTIL FRONT PASSES LATE THIS EVENING. SCT'D SHRA AND ISOLD TSRA LIKELY TO DEVELOP ALONG THE FRONT LATE THIS AFTERNOON OVER WESTERN ILLINOIS AND MOVE ACROSS THE AREA THIS EVENING. COVERAGE/CONFIDENCE IN THUNDERSTORMS AT THE TERMINAL TOO LOW TO INCLUDE IN TAF AT THIS TIME...BUT WILL NEED TO BE CLOSELY MONITORED IN LATER AMENDMENTS. WIND SHIFT TO WEST LIKELY BEHIND THE FRONT BY LATE EVENING. SOME MODELS ARE SUGGESTING A PERIOD OF LOW CLOUDS BEHIND THE FRONT...BUT GIVEN SOMEWHAT LIMITED MOISTURE HAVE OPTED TO JUST INCLUDE SCT DECK IN TAF FOR NOW. IZZI //ORD AND MDW CONFIDENCE...UPDATED 12Z... * HIGH CONFIDENCE IN PREVAILING CIGS/VSBY THROUGH EVENING * MEDIUM CONFIDENCE IN WIND SPEED/GUSTS TODAY WITH HIGH CONFIDENCE IN DIRECTION * MEDIUM CONFIDENCE IN PRECIP TIMING * LOW CONFIDENCE IN TSRA POTENTIAL THIS EVENING * LOW CONFIDENCE IN CIGS LATE LATE TONIGHT IZZI //OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z... SUNDAY NIGHT...SHRA/TSRA LIKELY LATE. MVFR PROBABLE SOME CHANCE OF BRIEF IFR LATE. MONDAY...SHRA/TSRA LIKELY EARLY. MVFR/BRIEF IFR POSSIBLE EARLY. TUESDAY THROUGH THURSDAY NIGHT...PERIODIC CHANCE FOR SHRA/TSRA. PERIODIC MVFR CIGS/VSBY LIKELY WITH BRIEF IFR POSSIBLE. FRIDAY...PROBABLE VFR. IZZI && .MARINE... 301 AM CDT HAVE OPTED TO CANCEL THE GALE WATCH FOR THE OPEN LAKE AS SHALLOW BUT STRONG MARINE LAYER LIKELY TO PREVENT MUCH OF THE STRONGER WINDS ALOFT FROM MIXING TO THE LAKE SURFACE TODAY INTO TONIGHT. SOME OF THE TALLER SHIPS COULD STILL SEE SOME GALE FORCE WIND GUSTS BUT GENERALLY LOOKS LIKE THE THREAT OF WIDESPREAD GALES WILL BE CONFINED TO THE NEARSHORE WATERS WITH STRONG OFFSHORE FLOW LIKELY TO RESULT IN GALES NEAR THE COAST. WINDS WILL VEER TO WEST BEHIND THE LOW TONIGHT AND THEN QUICKLY DIMINISH LATE TONIGHT/SUNDAY AS WEAK HIGH BUILDS OVER THE WESTERN LAKES SETTING STAGE FOR LAKE BREEZE CIRCULATION TO DOMINATE WINDS BY LATE SUNDAY. WAVE OF LOW PRESSURE LIKELY TO TRACK EAST ALONG THE FRONT AND RESULT IN INCREASING EASTERLY WINDS SUNDAY NIGHT BEFORE VEERING MORE WESTERLY AS THE LOW PASSES EAST ACROSS SOUTHERN LAKE MICHIGAN MONDAY. NEXT WEEK'S FORECAST IS VERY LOW CONFIDENCE WITH SOME OF THE MORE RELIABLE LONG RANGE MODELS SUGGESTING THAT FRONT COULD RETREAT NORTH WITH STRONG SOUTHERLY WINDS DEVELOPING...ESPECIALLY OVER SOUTHERN PORTIONS OF THE LAKE. HOWEVER...CURRENT THINKING IS THE MORE LIKELY SCENARIO WILL BE FOR FRESH EAST TO NORTHEAST WINDS WITH FRONT STALLING SOUTH OF THE LAKE AND SEASONABLY STRONG HIGH PRESSURE TRACKING EAST ACROSS SOUTHERN CANADA THROUGH MIDWEEK. IZZI && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...GALE WARNING...NEARSHORE WATERS UNTIL 10 PM SATURDAY. && $$  FXUS63 KLOT 251139 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 639 AM CDT THU APR 25 2013 .DISCUSSION... 325 AM CDT A WEAK COLD FRONT WILL QUICKLY PASS OVER THE AREA THIS MORNING BRINGING A FEW LIGHT SHOWERS...BUT THEN EXPECT NORTHERN ILLINOIS AND NORTHWEST INDIANA TO ENTER A RELATIVELY QUIET AND DRY PERIOD OF WEATHER WITH TEMPERATURE MODERATING TO AND EVENTUALLY ABOVE SEASONAL NORMS. MAIN CONCERN THIS MORNING WILL BE DEALING WITH TEMPERATURE TRENDS THROUGH THE UPCOMING WEEK. TODAY AND TONIGHT... A MID LEVEL DISTURBANCE AND ATTENDANT SURFACE COLD FRONT IS RACING EAST ACROSS NORTHERN ILLINOIS EARLY THIS MORNING. A BAND OF SHOWERS ASSOCIATED WITH THIS FEATURE HAS ALREADY PUSHED INTO CENTRAL PORTIONS OF THE CWA AND SHOULD BE EAST OF THE CHICAGO METRO AREA BY AROUND 11Z THIS MORNING WITH ONLY A FEW SPOTTY SHOWERS EXPECTED THEREAFTER. WITH SURFACE TEMPS STILL IN THE LOW TO MID 40S AHEAD OF THE FRONT...MAINLY EXPECT RAIN TO FALL THIS MORNING. CLOUDS SHOULD BEGIN TO CLEAR OUT LATER IN THE MORNING...THEN EXPECT CU FIELD TO DEVELOP SIMILAR TO YESTERDAY AS WE DEVELOP STEEP LOW LEVEL LAPSE RATES. EXPECT TEMPS TO BE A COUPLE DEGREES WARMER TODAY...TOPPING OUT IN THE LOW TO MID 50S ACROSS THE AREA. LATEST GUIDANCE INDICATES THAT THERE MAY BE SOME VERTICAL DEPTH TO THE CUMULUS TODAY...AND A FEW OF THE HI-RES MODELS ARE SPITTING OUT LIGHT QPF. IN ADDITION A WEAK DISTURBANCE IS NOTED ON WV IMAGERY DROPPING SOUTHEAST ACROSS THE DAKOTAS. BOTH THE NAM AND GFS INITIALIZE WELL WITH THIS FEATURE...TAKING IT ACROSS THE CWA AROUND 18Z. INTRODUCED SOME ISOLATED SPRINKLES THIS AFTERNOON ACROSS PORTIONS OF THE CWA. FAR WESTERN AND NORTHERN CWA SHOULD STAY DRY DRIER SURFACE DEWPOINTS IN PLACE...AND ANTICYCLONIC FLOW WORKING INTO THE WESTERN CWA. FRIDAY THROUGH SUNDAY... SURFACE HIGH PRESSURE ASSERTS ITSELF OVER THE SOUTHEASTERN STATES AND EASTERN SEABOARD THROUGH THE PERIOD WITH GENERAL HEIGHT RISES ACROSS THE CENTRAL CONUS AS THE UPPER TROUGH EXITS TO THE EAST. H85 TEMPS GRADUALLY INCREASE THROUGH THE PERIOD...REACHING AROUND 10C BY SUNDAY EVENING. SHOULD SEE A GRADUAL WARMING TREND...WITH TEMPS INTO THE MID 60S FRIDAY AND SATURDAY AND THEN LOW POSSIBLY MID 70S AWAY FROM THE LAKE FRONT SUNDAY. SATURDAY AND SUNDAY...LIGHT SOUTHERLY WINDS WILL OFFER LITTLE IF ANY RESISTANCE TO A LAKE BREEZE PUSHING INLAND ACROSS FAR NORTHEASTERN ILLINOIS AND COOLING TEMPERATURES ALONG THE LAKE FRONT BACK INTO THE 50S. WILL HAVE TO KEEP AN EYE ON A MID LEVEL SHORTWAVE TROUGH THAT PUSHES ACROSS THE REGION POSSIBLY FRIDAY EVENING...WITH A WEAK SURFACE FRONT STALLING JUST TO OUR NORTH FRIDAY NIGHT AND SATURDAY. FORECAST SOUNDINGS INDICATE THE AIRMASS OUT AHEAD OF THE FRONT IS PRETTY DRY WITH POOR MIDLEVEL LAPSE RATES...SO PRECIPITATION SEEMS UNLIKELY THOUGH THE MODELS CONTINUE TO HINT AS SPOTTY SHOWERS DEVELOPING JUST TO OUR NORTH. MONDAY THROUGH WEDNESDAY... PATTERN BEGINS TO AMPLIFY EARLY NEXT WEEK AS STRONG AND PROGRESSIVE TROUGH DEVELOPS ACROSS THE WESTERN CONUS. LOCALLY...WARM ADVECTION INCREASES WITH MODELS INDICATING THE POTENTIAL FOR SOME CONVECTION AS THEY DEVELOP QUITE A BIT OF INSTABILITY...THOUGH HARD TO PINPOINT ANY FOCUS THIS FAR OUT. BUMPED TEMPERATURES UP SOME MONDAY AND TUESDAY INTO THE MID 70S. THE GFS AND ECMWF ARE HONING IN ON WEDNESDAY FOR A COLD FRONT TO PUSH ACROSS THE AREA. DEUBELBEISS && .CLIMATE... 1044 PM CDT ROCKFORD HAS YET TO REACH 70 DEGREES THIS YEAR. THE LATEST FIRST 70 DEGREE DAY EVER IN ROCKFORD WAS MAY 6TH 1971. IF ROCKFORD GOES THROUGH SATURDAY WITHOUT REACHING 70 THIS YEAR WILL BE THE 2ND LATEST FIRST 70 DEGREE DAY EVER IN ROCKFORD. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * ISOLATED LIGHT SHOWERS AND PATCHY MVFR CIGS THROUGH 15Z...THEN VFR. * STRONG GUSTY W WINDS THIS MORNING GRADUALLY DIMINISHING THIS AFTERNOON. * ISOLATED SPRINKLES POSSIBLE LATE MORNING-MID AFTERNOON. * OUTLOOK - STRONG GUSTY SW WINDS DEVELOPING FRIDAY. ALLSOPP //DISCUSSION...UPDATED 12Z... WINDS...COLD FRONT MOVING THROUGH THE AREA THIS MORNING. STRONG GUSTY SOUTHWEST WINDS ARE VEERING WEST. PRESSURE GRADIENT WILL LOOSEN THIS AFTERNOON AS A HIGH PRESSURE RIDGE REBUILDS INTO THE AREA. THIS WILL ALLOW WINDS AND GUSTINESS TO GRADUALLY SUBSIDE THROUGH THE AFTERNOON HOURS. ATMOSPHERE WILL DECOUPLE QUICKLY WITH SUNDOWN AND WINDS WILL BECOME LIGHT SOUTHWEST OVERNIGHT. OUTLOOK...AS THE HIGH PRESSURE SHIFTS EAST FRIDAY THE PRESSURE GRADIENT WILL STRENGTHEN AND SOUTHWEST WINDS WILL INCREASE TO 15 TO 25 KT BY AFTERNOON. CLOUD AND PRECIP TRENDS...MAIN BAND OF SHOWERS HAS PASSED BUT SPOTTY LIGHT SHOWERS OVER FAR NORTHERN IL AND SOUTHERN WI MAY AFFECT MAINLY RFD AND ORD THROUGH MID MORNING. DONT EXPECT ANY VSBY RESTRICTIONS WITH THESE SPOTTY LIGHT SHOWERS. COVERED THIS WITH VCSH. SCT-BKN STRATUS AROUND 2500 FT THIS MORNING. STEEP LOW LEVEL LAPSE RATES WILL DEVELOP AFTER A COUPLE HOURS OF SOLAR HEATING. EXPECT A BROKEN AND FAIRLY DEEP CUMULUS FIELD TO DEVELOP BY MID TO LATE MORNING. THIS WILL INITIALLY BE AROUND 3000-3500 FT BUT WILL BE LIFTING TO AROUND 5000 FT THIS AFTERNOON. COULD BE SUFFICIENT CLOUD DEPTH FOR A FEW SPRINKLES OR LIGHT SHOWERS LATE MORNING INTO MID AFTERNOON. HOWEVER...SURFACE HIGH PRESSURE RIDGE WILL BE BUILDING INTO THE AREA FROM THE WEST THIS AFTERNOON. THIS MAY LIMIT SHOWER DEVELOPMENT AND IN FACT CUMULUS FIELD SHOULD BE FLATTENING AND THINNING BY LATE AFTERNOON AND CLEARING BY EVENING. FAIR SKIES TONIGHT INTO THE WEEKEND. ALLSOPP //ORD AND MDW CONFIDENCE...UPDATED 12Z... * HIGH CONFIDENCE IN WIND FORECAST. * MEDIUM-HIGH CONFIDENCE IN CLOUD TRENDS. * LOW CONFIDENCE IN SPRINKLES LATE MORNING-MID AFTERNOON. ALLSOPP //OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z... FRIDAY NIGHT THROUGH TUESDAY...DRY/VFR. WEDNESDAY...CHANCE OF THUNDERSTORMS. ALLSOPP && .MARINE... 357 AM CDT LOW PRESSURE WAS OVER SOUTHERN LAKE SUPERIOR EARLY THIS MORNING WITH A COLD FRONT TRAILING TO THE ILLINOIS/IOWA BORDER. THE LOW AND FRONT WILL DRIVE ACROSS LAKE MICHIGAN THIS MORNING WITH A PERIOD OF BRISK WINDS VEERING FROM SW TO WNW THIS MORNING. HIGH PRESSURE WILL QUICKLY REBUILD INTO THE WESTERN GREAT LAKES THIS AFTERNOON AND WINDS WILL DIMINISH AND BACK SOUTHWEST BY EVENING. THE HIGH WILL SHIFT EASTWARD FRIDAY. MEANWHILE LOW PRESSURE WILL MOVE INTO HUDSON BAY WITH A WEAK TROF EXTENDING SOUTHWESTWARD TO THE UPPER MISSISSIPPI VALLEY. THIS WILL SET UP A STRONG PRESSURE GRADIENT ACROSS THE LAKE AND CAUSE STRONG SOUTH WINDS TO DEVELOP OVER THE LAKE FRIDAY. THIS GRADIENT WILL WEAKEN FRIDAY NIGHT. THERE WILL THEN BE A PROLONGED PERIOD INTO EARLY NEXT WEAK WITH LIGHT TO MODERATE S-SW FLOW OVER THE LAKE. ALLSOPP && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WWW.CRH.NOAA.GOV/CHICAGO FOLLOW US FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 271147 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 647 AM CDT SAT APR 27 2013 .DISCUSSION... 318 AM CDT TODAY THROUGH TONIGHT... IR IMAGERY EARLY THIS MORNING HAS COOLING CLOUD TOPS ACROSS THE OZARKS AS A COMPLEX OF THUNDERSTORMS SLOWLY SLIDES EAST ACROSS THIS AREA. FURTHER NORTH INTO SOUTHERN IL DRIER AIR REMAINS AND IS NOTED WITH MORE BREAKS IN THE CLOUD COVER. DEW POINTS ARE BEGINNING TO RISE ACROSS SOUTHERN IL INTO THE MID/UPR 40S...HOWEVER WELL TO THE NORTH ACROSS NORTHERN IL/NORTHWEST DEW POINTS ARE ARND 40S TO THE LOW 40S. SFC WINDS REMAIN LIGHT ACROSS THE NORTHERN CWFA EARLY THIS MORNING...WITH AN OCCASIONAL GUST INTO TO ARND 20 MPH. SFC TEMPS HAVE REMAINED MILD IN THE UPR 40S...TO THE LOW 50S AT DOWNTOWN CHICAGO THANKS TO A STEADY SOUTHWEST WIND KEEPING THE ONSHORE FLOW FROM MOVING INLAND. MOISTURE WILL STEADILY LIFT NORTH AS THE 500MB TROUGH SLIDES EAST FROM THE CENTRAL PLAINS INTO THE GREAT LAKES/OHIO VALLEY. THIS SHOULD HELP THICKEN THE CLOUD COVER ACROSS THE REMAINDER OF THE CWFA THIS AFTN/EVE. GUIDANCE HAS BACKED OFF ON BRINGING ANY PRECIP NORTH OF I-80. THEN THE MOISTURE SHIELD BECOMES ORIENTED FROM PONTIAC TO GARY AND POINTS EAST OF THIS LINE. TO THE NORTHWEST WEAK LLVL ANTI-CYCLONIC FLOW APPEARS PLAUSIBLE...WHICH SHOULD KEEP DRY CONDS FOR THIS AFTN/EVE. LCL HI-RES GUIDANCE SUPPORTS THIS SOLUTION THROUGH TONIGHT. WITH A LIGHT LLVL FLOW...WINDS ACROSS FAR NORTHEAST IL MAY BEGIN TO TURN EAST/NORTHEAST WITH A LAKE BREEZE FORMING AND SLOWLY MOVING INLAND. THUS HAVE MAINTAINED MENTION OF COOLER TEMPS FOR THE AREAS ADJACENT TO LK MICHIGAN. WITH ANTI-CYCLONIC FLOW BECOMES STRETCHED FROM THE CENTRAL PLAINS NORTHEAST THROUGH NORTHERN MICHIGAN. WITH SHOULD AID IN A PROLONGED PERIOD OF NORTHEAST WINDS ACROSS A PORTION OF NORTH/NORTHEAST IL...AND COOL TEMPS INTO THE MID/UPR 40S. CONFIDENCE...MEDIUM. SUNDAY THROUGH TUESDAY... WEAK 500MB TROUGH SLIDES EAST ACROSS THE OHIO VALLEY SUN EVENING...AND SHOULD BRING AN END TO THE SPRINKLES/SHOWERS ACROSS THE SOUTHEAST CWFA. MID-LVL RIDGING QUICKLY PUSHES IN FROM THE WEST FOR MON...WITH SOUTHERLY FLOW ALLOWING WARM AIR TO SURGE NORTH INTO THE REGION. 850MB TEMPS QUICKLY WARM TO 10-12 DEG C MON...THEN INTO THE MID TEENS TUE AFTN AHEAD OF THE FRONTAL BOUNDARY. MID-LVL HEIGHTS APPEAR TO LINGER FOR MUCH OF MON...SUGGESTING DIFFLUENT FLOW IN THE MID-LVLS AND RESULTING IN A LOWER PROB FOR PRECIP MON AFTN. HAVE TRIMMED BACK POPS MON/MON NGT...ALTHOUGH WITH INCREASING LLVL MOISTURE IT IS DIFFICULT TO GO WITH A COMPLETELY DRY FORECAST. SO HAVE HELD ONTO MENTION OF SLIGHT CHC SHRA/TSRA. THE EXCEPTION COULD BE THE FAR SOUTHEAST CWFA WHERE THE BEST CHC FOR DRY WX MON/MON NGT WILL OCCUR. CONFIDENCE...HIGH. TUESDAY THROUGH SATURDAY... MINIMAL CHANGES FROM PRIOR FORECASTS WITH AN ANOMALOUS WARM WEDGE OF AIR ADVECTING NORTH ACROSS THE CWFA TUE AND LINGERING INTO WED...POSSIBLY BRINGING 80 DEG AIR TO MANY LOCATIONS OF NORTHERN IL/NORTHWEST IN. HOWEVER...AS IS GENERALLY THE CASE WHEN THE PENDULUM SWINGS IN ONE DIRECTION IT WILL EVENTUALLY SWING IN THE INVERSE DIRECTION. THIS STILL APPEARS TO BE THE CASE LATER NEXT WEEK WHEN MUCH COOLER AIR AND A CUTOFF LOW PRESSURE SYSTEM DIGS INTO THE GREAT LAKES REGION. TUE WILL FEATURE MID-LVL RIDGING STEADILY DRIFTING EAST...BLENDING INTO THE DOWNSTREAM WESTERN ATLANTIC RIDGE. THIS FEATURE WILL THEN BEGIN TO AMPLIFY BY MID-NEXT WEEK. MEANWHILE A EASTERN PACIFIC/PAC-NW CONUS RIDGE WILL ALSO AMPLIFY. THIS CONTINUES TO POINT TOWARDS A TROUGH SLIDING SOUTH ACROSS THE CANADIAN ROCKIES INTO THE UPPER MIDWEST...AND EVENTUALLY THE GREAT LAKES/OHIO VALLEY REGIONS LATER NEXT WEEK. GUIDANCE HAS SHOWN SOME STRENGTHENING TO THE INTENSITY OF THE 500MB VORT MAX. ONCE THIS FEATURE ARRIVES ACROSS THE REGION...THE CHALLENGE WILL BE HOW QUICKLY IT WILL DEPART AS THE FORWARD PROGRESSION WILL BE HEAVILY INFLUENCED BY THE STRENGTH/PLACEMENT OF THE DOWNSTREAM RIDGE. IN THE NEAR SFC ENVIRONMENT OPERATIONAL SOLUTIONS CONTINUE TO FAVOR A SFC LOW LIFTING NORTHEAST ACROSS THE UPPER MIDWEST TUE...WITH A FRONTAL BOUNDARY TRAILING AND STRETCHING SOUTHWEST THROUGH THE SOUTHERN ROCKIES. GUIDANCE HAS SHOWN SOME SLOWING IN THE ARRIVAL OF THE FRONTAL BOUNDARY...AND MAY NOT OCCUR UNTIL LATER WED. WITH A STRONG SOUTH/SOUTHWEST PUSH OF WARM/MOIST AIR...IT IS CONCEIVABLE THAT WITH A SLOW MOVING FRONTAL BOUNDARY BOTH TUE/WED COULD END UP WITH HIGHS WELL INTO THE 70S TO ARND 80 DEG. HAVE HEDGED THE FORECAST TOWARDS A SLOWER FROPA...AND WILL TRIM BACK ON POPS TUE/TUE NGT AS A RESULT. WITH THE ABSENCE OF A SFC FEATURE TO GENERATE STRONG INSTABILITY/SHEAR...ANY CONVECTION DOES NOT APPEAR TO BE STRONG AT THIS POINT. NONETHELESS WITH PWAT VALUES ON THE INCREASE AND MOISTURE STREAMING NORTH FROM THE WESTERN GULF OF MEXICO...IT IS CONCEIVABLE THAT THIS COUPLED WITH A TIGHT PRESSURE GRADIENT IN THE NEAR SFC COULD PROVIDE ENOUGH LIFT TO SUPPORT SOME ROBUST UPDRAFTS. ENSEMBLES AND OPERATIONAL SOLUTIONS CONTINUE TO PROG A CUTOFF 500MB VORT MAX OVER THE OHIO VALLEY BY THE END OF NEXT WEEK...WHICH HAS MAINTAINED SOME DEGREE OF CONFIDENCE. AS A RESULT THIS SOLUTION POINTS TOWARDS MUCH COOLER AIR ADVECTING SOUTH INTO THE GREAT LAKES/OHIO VALLEY REGIONS...WITH TEMPS STRUGGLING TO REACH THE LOW/MID 50S FOR THE FINAL PERIODS OF THE CURRENT EXTENDED FORECAST. THERMAL TROUGH AT 850MB CONTINUES TO HOVER IN THE -6 TO -8 DEG C RANGE. GIVEN HOW EFFICIENT THE SFC CAN WARM...ANY BREAKS IN THE CLOUD COVER COULD EASILY RESULT IN QUICK DESTABILIZATION. ANTICIPATE THAT IF THIS OCCURS THAT THE POTENTIAL FOR ISOLATED LOW TOPPED CONVECTION...POSSIBLY MARGINALLY SEVERE WEATHER FOR THE FIRST FEW DAYS OF MAY COULD TRANSPIRE. OVERNIGHT FRI NIGHT TEMPS COULD BE COOL ENOUGH TO SUPPORT A FEW WET SNOW FLAKES MIXED WITH RAIN. CONFIDENCE PRECIPITATION...MEDIUM. CONFIDENCE IN TEMPERATURES...HIGH. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * WINDS SHIFTING TO THE E OR ENE ON A LAKE BREEZE THIS AFTERNOON. //DISCUSSION...UPDATED 12Z... HIGH PRESSURE REMAINS IN CONTROL OVER THE IMMEDIATE AREA THIS MORNING WITH AN INVESRION ALLOWING WINDS TO BE VERY LIGHT. THESE SHOULD COME UP AS MIXING ENSUES WITH LITTLE IN THE WAY OF IMMEDIATE CLOUD COVER. AN UPPER LOW WILL MEANDER ITS WAY TO CENTRAL IL BY THIS EVE. CLOUDS SHOULD THICKEN AND EVER SO GRADUALLY LOWER. LIGHT RAIN SHOWERS FROM THIS SYSTEM WILL LIKELY ENCROACH ON THE TRACONS SOUTHERN AREA LATE TODAY INTO TONIGHT...BUT SHOULD REMAIN SOUTH OF THE AIRPORTS THEMSELVES. LAKE BREEZE DEVELOPMENT IS ANTICIPATED TODAY AND COULD FORM AS QUICKLY AS LATE THIS MORNING. THIS SHOULD REACH AS FAR INLAND AS ORD BUT THE TIMING WILL BE TRICKY AS SOME MODEL SOURCES INDICATE AN EARLIER ARRIVAL THAN FORECAST. CLIMATOLOGY FAVORS A SHIFT TO 050-070 DEGREES WHILE THE PRESSURE PATTERN AND GUIDANCE WOULD INDICATE MORE 070-100. HAVE CONTINUED NEAR THE CENTER OF THIS ENVELOPE WITH 070 IN THE FORECAST. SPEEDS ARE MOST FAVORED TO BE RIGHT AROUND 10 KT FOR TWO-THREE HOURS AT AND AFTER THE LAKE BREEZE PASASGE. WIND DIRECTION MAY VERY WELL BECOME VARIABLE AFTER DARK TONIGHT BEFORE NORTHEAST FLOW ON SUNDAY. //ORD AND MDW CONFIDENCE...UPDATED 12Z... * HIGH CONFIDENCE IN LAKE BREEZE OCCURRING AND WIND SHIFT TO 50 TO 100 DEGREES...BUT MEDIUM CONFIDENCE IN PRECISE TIMING AND SPEED STAYING AT 10 KT OR LESS. IF ITS A DIFFERENT TIME...IT IS FAVORED TO BE SLIGHTLY EARLIER THAN GOING FORECAST. //OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z... SUNDAY NIGHT-MONDAY...VFR. MONDAY NIGHT-THURSDAY...CHC FOR SHOWERS AND SLT CHC OF THUNDER. MVFR PROBABLE FOR PART OF THIS TIME...ESPECIALLY BY WEDNESDAY. THURSDAY NIGHT-FRIDAY...CHANCE OF SHOWERS. MTF && .MARINE... 220 AM CDT WHILE THE LAKE WILL REMAIN SANDWICHED BETWEEN HIGH PRESSURE ACROSS THE EASTERN U.S. AND A DECAYING LOW PRESSURE TROUGH OVER THE UPPER MIDWEST...THE GRADIENT BETWEEN THESE TWO FEATURES WILL BE FAR LESS THAN YESTERDAY. FOR THE SOUTHERN HALF OF THE LAKE THIS WILL ALLOW LAKE BREEZE DEVELOPMENT TODAY WITH LIKELY SMALL SCALE HIGH PRESSURE AND VARIABLE WINDS OVER THE CENTER AXIS OF THE LAKE. SIMILAR WILL HAPPEN ON SUNDAY BUT ACROSS THE ENTIRE EXTENT OF THE LAKE. APPROACHING LOW PRESSURE FROM THE UPPER MIDWEST MONDAY NIGHT INTO TUESDAY WILL ALLOW FOR THE SYNOPTIC SOUTHERLY WINDS TO INCREASE. WITH QUITE A BIT OF WARM AIR FORECAST TO COME NORTHWARD THE INVERSION SHOULD BE STEEP...SO NOT MUCH DIFFERENCE IS EXPECTED IN SUSTAINED AND GUST SPEED AHEAD OF THAT SYSTEM. THERE IS A WIDE SPREAD ON THE EXACT DEVELOPMENT AND PROGRESSION OF THE LOW PRESSURE IN THE REGION DURING THE MIDDLE TO LATTER PART OF THE WEEK...BUT CONFIDENCE IS INCREASING THAT THE PATTERN WILL SLOW DOWN CONSIDERABLY. DEPENDING ON THE EXACT PATH OF THIS LOW...THE ADVECTION OF THE ANOMALOUSLY COOL AIR FOR THE FIRST DAYS OF MAY COULD LEAD TO GUSTY WINDS SOME TIME DURING THAT PERIOD...BUT CONFIDENCE IS QUITE LOW IN THIS AT THE PRESENT TIME. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WWW.CRH.NOAA.GOV/CHICAGO FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 272350 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 650 PM CDT SAT APR 27 2013 .DISCUSSION... 301 PM...MULTIPLE FORECAST CONCERNS AND CHALLENGES OVER THE NEXT 7 DAYS INCLUDING THE FIRST POTENTIAL 80 DEGREE DAY FOR MUCH OF THE CWA ON TUESDAY. IN THE SHORT TERM...LAKE BREEZE HAS MOVED INLAND ACROSS COOK/LAKE COUNTIES IN NORTHEAST IL WITH COOLER TEMPS BEHIND IT. TEMPS INLAND HAVE WARMED IN THE MID/UPPER 60S AND LIKELY A FEW 70S AS WELL. SHOWERS CONTINUE TO SLOWLY LIFT NORTH ACROSS CENTRAL IL ASSOCIATED WITH A CLOSED UPPER LOW WHICH WILL CONTINUE MOVING EAST/NORTHEAST TONIGHT INTO SUNDAY. SHOWERS WILL CONTINUE TO SPREAD NORTHEAST THIS EVENING WITH THE BEST COVERAGE GENERALLY SOUTHEAST OF A LINE FROM CHICAGO TO MENDOTA. AS THIS UPPER LOW DEPARTS SUNDAY MORNING SHOWER ACTIVITY WILL ALSO BEGIN TO DISSIPATE BUT COULD BE SOME DIURNALLY DRIVEN SHOWERS ON THE BACK SIDE OF THE UPPER LOW ACROSS FAR EASTERN IL/NORTHWEST INDIANA SUNDAY AFTERNOON. LOW TEMPS TONIGHT WILL BE SEVERAL DEGREES WARMER THAN THIS MORNING AND REMAIN IN THE UPPER 40S/LOWER 50S BUT HIGHS ON SUNDAY ARE A LITTLE MORE UNCERTAIN ACROSS THE EASTERN AREAS DEPENDING ON HOW FAST CLOUDS DEPART AND ANY ISOLATED SHOWERS IN THE AFTERNOON. THUS HAVE MAINTAINED GOING HIGHS RANGING FROM LOWER 70S WESTERN CWA TO LOWER/MID 60S EAST. WEAK GRADIENT WILL ALLOW ANOTHER LAKE BREEZE TO FORM SUNDAY AFTERNOON...WITH COOLER TEMPS BEHIND IT. A COLD FRONT WILL SLOWLY MOVE SOUTHEAST ACROSS THE UPPER LAKES AND MIDWEST SUNDAY INTO MONDAY...PERHAPS SAGGING INTO FAR NORTHERN IL MONDAY AFTERNOON BUT AS TWO NEW AREAS OF LOW PRESSURE DEVELOP... ONE OF SOUTHERN CANADA AND A SECOND OVER THE NORTHERN PLAINS... THIS FRONT/WIND SHIFT WILL WASH OUT LEAVING JUST THE UPPER WAVE TO GENERATE ANY SHOWER/THUNDER ACTIVITY AND EXPECT MUCH OF MONDAY TO BE DRY WITH THE BEST CHANCE OF ANY PRECIP ACROSS THE NORTHWEST CWA. AS THIS FEATURE DRIFTS EAST MONDAY NIGHT...THIS APPEARS THE TIME PERIOD FOR THE BEST CHANCE OF SHOWERS AND A FEW THUNDERSTORMS BUT CONFIDENCE STILL REMAINS SOMEWHAT LOW. WHILE LINGERING SHOWERS ARE POSSIBLE TUESDAY MORNING...HAVE TRENDED DRY TUESDAY AS STRONG SOUTHERLY FLOW DEVELOPS. SOUTHERLY WINDS COULD EASILY BE GUSTING 30-35 MPH AND WITH PLENTY OF EXPECTED SUNSHINE...HIGH TEMPS WILL EASILY REACH UPPER 70S AND HAVE BUMPED HIGHS INTO THE LOWER 80S ALL LOCATIONS...INCLUDING THE LAKE FRONT...AS SOUTHERLY FLOW WILL BE STRONG ENOUGH TO PREVENT ANY LAKE COOLING. THOUGH CONFIDENCE FOR LOWER 80S IS ONLY LOW TO MEDIUM GIVEN POSSIBLE CLOUD COVER/SHOWERS IN THE MORNING AND HOW DEEP LOW LEVELS ARE ABLE TO MIX BY AFTERNOON. FROM TUESDAY NIGHT THROUGH NEXT SATURDAY...OVERALL CONFIDENCE REMAINS LOW BUT SOME TRENDS ARE EMERGING. A COLD FRONT WILL BECOME NEARLY STATIONARY FROM THE UPPER LAKES INTO THE ARKLATEX REGION AS AN UPPER LOW DEVELOPS OVER THE PLAINS AND THEN REMAINS NEARLY STATIONARY INTO NEXT WEEKEND...AT LEAST AS ADVERTISED BY THE 12Z GFS/ECMWF. THIS DELAYS THE ARRIVAL OF THE COLDER AIR...PERHAPS BY A FEW DAYS. SO CONFIDENCE OF HIGHS BACK IN THE MID/UPPER 70S ON WEDNESDAY...WHICH MAY ALSO TURN OUT TO BE MAINLY DRY...IS INCREASING. BUT GIVEN THE COMPLEXITY OF THE UPPER LOW...VARIOUS WAVES ROTATING AROUND IT AND ASSOCIATED PRECIP...NOT TO MENTION ITS LOCATION...AS WELL AS POSSIBLE EASTERLY FLOW OFF THE LAKE... NOT READY TO MAKE SIGNIFICANT CHANGES TO EITHER TEMPS OR POPS FROM THIS DISTANCE AND IF CURRENT TRENDS CONTINUE...WEDNESDAY NIGHT INTO THURSDAY NIGHT COULD END UP WARMER/DRIER. CMS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * LIGHT RAIN POSSIBLE OVERNIGHT * MVFR CIGS POSSIBLE LATE TONIGHT INTO SUNDAY MORNING IZZI //DISCUSSION...UPDATED 00Z... LOW PRESSURE SYSTEM WILL TRACK SOUTH OF THE TERMINALS TONIGHT WITH THE NORTHERN FRINGES OF THE SYSTEMS PRECIPITATION FLIRTING WITH THE CHGO TERMINALS OVERNIGHT. LARGE BANK OF STRATUS ON THE BACK SIDE OF THE SYSTEM WILL LIKELY BLANKET THE AREA SUNDAY MORNING AND POTENTIALLY INTO THE AFTERNOON. CLOSER TO THE TRACK OF THE LOW AND WHERE COLUMN GETS SATURATED BY PRECIP IS WHERE BETTER CHANCES OF MVFR CIGS WILL RESIDE...FOR OUR TERMINALS MVFR CIGS ARE CERTAINLY POSSIBLE BUT CONFIDENCE IS NOT ALL THAT HIGH SO WENT WITH BORDERLINE LOW END VFR/HIGH END MVFR BUT THIS COULD END UP BEING TOO OPTIMISTIC. LAKE BREEZE INFLUENCED WINDS WILL SUBSIDE THIS EVENING AND BECOME LIGHT AND VARIABLE TONIGHT BEFORE LOCKING IN MORE NORTHEASTERLY SUNDAY AS THE LOW PULLS AWAY. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * MEDIUM CONFIDENCE IN RAIN CHANCES TONIGHT * LOW CONFIDENCE IN CIG CATEGORY LATER TONIGHT INTO SUNDAY MORNING * HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS IZZI //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY...CHANCE SHRA/TSRA...MAINLY AT NIGHT. OTHERWISE GENERALLY VFR. TUESDAY...GENERALLY VFR. GUSTY SSW WINDS POSSIBLE. WEDNESDAY AND THURSDAY...PERIODS OF SHRA/TSRA POSSIBLE. AT LEAST PERIODIC MVFR PROBABLE. FRIDAY...CHANCE OF SHRA. MVFR CIGS POSSIBLE. IZZI && .MARINE... 340 PM CDT ONLY LIGHT TO MODERATE BREEZES FORECAST FOR LAKE MI UNTIL MON NIGHT AND TUE WHEN S WINDS WILL THEN FRESHEN AS THE PRESSURE GRADIENT TIGHTENS BETWEEN A RIDGE OF HIGH PRESSURE PARKED OVER CANADIAN MARITIMES...THE GULF OF SAINT LAWRENCE AND ALONG THE NEW ENGLAND AND NORTHEASTERN COASTS AND LOW PRESSURE TREKKING E ALONG OR NEAR THE 49TH PARALLEL. THE COLD FRONT TRAILING FROM THIS LOW WILL MOVE INTO THE UPPER MIDWEST AS THE LOW TURNS NORTHEASTWARD ACROSS ONTARIO TO HUDSON BAY TUE AND TUE NIGHT. WITH THE LOW MOVING FURTHER AWAY WINDS WILL DIMINISH. THE COLD FRONT WILL NOT CROSS LAKE MI UNTIL WED...WHEN THE WIND THEN SHIFTS TO OUT OF THE N AND INCREASES BACK TO A STRONG BREEZE AS HIGH PRESSURE BUILDS SE FROM ALBERTA AND SASKATCHEWAN BEHIND THE COLD FRONT. NICE TO HAVE BOTH THE N AND S LAKE MI BUOYS BACK FOR MONITORING OPEN WATER CONDITIONS. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 282353 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 653 PM CDT SUN APR 28 2013 .DISCUSSION... 543 PM CDT GOING TO THROW OUT A DENSE FOG ADVISORY ALONG THE LAKE FOR NW INDIANA AND COOK COUNTY ILLINOIS. VISIBLE SATELLITE IMAGERY AND THE FEW WEBCAMS WE CAN FIND ONLINE HAVE SHOWN DENSE FOG FESTERING ALONG AND MAINLY JUST OFF THE SHORE. HAVE BEEN IN TOUCH WITH CHICAGO OEMC AND THEIR NETWORK OF WEBCAMS ALONG LAKE SHORE DRIVE SHOW THAT VERY DENSE FOG HAS NOW OVERSPREAD LAKESHORE DR WITH VISIBILITY ONLY A COUPLE CAR LENGTHS. REALLY DONT HAVE A GOOD FEEL FOR HOW LONG THE FOG WILL LAST...SO GOING TO START WITH A 03Z END TIME FOR THE NPW...WILL MONITOR TRENDS EARLY THIS EVENING AND IF IT APPEARS FOG EXPANDS OR PERSISTS AFTER SUNSET MAY NEED TO EXTEND THE END TIME OF THE ADVISORY TO LAST THROUGH THE NIGHT. IZZI/CMS //PREV DISCUSSION... 334 PM CDT THE STORY FOR THE FIRST HALF OF THE WEEK WILL BE INCREASING WARMTH WITH SOUTHERLY FLOW DEVELOPING TOMORROW BEHIND A WARM FRONT LIFTING THROUGH THE AREA AND AHEAD OF A VERY SLOWLY APPROACHING COLD FRONT. THE PASSAGE OF THE WARM FRONT AND THE PROXIMITY OF THE COLD FRONT WILL SUPPORT INCREASED CHANCES FOR SHOWERS AND THUNDERSTORMS ACROSS NORTHERN ILLINOIS TOMORROW AND TOMORROW NIGHT. IN FAR NW IL THE FCST MODELS ALSO ARE SHOWING 0-6KM SHEAR OF 40-50 KTS...CAPE IN THE 1000-2000 J/KG RANGE...AND ENHANCED LOW LEVEL HELICITY ESPECIALLY NEAR THE SFC BOUNDARIES...SO LATEST SPC OUTLOOK HAS A PORTION OF THE FORECAST AREA IN A TINY SLIGHT RISK FOR SEVERE TOMORROW. STRONG SOUTHERLY FLOW THEN TAKES OVER EARLY TUESDAY AND PUSHES THE BOUNDARIES FARTHER NORTH. THIS SOUTHERLY FLOW PERSISTS THROUGH AT LEAST TUESDAY NIGHT...AND PERHAPS INTO WEDNESDAY FOR SOUTHEASTERN PORTIONS OF THE FORECAST AREA IN EASTERN ILLINOIS AND NW INDIANA. BY WEDNESDAY IF THE COLD FRONT IS FINALLY ABLE TO MAKE ITS WAY INTO THE AREA...NORTHERN PORTIONS OF THE AREA COOL OFF AND RAIN CHANCES INCREASE. FOR THE TEMPERATURE FORECAST IT IS SHAPING UP TO BE A CHALLENGING WEEK...STARTING WITH POSSIBLE NEAR RECORD HIGHS TUESDAY THEN GREAT UNCERTAINTY IN THE LATTER HALF OF THE WEEK AS A CUTOFF UPPER LOW PIVOTS OVERHEAD. GUIDANCE IS IN PRETTY GOOD AGREEMENT THAT TUESDAY WILL BE WARM...LIKE 20 DEGREES ABOVE NORMAL...SO THE QUESTION IS HOW HIGH TO GO. LATEST MODELS HAVE NOT BACKED OFF ON THE IDEA OF STRONG SOUTHWEST WINDS AND 925 MB TEMPERATURES AROUND 19C WHICH WOULD SUPPORT MID TO UPPER 80S AT THE SURFACE FOR PORTIONS OF THE AREA. GIVEN THE CONCURRENT POSSIBILITY OF DIURNAL CLOUDINESS AND SOME ISOLATED SHOWERS LATE IN THE DAY...WILL NOT GO QUITE THAT WARM IN THE FORECAST JUST QUITE YET...BUT WILL CONTINUE THE TREND UPWARD IN THAT DIRECTION. THERE IS A POSSIBILITY THIS WARMTH COULD BE REPEATED WEDNESDAY BUT WITH EVEN LESS CERTAINTY CONCERNING PRECIP AND CLOUD COVER...HAVE KEPT MOST LOCATIONS COOLER THAN TUESDAY EXCEPT IN THE FAR SOUTH. FOR THURSDAY INTO THE WEEKEND THE INFLUENCE OF THE UPPER LOW WILL KEEP ALL AREAS COOLER BUT NOT UNSEASONABLY COOL...WITH PERSISTENT CHANCE TO SLIGHT CHANCE OF SHOWERS. LENNING && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * CHANCE FOR SOME VSBY RESTRICTIONS IN BR OVERNIGHT WITH OUTSIDE CHANCE OF IFR OR LOWER CIGS IZZI //DISCUSSION...UPDATED 00Z... VFR STRATOCUMULUS DECK NEAR THE TERMINALS EXPECTED TO DISSIPATE THIS EVENING...HOWEVER VISIBLE SATELLITE IMAGERY DOES SHOW A BLOSSOMING AREA OF FOG AND VERY LOW STRATUS OVER THE LAKE. SMALL POTENTIAL EXISTS FOR THIS FOG/STRATUS TO GET BLOWN/DEVELOP INLAND THIS EVENING...BUT MOST LIKELY SCENARIO KEEPS IT EAST OF THE TERMINALS AND VERY LOW STUFF OUT OF TAFS. WILL MONITOR THIS EVENING FOR POSSIBLE AMDS. ANY FOG/STRATUS WILL BURN OFF BY MID MORNING MONDAY WITH SOUTHERLY WINDS DEVELOPING. COULD SEE SOME OCNL GUSTS IN THE MID TO UPPER TEENS...BUT WITH ENCROACHING MID- UPPER LEVEL DECK THINK GUSTS MAY BE MORE OF A SPORADIC CONDITION VS PREVAILING. WEAKENING COLD FRONT COULD KICK OF SCTD SHRA/TSRA TOWARD MS RIVER LATE IN AFTERNOON INTO TOMORROW EVENING...BUT ACTIVITY LIKELY TO REMAIN OF RFD THRU 00Z AND ORD THROUGH AT LEAST EARLY EVENING. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * MEDIUM CONFIDENCE IN VSBY/CIGS TONIGHT * HIGH CONFIDENCE IN ALL OTHER ELEMENTS IZZI //OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z... TUESDAY...VFR. SOUTHERLY WINDS GUSTING TO 30KT POSSIBLE IN AFTERNOON. WEDNESDAY...GOOD CHANCE OF SHRA/TSRA...ESPECIALLY AT NIGHT. PREVAILING VFR MOST PROBABLE. THURSDAY AND FRIDAY...OCNL SHRA AND TSRA. PREVAILING MVFR PROBABLE AND IFR POSSIBLE. SATURDAY...CHANCE OF SHRA/POSSIBLE TSRA. PREVAILING MVFR PROBABLE. IZZI && .MARINE... 348 PM CDT THERE WILL BE LIGHT TO MODERATE BREEZES TONIGHT AND MON AS A WEAK RIDGE OF HIGH PRESSURE WILL PASS OVER THE LAKE BETWEEN LOW PRESSURE IN FAR NE IND CONTINUING TO SLOWLY MOVE NE TO THE THUMB OF LOWER MI BY MORNING WHILE A TROUGH OF LOW PRESSURE MOVES FROM NW MN TO CENTRAL WI BEFORE DISSIPATING DURING MON. LOW PRESSURE IN THE NORTHERN PLAINS WILL MOVE NE TO CENTRAL ONTARIO MON NIGHT AND TUE...CONTINUING ON TO SOUTHERN HUDSON BAY BY WED MORNING. THE LOW AND THE APPROACH OF THE ATTENDANT COLD FRONT WILL CAUSE S WINDS TO INCREASE TO A STRONG BREEZE. A COLD FRONT TRAILING SW FROM THIS LOW WILL MOVE OVER NORTHERN AND CENTRAL LAKE MI LATE WED NIGHT SHIFTING WINDS TO OUT OF THE N...WITH THE COLD FRONT PASSING SE OF THE LAKE BY WED EVENING. AS A LARGE RIDGE OF HIGH PRESSURE MOVES SLOWLY E FROM CENTRAL CANADA AND THE PLAINS WED NIGHT AND THU N WINDS WILL BE INCREASING BACK TO A STRONG BREEZE. LOW PRESSURE OF 29.9 INCHES WILL MOVE NORTHEASTWARD FROM THE. WITH LIGHT WINDS ON SOUTHERN LAKE MI TONIGHT AND DEW POINTS IN THE UPPER 40S AND LOWER 50S OVER COOLER WATER FOG IS LIKELY TONIGHT. IT SHOULD REMAIN A LIGHT FOG AS A WEAK SW WINDS DEVELOPS DURING THE PREDAWN HOURS GENERATING AT LEAST MARGINAL MIXING IN THE BOUNDARY LAYER OVER THE WATER. WITH S WINDS BLOWING OFFSHORE AND INCREASING DURING TUE A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR STRONG WINDS ALONG THE SHORE DURING THE AFTERNOON. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...DENSE FOG ADVISORY...ILZ014 UNTIL 10 PM SUNDAY. IN...DENSE FOG ADVISORY...INZ001-INZ002 UNTIL 10 PM SUNDAY. LM...DENSE FOG ADVISORY...LMZ080-LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745-LMZ777-LMZ779-LMZ878 UNTIL 10 PM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 082020 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 320 PM CDT WED MAY 8 2013 .DISCUSSION... 320 PM CDT SHORT TERM...TONIGHT THROUGH FRIDAY PRIMARY CONCERN IS SHOWER/TSTORM CHANCES AND SEVERE POTENTIAL LATE TONIGHT THROUGH TOMORROW. DIURNAL SHRA THAT HAVE DEVELOPED OVER SOUTHEAST SECTIONS WILL DISSIPATE BEFORE DARK. IN ADDITION...SHRA/ISOLATED TSRA WEST OF THE MS RIVER ARE ALSO EXPECTED TO DISSIPATE WITH LOSS OF DAYTIME INSTABILITY THOUGH THEY WILL TRY TO MAKE THEIR WAY EAST OF THE RIVER THIS EVENING. THUS HAVE CARRIED SLIGHT POPS FOR THE FAR WESTERN CWA. ATTENTION THEN TURNS TO CLOSED UPPER LOW MEANDERING OVER THE NORTHERN PLAINS NOTED ON WV IMAGERY THIS AFTERNOON. THIS CLOSED LOW WILL BECOME AN OPEN WAVE LATE TONIGHT...WITH WEAK SURFACE LOW PRESSURE DEVELOPING ALONG FRONTAL BOUNDARY OVER THE MID MISSOURI VALLEY BY EARLY THURSDAY. AS THIS OCCURS...THE LOW LEVEL JET WILL START TO RAMP UP...WITH MOISTURE TRANSPORT STARTING TO FEED INTO FAR SOUTHWEST/WESTERN CWA...SUPPORTING INCREASING SHRA CHANCES...WITH MUCH OF THE REST OF THE CWA REMAINING DRY THROUGH THE NIGHT. INCREASING CLOUDS LIKELY TO KEEP TEMPERATURES QUITE MILD AFTER THE WARM AFTERNOON...WITH SOME LOCATIONS NOT DIPPING BELOW 60 DEGREES. CLOSED SURFACE AND 850 MB LOWS LEND CONCERNS WITH RESPECT TO SEVERE POTENTIAL AND ALSO EFFICIENT MOISTURE TRANSPORT ON THURSDAY. THE TREND PARTICULARLY ON NCEP GUIDANCE TODAY AND ESPECIALLY ON THE GFS HAS BEEN FOR A DEEPER SURFACE AND ASSOCIATED 850 MB LOW/SUB 1010 MB...WHICH RESULTS IN STRONGER WIND FIELDS. HOWEVER...TO NOTE...TYPICALLY CONSISTENT ECMWF HAS COME IN WEAKER/SLIGHTLY FARTHER SOUTH WITH ITS LATEST RUN SO IT IS ENTIRELY POSSIBLE THAT GFS IS A BIT OF AN OUTLIER. HAVE HIGH CONFIDENCE IN WIDESPREAD SHOWER COVERAGE TOMORROW...WITH THETA E ADVECTION AND LOW LEVEL MOIST ADVECTION CONTINUING TO RAMP UP ACROSS THE CWA...BUT LOWER CONFIDENCE ON NATURE OF SEVERE THREAT. THIS IS BECAUSE OF CLOUD COVER AND ITS EFFECT ON HIGH TEMPERATURES...LEVEL OF MOISTURE RETURN/DO DEWPOINTS APPROACH OR EXCEED 60 DEGREES?/AND STRENGTH OF WIND FIELDS. THINK PLACEMENT OF DAY 2 SLIGHT RISK BY SPC IS REASONABLE AND MAIN THREATS WOULD BE SEVERE WIND GUSTS AND MARGINALLY SEVERE HAIL (WEAK MID LEVEL LAPSE RATES). ALSO PROXIMITY OF SURFACE LOW WILL RESULT IN BACKED SURFACE WINDS FOR SOUTHEAST CWA...WHICH DEPENDING ON HOW STRONG LOW LEVEL WIND FIELDS ARE COULD ALSO RESULT IN A CONDITIONAL THREAT FOR ISOLATED TORNADOES...AS 0-3 KM SRH VALUES COULD EXCEED 200-300 M2/S2. CURRENTLY HAVE HIGHS SIMILAR TO PREVIOUS IN LOW/MID 70S FOR SLIGHT RISK AREA...BUT IF THERE IS LESS CLOUD COVER AND INSTABILITY OVER 1000 J/KG...PLUS STRONGER WIND FIELDS SHOWN BY GFS AND NAM...CONCERN WILL INCREASE FOR SEVERE WX TOMORROW AFTERNOON INTO EARLY TOMORROW EVENING. PWATS INCREASE TO UPWARDS OF 1.25 INCHES TOMORROW EVENING AND GOOD MOISTURE TRANSPORT AND CONVERGENCE...PLUS FORECAST SOUNDINGS INDICATE WARM CLOUD DEPTHS OVER 9KFT OVER NRN HALF TO 2/3 OF CWA TOMORROW EVENING. PLACEMENT AND TIMING MAY NEED SOME REFINING...BUT GUIDANCE IS SHOWING A CONSISTENT SIGNAL FOR AN AXIS OF HEAVY QPF THAT COULD BRING A DECENT SWATH OF THE AREA AT OR IN IN EXCESS OF 1 INCH OF RAINFALL...PSBLY APPROACHING 1.5 INCHES IN MORE PERSISTENT CONVECTION. SLOWER NAM TRACK OF SURFACE LOW ALSO COULD KEEP SEVERE THREAT OVER SOUTHEASTERN CWA GOING INTO THE MID EVENING HOURS. WILL NEED TO WATCH FOR THIS. COLD FRONT WILL BEGIN TO PUSH THROUGH CWA OVERNIGHT...WITH LOWS IN THE UPPER 40S BLEEDING INTO AREAS NORTH OF I-80 BY DAYBREAK. ELEVATED INSTABILITY WILL WANE LATE THURSDAY NIGHT INTO FRIDAY...SO MUCH OF ACTIVITY ALONG AND BEHIND THE COLD FRONT IS EXPECTED TO BE MAINLY SHOWERS...SO REMOVED THUNDER CHANCES AFTER DAYBREAK FRIDAY. HAVE INDICATED HIGHER CHANCE POPS IN THE MORNING...WITH LOW SHRA CHANCES CONFINED TO THE SOUTHERN CWA BY THE AFTERNOON AS THE FRONT CONTINUES TO PUSH SOUTH. 850 MB TEMPS AROUND +6 STILL SUPPORT HIGHS IN THE 60S AWAY FROM THE LAKE DESPITE ONLY GRADUALLY ERODING CLOUD COVER. HOWEVER...STRONG ONSHORE FLOW WILL KEEP LAKEFRONT AREAS QUITE CHILLY...POSSIBLY ONLY AROUND 50 DEGREES...WITH GUSTS APPROACHING 30 MPH. RC *REMAINDER OF DISCUSSION TO FOLLOW SHORTLY... && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * LIGHT EASTERLY WINDS...BECOMING LIGHT AND VARIABLE THIS EVENING. * INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS DURING THE DAY ON THURSDAY. PAW //DISCUSSION...UPDATED 18Z... A BROAD HIGH PRESSURE RIDGE IS OVER THE AREA THIS AFTERNOON WITH LIGHT WINDS AND VFR-LEVEL CLOUDS. THE RIDGE WILL MOVE TO THE EAST OVERNIGHT. THEN A FRONTAL SYSTEM WILL BE MOVING INTO THE AREA ON THURSDAY. CLOUDS INCREASING AHEAD OF THIS FRONTAL SYSTEM...BECOMING VFR-LEVEL CEILINGS BY DAWN ON THURSDAY. CHANCES FOR SHRA AND TSRA INCREASING THROUGH THE DAY AND INTO EVENING THURSDAY. CONFIDENCE IS LOW IN THE EXACT TIMING OF PRECIPITATION AND CEILING/VISIBILITY DETAILS AT THIS POINT. PAW //ORD AND MDW CONFIDENCE...UPDATED 20Z... * HIGH CONFIDENCE IN WIND TREND THIS AFTERNOON AND EVENING. * MEDIUM CONFIDENCE IN SHRA/TSRA OCCURRING ON THURSDAY...LOW CONFIDENCE IN TIMING AND DETAILS. PAW //OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z... THURSDAY NIGHT...SHRA/TSRA LIKELY...MVFR WITH IFR POSSIBLE. FRIDAY...MVFR CIGS POSSIBLE...MAINLY EARLY. GUSTY NORTH-NORTHEASTERLY WINDS. SATURDAY THROUGH MONDAY...GENERALLY VFR. TUESDAY...STRONG SOUTHERLY WINDS...OTHERWISE VFR. KJB && .MARINE... 221 PM CDT THE FORECAST CONCERNS OVER LAKE MICHIGAN CENTER ON A WEATHER SYSTEM PASSING EARLY FRIDAY MORNING. THE CURRENT HIGH PRESSURE WILL GIVE WAY TO A COLD FRONT EASING DOWN THE LAKE THURSDAY. AS LOW PRESSURE DEVELOPS AND MOVES NORTHEAST ALONG THIS DURING THURSDAY AFTERNOON AND NIGHT...THE GRADIENT WILL INCREASE QUICKLY ACROSS THE LAKE. WINDS LATE THURSDAY NIGHT INTO EARLY FRIDAY WILL FURTHER BE AIDED BY THE COLD AIR ADVECTION ACROSS THE LAKE. ITS POSSIBLE OCCASIONAL GALES ARE SEEN IN THE MID LAKE SECTION DURING THAT PERIOD. WINDS WILL GRADUALLY DIMINISH LATER FRIDAY...BUT A SECONDARY COLD FRONT FRIDAY NIGHT INTO EARLY SATURDAY MORNING WILL KEEP NORTHWEST WINDS INCREASED. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 082215 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 515 PM CDT WED MAY 8 2013 .DISCUSSION... 320 PM CDT SHORT TERM...TONIGHT THROUGH FRIDAY PRIMARY CONCERN IS SHOWER/TSTORM CHANCES AND SEVERE POTENTIAL LATE TONIGHT THROUGH TOMORROW. DIURNAL SHRA THAT HAVE DEVELOPED OVER SOUTHEAST SECTIONS WILL DISSIPATE BEFORE DARK. IN ADDITION...SHRA/ISOLATED TSRA WEST OF THE MS RIVER ARE ALSO EXPECTED TO DISSIPATE WITH LOSS OF DAYTIME INSTABILITY THOUGH THEY WILL TRY TO MAKE THEIR WAY EAST OF THE RIVER THIS EVENING. THUS HAVE CARRIED SLIGHT POPS FOR THE FAR WESTERN CWA. ATTENTION THEN TURNS TO CLOSED UPPER LOW MEANDERING OVER THE NORTHERN PLAINS NOTED ON WV IMAGERY THIS AFTERNOON. THIS CLOSED LOW WILL BECOME AN OPEN WAVE LATE TONIGHT...WITH WEAK SURFACE LOW PRESSURE DEVELOPING ALONG FRONTAL BOUNDARY OVER THE MID MISSOURI VALLEY BY EARLY THURSDAY. AS THIS OCCURS...THE LOW LEVEL JET WILL START TO RAMP UP...WITH MOISTURE TRANSPORT STARTING TO FEED INTO FAR SOUTHWEST/WESTERN CWA...SUPPORTING INCREASING SHRA CHANCES...WITH MUCH OF THE REST OF THE CWA REMAINING DRY THROUGH THE NIGHT. INCREASING CLOUDS LIKELY TO KEEP TEMPERATURES QUITE MILD AFTER THE WARM AFTERNOON...WITH SOME LOCATIONS NOT DIPPING BELOW 60 DEGREES. CLOSED SURFACE AND 850 MB LOWS LEND CONCERNS WITH RESPECT TO SEVERE POTENTIAL AND ALSO EFFICIENT MOISTURE TRANSPORT ON THURSDAY. THE TREND PARTICULARLY ON NCEP GUIDANCE TODAY AND ESPECIALLY ON THE GFS HAS BEEN FOR A DEEPER SURFACE AND ASSOCIATED 850 MB LOW/SUB 1010 MB...WHICH RESULTS IN STRONGER WIND FIELDS. HOWEVER...TO NOTE...TYPICALLY CONSISTENT ECMWF HAS COME IN WEAKER/SLIGHTLY FARTHER SOUTH WITH ITS LATEST RUN SO IT IS ENTIRELY POSSIBLE THAT GFS IS A BIT OF AN OUTLIER. HAVE HIGH CONFIDENCE IN WIDESPREAD SHOWER COVERAGE TOMORROW...WITH THETA E ADVECTION AND LOW LEVEL MOIST ADVECTION CONTINUING TO RAMP UP ACROSS THE CWA...BUT LOWER CONFIDENCE ON NATURE OF SEVERE THREAT. THIS IS BECAUSE OF CLOUD COVER AND ITS EFFECT ON HIGH TEMPERATURES...LEVEL OF MOISTURE RETURN/DO DEW POINTS APPROACH OR EXCEED 60 DEGREES?/AND STRENGTH OF WIND FIELDS. THINK PLACEMENT OF DAY 2 SLIGHT RISK BY SPC IS REASONABLE AND MAIN THREATS WOULD BE SEVERE WIND GUSTS AND MARGINALLY SEVERE HAIL (WEAK MID LEVEL LAPSE RATES). ALSO PROXIMITY OF SURFACE LOW WILL RESULT IN BACKED SURFACE WINDS FOR SOUTHEAST CWA...WHICH DEPENDING ON HOW STRONG LOW LEVEL WIND FIELDS ARE COULD ALSO RESULT IN A CONDITIONAL THREAT FOR ISOLATED TORNADOES...AS 0-3 KM SRH VALUES COULD EXCEED 200-300 M2/S2. CURRENTLY HAVE HIGHS SIMILAR TO PREVIOUS INLOW/MID 70S FOR SLIGHT RISK AREA...BUT IF THERE IS LESS CLOUD COVER AND INSTABILITY OVER 1000 J/KG...PLUS STRONGER WIND FIELDS SHOWN BY GFS AND NAM...CONCERN WILL INCREASE FOR SEVERE WX TOMORROW AFTERNOON INTO EARLY TOMORROW EVENING. PWATS INCREASE TO UPWARDS OF 1.25 INCHES TOMORROW EVENING AND GOOD MOISTURE TRANSPORT AND CONVERGENCE...PLUS FORECAST SOUNDINGS INDICATE WARM CLOUD DEPTHS OVER 9KFT OVER NRN HALF TO 2/3 OF CWA TOMORROW EVENING. PLACEMENT AND TIMING MAY NEED SOME REFINING... BUT GUIDANCE IS SHOWING A CONSISTENT SIGNAL FOR AN AXIS OF HEAVY QPF THAT COULD BRING A DECENT SWATH OF THE AREA AT OR IN IN EXCESS OF 1 INCH OF RAINFALL...PSBLY APPROACHING 1.5 INCHES IN MORE PERSISTENT CONVECTION. SLOWER NAM TRACK OF SURFACE LOW ALSO COULD KEEP SEVERE THREAT OVER SOUTHEASTERN CWA GOING INTO THE MID EVENING HOURS. WILL NEED TO WATCH FOR THIS. COLD FRONT WILL BEGIN TO PUSH THROUGH CWA OVERNIGHT...WITH LOWS IN THE UPPER 40S BLEEDING INTO AREAS NORTH OF I-80 BY DAYBREAK. ELEVATED INSTABILITY WILL WANE LATE THURSDAY NIGHT INTO FRIDAY... SO MUCH OF ACTIVITY ALONG AND BEHIND THE COLD FRONT IS EXPECTED TO BE MAINLY SHOWERS...SO REMOVED THUNDER CHANCES AFTER DAYBREAK FRIDAY. HAVE INDICATED HIGHER CHANCE POPS IN THE MORNING...WITH LOW SHRA CHANCES CONFINED TO THE SOUTHERN CWA BY THE AFTERNOON AS THE FRONT CONTINUES TO PUSH SOUTH. 850 MB TEMPS AROUND +6 STILL SUPPORT HIGHS IN THE 60S AWAY FROM THE LAKE DESPITE ONLY GRADUALLY ERODING CLOUD COVER. HOWEVER...STRONG ONSHORE FLOW WILL KEEP LAKEFRONT AREAS QUITE CHILLY...POSSIBLY ONLY AROUND 50 DEGREES...WITH GUSTS APPROACHING 30 MPH. LONG TERM...FRIDAY NIGHT THROUGH THURSDAY... THE MAIN CONCERNS IN THIS PERIOD LIE WITH A STRONG PUSH OF COLD AIR SATURDAY INTO SUNDAY...FOLLOWED QUICKLY BY A BIG WARM UP EARLY NEXT WEEK. FRIDAY NIGHT WILL BE DRY AND COOL WITH LOWS IN THE 40S...BUT AN UNSEASONABLY DEEP UPPER TROUGH WILL PUSH INTO THE UPPER GREAT LAKES REGION BY SATURDAY...WITH A STRONG COLD FRONT TRAILING FROM SURFACE LOW PRESSURE. THIS FRONT COULD TOUCH OFF A FEW SHRA AS IT PUSHES THROUGH THE CWA ON SATURDAY...BUT THE BIG STORY WILL BE THE 850 MB TEMPS COOLING TO BELOW 0C SATURDAY NIGHT...LEAVING A COOL BUT MOSTLY SUNNY MOTHERS DAY. SOME CONCERN WITH FROST POTENTIAL AS EARLY AS SATURDAY NIGHT...BUT HIGH PRESSURE SHOULD BE FAR ENOUGH WEST TO MAINTAIN A GRADIENT AND KEEP TEMPS FROM BOTTOMING OUT TOO MUCH. AFTER HIGHS ONLY IN THE 50S ON MOTHERS DAY...HIGH PRESSURE WILL BE OVER THE REGION SUNDAY NIGHT YIELDING MUCH LIGHTER WINDS. COUPLED WITH CLEAR SKIES AND DRY AIR MASS...WITH DEW POINTS ONLY AROUND 30...STAGE COULD BE SET FOR LOWS NEAR FREEZING IN SOME AREAS EARLY MONDAY AND ALSO FROST POTENTIAL. FOR NOW...LOWERED TEMPS FROM BLEND OF PREVIOUS FCST AND CONSENSUS GUIDANCE TO MID AND UPPER 30S...BUT COULD SEE THEM BEING A FEW DEGREES COOLER THAN THIS. THEN EARLY NEXT WEEK...UPPER RIDGE QUICKLY AMPLIFIES OVER THE AREA...WITH RAPIDLY WARMING TEMPS ALOFT. ON MONDAY...HIGHS WILL WARM NICELY TO THE MID 60S AFTER THE CHILLY START. THEN TUES... 850 TEMPS SOAR TO +18 TO +20C IN GUSTY SOUTHWESTERLY BDRY LAYER FLOW. 850 MB CLIMO FOR OUR WOULD SUGGEST MID 80S AT A MINIMUM IN MID MAY WITH THESE TEMPS ALOFT...BUT FCST SOUNDINGS SUGGEST HOW DEEP WE MIX WILL BE A LIMITING FACTOR/IE. TO JUST OVER 900 MB ON THE GFS. NONETHELESS...BUMPED TEMPERATURES UP FROM PREVIOUS FCST AND CONSENSUS BLEND TO NEAR/AROUND 80 DEGREES AND THIS CERTAINLY COULD BE CONSERVATIVE. GUIDANCE DIVERGES SOME ON WEDNESDAY AS A COLD FRONT COULD SLIP SOUTH THROUGH THE AREA...BUT IT APPEARS IT WILL BE ANOTHER WARM DAY WITH HIGHS AT LEAST INTO THE UPPER 70S...WITH A POTENTIAL CHANCE FOR SHRA/TSRA THAT MAY HOLD OFF TIL LATE WEDS/WEDS NIGHT AS UPPER LEVEL ENERGY ARRIVES FROM THE WEST. RC && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 22Z... * CHANCES INCREASING OF RAIN AND AS THURSDAY PROGRESSES...BECOMING LIKELY BY EARLY AFTERNOON WITH A CHANCE OF A FEW THUNDERSTORMS. * POTENTIAL FOR DETERIORATION FROM VFR TO MVFR CIG AND VSBY CONDITIONS BY LATE AFTERNOON. TRS //DISCUSSION...UPDATED 22Z... MINIMAL CHANGES TO FCST LATE AFTERNOON THROUGH TONIGHT. HAVE IGNORED THE OCNL SPURIOUS GUSTS REPORTED AT ORD AS OFTEN SEEN THERE WITH SFC WIND FROM THE E BUT NO GUSTINESS REPORTED IN METAR FROM NEARBY SITES. ATTRIBUTED TO LOCATION OF ASOS BEING SUSCEPTIBLE TO INFLUENCE BY VORTICIES/EDDIES GENERATED BY ARRIVING ACFT. PREVIOUS DISCUSSION...UPDATED 18Z... A BROAD HIGH PRESSURE RIDGE IS OVER THE AREA THIS AFTERNOON WITH LIGHT WINDS AND VFR-LEVEL CLOUDS. THE RIDGE WILL MOVE TO THE EAST OVERNIGHT. THEN A FRONTAL SYSTEM WILL BE MOVING INTO THE AREA ON THURSDAY. CLOUDS INCREASING AHEAD OF THIS FRONTAL SYSTEM... BECOMING VFR-LEVEL CEILINGS BY DAWN ON THURSDAY. CHANCES FOR SHRA AND TSRA INCREASING THROUGH THE DAY AND INTO EVENING THURSDAY. CONFIDENCE IS LOW IN THE EXACT TIMING OF PRECIPITATION AND CEILING/VISIBILITY DETAILS AT THIS POINT. PAW //ORD AND MDW CONFIDENCE...UPDATED 22Z... * HIGH CONFIDENCE ALL ELEMENTS THROUGH TONIGHT. * MEDIUM CONFIDENCE TIMING SHRA/RA/TS THU. * MEDIUM CONFIDENCE IN REMAINING VFR AT LEAST THOUGH LATE. TRS //OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z... THURSDAY NIGHT...SHRA/TSRA LIKELY...MVFR WITH IFR POSSIBLE. FRIDAY...MVFR CIGS POSSIBLE...MAINLY EARLY. GUSTY N-NNE WIND. SATURDAY THROUGH MONDAY...GENERALLY VFR. TUESDAY...STRONG SOUTHERLY WINDS...OTHERWISE VFR. KJB && .MARINE... 221 PM CDT THE FORECAST CONCERNS OVER LAKE MICHIGAN CENTER ON A WEATHER SYSTEM PASSING EARLY FRIDAY MORNING. THE CURRENT HIGH PRESSURE WILL GIVE WAY TO A COLD FRONT EASING DOWN THE LAKE THURSDAY. AS LOW PRESSURE DEVELOPS AND MOVES NORTHEAST ALONG THIS DURING THURSDAY AFTERNOON AND NIGHT...THE GRADIENT WILL INCREASE QUICKLY ACROSS THE LAKE. WINDS LATE THURSDAY NIGHT INTO EARLY FRIDAY WILL FURTHER BE AIDED BY THE COLD AIR ADVECTION ACROSS THE LAKE. ITS POSSIBLE OCCASIONAL GALES ARE SEEN IN THE MID LAKE SECTION DURING THAT PERIOD. WINDS WILL GRADUALLY DIMINISH LATER FRIDAY...BUT A SECONDARY COLD FRONT FRIDAY NIGHT INTO EARLY SATURDAY MORNING WILL KEEP NORTHWEST WINDS INCREASED. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 132331 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 631 PM CDT FRI SEP 13 2013 .DISCUSSION... 251 PM CDT THE MAIN CONCERNS DURING THE PERIOD WILL BE PRECIPITATION CHANCES AND TIMING...ESPECIALLY ON SUNDAY. CURRENTLY...COOL CANADIAN HIGH PRESSURE IS BUILDING ACROSS THE WESTERN GREAT LAKES. THIS CONTINUES TO PRODUCE SOME GUSTY NORTHERLY FLOW DOWN LAKE MICHIGAN AND INTO NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. THE ACCOMPANYING COOL AUTUMN AIRMASS ALSO CONTINUES TO LEAD TO LAKE EFFECT STRATOCU...AFFECTING EASTERN ILLINOIS AND POINTS EASTWARD INTO INDIANA. THIS CLOUD COVER SHOULD CONTINUE TO DISSIPATE LATE THIS AFTERNOON AND INTO THIS EVENING. THIS HIGH WILL BECOME CENTERED ACROSS THE AREA OVERNIGHT TONIGHT...AND THIS LOOKS TO SETUP IDEAL CONDITIONS FOR A CHILLY NIGHT AS THE DRIER AIR MASS SHOULD ALLOW TEMPERATURES TO RADIATE EFFICIENTLY. I EXPECT MOST AREAS AWAY FROM THE CITY WILL DROP INTO THE 40S...WITH LOW TO MID 40S LIKELY IN MOST AREAS. SOME OF THE COLDEST SPOTS...IN THE FOX VALLEY...COULD EVEN DROP INTO THE UPPER 30S. SOME PATCHY GROUND FOG MAY ALSO DEVELOP LATE WITH LIGHT WINDS...BUT THE THREAT FOR SIGNIFICANT FOG APPEARS LOW DUE TO DRY AIR MASS...SO I HAVE DECIDED TO LEAVE THE MENTION OUT OF THE FORECAST. SATURDAY APPEARS TO BE A GREAT DAY ACROSS THE AREA. THE SURFACE HIGH WILL SHIFT EASTWARD ACROSS THE OHIO VALLEY SETTING UP A RETURN TO SOUTHERLY FLOW ACROSS THE REGION. THIS SHOULD HELP TEMPERATURES WARM INTO THE LOW TO MID 70S AREA-WIDE. MOISTURE WILL BEGIN INCREASING ACROSS THE MID MISSISSIPPI VALLEY SATURDAY NIGHT AS A SOUTHWESTERLY LOW LEVEL JET KICKS UP IN ADVANCE OF THE NEXT SYSTEM EXPECTED TO DIG SOUTHEASTWARD OUT OF CANADA. THE MODELS ARE IN DECENT AGREEMENT THAT THIS DEEPER MOISTURE WILL BE TRANSPORTED EAST-NORTHEASTWARD ACROSS NORTHERN ILLINOIS/NORTHWESTERN INDIANA AS WELL SUNDAY MORNING AHEAD OF A COLD FRONTAL BOUNDARY. GUIDANCE INDICATES PWATS IN THE NEIGHBORHOOD OF 1.4 TO 1.5 INCHES ACROSS THE AREA ON SUNDAY. THIS SHOULD SUPPORT A DECENT RAINFALL EVENT FOR THE AREA SUNDAY. IT APPEARS THE PRECIPITATION COULD START AROUND OR JUST PRIOR TO DAYBREAK SUNDAY ACROSS NORTH CENTRAL ILLINOIS. HOWEVER...CHANCES SHOULD INCREASE QUICKLY ACROSS NORTHERLY ILLINOIS DURING THE MORNING HOURS...AS THE COMBINATION OF GOOD ISENTROPIC ASCENT AND INCREASING FORCING FOR ASCENT FROM THE +DCVA ASSOCIATED WITH THE APPROACHING MID-LEVEL WAVE COINCIDE. WITH THIS IN MIND...I INCREASED POPS INTO THE DEFINITE CATEGORY FOR THE AREA ON SUNDAY MORNING. I CHOOSE TO CONTINUE THE SLIGHT CHANCE MENTION OF THUNDER IN THE LATEST FORECAST. HOWEVER...LAPSE RATES DO NOT APPEAR TO BE VERY FAVORABLE FOR MUCH THUNDER ACROSS THE AREA. WITH THE EXTENT OF RAIN SHOWERS AND CLOUD COVER ACROSS THE AREA ON SUNDAY...TEMPERATURES WILL LIKELY REMAIN FAIRLY COOL IN THE LOW TO MID 60S ACROSS THE AREA...ESPECIALLY NORTH. THINGS LOOK TO DRY OUT SUNDAY NIGHT AS ANOTHER COOL CANADIAN HIGH BUILDS IN ACROSS THE GREAT LAKES REGION. THIS SHOULD SET UP ONSHORE FLOW ACROSS THE AREA INTO MONDAY...AND CONTINUED COOL CONDITIONS IN THE UPPER 60S TO LOWER 70S. THE PROGRESSIVE NATURE OF THE UPPER AIR PATTERN ACROSS THE CONUS LOOKS TO ALLOW ANOTHER STORM SYSTEM TO TAKE SHAPE ACROSS THE NORTHERN PLAINS BY TUESDAY/TUESDAY NIGHT. THIS SHOULD SET UP SOUTHERLY FLOW ACROSS THE LOWER GREAT LAKES ALLOWING A WARMER AND MORE MOIST AIRMASS TO RETURN AGAIN FOR MID WEEK. IT ALSO APPEARS THERE WILL BE DECENT CHANCES OF PERIODS OF SHOWERS AND STORMS ACROSS THE AREA AROUND MIDWEEK AS A QUASI ZONAL FLOW PATTERN ACROSS THE AREA PROMISES TO REMAIN DISTURBED. KJB && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * NONE IZZI //DISCUSSION...UPDATED 00Z... NNE WINDS WILL VEER EASTERLY THIS EVENING QUICKLY DIMINISHING EARLY. SOME LOW END VFR OR POSSIBLY HIGH END VFR LAKE EFFECT CLOUDS COULD PROPAGATE BACK WEST INTO NE IL THIS EVENING BUT GENERALLY EXPECT SCT V BKN CONDITIONS AT WORST LATER THIS EVENING WITH CIGS AT OR ABOVE 2500FT. OTHERWISE NO CONCERNS THIS TAF CYCLE. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH CONFIDENCE FORECAST IZZI //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY...OCNL SHRA WITH ISOLD TSRA POSSIBLE. MVFR PROBABLE WITH IFR POSSIBLE. MONDAY AND TUESDAY...GENERALLY VFR. WEDNESDAY AND THURSDAY...SOME POTENTIAL EXISTS FOR SHRA/TSRA. IZZI && .MARINE... 207 PM CDT HIGH PRESSURE IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND WILL SPREAD OVER THE LAKE THIS EVENING. WINDS AND WAVES WILL CONTINUE TO SUBSIDE WITH SOUTHWEST WINDS EXPECTED OVER THE NORTH HALF OF THE LAKE BY SATURDAY MORNING. WINDS OVER THE SOUTH HALF OF THE LAKE WILL BE SOUTHEAST WITH THE WHOLE LAKE HAVING SOUTHWEST WINDS SATURDAY AFTERNOON. THIS IS DUE TO A PROGRESSIVE PATTERN WHERE THE HIGH QUICKLY SHIFTS TO THE EAST AND A LOW PRESSURE TROUGH/COLD FRONT PASSES OVER THE LAKE SUNDAY AFTERNOON. EXPECTING WINDS TO PICK UP OVER THE NORTH HALF OF THE LAKE SATURDAY UNDER THE TIGHT PRESSURE GRADIENT AHEAD OF THE TROUGH. GUSTS UP TO 25 KT ARE POSSIBLE. THE TROUGH CONTINUES TO THE SOUTHEAST SUNDAY NIGHT WITH ANOTHER HIGH PRESSURE SYSTEM EXPECTED MONDAY. WINDS TURN NORTH BEHIND THE COLD FRONT/TROUGH SUNDAY AFTERNOON AND NIGHT WITH GUSTS UP TO 25KT. OCCASIONAL GUSTS TO 30KT MAY BE POSSIBLE BUT LEFT THEM OUT OF THE FORECAST FOR NOW. WAVES BUILD OVER THE NEARSHORE ZONES SUNDAY NIGHT SO STILL EXPECTING SMALL CRAFT ADVISORY CONDITIONS THROUGH AT LEAST MONDAY EVENING...PERHAPS THROUGH EARLY MONDAY NIGHT. THE HIGH MOVES OVER NEW ENGLAND TUESDAY WITH WINDS BECOMING SOUTH TO SOUTHEAST. SOUTH WINDS INCREASE IN SPEED TUESDAY NIGHT AND WEDNESDAY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN THE DEPARTING HIGH AND APPROACHING LOW PRESSURE SYSTEM. THE LOW IS PROGGED TO PASS NORTH OF THE LAKE WITH WINDS BECOMING WEST BEHIND THE LOWS COLD FRONT WEDNESDAY NIGHT/THURSDAY. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014 UNTIL 5 AM SATURDAY. IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 5 AM SATURDAY. LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 5 AM SATURDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 141143 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 643 AM CDT SAT SEP 14 2013 .DISCUSSION... 303 AM CDT MAIN CONCERNS FOR THE FORECAST PERIOD WILL BE THE PERIODIC CHANCES FOR PCPN...ESPECIALLY THE TIMING AND DURATION OF PCPN OVERSPREADING THE AREA LATE SATURDAY NIGHT THROUGH SUNDAY AND ANY ASSOCIATED THUNDERSTORM CHANCES. FOR THE REMAINDER OF THE NIGHT AND THROUGH THE DAY TODAY...RATHER PLEASANT CONDITIONS WILL PREVAIL AS HIGH PRESSURE CONTINUES TO SETTLE THROUGH THE OHIO VALLEY AND THEN SPREAD INTO THE MID ATLANTIC REGION. TO THE WEST...A LOW PRESSURE SYSTEM IS DEVELOPING OVER THE CENTRAL PLAINS...ASSOCIATED WITH A MIDDLE STREAM SHORT WAVE LIFTING OUT OF THE CENTRAL ROCKIES. AS THE SFC LOW TRACKS EAST ACROSS THE PLAINS...WINDS OVER THE LOCAL AREA WILL EVOLVE FROM NEAR CALM TO SOUTHERLY. W WEAK LAKE BREEZE MAY STILL DEVELOP THIS AFTERNOON...TURNING WINDS ALONG THE LAKEFRONT MORE SELY...THOUGH WITH WINDS AT THE TOP OF THE BOUNDARY LAYER BECOMING A LITTLE MORE SSWLY INCREASING TO 10-15KT...THE LAKE BREEZE SHOULD HUG THE COAST. THE MAIN EFFECT OF THIS WILL BE TO LIMIT TEMPERATURES ALONG THE LAKEFRONT TO THE MIDDLE 60S...WHILE THE REMAINDER OF THE AREA SHOULD SEE TEMPERATURES CLIMB INTO THE LOWER 70S UNDER SUNNY SKIES. LATER TONIGHT...AS THE LOW MOVES INTO THE UPPER MISSOURI VALLEY...A STRONG POLAR COLD FRONT WILL DROP INTO THE UPPER GREAT LAKES REGION. THIS...COMBINED WITH HIGH PRESSURE BUILDING OUT OF CENTRAL CANADA...WILL FORCE THE MIDDLE STREAM SHORT WAVE AND THE ASSOCIATED SFC FEATURES TO TRACK MORE EASTERLY...WITH PCPN BEGINNING TO MOVE INTO NWRN IL BY AROUND MIDNIGHT. THIS IS SHAPING UP TO BE A FAIRLY DYNAMIC SYSTEM...WITH SOME PHASING OF THE NRN AMD MIDDLE STREAMS OCCURRING OVER THE UPPER MIDWEST. THROUGH THE EVENING...DEEP LAYER MOISTURE SHOULD BE ON THE INCREASE WITH THE SHORT RANGE MODEL GUIDANCE INDICATING PWATS INCREASING TO IN EXCESS OF 1 INCH BY EARLY SUNDAY MORNING AND CONTINUING TO RISE THROUGH THE DAY ON SUNDAY TO SLIGHTLY IN EXCESS OF 1.5 INCHES. AS THE MIDDLE AND NRN STREAMS PHASE ON SUNDAY...A MEAN UPPER TROUGH WILL DEEPEN...EXTENDING FROM NERN CANADA SOUTHWEST THROUGH THE MIDDLE MISSISSIPPI VALLEY. THE SYNOPTIC SCALE PATTERN WILL BECOME A LITTLE LESS PROGRESSIVE THROUGH SUNDAY NIGHT AS UPPER RIDGING BUILDS OVER THE ROCKIES AND OUT OVER THE WRN PLAINS. THIS ALL SIGNALS THE POTENTIAL FOR THE FIRST EXTENDED PERIOD OF PCPN IN QUITE SOME TIME. IT IS QUITE LIKELY THAT ALL DAY SUNDAY MAY BE A WASHOUT WITH RAIN LINGERING INTO THE EVENING HOURS. THE FOCUS FOR THE HEAVIEST RAIN SHOULD BE OVER THE NWRN PORTIONS OF THE CWA...WHERE THE MOST FAVORABLE INSTABILITY IS EXPECTED TO SET UP...AND THUS WHERE THERE WILL BE THE GREATEST CHANCES FOR ANY EMBEDDED THUNDERSTORMS. A STORM TOTAL OF AROUND 1 INCH OF RAIN OVER THE 30 HOUR PERIOD FROM 06Z SUNDAY THROUGH 12Z MONDAY. PCPN AMOUNTS ARE EXPECTED TO GRADUALLY TAPER OFF TO THE SOUTHEAST AS ANY THUNDERSTORM ACTIVITY BECOMES LESS LIKELY...WITH AROUND A HALF INCH OR SO ALONG A LINE FROM CHICAGO TO PONTIAC AND ONLY AROUND A QUARTER INCH OF PCPN OVER THE FAR SERN PORTIONS OF THE CWA. FOR TEMPERATURES ON SUNDAY...THERE SHOULD BE A DISTINCT CONTRAST BETWEEN LOCATIONS NORTH AND SOUTH OF THE ILLINOIS/KANKAKEE RIVERS. THE COLD FRONT ASSOCIATED WITH THE NORTHERN STREAM SYSTEM SHOULD STALL OUT INVOF THE RIVERS WITH TEMPERATURES DROPPING OFF TO THE LOW 60S TOWARD THE WISCONSIN BORDER...WHILE LOCATIONS SOUTH OF THE BOUNDARY WILL HAVE THE POTENTIAL TO RISE INTO THE MIDDLE 70S BEFORE THE SYSTEM PUSHES THROUGH THE REGION. BY MONDAY MORNING...THE LARGER SCALE PCPN WILL FINALLY COME TO AN END...BUT WITH POLAR HIGH PRESSURE BUILDING OVER THE GREAT LAKES REGION...COOL NELY FLOW...AN INVERSION ALOFT AT 800MB AND SFC-850MB DELTA-T VALUES OF 15-17C WILL BRING A CHANCE FOR SOME LAKE EFFECT SHOWERS TO LOCATIONS IN COOK AND LAKE COUNTY IL NEAR THE LAKE. THE POTENTIAL FOR LAKE EFFECT CLOUDINESS AND SHOWERS SHOULD COME TO AN END BY MONDAY AFTERNOON AS THE INVERSION HIGH LOWERS AND ANY UNSTABLE LAPSE RATES THROUGH THE LOWER LEVELS DIMINISH. TEMPERATURES ON MONDAY SHOULD REMAIN LOWEST NEAR THE LAKE...ONLY REACHING THE MIDDLE 60S...WHILE THE REMAINDER OF THE AREA SHOULD SEE TEMPERATURES IN THE UPPER 60S TO MIDDLE 70S. FOR THE LONGER TERM FORECAST PERIOD...FROM TUESDAY THROUGH FRIDAY...DECREASING AMPLITUDE TO THE PATTERN ALOFT WILL ALLOW FOR A SERIES OF SHORTWAVES TO RIPPLE THROUGH THE FASTER UPPER LEVEL FLOW...BRINGING PERIODIC CHANCES FOR PCPN FOR THE REST OF THE WEEK. GIVEN THE UNCERTAINTIES IN TIMING OF INDIVIDUAL SHORTWAVES...HAVE GENERALLY LIMITED POPS TO SLIGHT CHANCE TO CHANCE RANGES. THERE SHOULD BE CHANCES FOR SOME THUNDERSTORMS WITH THE SHOWERS AS AN EXTENDED PERIOD OF WARM/MOIST ADVECTION PERSISTS THROUGH THURSDAY...AHEAD OF THE NEXT UPSTREAM LONGWAVE TROUGH AND ASSOCIATED SFC COLD FRONT. TEMPERATURES THROUGH THE PERIOD SHOULD GRADUALLY REBOUND BACK INTO THE LOWER 80S BY THURSDAY WITH THE CHANCES FOR SHOWERS AND THUNDERSTORMS. THE NEXT COLD FRONT IS EXPECTED TO PUSH THROUGH THE REGION TOWARD THE END OF THE FORECAST PERIOD...BRINGING BACK SOME MORE AUTUMNAL WEATHER BY NEXT WEEKEND. KREIN && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * SSW WINDS AROUND 10 KT THIS AFTERNOON WITH A FEW HIGHER GUSTS POSSIBLE. //DISCUSSION...UPDATED 12Z... THE CENTER OF HIGH PRESSURE CONTINUES TO MOVE OVER THE AREA THIS MORNING WITH VARIABLE WINDS AT TIMES. A FEW STRATOCU CLOUD FRAGMENTS LEFTOVER FROM THE LAKE INDUCED PUSH ON FRIDAY CONTINUE TO BE SEEN IN OBSERVATIONS AND ON SATELLITE NEAR THE LAKE MI SHORE. SSW WINDS SETTLE IN BY LATER THIS MORNING AND ESPECIALLY THIS AFTERNOON. THE SPEEDS WILL HANG NEAR 10 KT INTO THIS EVE. HIGH CLOUDS WILL GRADUALLY LOWER AND THICKEN INTO TONIGHT AS LOW PRESSURE MOVES EAST FROM THE CENTRAL PLAINS. THIS LOW WILL WEAKEN BUT A NORTHERN STREAM COLD FRONT WILL STILL MOVE SOUTHWARD INTO THE AREA BY SUNDAY AFTERNOON AND EVE. THERE SHOULD BE A ZONE OF SHOWERS...POSSIBLY EVEN A LARGER AREA OF RAIN AND ISOLATED THUNDER...ASSOCIATED WITH THIS DURING SUNDAY. //ORD AND MDW CONFIDENCE...UPDATED 12Z... * HIGH CONFIDENCE IN WIND DIRECTION THIS AFTERNOON AND TONIGHT. LOW CONFIDENCE IF SPEEDS WILL REMAIN BELOW 10 KT. //OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z... SUNDAY NIGHT...AT LEAST MVFR PROBABLE WITH A CHC FOR IFR. CHC OF -RA. MONDAY...MVFR POSSIBLE IN THE MORNING. TUESDAY...CHC OF TSRA DURING THE NIGHT. WEDNESDAY-THURSDAY...CHC OF TSRA. FRIDAY...SLGT CHC OF SHRA. MTF && .MARINE... 222 AM CDT CANADIAN HIGH PRESSURE IS CENTERED OVER THE SOUTHERN PART OF THE LAKE THIS MORNING. WHILE THIS HAS BROUGHT WINDS WAY DOWN FROM THE SPEEDS THEY WERE ON FRIDAY...WAVES HAVE BEEN SLOWER TO SUBSIDE AS IS TYPICAL. HEIGHTS SHOULD DROP BELOW 4 FT BY DAYBREAK IN NEARSHORE AREAS AND WILL ALLOW SMALL CRAFT AND BEACH HAZARD HEADLINES TO EXPIRE. IN ADVANCE OF A COLD FRONT...SOUTHERLY FLOW WILL ENVELOP THE LAKE AS TODAY PROGRESSES. THE FRONT WILL DROP SOUTH ACROSS THE LAKE ON SUNDAY INTO SUNDAY EVENING. HAVE FORECAST THE FRONTAL MOVEMENT AND ASSOCIATED WIND SHIFT TO NORTHERLY QUICKER THAN MOST COMPUTER MODEL GUIDANCE BASED ON WHAT IS USUAL IN THESE SITUATIONS....ESPECIALLY ACROSS THE WESTERN HALF OF THE LAKE. WITH THIS REASONING...THE FORECAST WIND SHIFT TO NORTHERLY AND AN INCREASE IN SPEED IS EXPECTED TO REACH THE IL NEARSHORE DURING THE EARLY TO MID EVE ON SUNDAY. THE PROGRESSIVE PATTERN CONTINUES DURING THE MIDDLE TO LATTER PART OF THE WEEK WITH HIGH PRESSURE IN CONTROL BRIEFLY ON MONDAY AFTERNOON AND NIGHT THEN SOUTHERLY FLOW BACK FOR MIDWEEK. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 272001 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 301 PM CDT FRI SEP 27 2013 .DISCUSSION... 301 PM CDT PRIMARY FORECAST CONCERN IS WARM TEMPERATURES ON SATURDAY FOLLOWED BY RAIN/THUNDER POTENTIAL ASSOCIATED WITH COLD FRONT PASSAGE LATE SATURDAY INTO EARLY SUNDAY. SHORT TERM...TONIGHT THROUGH MONDAY... CLEAR SKIES AND DRY AIR MASS WILL ENABLE FOR DECENT COOLING TONIGHT EVEN AFTER WARM AFTERNOON. COULD SEE A FEW LOCATIONS OVER FAR EASTERN CWA CLOSER TO CENTER OF HIGH DIP INTO UPPER 40S. OTHERWISE...LOW/MID 50S OUTSIDE OF DOWNTOWN CHICAGO AND UPPER 50S/LOW 60S IN THE CITY. LOOKING AT STEADY SOUTHEAST FLOW...BUT IF BOUNDARY LAYER CAN DECOUPLE...MAY NEED TO ADJUST RURAL AND SUBURBAN TEMPS DOWN A BIT. COLD FRONT AND LONGWAVE TROUGH WILL APPROACH FROM THE WEST ON SATURDAY. THE CWA WILL REMAIN UNDER THERMAL RIDGE AND INCREASING GRADIENT WILL SUPPORT GUSTY SOUTHERLY WINDS...FINALLY BRINGING THE WARMTH ALL THE WAY TO THE IL LAKEFRONT. PRIMARY UNCERTAINTY LIES WITH HOW FAST CLOUD COVER INCREASES FROM THE WEST. DID NOT MAKE BIG CHANGES TO PREVIOUS FORECAST HIGHS AS THEY ARE WELL SUPPORTED BY UPPER AIR CLIMO FOR LATE SEPTEMBER...BUT THINK CLOUD COVER WILL HOLD OFF LONG ENOUGH FOR LOW 80S EVEN IN NW CWA. A FEW MID 80S ARE POSSIBLE SOUTH OF I-80. A BAND OF RAIN/PSBL EMBEDDED THUNDER IS LIKELY TO BE PUSHING INTO NORTHWEST CWA BY LATE AFTERNOON. DESPITE VERY WEAK LAPSE RATES AND LIMITED MOISTURE RETURN RESULTING IN VERY LITTLE INSTABILITY...SET-UP WILL BE MORE OF A HYBRID COLD SEASON EVENT SO STRONG FRONTAL CONVERGENCE AND MOISTURE TRANSPORT UP TO 700 MB COUPLED WITH A GLANCING BLOW FROM DECENT HEIGHT FALLS WILL SUPPORT A SOLID BAND OF RAIN SHOWERS AND ISOLD EMBEDDED THUNDER. HAVE FURTHER BUMPED UP POPS IN CATEGORICAL RANGE IN ASSOCIATION WITH FRONTAL BAND TOMORROW EVENING AND NIGHT WITH JUST A SLIGHT LINGERING CHANCE OF SHOWERS FOR FAR SOUTHEAST CWA SUNDAY MORNING IF FRONT SLOWS A BIT. DURATION WILL BE LIMITING FACTOR IN HOW MUCH RAIN FALLS WITH THIS EVENT...BUT TONGUE OF PWATS OF 1.8 TO 1.9 INCHES AND DEEP WARM CLOUD DEPTHS INDICATE THAT A STEADY MODERATE RAIN IS FAVORED AND SOME LOCATIONS COULD SEE A BIT IN EXCESS OF 0.5 INCHES OF MUCH NEEDED RAINFALL. AIR MASS BEHIND FRONT ON SUNDAY WILL NOT BE ALL THAT COOL FOR THIS TIME OF YEAR SO EXPECTING HIGHS AROUND NORMAL IN FULL SUNSHINE...WITH LAKE BREEZE EXPECTED TO KEEP LAKESHORE AREAS A BIT COOLER. VERY DRY AIR MASS AND RIDGE OVERHEAD WILL ALLOW FOR A CHILLY SUNDAY NIGHT HOWEVER...WITH LOWS IN OUTLYING AREAS IN THE LOWER-MID 40S. MADE MINOR DOWNWARD ADJUSTMENT TOWARD MAV/MET. RAPID HEIGHT RISES AND WAA ON MONDAY WILL BRING TEMPS SEVERAL DEGREES ABOVE NORMAL...BUT LIGHT GRADIENT CLOSE TO RIDGE AXIS AND SOUTHEAST SYNOPTIC FLOW WILL ALLOW FOR A LAKE BREEZE TO COOL OFF IL LAKEFRONT. LONG RANGE...MONDAY NIGHT THROUGH FRIDAY... RIDGING ALOFT AND 925 MB/850 TEMPS NEAR 20/MID TEENS RESPECTIVELY WILL RESULT IN A SPLENDID SUMMER LIKE START TO OCTOBER. KEPT PREVIOUS FORECAST HIGHS INTO LOWER 80S ON TUESDAY AND THEN ADJUSTED GUIDANCE BLEND UPWARD ON WEDS AS THERMAL PROFILES WILL BE ALMOST IDENTICAL. UNCERTAINTY INCREASES GREATLY LATER IN THE WEEK AS GFS AND ITS ENSEMBLES BODILY PUSH EASTWARD A DEEP WESTERN TROUGH AND ASSOCIATED SURFACE LOW EASTWARD. IT APPEARS THAT A WARM FRONT MAY LIFT NORTH WEDS NIGHT...SO HAVE SLIGHT POPS NORTH OF I-80...BUT THEN SYNOPTICALLY EVEN WITH QUICKER GFS OUR AREA LOOKS TO BE FIRMLY IN THE WARM SECTOR THURSDAY. THINK THAT CAPPING DUE TO RIDGING ALOFT WILL PRECLUDE WIDESPREAD PRECIP THAT GFS AND ECMWF ARE ADVERTISING. 12Z ECMWF HAS SPED UP FROM PREVIOUS RUN WITH APPROACH OF COLD FRONT...SO DID KEEP SLIGHT POPS IN THE NORTH AND WEST THURS NIGHT AND SLIGHT POPS AREA WIDE ON FRIDAY. WOULD LIKE TO SEE BETTER RUN TO RUN CONSISTENCY UNTIL INCREASING POPS THURSDAY NIGHT INTO FRIDAY. THURSDAY COULD END UP JUST AS WARM AS TUES AND WEDS...WITH COOLING FRIDAY...ESPECIALLY IF FASTER FROPA ENDS UP VERIFYING. RC && .FIRE WEATHER... SOUTH WINDS WILL INCREASE SATURDAY AND LIKELY GUST TO AROUND 30 MPH BY SATURDAY AFTERNOON. WHILE RH VALUES ARE FORECAST TO REMAIN ABOVE RED FLAG CRITERIA...THE STRONG WINDS AND VERY DRY FUELS WILL RESULT IN AN ENHANCED FIRE DANGER...PARTICULARLY SOUTHERN/EASTERN CWA WHERE CLOUDS WILL ARRIVE THE LATEST AND RH VALUES ARE LIKELY TO DROP TO BETWEEN 30 AND 40 PERCENT. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * PSBL WINDS TURNING TO 110 DEG AT ORD AND 100 DEG AT MDW. SPEEDS HOVERING ARND 10KT AT ORD/MDW...OCCASIONAL WIND TO 12KT AT MDW. * WINDS TURNING SOUTHEAST THIS EVENING TO ARND 7-9KT. * WINDS BECOMING GUSTY AFT DAYBREAK SAT CLOSER TO 15Z AND BEYOND...WITH GUSTS UP TO 20-25KT FROM THE SOUTH. BEACHLER //DISCUSSION...UPDATED 18Z... HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD COVER ACROSS NORTHERN IL/NORTHWEST IN AIRFIELDS...WITH A LIGHT GRADIENT PRODUCING WINDS ARND 8KT OR LESS. ALTHOUGH A LAKE BREEZE WAS BEGINNING TO PUSH INLAND...AND WAS NEARING MDW ARND 19Z. SPEEDS MAY BRIEFLY BUMP UP TO 10KT WITH THE BREEZE...OTHERWISE SPEEDS WILL REMAIN JUST UNDER THIS. FOR ORD IT APPEARS THE DIRECTIONS WILL FLIRT WITH 110-120 DEG THIS AFTN...OTHERWISE DIRECTIONS WILL REMAIN 130 DEG. AT GYY THE LAKE BREEZE WILL TURN WINDS MORE EASTERLY OR 080-090 DEG. THEN AFT SUNSET WINDS WILL TURN SOUTHEASTERLY ARND 8KT OR LESS. THE GRADIENT ACROSS THE CENTRAL PLAINS WILL CONTINUE TO PROGRESS EAST TOWARDS NORTHERN IL. THIS WILL EVENTUALLY ARRIVE OVER OUR AIRFIELDS SAT MORNING...AND WITH SOME HEATING OF THE SURFACE THIS WILL ALLOW GUSTS TO BEGIN SHOWING UP IN THE OBSERVATIONS ARND 15-16Z SAT. GUIDANCE HAS CONTINUED TO INDICATE GUSTS TO 20KT AT THE ONSET...THEN POSSIBLY INCREASING TO 25KT BY EARLY AFTN FROM THE SOUTH. CLOUD COVER WILL SLOWLY THICKEN SAT AFTN...BUT REMAIN VFR THRU THE END OF THE CURRENT TAF PERIOD. ANY PRECIP WITH THE APPROACH OF A FRONTAL BOUNDARY WILL HOLD OFF UNTIL AFT 21Z AND MAY DELAY EVEN LONGER OR CLOSER TO 00Z SUN. SO HAVE CONTINUED TO FEATURE A DRY TAF PERIOD. BEACHLER //ORD AND MDW CONFIDENCE...UPDATED 20Z... * HIGH CONFIDENCE IN WIND SPEEDS. MEDIUM/HIGH CONFIDENCE IN WIND DIR THRU 00Z SAT. * HIGH CONFIDENCE IN WIND DIR/SPEEDS AFT 00Z SAT. * HIGH CONFIDENCE IN WINDS/SKY COVER SAT. * MEDIUM CONFIDENCE IN PRECISE TIME OF GUSTS AND SPEEDS. BEACHLER //OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z... SATURDAY NIGHT...SHRA WITH A CHANCE OF TSRA. SUNDAY-THURSDAY...VFR WITH A CHANCE OF MVFR FOG IN THE MORNINGS. KJB && .MARINE... 255 PM CDT HIGH PRESSURE TO THE NE IS SLOWLY SHIFTING EAST AND WILL MOVE OVER THE NORTHERN ATLANTIC COAST SUNDAY EVENING. A LOW PRESSURE TROUGH OVER THE GREAT PLAINS SHIFTS NNE THROUGH SUNDAY. S TO SE WINDS WILL BECOME S ACROSS THE LAKE AND INCREASE TO 20-25 KT. STRONG S WINDS CONTINUE SATURDAY WITH WINDS UP TO 30 KT OVER THE NORTHERN HALF OF THE LAKE. NOTE GUIDANCE IS INDICATING GALE FORCE GUSTS JUST 200 FEET OFF THE DECK TOMORROW AFTERNOON. MODEL SOUNDINGS SUGGEST A VERY STABLE LAYER SO NOT EXPECTING ANY GALE FORCE GUSTS TO REACH THE SURFACE OF THE LAKE...BUT TALLER BOATS WILL LIKELY EXPERIENCE WINDS STRONGER THAN FORECAST. MAY SEE OCNL GUSTS UP TO 30 KT OVER THE SOUTHERN HALF...BUT WILL STICK WITH 20-25KT FOR NOW. ISSUED A SMALL CRAFT ADVISORY FOR ALL OF THE NSH ZONES DUE TO STRONG WINDS. HAZARDOUS WAVES ARE ONLY POSSIBLE OVER FAR NORTHERN LAKE COUNTY IL WHERE SOUTHEAST WINDS WILL HAVE THE LARGEST FETCH. OTHERWISE THE OFFSHORE FLOW SHOULD NOT PRODUCE HAZARDOUS WAVES OVER THE NSH ZONES. THE LOWS COLD FRONT SLIDES THROUGH SATURDAY NIGHT WITH NW WINDS UP TO 20 KT EXPECTED BEHIND IT. A BROAD AND WEAK SURFACE RIDGE SETS UP OVER THE EASTERN THIRD OF THE U.S. SUNDAY THROUGH EARLY TUESDAY. WINDS INCREASE OVER THE FAR NORTHERN END OF THE LAKE MONDAY AS A LOW PRESSURE SYSTEM APPROACHES FROM THE WEST. SPEEDS WILL BE AT LEAST 20-25 KT WITH 30 KT POSSIBLE. WINDS DIMINISH AND BECOME SW BEHIND THE LOW TUESDAY NIGHT. LOOKING VERY VERY FAR DOWN THE ROAD...THE MODELS ARE SHOWING A DEEP LOW MOVING DIRECTLY OVER THE LAKE LATE NEXT WEEK AND GUIDANCE IS ALREADY INDICATING GALES ARE POSSIBLE. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745...10 AM SATURDAY TO 10 PM SATURDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 132041 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 306 PM CDT SUN OCT 13 2013 .DISCUSSION... 305 PM CDT THE CHALLENGES WITH THE FORECAST ARE FROST POTENTIAL TONIGHT...FOLLOWED BY MORNING CLOUDS OFF THE LAKE ON MONDAY AND THEN RAIN CHANCES TUESDAY. FINALLY THE SUBSEQUENT NOTEWORTHY COOL DOWN INTO NEXT WEEK WILL BECOME A GREATER FORECAST CHALLENGE AS THIS WEEK PROGRESSES. SYNOPSIS...EXPANSIVE 1030MB CANADIAN HIGH PRESSURE IS IN PLACE ACROSS THE UPPER MIDWEST AND WILL SHIFT DIRECTLY OVER THE AREA BY EVENING. COOL BUT MORE SEASONAL 850MB TEMPS WERE OBSERVED ACROSS THE AREA THIS MORNING...INCLUDING +3C AT DVN. ALMOST ALL 12Z GUIDANCE INITIALIZED TOO MILD WITH THIS LOW-LEVEL COOL AIR. THAT MAY BE ONE REASON WHY MOST OF THE GUIDANCE SOLUTIONS FOR TEMPS TONIGHT ARE LIKELY TOO WARM. TONIGHT...SATELLITE REVEALS THE ONLY CLOUDS IN THE IMMEDIATE REGION ARE ACROSS NORTHERN LAKE MI...AND THESE ARE IN PLACE THANKS TO THE COLD AIR MASS MOVING OVER THE STILL MILD WATERS. AS THE HIGH DOES MOVE OVER THE AREA...850-1000MB LOW WILL TURN MORE NORTHERLY AND THEN NORTHEASTERLY. SPEEDS WILL DROP BUT ARE LIKELY ENOUGH TO ADVECT LAKE-INDUCED STEEP LAPSE RATES AND SATURATION ON TOP OF THIS INDICATIVE OF STRATOCU INTO FAR NW IN AND THEN FAR NE IL AFTER MIDNIGHT. NAM AND LOCAL ARW SOUNDINGS AND LOW-LEVEL RH FIELDS ARE IN AGREEMENT TO THIS SOLUTIONS...ALONG WITH SPC WRF COLUMN CONDENSATE WHICH SEEMS TO DO WELL WITH STRATOCU IN THESE SITUATIONS. THIS WILL LIKELY SLOW OR EVEN HALT THE TEMPERATURE DROP LATE TONIGHT IN DOWNTOWN CHICAGO AND OTHER LAKE ADJACENT AREAS. FOR THE REMAINDER OF THE CWA...A PICTURE PERFECT RADIATIONAL COOLING EVENING AND OVERNIGHT IS IN SHAPE AS THE ATMOSPHERE SHOULD DECOUPLE BY EARLY TO MID EVE. HAD ADJUSTED THE HOURLY TEMPERATURE TREND TO REFLECT QUICK COOLING...AND FOR MINS HAVE CONSIDERED LAST NIGHT TEMPS STRONGLY AS A BASELINE AS OPPOSED TO ANY GUIDANCE SOURCE. THERE IS LITTLE REASON FOR OUTLYING AREAS TO BE WARMER THAN THEY WERE THIS MORNING...AND CURRENT SURFACE DEW POINTS LEAN THAT ROUTE AS WELL AS THE BOUNDARY LAYER IS WELL MIXED TODAY. SO EXPECTING WIDESPREAD 32 TO 35 ACROSS NORTH CENTRAL IL WITH MID TO UPPER 30S ELSEWHERE IN OUTLYING AREAS. CONSIDERING COCORAHS OBSERVER COMMENTS THIS MORNING REPORTING PATCHY FROST...WOULD EXPECT CLOSER TO A WIDESPREAD FROST IN NORTH CENTRAL IL. CONSIDERING THE MILD NIGHT AS OF RECENT...WE HAVE GONE AHEAD AND COLLABORATED A FROST ADVISORY FOR LATE TONIGHT...THE FIRST SUCH ADVISORY OF THE SEASON. MONDAY...THE HIGH WILL REMAIN IN CONTROL ON COLUMBUS DAY. THE LAKE EFFECT CLOUDS ARE ANTICIPATED TO LINGER IN NORTHEAST IL...POSSIBLY AS FAR WEST AS NORTH CENTRAL IL...BUT AMOUNT OF COVERAGE IS LOW CONFIDENCE. THE CLOUD DEPTH LOOKS TO BE AT OR UNDER 3K FT AT MOST OVER THE LAKE SO ANY STRATOCU MAY BEGIN TO THIN QUICKLY BY LATE MORNING. MIXING LOOKS TO BE TO 875MB...AND THAT SHOULD SUPPORT 60S ACROSS THE AREA. TUESDAY AND WEDNESDAY...A PRONOUNCED UPPER TROUGH ACROSS UT/NV WILL SHIFT ENE INTO THE UPPER MIDWEST DURING THIS PERIOD...AND THIS WILL BE THE FIRST OF MULTIPLE UPPER WAVES EVOLVING EASTWARD ACROSS NORTH AMERICA DURING THE MIDDLE OF THIS WEEK. TOGETHER THESE WILL CARVE OUT A LONG WAVE TROUGH OVER THE CENTRAL PART OF THE CONTINENT...EXTENDING INTO THE MIDWEST BY WEEKS END. THIS FIRST WAVE ON TUESDAY LOOKS TO BRING THE BEST CHANCE OF RAIN TO THE AREA AS PRONOUNCED HEIGHT FALLS MOVE ACROSS THE AREA ALONG WITH DYNAMIC SUPPORT FOR ENHANCED LIFT AHEAD OF THE SYSTEM COOL FRONT. THE GFS REMAINS THE QUICKEST SOLUTION WITH THIS...BUT NOT BY MUCH AT ALL. THE MEAN OF THE SOLUTIONS PAINTS THE MORNING AND EARLY AFTERNOON WILL BE THE BEST CHANCE FOR WIDESPREAD SHOWERS AS THE MOISTURE TRANSPORT MAX POINTS INTO THE REGION. AS THE COLD FRONT SHIFTS EASTWARD THROUGH THE AREA LIKELY DURING TUESDAY AFTERNOON...THIS MAY PRESENT A BETTER CHANCE FOR THUNDER. INSTABILITY RETURN LOOKS TO BE VERY MODEST AT BEST...ESPECIALLY IF THERE IS MORNING WIDESPREAD CLOUDS AND RAIN. THE DRY SLOT STILL LOOKS TO EVOLVE OVER TUE NIGHT WITH ANY PRECIP LIKELY TO BE LIGHT AT THAT POINT. COLD AIR ADVECTION WRAPS AROUND THIS SYSTEM AND PREVAILS ON WED WITH HIGHS 10 TO 15 DEGREES COOLER THAN TUE. SMALL CHANCES FOR SHOWERS ARE IN WEDNESDAY AS THE COLD CORE SYSTEM MOVES OVERHEAD. THURSDAY AND BEYOND...THE SUCCESSIVE SHORT WAVE TROUGHS WILL LEAD TO PROGRESSIVE THICKNESS FALLS AND COOLING TEMPS. THE 850 0C ISOTHERM DROPS SOUTH INTO THE AREA ON FRIDAY IN THE GFS/EC MEAN SOLUTION WITH AN ASSOCIATED COLD FRONT. THIS SETS THE STAGE FOR THE FIRST POSSIBLE WIDESPREAD FREEZE ON FRIDAY OR SATURDAY NIGHT IF INDEED HIGH PRESSURE FOLLOWS WHICH IT LOOKS TO. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * NNW WINDS BECOMING NNE BY 2230Z FOR ORD AND 2130Z FOR MDW...THIS AFTERNOON. * POSSIBLE HIGH END MVFR CEILINGS LATE TONIGHT INTO MONDAY MORNING AS CLOUDS MOVE OFF OF THE LAKE. RODRIGUEZ //DISCUSSION...UPDATED 18Z... HIGH PRESSURE CONTINUES TO BUILD EAST ACROSS THE REGION...WITH CLEAR SKIES AND NORTHWEST WINDS PREVAILING. AS SKIES REMAIN CLEAR THIS AFTERNOON INTO EVENING...EXPECT THE GENERAL PATTERN AND LAKE INFLUENCE TO SUPPORT A WIND SHIFT TO THE NORTHEAST THIS AFTERNOON WITH GYY FIRST OBSERVING THIS SHIFT AND THEN MDW/ORD TO THEN FOLLOW. EAST NORTHEAST WINDS WILL THEN PREVAIL THROUGH THE REMAINDER OF THE PERIOD. CURRENT CLOUDS OVER THE LAKE ARE EXPECTED TO MOVE BACK WEST ACROSS THE TERMINALS LATER TONIGHT AS BOUNDARY LAYER FLOW VEERS. THIS SHOULD BRING A PERIOD OF CEILINGS TONIGHT WITH HEIGHTS HOVERING AROUND 3KFT...BUT WITH POTENTIAL FOR CEILINGS TO BE SLIGHTLY LOWER. THIS CLOUD COVER SHOULD REMAIN FAIRLY PROGRESSIVE AND EXIT BY MID MORNING. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 20Z... * MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION. * MEDIUM CONFIDENCE WITH CEILING TRENDS LATE TONIGHT/MONDAY MORNING. RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z... MONDAY...VFR. TUESDAY...LIKELY SHRA WITH A CHANCE OF TSRA...OTHERWISE VFR. WEDNESDAY...CHANCE OF SHRA...OTHERWISE VFR. THURSDAY...VFR. FRIDAY...VFR. RODRIGUEZ && .MARINE... 225 PM CDT WINDS WILL VEER TO OUT OF THE NORTH AND NORTHEAST AND DIMINISH TONIGHT AS HIGH PRESSURE CENTERED OVER NORTHWEST IOWA AT MID AFTERNOON BUILDS ACROSS THE UPPER MIDWEST AND UPPER GREAT LAKES DURING THE NIGHT. AS THE HIGH CONTINUES ON ACROSS ONTARIO TO SOUTHERN QUEBEC MONDAY AND MONDAY NIGHT LOW PRESSURE WILL BE ORGANIZING OVER THE CENTRAL HIGH PLAINS AND DEEPENING AS IT MOVES NORTHEASTWARD TO SOUTHERN MINNESOTA. WITH THE WESTERN GREAT LAKES BETWEEN THE DEPARTING HIGH AND THE APPROACHING STRENGTHENING LOW WINDS ON LAKE MICHIGAN INCREASE TO MODERATE AND FRESH BREEZES WHILE VEERING TO OUT OF THE SOUTHEAST AND SOUTH DURING MONDAY NIGHT AND TUESDAY. THE LOW MOVES ACROSS NORTHERN WISCONSIN AND THE EASTERN UPPER PENINSULA OF MICHIGAN TUESDAY NIGHT AND WEDNESDAY. AS IT DOES IT WILL PUSH A COLD FRONT EASTWARD ACROSS LAKE MICHIGAN. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011- ILZ012-ILZ019...3 AM MONDAY TO 8 AM MONDAY. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 190841 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 341 AM CDT SAT OCT 19 2013 .DISCUSSION... 322 AM CDT SYNOPSIS...VERY ACTIVE PATTERN EXPECTED OVER THE NEXT WEEK. BELOW NORMAL TEMPS TODAY AND TONIGHT GIVE WAY TO WELL ABOVE NORMAL TEMPS TOMORROW...AND THEN CONTINUED BELOW NORMAL CONDITIONS AND PERIODIC CHANCES OF RAIN THROUGH THE NEXT WEEK. THE FIRST AREA WIDE FREEZE IS ALSO EXPECTED MONDAY NIGHT. TODAY AND TONIGHT... LIGHT SHOWERS AND DRIZZLE EXTEND EAST OF A LINE FROM DOWNTOWN CHICAGO THROUGH MENDOTA EARLY THIS MORNING AS AN UPPER LEVEL WAVE PASSES TO OUR SOUTHEAST. THE TROUGH AXIS OF THE UPPER LEVEL TROUGH IS CURRENTLY JUST WEST OF THE MISSISSIPPI RIVER AND IT WILL MOVE OVER THE CWA TODAY. THINKING LIGHT SHOWERS WILL REMAIN EAST OF A GARY TO PONTIAC LINE AND SHIFT EAST THROUGH THIS MORNING LEADING TO DRY CONDITIONS ACROSS THE CWA BY MID MORNING. AFTER A FEW DRY HOURS...THINKING ANOTHER BAND OR TWO OF SHOWERS WILL DEVELOP OVER NORTH CENTRAL IL AHEAD OF THE TROUGH AXIS. THE OTHER STORY FOR TODAY AND TONIGHT IS TEMPERATURES. LOOKING AT HIGH TEMPS IN THE MID 50S...BUT MUCH COOLER AIR MOVES IN WITH THE TROUGH AXIS. GUIDANCE SUGGESTS 0 TO -2C AT 850MB...BUT LINGERING CLOUD COVER WILL BE AN ISSUE. AIRED ON THE SIDE OF CAUTION AND DID NOT BOTTOM OUT TEMPS...SO IF WE CLEAR OUT MORE THAN FORECAST TONIGHT...EXPECT MUCH COLDER LOWS TONIGHT. DO THINK THAT WE WILL SEE PATCHY TO WIDESPREAD FROST ACROSS THE CWA...WITH THE MOST WIDESPREAD FROST ACROSS THE IL/WI STATE LINE AND ACROSS OGLE...LEE...DE KALB...AND KANE COUNTIES. AS SUCH HOISTED A FROST ADVISORY FOR THOSE 8 COUNTIES. SUNDAY THROUGH MONDAY NIGHT... THE UPPER LEVEL PATTERN BECOMES MORE ZONAL SUNDAY BEFORE ANOTHER UPPER LEVEL TROUGH PASSES TO OUR NORTH MONDAY. A SURFACE LOW WILL MOVE INTO SASKATCHEWAN THIS MORNING AND PROCEED TO MOVE OVER LAKE SUPERIOR LATE SUNDAY NIGHT INTO MONDAY. GUIDANCE HAS THE LOW FURTHER NORTH AND STILL THINKING THE MAJORITY OF PRECIP WILL REMAIN CLOSER TO THE LOW. THE LOWS WARM FRONT LIFTS NORTH THROUGH THE REGION SUNDAY AND HIGH TEMPS WILL SOAR INTO THE 60S. GUSTY SOUTH WINDS WILL DEVELOP BEHIND THE FRONT WITH MAX GUSTS IN EXCESS OF 30 MPH POSSIBLE. THE LOWS COLD FRONT SWINGS THROUGH SUNDAY EVENING/NIGHT AND EXPECTING A FEW SHOWERS ALONG IT...BUT NOTHING SIGNIFICANT. LIFT AND MOISTURE SEEM MARGINAL ALONG THE FRONT THEREFORE KEPT POPS AT CHANCE OR LOWER. THE LOW LINGERS A BIT OVER LAKE SUPERIOR BEFORE FINALLY MOVING INTO QUEBEC TUESDAY. 850MB TEMPS FALL TO 4 TO -2C BEHIND THE COLD FRONT WITH LOW TEMPS IN THE LOW TO MID 40S. LINGER CLOUD COVER SHOULD KEEP US FROM GETTING TOO COLD. MONDAY WILL BE BLUSTERY WITH HIGH TEMPS IN THE UPPER 40S TO MID 50S AND STRONG WEST WINDS GUSTING UP AROUND 30 MPH IN THE AFTERNOON. CLOUDS FINALLY CLEAR OUT OVERNIGHT AND EXPECTING TO HAVE OUR FIRST WIDESPREAD FREEZE MONDAY NIGHT. TEMPS TUMBLE TO AROUND FREEZING FOR ALL AREAS EXCEPT THE IMMEDIATE LAKE SHORE. A FREEZE WARNING WILL BE NEEDED FOR MONDAY NIGHT PUTTING AN END TO THE 2013 GROWING SEASON. EXTENDED...TUESDAY THROUGH NEXT FRIDAY... A SECOND TROUGH AXIS PASSES THROUGH NORTHERN IL WEDNESDAY AND ADDITIONAL WEAK IMPULSES PASS OVER THE REGION THROUGH THE END OF THE WEEK. PERSISTENT NORTHWEST FLOW REMAINS OVER THE REGION AS WELL. HAVE A SLIGHT CHANCE OF PRECIP IN THE FORECAST FOR TUESDAY NIGHT AND WEDNESDAY AHEAD OF THE FIRST TROUGH AXIS. COULD EVEN SEE A RAIN/SNOW MIX TUESDAY NIGHT AS THE ATMOSPHERIC COLUMN IS AT OR BELOW FREEZING. KEPT THE REST OF THE FORECAST DRY WITH BELOW NORMAL TEMPERATURES. TEMPS ARE RATHER CONSISTENT AS THE AIRMASS DOES NOT FLUCTUATE MUCH FOR MOST OF NEXT WEEK. HIGH TEMPS IN THE 40S AND LOW TEMPS IN THE LOW 30S TO UPPER 20S. JEE && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * GUSTY WSW WINDS TODAY. * ISOLD SHRA POSSIBLE LATE THIS AFTERNOON/EARLY THIS EVE. //DISCUSSION...UPDATED 06Z... AN UPPER LEVEL DISTURBANCE CENTERED ACROSS MO EARLY THIS MORNING WILL PROGRESS NORTHEAST THROUGH DAYBREAK. THIS WILL SPREAD PATCHY LIGHT RAIN TO AT LEAST NEAR MDW AND GYY. CLOUDS MAY BREAK AFTER SUNRISE THROUGH MID-MORNING...BUT SCT TO BKN VFR CLOUDS SHOULD FILL IN BY LATE MORNING/EARLY AFTERNOON. A SURFACE LOW PRESSURE MOVING EAST OVER THE UPPER GREAT LAKES THIS AFTERNOON WILL CREATE SHOWERS OVER WI WITH PROBABLY AT LEAST ISOLATED SHRA NEAR THE WI/IL STATE LINE. SOME OF THESE MAY REACH RFD/DPA/ORD LATE IN THE DAY INTO EARLY THIS EVE. //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH FOR WINDS. * LOW FOR SHRA OCCURRING AT AIRFIELDS...BUT MEDIUM TO HIGH THAT IT WILL BE VFR IF THEY DO OCCUR. //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY...STRONG SOUTH WINDS POSSIBLE IN THE AFTERNOON. VFR. MONDAY...MVFR CIGS LIKELY. TUESDAY THROUGH THURSDAY...MVFR CIGS POSSIBLE. MTF/IZZI && .MARINE... 330 AM CDT A VERY ACTIVE PERIOD OVER THE LAKE IS SET TO UNFOLD INTO EARLY NEXT WEEK. MULTIPLE LOW PRESSURE SYSTEMS WITH CONTINUED SUCCESSIVE COLD FRONTS WILL KEEP WINDS UP AND WAVES HIGH...ESPECIALLY SUNDAY NIGHT THROUGH EARLY TUESDAY. FIRST...SOUTHWEST TO WEST WINDS WILL CONTINUE TODAY WITH GENERAL LOW PRESSURE ACROSS LAKE SUPERIOR AND SOUTHERN ONTARIO. GUSTS WILL BE NEAR SMALL CRAFT ADVISORY CRITERIA IN BOTH THE IL AND IN NEARSHORE AREAS...THOUGH THE HIGHEST WAVES WILL BE CONFINED EAST OF GARY AND THAT IS WHERE WE HAVE ISSUED THE HEADLINE FOR NOW. WATERSPOUTS WILL REMAIN A THREAT TODAY WITH THE STEEP LAKE-INDUCED LAPSE RATES AND CLOUD DEPTHS. THE EASTERN HALF OF THE LAKE WILL BE MOST FAVORED. LOW PRESSURE WILL MOVE EAST ACROSS THE UPPER MISSISSIPPI VALLEY ON SUNDAY AND THEN NORTHEAST OVER THE UPPER LAKES ON SUNDAY NIGHT...WHERE IT HAS BEEN CONSISTENTLY FORECAST TO DEEPEN. THE PATH OF THE LOW CENTER AND WITHIN THE DEEPENING PHASE...COUPLED WITH THE STRENGTH OF COLD AIR ADVECTION WRAPPING AROUND THE SYSTEM...IS LIKELY TO BRING AT LEAST TEMPORARY PERIODS OF GALES SUNDAY NIGHT THROUGH MONDAY AND EVEN POSSIBLY INTO EARLY TUESDAY. FOR THAT REASON AND WITH THIS BEING THE PROBABLE FIRST HEARTY GALE EVENT OF THE SEASON...HAVE ISSUED A GALE WATCH WHERE CONFIDENCE IS HIGHEST. ONE TRICKY ASPECT OF THIS EVENT IS THAT WITH THE SOUTHERLY WINDS AHEAD OF THE LOW ON SUNDAY AFTERNOON INTO SUNDAY NIGHT. THESE MAY APPROACH GALES THEMSELVES OVER THE SOUTHERN PART OF THE LAKE...INCLUDING IN THE NEARSHORE ZONES /MAINLY INDIANA/. AT THIS TIME HAVE NOT ISSUED ANY HEADLINE BUT THIS WILL NEED TO BE MONITORED. THE PRIMARY BIG WIND/WAVE TIME WILL REMAIN LATE SUN NIGHT-EARLY TUE. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012...1 AM SUNDAY TO 8 AM SUNDAY. IN...NONE. LM...GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567- LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...3 AM MONDAY TO 3 AM TUESDAY. SMALL CRAFT ADVISORY...LMZ744-LMZ745...NOON SATURDAY TO 10 PM SATURDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 210837 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 337 AM CDT MON OCT 21 2013 .DISCUSSION... 329 AM CDT SYNOPSIS...MORE FALL LIKE WEATHER RETURNS TODAY ALONG WITH NUMEROUS FORECAST COMPLICATIONS. CLOUD COVER WILL DIRECTLY IMPACT LOW TEMPS TONIGHT AND MAY DELAY THE FIRST AREA WIDE FREEZE. HOWEVER HAVE ENOUGH CONFIDENCE TO GO WITH A FREEZE WATCH FOR A CWA WIDE FREEZE WATCH FOR TONIGHT. SNOW IS STILL POSSIBLE TUESDAY/TUESDAY NIGHT AND THEN CONTINUED BELOW AVERAGE TEMPS FOR THE REMAINDER OF THE WEEK. TODAY AND TONIGHT... AN UPPER LEVEL CLOSED LOW CURRENTLY OVER SW ONTARIO WILL PASS OVER LAKE SUPERIOR TODAY WHILE ITS WEAKENING TROUGH AXIS PASSES OVER THE REGION TONIGHT. AT THE SURFACE LOW PRESSURE IS OVER NORTHERN LAKE MICHIGAN AND IT WILL MOVE OVER ONTARIO LATE THIS MORNING. THE LOWS COLD FRONT STRETCHES FROM KENOSHA WI TO MOLINE IL TO KIRKSVILLE MO AND IT WILL MOVE THROUGH THE CWA THROUGH THIS MORNING. TEMPERATURES BEHIND THE FRONT ARE IN THE UPPER 30S WITH NORTHWEST WINDS GUSTING TO 20 KT. OVERHEAD WE ARE STILL SEEING A FEW BANDS OF SHOWERS AND EXPECTING THOSE TO WEAKEN AND PUSH EAST AS THE COLD FRONT SWINGS THROUGH. CLOUD COVER IS THICK BEHIND THE COLD FRONT AND THINKING WE WILL HAVE OVERCAST SKIES THROUGH THIS EVENING. THIS IS GOING AGAINST GUIDANCE...BUT SEE NO REASON TO TRUST GUIDANCE WHEN IT COMES TO SKY COVER SINCE IT IS ALREADY NOT CATCHING THE STRATUS TO OUR WEST. EXPECTING TODAY TO BE DRY WITH WEST WINDS GUSTING UP TO 20 KT. TEMPS ARE TRICKY...AND WENT A DEGREE OR TWO WARMER TODAY DUE TO THE CLOUD COVER. THIS WOULD SIT WELL WITH TRENDS EARLY THIS MORNING AS WE HAVE STAYED WARMER THAN PREVIOUSLY THOUGHT. TONIGHTS FORECAST IS VERY CLOSELY TIED TO CLOUD COVER. THINKING THE STRATUS WILL STICK AROUND AS LONG AS WE HAVE CYCLONIC FLOW FROM THE LOW OVERHEAD. FOR NOW HAVE US SCATTERING OUT THIS EVENING...BUT WE COULD HOLD ON TO CLOUDS LONGER. LOW TEMPS WILL BE DIRECTLY INFLUENCED BY THE CLOUD COVER AS WE ARE ALREADY SEEING EARLY THIS MORNING. RAISED OVERNIGHT MINS BY A DEGREE OR TWO AND STILL LOOKING AT TEMPS AT OR BELOW FREEZING ACROSS THE CWA. AS SUCH GOING TO ISSUE A FREEZE WATCH FOR THE ENTIRE CWA. CONFIDENCE IS JUST SLIGHTLY OVER 50 PERCENT IN SEEING WIDESPREAD FROST/FREEZE TONIGHT...SO JUST GOING WITH A WATCH FOR NOW. TUESDAY AND TUESDAY NIGHT... A SECOND TROUGH AXIS OVER MANITOBA SINKS SOUTH AND PASSES OVER SOUTHERN WI/NORTHERN IL TUESDAY EVENING. A SURFACE LOW CURRENTLY OVER ALBERTA MOVES OVER THE NORTHERN PLAINS THIS EVENING AND THEN OVER SOUTHERN IL TUESDAY AFTERNOON/EVENING. THE GFS IS STILL TOO FAST WITH THIS SYSTEM WHEN COMPARED TO OTHER GUIDANCE SO WILL CONTINUE WITH A MEAN SOLUTION SIMILAR TO THE ECMWF AND NAM. HAVE PRECIP ENTERING THE CWA TUESDAY MORNING AS RAIN. 850MB TEMPS FALL TO -2 TO -6C TUESDAY AND SURFACE TEMPS WILL BE A FEW DEGREES ABOVE FREEZING. HOWEVER THERE IS A DRY LAYER NEAR THE SURFACE AND DIABATIC COOLING COULD LOWER TEMPS TO FREEZING ALLOWING SOME SNOW TO FALL. NOT EXPECTING ANY ACCUMULATING SNOW DUE TO WARM GROUND AND LACK OF CONFIDENCE IN WHEN RAIN WOULD TURN OVER TO SNOW. FOR WHAT ITS WORTH...GUIDANCE IS STILL INDICATING A FEW TENTHS OF SNOW POSSIBLE TO THE NORTH AND AROUND 2 INCHES TO THE SOUTH. PRECIP WILL SHIFT EAST AND DEVELOP MORE OF A LAKE EFFECT INFLUENCE LATE TUESDAY NIGHT OVER NORTHWEST INDIANA...PRIMARILY OVER PORTER COUNTY AT THIS POINT BASED ON WINDS DOWN THE LAKE. BELOW FREEZING TEMPS ARE EXPECTED OVERNIGHT WITH LOWS AT OR BELOW FREEZING. MIN WIND CHILLS COULD BE IN THE UPPER TEENS TUESDAY NIGHT IN THE OUTLYING AREAS WHERE SKIES WILL CLEAR. WEDNESDAY THROUGH FRIDAY... NORTHWEST FLOW ALOFT SETS UP FOR LATE THIS WEEK. A SURFACE HIGH SLIDES SOUTH FROM SASKATCHEWAN THROUGH THE PLAINS TO THE GULF COAST BY WEDNESDAY NIGHT. IT THEN SPREADS OUT ACROSS THE SE U.S. THROUGH THURSDAY NIGHT. COULD SEE A FEW LINGERING LAKE EFFECT RAIN SHOWERS WEDNESDAY MORNING OVER NW INDIANA BUT EXPECTING THOSE TO SHIFT EAST BY MIDDAY ON WEDNESDAY. ANOTHER WEAK SURFACE LOW PASSES TO OUR WEST AND SOUTH WEDNESDAY NIGHT/THURSDAY. GUIDANCE TRIES TO PRODUCE PRECIP OVER THE REGION AS A WEAK UPPER LEVEL SHORTWAVE MOVES THROUGH NORTHERN IL WEDNESDAY NIGHT...BUT GUIDANCE HAS BEEN INCONSISTENT WITH THE TRACK OF THIS LOW/SHORTWAVE AND THE PRECIP SO WENT WITH A DRY FORECAST OTHER THAN PERIODIC CHANCES OF LAKE EFFECT RAIN OVER NORTHWEST INDIANA. GIVEN THAT THE LAKE WATER IS STILL 50+ DEGREES...THINKING A WARM LAYER FROM THE LAKE WILL KEEP ANY PRECIP THAT FALLS LIQUID. TEMPS FOR LATE THIS WEEK ARE HIGHS IN THE 40S AND OVERNIGHT LOWS AROUND 30 WEDNESDAY AND THURSDAY NIGHT...AND A BIT WARMER IN THE LOW 30S FRIDAY NIGHT. SATURDAY AND SUNDAY... NORTHWEST FLOW REMAINS INTACT GOING INTO THE WEEKEND WITH AN UPPER LEVEL TROUGH AXIS MOVING THROUGH LATE SATURDAY NIGHT INTO SUNDAY. AT THE SURFACE GUIDANCE CONTINUES TO SUGGEST A SURFACE LOW WILL PASS TO OUR NORTH WHILE THE SURFACE HIGH SPREADS OVER THE SE US. THE GFS REMAINS FASTER AND FURTHER SOUTH WITH THE LOW WHILE THE ECMWF KEEPS A MORE EXPANSIVE HIGH OVER THE SOUTHEAST U.S. WITH THE LOW OVER CANADA. NOTE HOWEVER THAT THE LATEST 12Z ECMWF HAS COME FURTHER SOUTH WITH THE LOW OVER LAKE SUPERIOR. GIVEN THE DISCREPANCIES KEPT ALLBLEND POPS AND WILL WAIT TO SEE HOW THE MODELS LINE UP IN THE FUTURE. A BRIEF WARM UP IS STILL EXPECTED AS THE UPPER LEVEL PATTERN PUSHES EAST ALLOWING WARMER AIR TO MOVE INTO THE REGION SATURDAY. SW WINDS ALONG WITH WAA HAVE 850MB TEMPS AT 0 TO 6C SATURDAY WITH HIGHS IN THE LOW 50S. THEN WINDS SHIFT TO NW BEHIND THE TROUGH AXIS AND COLDER AIR RETURNS FOR SUNDAY...HOW COLD DEPENDS ON HOW FAR SOUTH THE NEXT SYSTEM SINKS. JEE && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * GUSTY WEST WINDS TODAY. * MVFR CIGS PROBABLE THIS MORNING INTO MID-AFTERNOON WITH A CHANCE OF LINGERING INTO EVEN TONIGHT. //DISCUSSION...UPDATED 06Z... LOW PRESSURE WILL CONTINUE TO DEEPEN AS IT MOVES FROM THE CENTRAL GREAT LAKES NORTHWARD THROUGH THIS MORNING. THIS WILL STEER A COLD FRONT ACROSS THE AREA PRIOR TO DAYBREAK...TURNING WINDS WESTERLY. SPORADIC GUSTS TO 15-18KT WILL BE SEEN WITH THIS BEFORE MORE FREQUENT TO 20KT OR HIGHER LATE THIS MORNING INTO AFTERNOON. MVFR CIGS ARE LIKELY...WITH THE LOWEST MAINLY IN A PERIOD OF TIME NOT FAR BEHIND THE FRONT WHERE THE MOST ROBUST COLD AIR ADVECTION IS LOCATED. OBSERVATIONS MATCH THIS TREND...WITH CIGS AS LOW AS AROUND 2000 FT. CIGS SHOULD INCH THEIR WAY UPWARD AND MAYBE HAVE A FEW HOLES LATE THIS AFTERNOON INTO THIS EVE. WINDS WILL EASE AND BACK SLIGHTLY TONIGHT. //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH IN WIND SHIFT TIME TO WESTERLY. MEDIUM CONFIDENCE IN SPEEDS THROUGHOUT THE TAF PERIOD. * LOW IN MVFR CIG ARRIVAL TIME. MEDIUM CONFIDENCE THAT CIGS WILL REMAIN ABOVE 1500 FT. //OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z... TUESDAY...CHANCE OF -RA OR -SN. MVFR CIGS PROBABLE. WEDNESDAY THROUGH FRIDAY...AT LEAST PERIODIC MVFR CIGS POSSIBLE. SATURDAY...PROBABLY VFR. MTF/IZZI && .MARINE... 330 AM CDT SOME MINOR CHANGES MADE TO THE FORECAST TO EASE WINDS SLIGHTLY...WHICH HAVE RESULTED IN A DAMPENING OF FORECAST WAVES. NO CHANGES TO HEADLINES AT THIS TIME...BUT GALE FORCE WINDS ACROSS THE SOUTHERN PART OF THE LAKE MAY BE MORE OCCASIONAL THAN EARLIER THOUGHT BASED ON OBSERVATIONAL AND GUIDANCE TRENDS. THE STRONG COLD FRONT PROGRESSED ACROSS THE LAKE IN THE WEE HOURS OF THIS MORNING. MUCH COLDER AIR IN THE WAKE OF THIS IS ALLOWING FOR GUSTY WEST TO NORTHWEST WINDS. OCCASIONAL GALES WILL BE SEEN...WITH THE MORE PREVALENT GALES CONFINED TO THE NORTHERN AND EASTERN HALVES OF THE LAKE. AS THE CENTER OF THE PARENT LOW PRESSURE SYSTEM REORGANIZES JUST NORTH OF THE LAKES TONIGHT...ANOTHER COLD FRONT WILL PUSH ACROSS THE NORTHERN PART OF THE LAKE LATE TONIGHT INTO EARLY TUESDAY. THIS SHOULD CONTINUE GALES AND SUPPORT THE HIGHEST WAVES ACROSS THE LAKE BEING IN THE FAR NORTH. NORTHWEST TO WEST WINDS WILL CONTINUE THROUGH THE WEEK WITH GUSTS OVER THE OPEN WATER OF AROUND 25 KT. AS THE FLOW TURNS SLIGHTLY MORE ONSHORE FOR THE INDIANA NEARSHORE AREAS...AN EXTENSION OR A NEW ISSUANCE OF A SMALL CRAFT ADVISORY MAY BE NEEDED FOR TUESDAY NIGHT INTO WEDNESDAY. FINALLY...FOR TONIGHT INTO TUESDAY THERE IS CERTAINLY SUPPORT FOR THUNDER AS WELL AS EVEN WATERSPOUTS FOR PARTS OF EASTERN LAKE MI...NAMELY THE NORTHEAST. LAKE-INDUCED INSTABILITY WILL BE REALIZED WITH THE COLD AIR OVERRIDING THE WARM WATER...AND THIS WILL BE SUFFICIENT ENOUGH FOR CLOUD DEPTHS SUPPORTIVE OF WATERSPOUTS. THE ONLY CAVEAT IS LOW-LEVEL WIND SPEEDS LOOK A LITTLE STRONG FOR WATERSPOUTS TODAY AND POSSIBLY EVEN INTO THIS EVE...WITH THE BEST CHANCES LATE TONIGHT INTO TUESDAY. HAVE CONTINUED MENTION IN THE FORECAST. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...FREEZE WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011- ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023- ILZ032-ILZ033-ILZ039...1 AM TUESDAY TO 8 AM TUESDAY. IN...FREEZE WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...1 AM TUESDAY TO 8 AM TUESDAY. LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777- LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 4 AM TUESDAY. GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 10 AM TUESDAY. SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM TUESDAY. SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 220847 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 347 AM CDT TUE OCT 22 2013 .DISCUSSION... 343 AM CDT USUALLY IT WOULD BE ANOTHER FEW WEEKS OR EVEN LONGER IN OUR FORECAST AREA BEFORE INTERROGATING SEVERAL OF THE FORECAST INGREDIENTS THAT WERE THE FOCUS THIS MORNING. CHALLENGES WERE LOOKING AT PRECIP TYPE AND INTENSITY TODAY...TO SEE IF SOME PLACES COULD GET SOME BRIEF ACCUMULATION NAMELY NEAR THE I-80 /FIRST SUCH ACCUMULATION IN OVER 15 YEARS AND LONGER FOR SOME/...AND THEN LOOKING AT LAKE EFFECT PRECIP POTENTIAL AND TYPE FOR MAINLY PORTER COUNTY INDIANA LATE TONIGHT AND WEDNESDAY MORNING. SYNOPSIS...VIGOROUS SHORT WAVE ENTERING WESTERN IA EARLY THIS MORNING ON A 120+ JET IS BEGINNING TO CURL MORE SE AROUND THE BASE OF THE LONG WAVE TROUGH RESPONSIBLE FOR OUR COLD LATE OCTOBER SNAP. A SURFACE REFLECTION IS DEPICTED IN OBSERVATIONS WITH A BROAD LOW ACROSS WESTERN IA WHICH WILL TIGHTEN AND DEEPEN THROUGH THIS MORNING. SOME LIGHT RAIN IS SEEN ACROSS PARTS OF CENTRAL AND WESTERN IA IN THE WARM AIR ADVECTION FLANK OF THIS CLIPPER. MODEL PREFERENCE...MODEL GUIDANCE IS IN GOOD GENERAL AGREEMENT OF THIS WAVE TRANSITIONING EAST SOUTHEAST THIS AFTERNOON ACROSS CENTRAL IL WITH SOME VARIABILITY IN LATITUDE OF ITS KEY FEATURES...WHICH OF COURSE DICTATE ALL THE KEY ELEMENTS SUCH AS PLACEMENT OF HEAVIER PRECIP AND SUBTLE THERMAL DIFFERENCES THAT INFLUENCE WHERE TRANSITION TO RA/SN MIGHT OCCUR. HAD LEANED A LITTLE MORE TO THE 00Z NAM WHICH HAS VERY CLOSE SUPPORT BY THE 00Z EC AND THE 03Z SREF MEAN. IT SHOULD BE NOTED THIS 00Z NAM HAD SHIFTED SLIGHTLY FURTHER SOUTH THAN ITS PRECEDING 18Z RUN...AND NOW THE 06Z SOLUTION HAS EVEN SHIFTED A BIT FURTHER SOUTH. THE TREND FROM THAT OF TIGHTENING THE PRECIP GRADIENT ON THE NORTH SIDE HAS ALSO BEEN NOTED WHICH MAKES GOOD SENSE WITH HOW THIS SYSTEM IS ORIENTED AND ITS GENERALLY COMPACT NATURE AND QUICK MOVEMENT. THE MAIN POINT WITH THIS IS IT BASICALLY KEEPS PRECIP OUT OF CHICAGO. HAVE NOT GONE THAT SHARP BUT HAVE TIGHTENED THAT NORTHERN GRADIENT. TODAY AND TONIGHT...THE UPPER WARM AND MOIST ASCENT AHEAD OF THE CLIPPER SHOULD LEAD TO A BLOSSOMING OF RADAR ECHOES ACROSS THE WESTERN FORECAST AREA BY LATER THIS MORNING. GOOD CONVERGENCE AND THERMAL GRADIENT TIGHTENING IN THE MID-LEVELS...WITH SUPPORTIVE LAPSE RATES...WILL LIKELY CREATE SOME TEMPORARY MORE INTENSE WEST- TO-EAST CORRIDORS. MOST HIGH RESOLUTION GUIDANCE BOTH LOCALLY AND NATIONALLY TEND TO INDICATE THIS...ALTHOUGH AGAIN WITH DISCREPANCIES IN HOW FAR NORTH...SOME AS FAR NORTH AS AROUND I-88...OTHERS TOWARD PEORIA TO BLOOMINGTON/NORMAL. THIS HEAVIER PRECIP IS IMPORTANT BECAUSE MARGINAL THERMAL PROFILES WOULD NEED THE DIABATIC COOLING TO THE WET BULB /OR COOLER/ TO ENABLE SNOW TO MIX IN TO THE SURFACE. HAVE GENERALLY FAVORED THE LEE/LASALLE/LIVINGSTON COUNTIES THE MOST THIS AFTERNOON...AS THAT CORRIDOR OF WET BULB COOLING AT THE SURFACE /TEMPS DROPPING INTO THE MID 30S/ SHOULD BE SHIFTING SOUTHEAST THROUGH THOSE COUNTIES. IF SNOW CAN MATERIALIZE...TEMPORARY RATES COULD CERTAINLY BE ENOUGH TO BRING DOWN VISIBILITY QUICKLY...AND ITS POSSIBLE THOUGH NOT REALLY FAVORED TO SEE SOME LIGHT SLUSHY ACCUMULATION. LATE IN THE DAY AND THIS EVE THE PROFILES BECOME MORE SUPPORTIVE TO SEE A MIX ACROSS THE WHOLE AREA...BUT THE OVERALL STRONGER FORCING IS WEAKENING AS THE CLIPPER TRANSITIONS AWAY. SO REALLY NOT EXPECTING ANY ACCUMULATION ELSEWHERE IF ANY OTHER PLACES CAN ACTUALLY CHANGE OVER. IN MUCH OF THE CHICAGO METRO /OUTSIDE OF THE FAR SOUTHWEST AND SOUTH/ THE PROFILES JUST APPEAR TOO WARM TO SUPPORT A LONG CHANGEOVER IF ANY GIVEN MORNING MODERATION IN TEMPS. LAKE EFFECT...IN THE WAKE OF THE CLIPPER AND ITS SURFACE LOW REFLECTION MOVING INTO INDIANA...WINDS WILL TURN MORE NORTHERLY AND DOWN THE FETCH OF THE LAKE. IT APPEARS THEIR IS A 6 TO 12 HOUR WINDOW OF GOOD N-S CONVERGENCE INTO MAINLY NW IN. MODERATE TO EXTREME LOW-LEVEL INSTABILITY WILL BE IN PLACE OVER THE LAKE GIVEN 850MB TEMPERATURES OF -4C TO -6C. NAM PROFILES OVER THE LAKE GIVEN MODIFIED PARCELS NEAR THE SURFACE LAKE TEMPERATURES SUPPORT CLOUD DEPTHS OF 15K FT. ITS NOTED THIS MORNING THAT THE AIR TEMPERATURE AT THE SOUTH BUOY IS ONLY 42 DESPITE A WATER TEMPERATURE OF 60. SO THE INSTABILITY MAY NOT BE AS EXTREME AS SOME MODIFIED GUIDANCE SHOWS...BUT STILL AMPLE FOR DECENT SHOWERS. PRECIP TYPE IS A REAL CHALLENGE AND AGAIN BASED ON INTENSITY. IT WOULD SEEM ALONG THE IMMEDIATE LAKE SHORE WITH ONSHORE FLOW IT WOULD BE TOUGH TO GET EVEN A CHANGEOVER. INLAND THERE IS CERTAINLY THAT CHANCE AND IF THE CONVERGENCE IS STRONG...THEN THAT INSTABILITY WILL TRAIN INLAND POTENTIALLY CREATING A PROBLEM FOR QUICK ACCUMULATION IF COLD ENOUGH WITH HEAVY SUSTAINED RATES. HAVE ADDED UNDER AN INCH OF ACCUMULATION IN EASTERN PORTER COUNTY...BUT CERTAINLY THE CHANCE IS THERE FOR MORE. FOR NOW THOUGH...THERMAL PROFILES ARE AWFULLY MARGINAL AND WITH THE CAVEAT OF ONSHORE FLOW POTENTIALLY LEADING TO RAIN SHOWERS FOR MUCH OF THAT TIME. BEYOND...MORE TRANQUIL CONDITIONS PREVAIL HOWEVER STILL UNDER NORTHWEST FLOW ALOFT...SO BELOW NORMAL TEMPERATURES CONTINUE. THE BACK SIDE OF THE TROUGH SHIFTS EAST AS DOES ITS JET...SO THE PATH FOR SHORT WAVES WILL BE MORE TO THE NORTH AND EAST BY THURSDAY...MEANING LESS OF A CHANCE FOR PRECIP. LAKE EFFECT ORIENTATION LOOKS TO BE EAST OF OUR INDIANA COUNTIES ON MOST OF THESE DAYS. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * RAIN EXPECTED THIS AFTN...WITH A CHANCE OF MIXING OR CHANGING TO WET SNOW. BETTER CHANCE OF SNOW AT MDW. * IF SNOW DEVELOPS...IFR CONDITIONS ARE LIKELY. JEE //DISCUSSION...UPDATED 06Z... VFR STRATUS CURRENTLY OVER IOWA WILL MOVE OVER THE TERMINALS EARLY THIS MORNING AND EXPECTING W TO NW WINDS TO CONTINUE THROUGH THE FORECAST PERIOD. LOW PRESSURE OVER SOUTH DAKOTA WILL MOVE OVER SOUTHERN IL THIS AFTN/EVENING. AN UPPER LEVEL TROUGH AXIS WILL ALSO MOVE OVER THE REGION THIS AFTERNOON PROVIDING ADDITIONAL FORCING FOR PRECIP. THINKING THE MAJORITY OF PRECIP AND HEAVIEST PRECIP WILL STICK CLOSER TO THE LOW...BUT GUIDANCE IS STILL SUGGESTING PRECIP WILL GET AS FAR NORTH AS ORD AND POSSIBLY RFD. FOR SNOW...WE WILL BE ABOVE FREEZING THIS AFTN AND EXPECTING THE AREAS WITH HEAVIER PRECIP TO COOL AND ALLOW SNOW TO MIX WITH RAIN OR COMPLETELY TURN OVER TO SNOW FOR A TIME. THE AREA WITH THE BEST CHANCE FOR COMPLETE CHANGE OVER AND ACCUMULATION IS WELL SOUTH OF THE TERMINALS...BUT LARGE WET SNOWFLAKES WILL QUICKLY REDUCE VISIBILITY. SO THINKING ORD...RFD...AND DPA WILL BE FAR ENOUGH NORTH THAT RASN WITH MVFR VSBY IS THE MOST LIKELY SITUATION GIVEN HOW FAR REMOVED THEY ARE FROM THE LOW AND BEST FORCING. MDW AND GYY HAVE THE BEST CHANCE FOR A COMPLETE CHANGE OVER TO SNOW AND IFR VSBY AND CIGS. TIED IFR CIGS TO SNOW DUE TO THE LOW LEVEL COOLING NEEDED FOR SNOW. SNOW SHOULD SHIFT EAST OF MDW THIS EVENING ALLOWING CIGS TO COME BACK UP TO VFR. THE WINDOW OF SNOW WILL PROBABLY BE VERY NARROW AT MDW...BUT SINCE CONFIDENCE IS LOW ON WHEN THE CHANGE OVER WILL BE...LEFT A WIDER WINDOW TO COVER THE ENTIRE PERIOD THAT SNOW IS POSSIBLE. GYY ON THE OTHER HAND WILL BE AT THE MERCY OF THE LAKE AS THE LAKE EFFECT PRECIP MACHINE TURNS ON THIS EVENING. THE BEST CHANCE FOR ADDITIONAL LAKE EFFECT PRECIP IS OVER PORTER COUNTY IN...BUT DECIDED TO LEAVE GYY WITH IFR CIGS AND -SNDZ THROUGH 06Z. JEE //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM-HIGH CONFIDENCE IN PRECIP GETTING AS FAR NORTH AS MDW...MEDIUM CONFIDENCE IN PRECIP MAKING IT TO ORD. * MEDIUM-HIGH CONFIDENCE IN PRECIP MIXING OR CHANGING OVER TO SNOW AT MDW...MEDIUM CONFIDENCE AT ORD. * HIGH CONFIDENCE IN IFR CONDITIONS IF PRECIP MIXES OR TURNS OVER TO SNOW. * MEDIUM CONFIDENCE IN TIMING OF PRECIP. * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS. JEE //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY AND THURSDAY...MVFR CIGS POSSIBLE. FRIDAY...VFR PROBABLE. SATURDAY...POTENTIAL FOR SOME MVFR CIGS...MAINLY LATE. SUNDAY...VFR PROBABLE. IZZI && .MARINE... 324 AM CDT FOR HEADLINES...WILL LEAVE THE GALE WARNING AS IS AS GALES SHOULD SUBSIDE BY MID MORNING. WILL ALSO LEAVE THE SMALL CRAFT ADVISORY AS IS. ANOTHER SMALL CRAFT ADVISORY WILL BE NEEDED FOR HIGH WAVES TONIGHT FOR ALL OF THE NEARSHORE ZONES BUT WAS NOT SURE HOW FAR NORTH TO GO WITH THE ADVISORY AT THIS TIME. BASED ON THIS RUN OF THE WAVE MODEL...HAZARDOUS WAVES COULD BE IN PLACE THROUGH FRIDAY EVENING. LOW PRESSURE IS OVER SOUTHERN ONTARIO WITH A TROUGH OF LOW PRESSURE THROUGH LAKE SUPERIOR. THE TROUGH WILL ROTATE OVER THE FAR NORTHERN END OF THE LAKE THIS MORNING. WEST GALES CONTINUE OVER THE NORTHERN END OF THE LAKE THIS MORNING AND EXPECTING THOSE TO DIMINISH THROUGH MID MORNING AS THE LOW PULLS OFF TO THE NORTHEAST. STEEP LAPSE RATES ESPECIALLY OVER THE EASTERN HALF OF THE LAKE WILL RESULT IN A SLIGHT CHANCE OF THUNDERSTORMS AND WATERSPOUTS THROUGH WEDNESDAY AFTERNOON. NORTHWEST WINDS 15-25 KT BUILD ACROSS THE LAKE THROUGH THURSDAY NIGHT AS A PARADE OF SURFACE SYSTEMS MARCHES DOWN THE PLAINS. HIGH PRESSURE CLOSELY FOLLOWED BY A WEAK LOW PRESSURE SYSTEM TRAVEL DOWN THE PLAINS TODAY THROUGH WEDNESDAY NIGHT WITH A LARGER HIGH PRESSURE SYSTEM BUILDING OVER THE PLAINS WEDNESDAY NIGHT INTO FRIDAY. A STRONGER LOW PRESSURE SYSTEM THEN DROPS OUT OF NORTHERN MANITOBA AND PASSES OVER THE NORTHERN GREAT LAKES FRIDAY NIGHT/SATURDAY. ITS COLD FRONT PASSES OVER THE LAKE SATURDAY. THE GRADIENT TIGHTENS OVER THE LAKE BETWEEN THE APPROACHING LOW AND HIGH OVER THE SOUTHEAST U.S. FRIDAY NIGHT...RESULTING IN SOUTHWEST WINDS TO AT LEAST 30 KT WITH A CHANCE OF LOW END GALES OVER THE SOUTHERN END OF THE LAKE. WINDS BECOME NORTHWEST TO 30KT BEHIND THE COLD FRONT. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...FREEZE WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022- ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 8 AM TUESDAY. IN...FREEZE WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 8 AM TUESDAY. LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 10 AM TUESDAY. SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 272315 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 615 PM CDT SUN OCT 27 2013 .DISCUSSION... 216 PM CDT TONIGHT... ABUNDANT SUNSHINE ACROSS THIS AFTERNOON AS ANTI-CYCLONIC FLOW SLOWLY DRIFTS SOUTHEAST ACROSS THE TENN VALLEY. A CHANNEL OF SLIGHTLY STRONGER SOUTHWEST FLOW OVER THE CENTRAL PLAINS/UPPER MIDWEST...WILL SLOWLY SLIDE OVERHEAD OF THE CWFA...AS SOUTHWEST FLOW LINGERS THROUGH THIS EVENING. A FRONTAL BOUNDARY LOCATED ACROSS THE UPPER MIDWEST STRETCHING SOUTHWEST THROUGH SOUTH DAKOTA...WILL CONTINUE TO APPROACH THE CWFA OVERNIGHT. THIS WILL ALLOW FLOW TO FLIP FROM SOUTHWEST TO NORTH/NORTHEAST DURING THE PRE-DAWN HOURS MON. VERY DRY SFC CONDS CONTINUE WITH DEW POINTS HOLDING THIS AFTN IN THE UPR 20S/LOW 30S. WINDS WILL QUICKLY DIMINISH ARND SUNSET...AND WITH THE DRY CONDS AND LACK OF CLOUDS...TEMPS WILL QUICKLY RADIATE INTO THE LOW 40S BY 9PM THEN SLOWLY FALL INTO THE MID/UPR 30S. SLIGHTLY WARMER ALONG THE IMMEDIATE LAKESHORE IN THE MID 40S. CONFIDENCE...HIGH. MONDAY THROUGH TUESDAY... STRONG ANTI-CYCLONIC SFC FEATURE PUSHES SOUTHEAST FROM CANADA INTO THE UPPER MIDWEST...WHICH WILL ALLOW A TIGHT PRES GRADIENT TO DEVELOP ALONG THE LEE-SIDE AS IT SLIDES ACROSS LAKE MICHIGAN/NORTHERN IL. LCL HI-RES GUIDANCE CONTINUES TO SUGGEST INCREASED LLVL MOISTURE PROGRESSIVELY SLIDING SOUTH ACROSS THE LAKE EARLY MON AND ARRIVING ACROSS NORTHEAST IL ARND DAYBREAK. WITH COLD AIR ADVECTING ACROSS THE WARMER LAKE...IT IS LIKELY THAT SOME LIFT COULD GENERATE SPRINKLES IN THE MORNING FAR FAR NORTHEAST IL. THE LARGER CHALLENGE FOR MON WILL BE HIGH TEMPS. WITH THE STRONG NORTHEAST FLOW INFLUENCE AND CLOUD COVER...TEMPS ALONG FAR NORTHEAST/NORTHERN IL WILL LIKELY HOLD IN THE UPR 40S TO ARND 50. FURTHER SOUTHWEST WHERE THE LAKE SHADOW IS NOT AS STRONG AND CLOUDS WILL NOT BE AS THICK...TEMPS SHUD WARM INTO THE MID/UPR 50S. THE FRONTAL BOUNDARY WILL BECOME A QUASI-STATIONARY FEATURE MON NGT ORIENTED ALONG SOUTHERN IOWA EAST THROUGH SOUTHERN IN. STRONG CANADIAN SFC RIDGE WILL SLOWLY SLIDE EAST AND BECOME CENTERED OVER LAKE HURON EARLY TUE...WITH LLVL FLOW ACROSS THE CWFA TURNING EASTERLY. THIS WILL LIKELY AID IN KEEPING TEMPS ALONG THE IMMEDIATE LAKESHORE MON NGT SLIGHTLY WARMER WITH A FEED OFF OF LAKE MICHIGAN. HOWEVER WITH LINGER CLOUDS AND MECHANICAL MIXING OVERNIGHT MON...TEMPS AWAY FROM LAKE MICHIGAN WILL ONLY COOL INTO THE UPR 30S TO LOW 40S. LLVL FLOW WILL REMAIN EASTERLY TUE...AS THE QUASI-STATIONARY BOUNDARY REMAINS WELL SOUTH OF THE FORECAST AREA. TEMPS TUE WILL BE MAINLY IN THE LOW/MID 50S. GUIDANCE CONTINUES TO DIFFER ON THE STRENGTH OF THE DOWNSTREAM RIDGE...AND PLACEMENT...WHICH WILL STEER THE TIMING/PLACEMENT OF THE APPROACHING UPSTREAM TROUGH AXIS FOR LATER IN THE WEEK. CONFIDENCE IN TEMPS...MEDIUM/HIGH. WEDNESDAY THROUGH FRIDAY... MID-WEEK HAS PREVIOUSLY BEEN ADVERTISED AS THE FOCAL POINT FOR THE WEEKS FORECAST...AND THIS CONTINUES TO BE THE LARGEST CONCERN FOR THE NEXT SEVERAL DAYS. GUIDANCE CONTINUES TO PROG A TROUGH AXIS SLOWLY LIFTING NORTHEAST FROM THE SOUTHWEST CONUS TUE AFTN...WITH A LARGE RIDGE OVER THE GULF OF MEXICO. FOR WED...THIS FEATURE WILL CONTINUE TO APPROACH THE FORECAST AREA. THE RIDGE OVER THE GULF SHIFTS EAST...ALLOWING RETURN FLOW MOISTURE TO SLIDE NORTH ACROSS THE OZARKS IN ADVANCE OF THE TROUGH AXIS/LLVL VORT MAX. THIS WILL LIFT THE QUASI-STATIONARY BOUNDARY NORTH ACROSS THE CWFA MIDDAY WED...WITH MAX TEMPS LIKELY NOT OCCURRING UNTIL WED EVENING. THUS HAVE OPTED TO NOT UTILIZE A DIURNAL CURVE FOR WED...AND PLACED MAX TEMPS CLOSER TO 00-03Z THUR. WITH TEMPS SLOWLY CLIMBING WELL INTO THE 50S/LOW 60S. THEN A MILD NIGHT WED INTO THUR...WITH NEARLY STEADY TEMPS. IN ADDITION TO THE DELAYED WARM TEMPS...A STRONG THERMAL RIDGE CONTINUES TO BE PROGGED ACROSS THE AREA WED/THUR WITH TEMPS ALOFT WARMING TO ARND 10-12 DEG C. ENSEMBLES CONTINUE TO PAINT PWAT VALUES ARND 3 SIGMA OR 1.2-1.6" WED NIGHT-THUR...WITH A STRONG NOCTURNAL LLVL JET POINTED TOWARDS THE FORECAST AREA. INSTABILITY AT THIS TIME DOES NOT APPEAR TO BE TOO SIGNIFICANT ACROSS THE AREA...AND WITH CONSIDERABLE SOLAR SHIELDING...IT IS LIKELY ANY CONVECTION WOULD BE FOCUSED WELL SOUTH OF THE FORECAST AREA. HOWEVER...GUIDANCE DOES SUGGEST SOME ELEVATED INSTABILITY AND FOR THIS HAVE HELD ONTO A MENTION OF SLIGHT THUNDER. THE BIGGER CONCERN WITH THE UPCOMING SYSTEM IS FOCUSED WITH THE QPF TOTALS...WHICH COULD BE IN EXCESS OF 1.00". THE EC CONTINUES TO FAVOR A SLOWER EVOLUTION AND DELAYED FRONTAL PASSAGE...WITH THE SFC LOW LIFTING ACROSS EXTREME NORTHEAST IL LATE THUR NIGHT. MEANWHILE THE GFS SOLUTION FAVORS A CONTINUED PROGRESSIVE APPROACH WITH A DRY SLOT ARRIVING THUR AFTN/EVE...AND THE LOW PASSING OVER LAKE SUPERIOR THUR AFTN. SO CONSIDERABLE DISCREPANCIES REMAINS WITH THE TRACK...WHICH WILL HAVE A SIGNIFICANT IMPACT ON THE INTENSITY/TIMING OF QPF AND FRONTAL PASSAGE. 500MB TROUGH AXIS ARRIVES FRI...AND WILL PUSH THE BULK OF THE MOISTURE TO THE EASTERN GREAT LAKES REGION. COOLER AND MORE SEASONAL AIR WILL RETURN FOR THE END OF THE WEEK...WITH TEMPS FRI MAINLY IN THE LOW 50S. CONFIDENCE...MEDIUM. CONFIDENCE IN PERIODS OF MODERATE RAIN...MEDIUM/HIGH. SATURDAY THROUGH SUNDAY... ENSEMBLES FOR THE UPCOMING WEEKEND ARE IN RELATIVELY GOOD AGREEMENT...WITH A 500MB TROUGH OVERHEAD SAT. THEN THE TROUGH BEGINS TO WEAKEN AS THE FLOW APPEARS TO FLATTEN...TRANSITIONING INTO A SEMI-ZONAL PATTERN FOR THE SECOND HALF OF THE WEEKEND. OVERALL THE WEEKEND LOOKS TO BE QUIET AT THIS TIME...WITH DRY CONDITIONS OVER THE CWFA AND TEMPS MAINLY IN THE 50S AND OVERNIGHT LOWS IN THE 30S. CONFIDENCE...MEDIUM/HIGH. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * WIND SHIFT TO NE LIKELY MONDAY MORNING * MVFR STRATUS LIKELY ARRIVING MONDAY MORNING AND LINGERING INTO THE AFTERNOON IZZI //DISCUSSION...UPDATED 00Z... WEATHER NIL THROUGH TONIGHT WITH COLD FRONT EXPECTED TO MOVE THROUGH THE REGION VERY LATE TONIGHT INTO MONDAY MORNING. WINDS WILL SHIFT TO LIGHT NORTH INITIALLY BEHIND THE FRONT BEFORE LOCKING IN FROM THE NORTHEAST AND LIKELY ATTAINING SOME GUSTINESS...PARTICULARLY AT ORD WHICH TENDS TO GUST VERY EFFICIENTLY WITH NORTHEAST WINDS. MULTIPLE HIGH-RES MODELS ARE SHOWING THE DEVELOPMENT OF A WEAK SURFACE LOW OVER SOUTHERN LAKE MICHIGAN LATE TONIGHT INTO EARLY MONDAY MORNING WHICH WOULD SLOW THE ARRIVAL OF THE BETTER FRONTAL PUSH AND SUBSEQUENT MVFR CIGS BY SEVERAL HOURS. WHAT LITTLE MVFR THERE IS UPSTREAM BEHIND THE FRONT CURRENTLY LAGS WELL BEHIND THE INITIAL WIND SHIFT...THOUGH SUSPECT WITH ONSET OF DIURNAL COOLING THE MVFR CIGS COULD TRY AND CATCH UP WITH THE FRONT SOME TONIGHT. ONCE CIGS MOVE IN CONTINUED FEED OF MOISTURE OFF THE LAKE WILL PROBABLY RESULT IN BKN MVFR CIGS PERSISTING THROUGH THE DAY MONDAY INTO MONDAY EVENING...THOUGH SOME TENDENCY WILL EXIST FOR CIGS TO DIURNALLY LIFT SOME MONDAY AFTERNOON. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH CONFIDENCE IN FORECAST THROUGH 12Z MONDAY * MEDIUM-HIGH CONFIDENCE IN MVFR CIGS DEVELOPING...LOW TO MEDIUM CONFIDENCE ON TIME OF ARRIVAL INTO ORD/MDW * MEDIUM CONFIDENCE IN MVFR CIGS PERSISTING THROUGH THE DAY MONDAY IZZI //OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z... TUESDAY...EAST FLOW LIKELY. CHANCE OF RAIN...MAINLY TUE NIGHT. MVFR CIGS POSSIBLE. WEDNESDAY...EAST FLOW LIKELY. CHANCE OF RAIN...MAINLY WED NIGHT. MVFR CIGS PROBABLE WITH IFR CIGS POSSIBLE. THURSDAY...WEST FLOW LIKELY. OCNL SHRA/CHANCE TSRA. MVFR PROBABLE WITH SMALL CHANCE FOR IFR. FRIDAY AND SATURDAY...WEST FLOW LIKELY. MVFR CIGS PROBABLE. IZZI && .MARINE... 300 PM...A STRONG COLD FRONT WILL MOVE SOUTH ACROSS LAKE MICHIGAN LATER THIS EVENING AND OVERNIGHT. THE GRADIENT WILL QUICKLY TIGHTEN BEHIND THIS FRONT...ESPECIALLY ACROSS THE NORTH CENTRAL PART OF THE LAKE WHERE SOME GUSTS TO LOW END GALES WILL BE POSSIBLE. THIS APPEARS IT WILL BE SHORT-LIVED...PERHAPS JUST FOR AN HOUR OR TWO BEHIND THE FRONT. SO FOR NOW HAVE INCLUDED GUSTS WORDING BUT THIS WILL NEED TO BE MONITORED LATER THIS EVENING AND OVERNIGHT. WINDS WILL STILL BE STRONG AS THE FRONT CONTINUES SOUTH OVERNIGHT...BUT POTENTIAL FOR GALES WILL BE DECREASING. THIS FRONT WILL MOVE SOUTH OF LAKE MICHIGAN BY MID MORNING MONDAY...THOUGH THE STRONGEST WINDS MAY REMAIN ALONG THE ILLINOIS SHORE...AND POINTS NORTH. HIGH PRESSURE BUILDING OVER SOUTHERN CANADA TONIGHT WILL SPREAD SOUTHEAST ACROSS THE NORTHERN LAKES REGION MONDAY AFTERNOON AND MONDAY NIGHT AND BEGIN TO WEAKEN AS IT SLIDES EAST TO NEW ENGLAND TUESDAY AND TUESDAY NIGHT. THE PATH OF THIS HIGH WILL LIKELY MAINTAIN A STRONGER EASTERLY GRADIENT OVER THE SOUTHERN THIRD OR SO OF THE LAKE WITH 15-25KTS CONTINUING INTO TUESDAY AFTERNOON OR TUESDAY NIGHT BEFORE FINALLY DIMINISHING. LOW PRESSURE WILL DEVELOP OVER THE PLAINS MONDAY NIGHT AND TUESDAY AND MOVE NORTHEAST ACROSS THE WESTERN LAKES REGION WEDNESDAY NIGHT INTO THURSDAY AND THEN SLOW AS IT MOVES ACROSS THE NORTHERN LAKES THURSDAY INTO THURSDAY NIGHT. DEPENDING ON THE PATH/STRENGTHEN OF THIS SYSTEM...STRONG SOUTHERLY WINDS MAY DEVELOP WEDNESDAY NIGHT INTO THURSDAY WITH A PROLONGED PERIOD OF STRONG WESTERLY WINDS THURSDAY NIGHT THROUGH SATURDAY. CMS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741...4 AM MONDAY TO 3 PM TUESDAY. SMALL CRAFT ADVISORY...LMZ742-LMZ743...10 AM MONDAY TO 3 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 092329 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 529 PM CST SAT NOV 9 2013 .DISCUSSION... 317 PM CST MAIN FORECAST CONCERNS/CHALLENGES ARE WITH PRECIP TRENDS/TYPE ON MONDAY WITH THE POTENTIAL FOR MINOR SNOW ACCUMULATION ACROSS THE CWA...WITH GROWING CONCERNS FOR LAKE EFFECT SNOWFALL ACROSS NORTHWEST INDIANA MONDAY NIGHT INTO TUESDAY. IN THE NEAR TERM...PARTLY CLOUDY/SUNNY CONDITIONS WERE OBSERVED TODAY PRIMARILY ACROSS THE NORTHERN HALF OF THE CWA WITH MORE SUNNY CONDITIONS ACROSS THE SOUTHERN HALF. MORE MILD CONDITIONS OUT AHEAD OF AN APPROACHING TROUGH OF LOW PRESSURE AND ASSOCIATED COLD FRONT RESULTED IN RATHER WARM TEMPS FOR THIS TIME OF THE YEAR WITH MOST LOCATIONS IN THE MID/UPPER 50S...AND EVEN LOWER 60S ACROSS THE SOUTHERN HALF. THOUGH DESPITE THESE MILDER CONDITIONS...STRONGER WESTERLY WINDS PREVAILED TODAY. DO EXPECT THESE WEST/NORTHWEST WINDS AND GUSTS TO PERSIST THIS EVENING AND MOST OF THE NIGHT...AS THIS FRONT PUSHES THROUGH WITH COLDER TEMPS IN THE 30S EXPECTED FOR MOST AREAS. DO EXPECT CURRENT SCT CLOUDS ACROSS THE CWA TO DIMINISH/EXIT OVER THE NEXT COUPLE OF HOURS WITH GENERALLY CLEAR SKIES EXPECTED OVERNIGHT. ALTHOUGH...CURRENT UPSTREAM WAVE WILL SLIDE EAST/SOUTHEAST ACROSS THE REGION AND COULD BRING A MORE SOLID DECK OF CLOUD COVER NEAR NORTH/NORTHEAST ILLINOIS AND NORTHWEST INDIANA LATER THIS EVENING AND OVERNIGHT. SO FOR THOSE LOCATIONS WOULD EXPECT CLEAR SKIES TO BECOME MORE PARTLY CLOUDY...WITH THE REMAINDER OF THE CWA STAYING MORE CLEAR TONIGHT. PROGRESSIVE MID LEVEL WAVE AND ATTENDANT LINGERING SURFACE TROUGH WILL CONTINUE TO SHIFT WELL NORTHEAST OF THE CWA DURING THE DAY SUNDAY...WITH HIGH PRESSURE TO THE WEST QUICKLY SHIFTING EAST OVER THE CWA BY THE AFTERNOON. WITH THIS IN PLACE EXPECT SUNNY CONDITIONS FOR ALL AREAS SUNDAY...WITH THE COLDER AIRMASS THAT MADE ITS WAY SOUTH ACROSS THE CWA TONIGHT QUICKLY EXITING TO THE EAST AS WELL ON SUNDAY. ALTHOUGH...INITIAL COOLER CONDITIONS SHOULD LIMIT HIGH TEMPS ON SUNDAY DESPITE ONGOING WAA...WITH TEMPS IN THE MID TO UPPER 40S EXPECTED. DONT ANTICIPATE THIS PATTERN TO REMAIN IN PLACE TOO LONG...WITH AS SOON AS THE HIGH BUILDS ACROSS THE CWA...IT WILL QUICKLY SHIFT TO THE EAST/SOUTHEAST SUNDAY NIGHT. A STRONG AND LARGE UPPER LEVEL LOW WILL DROP SOUTHEAST ACROSS SOUTHERN CANADA SUNDAY NIGHT INTO MONDAY...WITH A STRONG MID LEVEL TROUGH SWINGING SOUTH ACROSS THE REGION. THIS WILL HELP A RATHER COLD AIRMASS TO COME BARRELING DOWN TOWARDS THE CWA...BEHIND AN APPROACHING SURFACE TROUGH AND STRONG COLD FRONT. ALTHOUGH THERE ARE SOME SUBTLE DIFFERENCES WITH TIMING OF THIS FRONT...IT DOES APPEAR THAT GENERAL CONSENSUS IS A LATE MORNING TIME FRAME FOR FROPA. DUE TO THE POTENCY OF THIS COLDER AIR SPILLING SOUTH ACROSS THE CWA...DO EXPECT WHAT LITTLE RISE IN TEMPS MONDAY MORNING TO QUICKLY COME DOWN BACK INTO THE 30S FOR MOST THE CWA INTO THE AFTERNOON. ANTICIPATED PRECIP WITH THIS SYSTEM COINCIDING WITH THIS TRANSITION TO A MUCH COLDER AIRMASS WILL CREATE A TRANSITION BACK TOWARDS WINTRY PRECIP. IT DOES APPEAR THAT THE COLUMN WILL COOL MORE THAN SUFFICIENTLY AND WITH DEEP MOISTURE/CRYSTALS PRESENT FOR A TRANSITION FROM INITIAL RAIN OVER TO A RAIN/SNOW MIX AND THEN ALL SNOW. SOME MINOR TIMING DIFFERENCES WITH THE PUSH OF THIS COLD AIR ALONG WITH THE EXTENT OF THE DURATION FOR ANY SNOWFALL OVER ANYONE AREA...DOES CREATE SOME UNCERTAINTY IF ANY AREA WILL OBSERVE ANY ACCUMULATIONS. UPPER LEVEL DYNAMICS COINCIDING WITH POTENTIAL FOR ANOTHER STRONG MID LEVEL TROUGH TO SWING AROUND ACROSS THE AREA AND THEN RESULT IN FRONTOGENETICAL FORCING CONTINUES TO REMAIN A POSSIBILITY...BUT I WONDER IF ANY ENHANCED FORCING WILL LINGER ENOUGH OVER ANYONE AREA TO PRODUCE ANYMORE THAN VERY MINOR ACCUMULATIONS INTO THE AFTERNOON. ALTHOUGH...IT IS STILL A BIT FAR OUT TO TRULY DIAGNOSE THESE SMALLER FEATURES THAT COULD CHANGE THIS THINKING...AND SO WILL HAVE TO MONITOR THIS TIME FRAME. LATEST GUIDANCE IS INDICATING POST FRONTAL PRECIP TO LINGER ACROSS THE SOUTHERN CWA INTO THE EARLY MONDAY EVENING. WITH THIS LINGERING PRECIP AND RATHER COLD TEMPS...DO THINK SOME AREAS SOUTH OF I-80 COULD POSSIBLY OBSERVE UP TO A HALF AN INCH OF SNOWFALL BEFORE THIS EXITS SOUTH OF THE CWA. WITH THIS COLDER AIR BARRELING DOWN THE LAKE...MORE THAN FAVORABLE THERMODYNAMIC CONDITIONS WILL PROVIDE A GOOD SETUP FOR LAKE EFFECT PRECIP MONDAY NIGHT INTO TUESDAY...AND AM GROWING A LITTLE CONCERNED FOR THE POSSIBILITY FOR SIGNIFICANT SNOW ACCUMULATIONS ACROSS NORTHWEST INDIANA. A LONG FETCH DOWN THE LAKE WITH A FAVORABLE SYNOPTIC PATTERN/CYCLONIC FLOW SHOULD ALLOW FOR AN EXTENDED PERIOD OF LAKE EFFECT PRECIP TO PERSIST BEHIND THE SYSTEM PRECIP...WITH A RAIN/SNOW MIX MORE PROBABLE LATE MONDAY AFTERNOON BEFORE A QUICK TRANSITION TO ALL SNOW IS LIKELY TO BE OBSERVED EARLY MONDAY EVENING INTO TUESDAY. BOUNDARY LAYER FLOW WILL KEEP ANY PRECIP IN NORTHWEST INDIANA...WITH PORTER COUNTY THE MORE PREFERRED LOCATION TO OBSERVE LES SNOW/SNOW BAND. DONT WANT TO GET INTO ANY AMOUNTS SINCE SMALLER SCALE FEATURES/RESIDENCE TIME OF ANY LES BAND WILL DICTATE SNOWFALL TOTALS...BUT THERE DOES APPEAR TO BE A DEFINITE POSSIBILITY FOR ADVISORY TYPE SNOWFALL ACROSS AT LEAST PORTER COUNTY WITH LOCALLY HIGHER AMOUNTS DEFINITELY NOT OUT OF THE QUESTION. RODRIGUEZ && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * SMALL CHANCE FOR BROKEN CIGS OF 2500-3500 FT TONIGHT. * WEST NORTHWEST GUSTS POSSIBLY INCREASING TO 25-30 KT FOR A 2-3 HR PERIOD THIS EVE. //DISCUSSION...UPDATED 00Z... LOW PRESSURE ACROSS THE NORTHERN GREAT LAKES WILL CONTINUE TO MOVE EAST TONIGHT. COLD AIR BEGINNING TO WRAP AROUND THIS SYSTEM WILL LEAD TO A SUBTLE COLD FRONT MOVING THROUGH THIS EVE WHICH CONCEIVABLY MAY RE-INCREASE WEST NORTHWEST WINDS. SPORADIC GUSTS OF UP TO 30 KT ARE POSSIBLE. WITHIN THIS REGIME THERE DOES EXIST SCT TO BKN CLOUDS UPSTREAM IN SOUTHEAST MN AND SOUTHWEST WI. SOME OF THESE MAY MAKE IT TO THE AREA BUT AM THINKING SUPPRESSION ALOFT WILL WIN OUT AND DISSOLVE MUCH OF ANY BROKEN CIGS THIS FAR SOUTH. A HIGH PRESSURE RIDGE WILL GRADUALLY MOVE OVER BY SUNDAY AFTERNOON. THIS WILL BE BRIEF THOUGH...AS A STRONG COLD FRONT APPROACHES THE REGION TO PASS THROUGH ON MONDAY. PRECIPITATION ALONG AND BEHIND THIS FRONT LOOKS TO BE RAIN CHANGING TO SNOW DURING MONDAY. //ORD AND MDW CONFIDENCE...UPDATED 00Z... * LOW IN WHETHER BROKEN CIGS WILL RETURN THIS EVE...BUT HIGH THAT THEY WOULD REMAIN ABOVE 1500 FT. * HIGH IN WIND TRENDS. LOW-MEDIUM IN GUST MAGNITUDE TONIGHT. //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY...CHC FOR RAIN DURING THE DAY WITH RAIN/SNOW LIKELY DURING THE AFTERNOON INTO EARLY EVE. LIKELY NO SNOW ACCUM. PERIODS OF IFR PROBABLE. TUESDAY-WEDNESDAY...VFR LIKELY. THURSDAY...SLIGHT CHC OF RAIN/SNOW DURING THE NIGHT. MVFR/IFR POSSIBLE. FRIDAY...VFR LIKELY. MTF && .MARINE... 129 PM CST DEEPENING AREA OF LOW PRESSURE IS TRAVERSING EAST ACROSS THE NORTHERN LAKES REGION TODAY WITH SW/W WINDS AROUND 30 KTS EXPECTED TO BECOME W/NW AND INCREASE TO GALES AGAIN THIS EVENING AS A COLD FRONT SWEEPS ACROSS THE LAKE. A GALE WARNING REMAINS IN EFFECT THIS EVENING THROUGH MID MORNING SUNDAY FOR THE OPEN WATERS. FOR THE ILLINOIS NEARSHORE WATERS...GALES MAY BE MARGINAL IN THE OFF SHORE FLOW...BUT AS THE COLD AIR ARRIVES LATE THIS EVENING/OVERNIGHT...MAY SEE A BURST IN THE WINDS WITH LOW END GALES POSSIBLE...ESPECIALLY AS YOU GET FARTHER FROM THE SHORE AND THE WARMER WATERS HAVE MORE TIME TO MODIFY THE INCOMING AIRMASS. FOR NOW WILL REMAIN WITH A STRONGLY WORDED SMALL CRAFT ADVISORY. WINDS/WAVES SHOULD DIMINISH THROUGH THE DAY SUNDAY AS HIGH PRESSURE BUILDS SOUTH OF THE LAKE...THEN WAVES BACK TO THE SOUTHWEST SUNDAY EVENING. SOUTHWEST FLOW INCREASES TO AROUND 30 KT AGAIN SUNDAY NIGHT AHEAD OF ANOTHER COLD FRONT. NORTHWEST GALES ARE POSSIBLE MONDAY BEHIND THE FRONT. YET ANOTHER DEEP AREA OF LOW PRESSURE TRAVERSING ACROSS JAMES BAY LATE WEDNESDAY MAY LEAD TO GALES PARTICULARLY ACROSS THE NORTHERN PORTIONS OF THE LAKE WEDNESDAY AND WEDNESDAY NIGHT. BMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 6 PM SATURDAY. GALE WARNING...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 4 AM SUNDAY. SMALL CRAFT ADVISORY...LMZ744-LMZ745...4 AM SUNDAY TO 3 PM SUNDAY. GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 9 AM SUNDAY. GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777- LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM SUNDAY. SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 9 AM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 120358 AAA AFDLOT AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 958 PM CST MON NOV 11 2013 .DISCUSSION... 955 PM CST NO MAJOR CHANGES PLANNED TO LAKE EFFECT SNOW ADVISORY OR FORECAST SNOWFALL AMOUNTS FOR PORTER COUNTY TONIGHT. HAVE ADJUSTED TEMPERATURES AND CLOUD TRENDS ELSEWHERE SLIGHTLY. LOOKING AHEAD TO TUESDAY NIGHT AS WELL...OBSERVATIONAL TRENDS AND LATEST GUIDANCE INDICATE THAT FORECAST READINGS WILL PROBABLY NEED TO BE LOWERED...WITH A CHANCE FOR SINGLE DIGITS AT SOME FAVORED OUTLYING LOCATIONS. COLD AIR HAS FLOODED THE REGION WITH 20S AT THE SURFACE AND 850MB TEMPS OF -14C NOT FAR UPSTREAM FROM THE 00Z GRB RAOB. MODIFYING THAT GRB SOUNDING FOR TEMP/DEW POINTS OBSERVED AT THE SOUTH BUOY...WHICH SHOULD BOTH REMAIN SOMEWHAT CONSISTENT TONIGHT...YIELDS CAPE VALUES OF AROUND 200 J/KG AND CLOUD DEPTHS OF AROUND 6000 FT /EL AROUND 9000 FT/. REGIONAL RADARS HAVE INDICATED A BLOSSOMING OF SHOWERS ACROSS THE SOUTHEAST PART OF THE LAKE WITH SOME ECHOES TOWARD MID-LAKE. THERE ARE SOME HIGHER ECHOES IN THERE ALONG WITH A STRAND OF COLDER CLOUD TOPS ON IR SATELLITE...WHICH SEEM TO LINE UP ACROSS THE SOUTHEAST PART OF THE LAKE WHERE LOW-LEVEL CONVERGENCE IS BASED ON OBSERVATIONS. CURRENTLY THAT IS POINTING INTO BERRIEN COUNTY MICHIGAN. NO SHORT TERM GUIDANCE HAS A VERY GOOD HANDLE ON WHERE THAT LOW- LEVEL CONVERGENCE IS...WITH NUMEROUS SOURCES HAVING A NORTHWEST WIND OVER THE MICHIGAN SHORE WHERE IT IS CURRENTLY NORTHEAST. CONVECTIVE ALLOWING GUIDANCE GENERALLY AGREES WOBBLING THAT AREA SLIGHTLY BACK TO THE WEST...WITH SHOWERS MOVING INTO PORTER COUNTY OVERNIGHT. THE HRRR REMAINS THE MOST AGGRESSIVE WITH THIS. WITH NO REAL CHANGE IN THE PRESSURE FIELD...GIVEN THE SURFACE HIGH MOVING SOUTHWARD ACROSS THE PLAINS...COULD ENVISION THIS STRUGGLES TO MOVE BACK WEST MUCH. BUT GIVEN THAT THE SHOWERS ALREADY EXIST AND ON A CONVERGENT AXIS POINT TOWARD SOMEWHERE IS PROBABLE TO GET HIGHER END ACCUMULATIONS...POTENTIALLY STILL JUST EAST OF THE AREA WITH A RAPID CUT-OFF TO THE WEST INTO OR JUST EAST OF PORTER COUNTY. SO IT REMAINS CHALLENGING...BUT THE TWO COUNTIES UNDER THE ADVISORY LOOK GOOD AT THIS TIME. OTHERWISE...HAVE BUMPED CLOUD COVER UP SOME LATER TONIGHT AS SOME COLD AIR STRATOCU IN EASTERN WI CONTINUES TO DRIFT SOUTH...AND SOME LAKE EFFECT CLOUDS MAY ACTUALLY WORK THEIR WAY INTO NORTHEAST ILLINOIS. ITS NOT IMPOSSIBLE SOME ISOLATED LAKE EFFECT SHOWERS...NOT SO MUCH A CONVERGENT AXIS OF THEM...BUT A FEW DRIFT INTO NORTHEAST ILLINOIS INCLUDING CHICAGO LATE TONIGHT. THIS MAY CAUSE A SLIGHT RE-INCREASE IN TEMPERATURES...BUT OVERALL READINGS SHOULD SLOWLY DROP. DEW POINTS CONTINUE TO LOWER THROUGH THE TEENS AND SET THE STAGE FOR VERY CHILLY TEMPERATURES ONCE THE WINDS EASE WHICH WILL BE THE CASE TUESDAY NIGHT. WILL PASS ALONG TO THE OVERNIGHT SHIFT THE PROBABILITY OF NEEDING TO LOWER...WHICH MOS GUIDANCE IS ALREADY INDICATING MAY BE A CHILLY ONE. MTF && .PREV DISCUSSION... 259 PM CST SEVERAL NEAR TERM FORECAST CONCERNS AND CHALLENGES WITH PRECIPITATION ENDING FROM NORTH TO SOUTH INTO THE EVENING...WITH LAKE EFFECT SNOW DEVELOPING THROUGH THE EVENING IMPACTING PORTIONS OF NORTHWEST INDIANA TO SOME DEGREE THROUGH THE OVERNIGHT. AFTERNOON WATER VAPOR IMAGERY SHOWS A DEEP UPPER LOW SPINNING OVER SOUTHERN JAMES BAY AS PART OF A BROAD UPPER TROUGH SPREADING ACROSS THE EASTERN HALF OF THE COUNTRY. RIDGING IS BUILDING OVER THE PACIFIC NORTHWEST AND BRITISH COLUMBIA AS ANOTHER UPPER LOW SPINS OVER THE WEST COAST WITH YET ANOTHER TROUGH JUST TO ITS WEST. AT THE SURFACE...LOW PRESSURE ASSOCIATED WITH THE JAMES BAY UPPER LOW IS MOVING INTO NORTHERN QUEBEC WITH A COLD FRONT TRAILING IT TO THE SOUTHWEST AND HAVING EXITED THE SOUTHERN CWA. STRONG HIGH PRESSURE IS SETTLING SOUTHWARD INTO THE PLAINS AND WESTERN GREAT LAKES. THIS EVENING...CURRENT POST FRONTAL BAND OF PRECIPITATION CONTINUES TO GRADUALLY WORK SOUTHWARD ACROSS THE CENTRAL AND SOUTHERN CWA. THIS BAND WILL CONTINUE SOUTHWARD THROUGH EARLY EVENING BEFORE ENDING ACROSS THE SOUTHERN CWA BY MID EVENING OR SO. FAIRLY INTENSE SNOWFALL PRODUCING VISIBILITY UNDER A MILE AT TIMES WILL CONTINUE AS THE COLDER AIR SPREAD SOUTH...WITH AREAS THAT ARE CURRENTLY RAIN CHANGING OVER. HAVE HAD REPORTS OF AROUND A HALF INCH OF ACCUMULATION ON GRASSY AND OTHER NON PAVED SURFACES AND EXPECT THAT THIS WILL CONTINUE TO BE THE TREND UNTIL THE SNOW WINDS DOWN. THE MAIN CONCERN WITH THIS WILL BE TEMPS FALLING BELOW FREEZING ACROSS AREAS THAT HAVE NOT ALREADY DONE SO THROUGH SUNSET. PRECIP MAY END BEFORE THIS OCCURS IN SOME AREAS BUT THIS WILL SET UP POTENTIAL FOR RESIDUAL MOISTURE ON VARIOUS SURFACES TO FREEZE BEFORE DRYING SO MOTORISTS AND PEDESTRIANS SHOULD BE ALERT. TONIGHT AND TUESDAY...THE FOCUS WILL BE ON LAKE EFFECT SNOW PLACEMENT TONIGHT THROUGH TUESDAY MORNING. THE UPPER LOW WILL CONTINUE EASTWARD TO THE GULF OF ST. LAWRENCE BY TUESDAY MORNING WITH AN ASSOCIATED TROUGH AXIS CROSSING THE LOCAL AREA. NORTHERLY LOW AND MID LEVEL FLOW WILL BE IN PLACE ACROSS LAKE MICHIGAN THIS EVENING AND OVERNIGHT WITH CONTINUED COLD ADVECTION BRINGING H85 TEMPS DOWN TO AROUND -12 C CREATING LAKE TO H85 DELTA-TS OF 20+C. GENERATING LAKE EFFECT WILL NOT BE A PROBLEM...ITS THE PLACEMENT THAT IS THE MAIN CHALLENGE. MEAN LOW LEVEL FLOW THIS EVENING WILL START OUT NORTHWESTERLY ACROSS NORTHERN PORTIONS OF THE LAKE AND NORTHERLY SOUTH AS THE COLDER AIR CONTINUES TO ADVECT IN. WITH TIME...THE MEAN FLOW WILL GAIN MORE OF A WEST COMPONENT/THOUGH STILL REMAINING NORTHWESTERLY OVERALL/ INTO TUESDAY MORNING. THE INITIAL CONVERGENCE LOOKS TO SET UP ACROSS NORTHERN SECTIONS OF THE LAKE CLOSER TO THE MICHIGAN SHORE BASED ON THE NORTHWEST DIRECTION AND FAIRLY STRONG SPEEDS FOCUSING FRICTIONAL CONVERGENCE CLOSER TO SHORE. THE BAND MAY ARC SOUTH OR SOUTHWEST AS IT DEVELOPS SOUTHWARD AS THE FLOW TURNS MORE NORTHERLY...BUT MAY STILL REMAIN FAIRLY CLOSE TO THE MICHIGAN SHORELINE. AM CONCERNED BY THE NEARLY DUE NORTH DIRECTION THIS EVENING BUT DEVELOPMENT OF MORE ORGANIZED BANDS MAY HOLD OFF UNTIL CLOSER TO MIDNIGHT. THIS MAY RESULT IN PORTER COUNTY AND EVEN PORTIONS OF JASPER COUNTY SEEING A PERIOD OF DECENT SNOWFALL LATER THIS EVENING AND EARLY TONIGHT BEFORE WINDS TURN SLIGHTLY NORTHWEST PUSHING THE BAND FURTHER EAST TOWARD DAYBREAK. MOST OF THE HIGH RES GUIDANCE HAS BEEN BULLISH ON KEEPING THE BAND CLOSER TO THE MICHIGAN SHORE AND INTO LAPORTE AND BERRIEN COUNTIES AND EVEN POINTS FURTHER EAST...WITH MUCH LESS ACTIVITY IN PORTER/JASPER. AM WONDERING IF THEY ARE A LITTLE TOO BULLISH ON HOW FAR EAST THE FOCUS BECOMES. WITH A STRONG NORTH COMPONENT HAVE A HARD TIME SEEING THE BAND DEVELOPING ALL THE WAY ON THE EAST SIDE OF THE LAKE AND MORE OR LESS STAYING THERE UNLESS TIMING OF ACTUAL PLUME DEVELOPMENT IS DELAYED UNTIL WINDS START TO TURN MORE NORTHWEST. INTERESTINGLY...SOME OF THE LATEST RAP GUIDANCE FALLS MORE IN LINE WITH THIS THOUGHT PROCESS. WHILE THERE IS SIGNIFICANT BUST POTENTIAL HERE...WILL GO AHEAD AND ISSUE A LAKE EFFECT SNOW ADVISORY FOR PORTER AND JASPER HIGHLIGHTING THE LATE EVENING AND OVERNIGHT HOURS AS THE PERIOD OF BEST HEAVY SNOW POTENTIAL ACROSS MAINLY THE EAST HALF OF EACH COUNTY. SNOWFALL RATES MAY BE QUITE INTENSE ON THE ORDER OF SEVERAL INCHES PER HOUR BUT THE DURATION IS STILL A QUESTION MARK. COMBINE THIS WITH GUSTY WINDS FAIRLY ROUGH CONDITIONS MAY DEVELOP ASSUMING THE BAND AFFECTS THESE AREAS. STILL CANNOT RULE OUT WARNING LEVEL SNOWS OVER 6 INCHES BUT WITH A FAIR AMOUNT OF SUPPORT FOR LESSER AMOUNTS HAVE A HARD TIME GOING WITH A WARNING AT THIS POINT. FOLLOWING THE IDEA THAT THE BAND WILL INITIALLY IMPACT PORTER/JASPER THEN SHIFT EASTWARD FEEL A BIT MORE COMFORTABLE GOING WITH AN ADVISORY THAN JUST KEEPING THE WATCH. THE EVENING SHIFT WILL NEED TO MONITOR CLOSELY. BEYOND THAT...LOWS WILL FALL INTO THE LOW TO MID 20S TONIGHT WITH READINGS CLOSER TO 30 NEAR AND DOWNWIND OF THE LAKE. DRY CONDITIONS WILL PERSIST ACROSS THE MAJORITY OF THE AREA WITH LAKE EFFECT SHOWERS ENDING EAST TUESDAY. HIGHS WILL ONLY MAKE IT INTO LOW TO MID 30S. WEDNESDAY AND BEYOND...DID NOT HAVE A WHOLE LOT OF TIME TO LOOK FURTHER AHEAD IN THE FORECAST PERIOD BUT HIGH PRESSURE WILL BE SETTLING INTO THE LOWER OHIO VALLEY WEDNESDAY AS THE WESTERN UPPER RIDGE IS SHUNTED EASTWARD. THIS WILL ALLOW MODEST WARM ADVECTION TO DEVELOP IN THE MID LEVELS WITH A STEADY SOUTHWEST WIND AT THE SURFACE AS THE HIGH SHIFTS EASTWARD. MAY BE A LITTLE TOO CONSERVATIVE WITH UPPER 30S HIGHS WITH ANY SNOWPACK IN NW INDIANA LIKELY KEEPING THINGS IN THE 30S REGARDLESS. THE UPPER RIDGE WILL BE BROKEN DOWN AS IT TRANSLATES EASTWARD AS A FAIRLY BROAD LONGWAVE TROUGH MOVES ACROSS THE ROCKIES AND INTO THE PLAINS THURSDAY. A WEAK SURFACE TROUGH IS EXPECTED TO ACCOMPANY THIS AND BRING A WEAK COOL FRONT ACROSS THE AREA THURSDAY NIGHT OR FRIDAY WITH A LOW CHANCE FOR RAIN/SNOW AT NIGHT AND SHOWERS DURING THE DAY. LOW AMPLITUDE FLOW WILL THEN MOVE ACROSS THE AREA SATURDAY WITH AN AMPLIFYING TROUGH SPREADING IN LATER IN THE WEEKEND AND EARLY NEXT WEEK. A SURFACE LOW IS FORECAST TO DEEPEN AS THE TROUGH AMPLIFIES BUT ECMWF/GFS ARE AT ODDS ON HOW QUICKLY THIS OCCURS. A WARMUP SHOULD OCCUR IN THE SOUTHERLY FLOW AHEAD OF THE LOW BUT THIS MAY BE BRIEF IF A FASTER SOLUTION PANS OUT. EITHER WAY MOIST SOUTHERLY FLOW POINTS TOWARD INCREASING PRECIP CHANCES SUNDAY WHICH MAY CONTINUE THROUGH MONDAY IF THE SLOWER SOLUTION PANS OUT. MDB && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 03Z... * GUSTY NORTH/NORTHWEST WINDS THROUGH TUESDAY MORNING...BECOMING MORE WESTERLY TUESDAY AFTERNOON. CMS //DISCUSSION...UPDATED 00Z... BACK EDGE OF THE SNOW WILL PASS THROUGH GYY IN THE NEXT HOUR AND THEN EXPECT DRY CONDITIONS AT ALL THE TERMINALS THROUGH THE PERIOD. ONE EXCEPTION IS LAKE EFFECT SNOW SHOWERS THAT WILL DEVELOP OVER SOUTHERN LAKE MICHIGAN LATER THIS EVENING AND CONTINUE INTO TUESDAY. IT APPEARS THESE WILL REMAIN EAST OF GYY... BUT THERE COULD BE A PERIOD BETWEEN 05Z-10Z WHEN THEY MOVE WEST... POTENTIALLY REACHING GYY. CONFIDENCE IS FAIRLY LOW THAT THESE SNOW SHOWERS WILL IMPACT GYY BUT OPTED TO MAINTAIN VCSH MENTION WITH THIS FORECAST. ONCE LOW CLOUDS CLEAR MDW/GYY EARLY THIS EVENING...MID/HIGH CLOUDS WILL SLOWLY CLEAR LATER THIS EVENING AND OVERNIGHT. AREA OF 4-5KFT STRATOCU OVER NORTHEAST WI AND THE UPPER PENINSULA WILL NEED TO BE WATCHED AS IT DRIFTS SOUTHEAST TONIGHT. WINDS WILL REMAIN NORTH/NORTHWEST THROUGH TUESDAY MORNING WITH SPEEDS IN THE 12-15KT RANGE WITH HIGHER GUSTS. QUITE A BIT OF WIND IN THE LOW LEVELS AND WITH THE COLD AIR SPREADING ACROSS THE REGION...EXPECT SOME OF THIS TO MIX TO THE SURFACE...ESPECIALLY THIS EVENING BUT AS SKIES CLEAR TONIGHT...POSSIBLE THAT GUSTS WILL BECOME LESS PREVAILING. WINDS TURN MORE NORTHWEST TUESDAY MORNING AND THEN MORE WESTERLY TUESDAY AFTERNOON...QUICKLY DIMINISHING WITH SUNSET TUESDAY EVENING. CMS //ORD AND MDW CONFIDENCE...UPDATED 03Z... * MEDIUM FOR WIND SPEEDS/GUSTS/DIRECTIONS THROUGH THE PERIOD. CMS //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... * WEDNESDAY AND THURSDAY...DRY/VFR. GUSTY SOUTHWEST WINDS. * FRIDAY...MVFR POSSIBLE. SLIGHT CHANCE OF SHRA. SLIGHT CHANCE OF SHSN BEFORE DAYBREAK. * SATURDAY...DRY/VFR. * SUNDAY...CHANCE OF SHRA. MVFR POSSIBLE. && .MARINE... 338 PM CST A COLD FRONT PUSHED DOWN THE LENGTH OF LAKE MI DURING LATE OVERNIGHT AND THIS MORNING WITH WINDS SHIFTING TO OUT OF THE NW AND N WITH 35 KT GALES. WINDS HAD FALLEN TO A BIT BELOW GALE FORCE ON THE N AND CENTRAL PORTIONS OF THE LAKE AT MID AFTERNOON...AND ARE EXPECTED TO DO SO ON THE S PORTION LATE THIS AFTERNOON. HOWEVER...A SECOND SURGE OF COLD AIR MOVING ACROSS NORTHERN WI AND THE U.P. OF MI WILL QUICKLY MOVE S DOWN THE LAKE LATE THIS AFTERNOON AND EARLY THIS EVENING WITH WINDS EXPECTED TO INCREASE BACK TO 35 KT GALES BEFORE GRADUALLY DIMINISHING OVERNIGHT AND CONTINUING TO DO SO DURING TUESDAY. WINDS BACK TO W TUE NIGHT AND SW WED...INCREASING TO 35-40 KT GALES AS A LARGE HIGH MOVES EAST-SOUTHEAST FROM THE CENTRAL PLAINS ACROSS THE MID MISSISSIPPI VALLEY AND REACHING THE SOUTHERN APPALACHIANS BY THU. SW GALES WILL CONTINUE THROUGH WED NIGHT INTO THU MORNING AS LOW PRESSURE THAT DEVELOPED OVER ALBERTA TUE DEEPENS AS IT MOVES QUICKLY E TO JAMES BAY BY THU MORNING. WINDS AND WAVES MEETING OR EXCEEDING OF SMALL CRAFT ADVISORY CRITERIA WILL ALONG THE IL SHORE UNTIL LATE TUE EVENING...AND INTO OVERNIGHT TUE. WINDS WILL LIKELY INCREASE BACK TO ABOVE SMALL CRAFT CRITERIA BY WED AFTERNOON. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...LAKE EFFECT SNOW ADVISORY...INZ002-INZ011 UNTIL NOON TUESDAY. LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ744-LMZ745-LMZ777- LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 AM TUESDAY. SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 9 PM TUESDAY. SMALL CRAFT ADVISORY...LMZ744-LMZ745...3 AM TUESDAY TO 3 AM WEDNESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 132327 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 527 PM CST WED NOV 13 2013 .DISCUSSION... 306 PM CST PRIMARY FORECAST CONCERN THIS AFTERNOON REVOLVES AROUND BIG WARM UP AND THE POTENTIAL FOR HEAVY RAIN AND THUNDERSTORMS WITH THIS WEEKEND'S STORM SYSTEM. DEEP UPPER TROUGH RESPONSIBLE FOR OUR FLING WITH OLD MAN WINTER THIS WEEK IS RAPIDLY MOVING EAST WITH STRONG ARCTIC HIGH PUSHING INTO THE MID SOUTH TODAY. THE COMBINATION OF THE RETREATING STRONG HIGH AND FAST/MOVING AND DEEPENING LOW MOVING TOWARD JAMES BAY HAS RESULTED IN INCREASINGLY STRONG SOUTH-SOUTHWESTERLY FLOW ACROSS THE AREA TODAY. GRADIENT REMAINS JUST AS STRONG TONIGHT...THOUGH WITH BETTER PRESSURE FALLS MOVING QUICKLY EAST INTO QUEBEC AND SOME NOCTURNAL DECOUPLING WOULD EXPECT GUSTINESS TO GRADUALLY ABATE TONIGHT. PRESSURE GRADIENT REALLY DOESNT RELAX MUCH THURSDAY...SO GUSTINESS LIKELY TO RETURN WITH ANOTHER BREEZY/WINDY DAY. TEMPERATURE FORECAST THE NEXT COUPLE OF DAYS WILL REMAIN TRICKY AS THE MODELS ARE INITIALIZING NEARLY A 2 INCH SNOW PACK ACROSS THE AREA AND ONLY VERY SLOWLY MELTING IT. THE ONLY SNOWPACK OF ANY SUBSTANCE LEFT IN OUR CWA IS OVER EASTERN PORTER COUNTY...AND THAT IS LIKELY TO MELT THE NEXT DAY OR SO. ELSEWHERE HAVE CONTINUED THE TREND FROM THE PREVIOUS FORECAST OF KEEPING FORECAST TEMPERATURES ABOVE GUIDANCE SINCE IT SEEMS TO BE SUFFERING THE EFFECTS OF THE PHANTOM SNOW COVER. THE SHIFT IN THE LONG WAVE PATTERN FROM EASTERN TROUGH/WESTERN RIDGE TO WESTERN TROUGH/BROAD EASTERN RIDGE SHOULD CONTINUE LATE THIS WEEK INTO THE WEEKEND. VIGOROUS SHORTWAVE OFF THE BRITISH COLUMBIA COAST WILL DIVE DOWN THE BACK OF THE AMPLIFYING TROUGH AND THEN EJECT NORTHEAST INTO THE MID MISSISSIPPI VALLEY LATER SATURDAY. THIS LEAD WAVE IS LIKELY TO SUPPORT SURFACE LOW DEVELOPMENT TO OUR NORTHWEST WHICH WILL RE-STRENGTHEN THE SOUTHERLY FLOW AFTER FRIDAY'S LULL AND BEGIN THE PROCESS OF DRAGGING UNSEASONABLY MOIST AIR NORTH INTO THE REGION. EXPECT SHOWERS AND POSSIBLY A COUPLE OF THUNDERSTORMS TO ACCOMPANY THIS LEAD WAVE LATER SATURDAY INTO SATURDAY EVENING...PARTICULARLY NORTHWEST HALF OF THE CWA. AREA SHOULD SEE A BIT OF A LULL IN THE PRECIP IN THE WAKE OF THIS FIRST WAVE LATER SATURDAY NIGHT INTO AT LEAST THE FIRST PORTIONS OF THE DAY SUNDAY. ATTENTION WILL THEN TURN TO THE REMAINDER OF THE LONG WAVE TROUGH WHICH WILL BEGIN THE PROCESS OF SHIFTING EASTWARD INTO THE CENTRAL CONUS SUNDAY. AS FULL TROUGH MOVES OUT LOOK FOR STRONG SURFACE LOW TO DEVELOP OVER THE CENTRAL PLAINS SAT NIGHT WHICH WILL THEN LIFT NORTHEAST INTO THE GREAT LAKES REGION SUNDAY. DEFINITELY SOME DIFFERENCES EXIST AMONG THE DETERMINISTIC MODELS WITH RESPECT TO THE EXPECT TRACK/TIMING/INTENSITY OF THIS LOW...BUT THEY DO AGREE ON THE GENERAL IDEA OF A DEEP SURFACE LOW TRACKING TO OUR NORTHWEST LATER SUNDAY INTO SUNDAY NIGHT. VERY STRONG LOW LEVEL JET AND A COUPLE DAYS OF RETURN FLOW FROM THE GULF OF MEXICO WILL RESULT IN AN UNSEASONABLY MOIST AIRMASS BEING TRANSPORTED NORTH INTO THE REGION IN ADVANCE OF THIS STRONG COLD FRONT AND LOW PRESSURE SYSTEM SUNDAY. SURFACE DEWPOINTS SATURDAY NIGHT INTO INTO SUNDAY LIKELY TO SURGE AT LEAST INTO THE MID TO UPPER 50S...WITH THE ECMWF STILL INSISTING ON BRINGING 60F+ DEWPOINTS INTO THE AREA. GENERAL SYNOPTIC SET-UP IN THE PAST THIS TIME OF YEAR HAS PRODUCED SEVERE WEATHER AND HEAVY RAINFALL...AND WHILE FAR FROM THE MOST LIKELY SCENARIO...THESE ARE THINGS THAT WE WILL NEED TO KEEP AN EYE ON. FORECAST LAPSE RATES LOOK FAIRLY WEAK BUT DEWPOINTS THAT HIGH THIS TIME OF YEAR COULD STILL RESULT IN WEAK BUT SUFFICIENT INSTABILITY FOR THUNDERSTORMS AND IF THE RIGHT ATMOSPHERIC DOMINOES FALL INTO PLACE EVEN SOME SEVERE THREAT. PWATS OF 250% OR MORE OF NORMAL OBVIOUSLY RAISES RED FLAGS FOR THE POTENTIAL FOR SIGNIFICANT RAINFALL AS WELL. GIVEN THE MODELS ARE LIKELY TO CHANGE THEIR TUNE SOME OVER THE NEXT COUPLE OF DAYS REALLY NO POINT IN DIGGING MUCH INTO THE DETAILS OF THE CURRENT RUNS. MEDIUM RANGE MODELS DO DIFFER ON THE INTENSITY OF THE COLD AIR MASS DIVING INTO THE AREA BEHIND THIS SYSTEM...WITH THE GFS PARTICULARLY BULLISH WITH H8 TEMPS DROPPING TO BELOW -18C BY TUESDAY. THE 12Z ECMWF HAS TRENDED A BIT COOLER THAN ITS PREVIOUS RUN BUT IS STILL CONSIDERABLY LESS INTENSE WITH THE COLD BLAST THAN THE GFS. HAVE BASICALLY SPLIT THE DIFFERENCE FOR NOW AND STUCK WITH THE "ALLBLEND" MODEL COCKTAIL FOR TEMPS EARLY NEXT WEEK. IF GFS ACTUALLY WERE TO PAN OUT THEN HIGHS IN THE 20S WOULD BE POSSIBLE BY TUESDAY...BUT ECMWF USUALLY WINS OUT IN THESE SITUATIONS SO WE WILL PROBABLY END UP IN THE 30S. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * LOW LEVEL WIND SHEAR TONIGHT * SSW WINDS (190-220) WITH OCNL GUSTS TO AROUND 20KT TONIGHT * SSW WINDS THURSDAY WITH MORE FREQUENT GUSTS UP TO AROUND 25KT IZZI //DISCUSSION...UPDATED 00Z... ONLY AVIATION WEATHER CONCERN NEXT 24-30 HOURS REVOLVES AROUND WIND AND WIND SHEAR THREAT. MODERATELY STRONG SOUTH-SOUTHWEST WINDS WILL CONTINUE TONIGHT WITH GUSTS TO AROUND 20KT GROWING LESS FREQUENT WITH TIME THIS EVENING. JUST OFF THE DECK 45-50KT LOW LEVEL JET WILL RESULT IN THE POTENTIAL FOR LLWS THROUGH MID MORNING THURSDAY WHEN BETTER LOW LEVEL MICING LESSENS THE THREAT...THOUGH THAT SAME MIXING WILL RESULT IN MORE GUSTINESS TO THE SOUTH SOUTHWEST WINDS. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH CONFIDENCE IN ALL FORECAST ELEMENTS IZZI //OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z... FRIDAY...VFR. SATURDAY...CHANCE OF SHOWERS LATE. MVFR POSSIBLE BY EVENING. SATURDAY NIGHT...SHOWERS LIKELY...MAINLY EARLY. MODERATELY STRONG SOUTH WINDS. MVFR PROBABLE WITH IFR POSSIBLE. SUNDAY...SHOWERS AND A CHANCE OF THUNDERSTORMS. MVFR LIKELY WITH IFR POSSIBLE. STRONG SOUTH WINDS. MONDAY AND TUESDAY...MVFR CIGS POSSIBLE. GUSTY WEST-NORTHWEST WIDS. IZZI && .MARINE... 238 PM CST A STRONG SOUTHWESTERLY GALE EVENT WILL CONTINUE THROUGH TONIGHT...GRADUALLY DIMINISHING WITH TIME. OCCASIONAL STORM FORCE GUSTS TO 50 KT ARE POSSIBLE ON THE NORTH HALF THROUGH MID EVENING...BUT FEEL THAT THE WINDOW OF TIME WHEN THEY ARE POSSIBLE IS SMALL AND FREQUENCY IS SUCH THAT AN UPGRADE TO A STORM WARNING WAS NOT WARRANTED. WILL NEED TO MONITOR THOUGH. THE GRADIENT WILL REMAIN TIGHTEST ON THE SOUTH HALF ON THURSDAY AND CONDITIONS WILL STILL BE UNSTABLE ENOUGH TO ENABLE FREQUENT GALE GUSTS INTO TOMORROW EVENING. THUS HAVE EXTENDED THE GALE WARNING FOR THE SOUTH HALF UNTIL THURSDAY EVENING. HAVE LOWER CONFIDENCE IN NEEDING TO EXTEND THE GALE WARNING FOR THE NEARSHORE WATERS BEYOND NOON THURSDAY...BUT HIGH CONFIDENCE IN HAZARDOUS SMALL CRAFT WINDS CONTINUING INTO THE EVENING. AFTER A BRIEF LULL FRIDAY...ATTENTION TURNS TO A STRONG STORM SYSTEM TAKING SHAPE OVER THE PLAINS AND LIFTING NORTHEAST. THIS SYSTEM WILL PULL NORTH UNSEASONABLY WARM CONDITIONS OVER THE LAKE...BUT THE GRADIENT STILL APPEARS TIGHT ENOUGH FOR GALES TO DEVELOP ON SATURDAY DESPITE INCREASING STABLE CONDITIONS. THE SYSTEM WILL LIFT NORTH INTO CANADA SUNDAY...BUT WILL BE FOLLOWED QUICKLY ON ITS HEELS BY A DEEPENING SECONDARY LOW. DUE TO SOME UNCERTAINTY AMONGST GUIDANCE IN TRACK AND TIMING OF THIS LOW...THERE COULD BE A BRIEF LULL IN THE STRONGER SOUTHERLY WINDS. HOWEVER...AS IT BECOMES A POWERHOUSE SUB 29.0 INCH STORM EARLY MONDAY AND A STRONG COLD FRONT SWEEPS ACROSS LAKE MICHIGAN...THERE LOOKS TO BE ANOTHER GOOD SET-UP FOR NORTHWESTERLY GALES MONDAY INTO TUESDAY. A VERY COLD AIRMASS POURING ACROSS THE LAKE WILL SUPPORT UNSTABLE CONDITIONS. RC && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779- LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM THURSDAY. GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567- LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ868 UNTIL NOON THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 260934 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 334 AM CST TUE NOV 26 2013 .DISCUSSION... 331 AM CST THE FOCUS OF THE MORNING FORECAST WAS ON THE NEXT 36 HOURS WITH SNOW SHOWER POTENTIAL LATER TODAY AND THIS EVENING...AND THEN LAKE EFFECT SNOW INTO NORTHWEST INDIANA INTO WEDNESDAY WHICH COULD HAVE NOTABLE IMPACTS ON HOLIDAY TRAVEL IN THAT AREA. THERE IS CONTINUED SPLIT FLOW SEEN THIS MORNING ON GOES WATER VAPOR IMAGERY ACROSS THE CENTRAL U.S. WITH A VIGOROUS CLOSED LOW DIVING SOUTHEASTWARD ACROSS THE GREAT LAKES REGION AND A PERSISTENT CLOSED LOW IN THE SOUTHERN PLAINS BEGINNING TO MIGRATE EASTWARD. THE FIRST SYSTEM WILL HAVE INFLUENCE OVER THE AREA TODAY AS ITS SURFACE REFLECTION OF A COLD FRONT CROSSES THE FORECAST AREA LATER THIS MORNING. THE COLD AIR WILL ACTUALLY LAG THE NORTHWEST WIND SHIFT BY A COUPLE/FEW HOURS. TEMPERATURES LOOK TO FALL BACK INTO THE 20S ACROSS NORTH CENTRAL ILLINOIS EARLY THIS AFTERNOON AS THAT OCCURS...AND SETS THE STAGE FOR LOW TEMPERATURES IN THE MID TEENS TONIGHT IN OUTLYING LOCATIONS. WITH THIS BEING A VIGOROUS UPPER TROUGH HAVING A NOTEWORTHY STRATOSPHERIC INTRUSION SEEN ON UPSTREAM CANADIAN UPPER AIR SOUNDINGS LAST EVE...A FURTHERING STRENGTHENING OF THE VORT AND OVERALL LOW-LEVEL COLD AIR ADVECTION SHOULD BE SEEN THROUGH TODAY. TOGETHER THAT SHOULD INCREASE CHANCES THAT AT LEAST SOME SNOW SHOWER DEVELOPMENT WILL OCCUR OVER THE AREA BY MID-AFTERNOON AND PERSISTING INTO THIS EVE. BELIEVE THAT EXPLICIT CONVECTIVE GUIDANCE IS UNDERDONE...AND SO CONTINUE THE ISOLATED MENTION ACROSS THE AREA IN THIS TIME. EVEN THOUGH COVERAGE MAY NOT BE THAT GREAT...WHERE SNOW SHOWERS DO OCCUR THEY COULD BRIEFLY PACK A PUNCH WITH SHARPLY LOWERED VISIBILITY. IN ADDITION...THE TIMING WOULD FAVOR THEM TO DOT THE AREA DURING THE LATE AFTERNOON/EARLY EVE COMMUTE. ATTENTION THEN TURNS TO TONIGHT AND WEDNESDAY WHERE A FAVORED SYNOPTIC SETUP FOR LAKE EFFECT SNOW INTO NORTHWEST INDIANA DEVELOPS. THE PHASING UPPER FLOW TO OUR EAST WILL SLOW DOWN THE PROGRESSION OF SURFACE FEATURES AND ALSO TURN THE FLOW MORE NORTHERLY DOWN THE LAKE IN AN ALREADY GOOD COLD AIR ADVECTION SCHEME. MANY OF THE PARAMETERS MENTIONED IN PREV AFDS CONTINUE TO BE MORE THAN SUPPORTIVE FOR ROBUST LAKE EFFECT SNOW DEVELOPMENT...INCLUDING 1.) STEEP LOW-LEVEL LAPSE RATES INDUCED BY THE WARMING OF THE NEAR-SURFACE TEMPERATURES OVER THE WATER YIELDING CAPES OF 400-700 J/KG...2.) CLOUD DEPTHS OF GREATER THAN 7000 FT WITH EQUILIBRIUM LEVELS AROUND 10000 FT AND 3.) THE DENDRITIC GROWTH AREA RESIDING WITHIN THE SATURATED LAYER. THE NORTH TO NORTH NORTHWEST LOW-LEVEL FLOW SHOULD MAXIMIZE A FETCH OF A COUPLE HUNDRED MILES OR MORE INTO THE AREA OF NORTHWEST INDIANA. EVEN PARCEL TRAJECTORIES FROM THE NAM AND GFS INDICATE GOOD RESIDUAL TIME OF >6 HRS FOR PARCELS OVER THE WARMER WATERS. FINALLY...CONVERGENCE/FOCUS IS FORECAST BY MOST HIGH RESOLUTION GUIDANCE WHICH SHOULD BE THE CASE GIVEN THE NEAR DUE NORTH SYNOPTIC FLOW. THE GREATEST CONVERGENCE TO MAXIMIZE ALL OF THIS ON A CONSENSUS OF BOTH HIGH RES AND GLOBAL MODELS IS JUST EAST OF THE AREA INTO LA PORTE COUNTY. HOWEVER...WHAT HIGH RESOLUTION CONVECTIVE ALLOWING GUIDANCE DOES SHOW IS "WOBBLING" OF THE BAND OR BANDS THAT DEVELOP AND A MAJORITY OF THEM PROVIDING SOLUTIONS THAT AT LEAST CLIP EASTERN PORTER COUNTY. WHILE THERE IS UNCERTAINTY ON PLACEMENT AND DURATION OF SNOWFALL AT ANY ONE SPOT...GIVEN THE IMPACTS ON HOLIDAY TRAVEL THAT EVEN TEMPORARY HEAVY SNOWFALL RATES COULD HAVE...WENT AHEAD AND ISSUED A WATCH FOR PORTER COUNTY EARLIER ON THE SHIFT. SNOWFALL AMOUNTS OF COURSE CAN VARY WILDLY WITH THESE LAKE EFFECT BANDS...BUT BOTH A MEAN QPF WITH 15-20:1 RATIOS ALONG WITH A COUPLE MATCHING ANALOGS FROM CIPS WOULD SUPPORT TOTAL SNOW WELL ABOVE SIX INCHES IN THE AREAS WHERE THIS BAND/BANDS RESIDE THE LONGEST. WITH THE STRONG NORTHERLY WIND COMPONENT...THAT COULD 1.) BRING NEAR-BLIZZARD CONDITIONS TO COME LOCATIONS NOT FAR FROM THE LAKE SHORE AND 2.) MAXIMIZE THE INLAND REACH OF THIS SNOW BAND...SO JASPER COUNTY MAY BE ADDED TO A HEADLINE FOR HEAVY SNOWFALL IN TIME. WILL GO AHEAD AND ISSUE AN SPS FOR THERE AND LAKE COUNTY TO HIGHLIGHT THE POSSIBILITY FOR LAKE EFFECT SNOW. BEYOND THIS PERIOD HAVE NOT MADE ANY SIGNIFICANT CHANGES TO THE GOING FORECAST. THANKSGIVING DAY LOOKS TRANQUIL BUT CONTINUED COLD. MODERATION IN TEMPERATURES LOOK TO THEN OCCUR INTO THE WEEKEND AS WE GET ON THE BACKSIDE OF THE SURFACE HIGH AND RETURN FLOW SETTLES IN. A COUPLE SHORT WAVES ARE SEEN IN THE QUASI-ZONAL PATTERN OVER THE WEEKEND WHICH LOOK TO AT LEAST BRING CLOUD COVER...BUT SHOULD KEEP NIGHTTIME MINS QUITE A BIT WARMER THAN THE NEXT FEW NIGHTS. IN ADDITION...SMALL POPS ARE THE RESULT FOR NUMEROUS PERIODS OF THE SOMEWHAT UNSETTLED PATTERN. TEMPERATURES AND THICKNESSES LOOK TO BE ON THE BORDER FOR RAIN OR SNOW IN SOME OF THESE PERIODS. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * WINDS BECOMING GUSTY OUT OF THE NORTHWEST BY THIS EVENING. * POTENTIAL FOR -SHSN VERY LATE THIS AFTERNOON AND EVENING WITH MVFR VIS AND CIGS. KJB //DISCUSSION...UPDATED 06Z... A COLD FRONT...ASSOCIATED WITH LOW PRESSURE ACROSS SOUTHERN ONTARIO...IS EXPECTED TO PUSH ACROSS THE AREA THIS MORNING. THE WINDS WILL SWITCH OUT OF THE NORTHWEST BEHIND THIS FRONT. HOWEVER...WIND SPEEDS SHOULD REMAIN BETWEEN 10 TO 15 KT UNTIL LATER IN THE AFTERNOON AND EVENING. A STRONG STORM SYSTEM...CURRENTLY ACROSS THE GULF COAST...IS EXPECTED TO LIFT NORTHWARD UP THE EAST COAST AS HIGH PRESSURE BUILDS ACROSS THE PLAINS STATES. THESE TWO PRESSURE SYSTEMS WILL PRODUCE A STOUT PRESSURE GRADIENT ACROSS THE AREA INTO WEDNESDAY...AND AS SUCH GUSTY NORTH-NORTH WESTERLY WINDS ARE LIKELY BEGINNING LATE THIS AFTERNOON AFTER 22-23 UTC AND CONTINUING TUESDAY NIGHT. IT APPEARS WIND SPEEDS WILL BE AROUND 15 KT WITH GUSTS UP TO 25 KT DURING THIS PERIOD. CLOUD COVER WILL LIKELY BE WITH US THROUGH THE PERIOD. HOWEVER...IT APPEARS THAT IT WILL BE AROUND 3-4,000 FEET FOR THE MOST PART...WHICH SHOULD NOT CAUSE ANY BIG ISSUES. THE ONLY PERIODS WHERE SOME LOWER CIGS AND VISIBILITIES COULD OCCUR IS LATE THIS AFTERNOON AND EVENING. A STOUT MID LEVEL DISTURBANCE IS EXPECTED TO DROP ACROSS THE AREA...AND THIS COMBINED WITH COLD PUSH COULD BE ENOUGH TO RESULT IN SOME SNOW SHOWERS WITH LOWER CIGS. BRIEF PERIODS OF LOWER CIGS AND VISIBILITIES IN THE MVFR RANGE ARE POSSIBLE. I INCLUDED A PROB 30 GROUP IN THE LATEST TAFS TO ADDRESS THIS POTENTIAL. KJB //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH CONFIDENCE IN STRONG NORTHWEST WINDS BY EARLY THIS EVENING. * MEDIUM CONFIDENCE IN -SHSN THIS EVENING. KJB //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...LAKE EFFECT MVFR CIGS PSBL. THURSDAY AND FRIDAY...VFR. SATURDAY...MVFR CIGS PSBL OVERNIGHT. SUNDAY...MVFR CIGS PSBL LENNING && .MARINE... 200 AM CST THE MAIN CONCERNS ON THE LAKE WILL BE TONIGHT THROUGH MUCH OF WEDNESDAY. A STRONG STORM SYSTEM IS EXPECTED TO MOVE UP THE EAST COAST DURING THIS TIME...AND AS HIGH PRESSURE BUILDS IN ACROSS THE MISSOURI VALLEY CONDITIONS WILL BECOME FAVORABLE FOR A PERIOD OF NORTHERLY GALES UP TO 35 TO 40 KT. THIS LOOKS TO BE THE MOST PRONOUNCED ACROSS SOUTHERN LAKE MICHIGAN AND ANY LAKE EFFECT BANDS OF SNOW THAT DEVELOP DURING THIS TIME COULD LEAD TO SOME LOCALLY HIGH WINDS IN EXCESS OF 35 TO 40 KT. THESE STRONG NORTHERLY WINDS WILL ALSO LIKELY AFFECT THE INDIANA NEAR SHORES. CONSIDERING THIS...I HAVE ISSUED A GALE WATCH FOR TONIGHT THROUGH EARLY WEDNESDAY EVENING. WINDS TO 30 KT AND HIGH WAVES OVER 5 FEET WILL ALSO LEAD TO SMALL CRAFT ADVISORY CONDITIONS ON THE ILLINOIS NEAR SHORE WATERS. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...LAKE EFFECT SNOW WATCH...INZ002...MIDNIGHT WEDNESDAY TO 6 PM WEDNESDAY. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 302259 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 459 PM CST SAT NOV 30 2013 .DISCUSSION... 252 PM CST SYNOPSIS...MORE SEASONAL TEMPERATURES WILL BE WITH US THROUGH EARLY NEXT WEEK...WITH TEMPS PEAKING MID WEEK. THEN TEMPS QUICKLY FALL TO WELL BELOW NORMAL BY NEXT WEEKEND. THERE A FEW SLIGHT CHANCES OF PRECIP EARLY NEXT WEEK WITH A MUCH BETTER CHANCE FOR PRECIP MID WEEK. THE MID WEEK SYSTEM WILL BRING MOSTLY RAIN WITH A CHANCE OF WINTRY PRECIP LATE NEXT WEEK. REST OF TODAY THROUGH SUNDAY... WEAK LOW PRESSURE IS OVER LAKE SUPERIOR AND NORTHERN WI WITH ITS COLD FRONT STRETCHING FROM MEDFORD WI THROUGH MASON CITY IA. THE LOW WILL CONTINUE EASTWARD AND DISSIPATE OVER THE EASTERN GREAT LAKES SUNDAY NIGHT. WE HAVE MIXED MUCH MORE THAN WE WERE EXPECTING TODAY...RESULTING IN HIGH TEMPS IN THE LOWER 50S. NOT BAD FOR LATE NOVEMBER! AS SUCH RAISED LOW TEMPS BY A COUPLE DEGREES TONIGHT. CLOUDS WILL ALSO BE INCREASING THIS EVENING AND OVERNIGHT LIMITING COOLING. AN UPPER LEVEL SHORTWAVE PASSES OVERHEAD TOMORROW MORNING WITH NO PRECIP EXPECTED. CAA ALOFT AND WEAK SURFACE FLOW LEAD ME TO BELIEVE WE WILL BE A BIT COOLER TOMORROW WITH HIGHS AROUND 40. MONDAY AND TUESDAY... ANOTHER SLIGHTLY DEEPER UPPER LEVEL SHORTWAVE ARRIVES MONDAY. THIS TROUGH IS ALSO FURTHER SOUTH MOVING RIGHT OVER NORTHERN IL...WHICH MAY PROVIDE JUST ENOUGH FORCING FOR A LITTLE LIGHT PRECIP. TEMPS WILL BE ON THE RISE THROUGH THE MORNING SO WENT WITH LIGHT SNOW AT FIRST TURNING OVER TO RAIN BY MONDAY AFTERNOON. THE PRECIP WILL TRAVEL EAST WITH THE SHORTWAVE THROUGH THE DAY. HIGH TEMPS ON MONDAY WILL ONCE AGAIN BE AROUND 40. AN UPPER LEVEL VORT STREAMER PASSES JUST TO THE NORTH LATE MONDAY NIGHT WHICH MAY PRODUCE A LITTLE LIGHT SNOW OVER NORTH CENTRAL IL. MAY SEE A LITTLE MORE PRECIP COVERAGE TUESDAY MORNING WITH PRECIP TURNING OVER TO RAIN AS TEMPS WARM. THE FORCING THEN LIFTS OFF TO THE NE SO KEPT A SLIGHT CHANCE OF PRECIP OVER NORTH CENTRAL IL TUESDAY AFTERNOON WITH THE MAJORITY OF PRECIP STAYING NORTH OF OUR REGION CLOSER TO THE VORT STREAMER. A STATIONARY FRONT THEN STRETCHES OVER NORTHERN IL TUESDAY NIGHT SO KEPT A SLIGHT CHANCE TO CHANCE OF RAIN GOING. WAA ALOFT WILL KEEP TUESDAY NIGHT TEMPS ABOVE FREEZING. WEDNESDAY THROUGH FRIDAY... THE UPPER LEVEL RIDGE SHIFTS TO THE EAST WITH SOUTHWEST FLOW SETTING UP THROUGH LATE FRIDAY. THE UPPER LEVEL TROUGH AXIS PASSES OVERHEAD SATURDAY. LONG DISTANCE GUIDANCE AGREES ON THE OVERALL PATTERN...BUT THE GFS AND ECMWF DIFFER GREATLY ON WHEN THESE FEATURES WILL IMPACT THE REGION. WENT WITH THE MORE STEADY ECMWF IN THE LONG TERM AS THE GFS LOOKS MUCH TOO FAST. A SURFACE LOW MOVES OVER THE CENTRAL PLAINS LATE TUESDAY NIGHT INTO WEDNESDAY WITH WAA IMPACTING THE REGION TUESDAY NIGHT THROUGH WEDNESDAY EVENING. WITH ALL OF THE WAA RAISED TEMPS TUESDAY NIGHT AND WEDNESDAY...AND HONESTLY...STILL THINK TEMPS ARE TOO LOW. COULD EASILY SEE AT LEAST LOW 50S ON WEDNESDAY. RAIN ARRIVES BEHIND THE WARM FRONT WEDNESDAY AFTERNOON WITH GUIDANCE BACKING OFF A LITTLE WITH QPF...TO AROUND 0.1 INCHES. THE LOWS COLD FRONT SWINGS THROUGH WED NIGHT/THURSDAY WITH TEMPS CRASHING BEHIND IT. COULD EASILY SEE A 10+ DEGREE DIFFERENCE IN HIGH TEMPS WEDNESDAY AND THURSDAY. PRECIP MAY LINGER A BIT BEHIND THE COLD FRONT...MEANING WINTRY PRECIP IS POSSIBLE. GUIDANCE INDICATES PRECIP WILL ALSO FORM AHEAD OF THE UPPER LEVEL TROUGH AXIS...RESULTING IN RAIN/SNOW THURSDAY BECOMING ALL SNOW THURSDAY NIGHT THROUGH LATE FRIDAY. ARCTIC AIR MOVES IN WITH THE TROUGH AXIS RESULTING IN HIGH TEMPS IN THE 20S LATE NEXT WEEK. MAY EVEN SEE HIGH TEMPS IN THE TEENS ON SATURDAY. CONFIDENCE IS HIGH THAT THE SYSTEM WILL IMPACT THE REGION MID NEXT WEEK...PRECIP WILL BE MOSTLY RAIN...AND IN TEMP TRENDS. MEDIUM CONFIDENCE IN HOW LONG PRECIP WILL LINGER. JEE && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * INCREASING POTENTIAL FOR MVFR CIGS SUN MORNING INTO THE AFTERNOON IZZI //DISCUSSION...UPDATED 00Z... WEAK COLD FRONT OVER WISCONSIN WILL MOVE SLOWLY SOUTH TONIGHT AND MOVE ACROSS THE TERMINALS EARLY SUNDAY MORNING. LIGHT WINDS ARE EXPECTED AHEAD OF AND BEHIND THE FRONT WITH DIRECTION BECOMING MORE NORTHWESTERLY LATE TONIGHT. SUNDAY WINDS WILL BECOME MORE NORTH BUT REMAIN GENERALLY LESS THAN 10 KT. POST FRONTAL STRATUS DECK LAGGING WELL BEHIND THE BOUNDARY NOW RAISING DOUBTS ABOUT HOW SOON IT WILL ARRIVE SUNDAY. MODEL FORECASTS APPEAR TO BE OFF DUE TO POOR INITIALIZATION OF SNOW COVER RESULTING IN LOW LEVEL RH TOO HIGH...PARTICULARLY WITH THE WRF-NAM. THIS RAISES A GREAT DEAL OF UNCERTAINTY REGARDING WHEN MVFR CIGS WILL DEVELOP SUNDAY. HAVE PUSHED BACK THE ONSET OF MVFR A FEW HOURS AND CONCERNED THAT THIS MAY STILL BE A BIT TOO SOON...BUT SHOULD SERVE AS A GOOD TREND/COMPROMISE FOR NOW. SHOULD GET A BETTER HANDLE ON TIMING OVERNIGHT AS OBSERVATIONAL TRENDS MAKE FOR A HIGHER CONFIDENCE FORECAST. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * MEDIUM CONFIDENCE IN MVFR DEVELOPING SUNDAY BUT LOW CONFIDENCE IN TIMING * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS IZZI //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY...MVFR PROBABLE. CHANCE OF -SN. MONDAY NIGHT INTO TUESDAY...MVFR CIGS POSSIBLE. WEDNESDAY...MVFR CIGS LIKELY WITH IFR POSSIBLE. CHANCE OF -RA. THURSDAY AND FRIDAY...MVFR CIGS LIKELY WITH IFR POSSIBLE. CHANCE OF -SN IZZI && .MARINE... 252 PM CST WINDS WILL TURN NORTH TONIGHT THROUGH THE OVERNIGHT BEHIND A COLD FRONT...BUT WILL BE LIGHTER AT 20 KT OR LESS DUE TO A WEAK PRESSURE GRADIENT. THE GENERALLY LIGHT WIND REGIME WILL CONTINUE SUNDAY INTO TUESDAY MORNING WITH WINDS GRADUALLY SHIFTING FROM NORTHEAST TO SOUTHEAST. UNCERTAINTY THEN INCREASES AMONGST MEDIUM RANGE GUIDANCE WITH TRACK AND TIMING OF LOW PRESSURE SYSTEM MOVING EAST FROM THE PLAINS. WITH THIS FORECAST PACKAGE HAVE FAVORED A SLOWER TIMING OF THIS SYSTEM...WHICH WILL RESULT IN INCREASINGLY STRONG SOUTHEAST TO SOUTH WINDS TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. A COLD FRONT IS THEN EXPECTED TO SWEEP ACROSS THE LAKE ON THURSDAY AS THE LOW TRACKS TO OR NORTH OF LAKE SUPERIOR BY THURSDAY. THIS WILL RESULT IN STRONGER SOUTHWEST TO WESTERLY WINDS. THE POTENTIAL EXISTS FOR A PERIOD OR TWO OF GALES IN ASSOCIATION WITH THIS SYSTEM...BUT DUE TO THE UNCERTAINTY...THERE ARE NO GALES IN THE FORECAST YET. THE ACTIVE PATTERN OVER THE LAKE THEN LOOKS TO CONTINUE INTO NEXT WEEKEND. RC && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 011137 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 537 AM CST SUN DEC 1 2013 .DISCUSSION... 302 AM CST TODAY... LOW PRESSURE IS SKIRTING EAST ACROSS THE CENTRAL GREAT LAKES WITH A TRAILING COLD FRONT SAGGING SOUTH ACROSS THE CENTRAL PART OF THE CWA EARLY THIS MORNING. A FEW RADAR RETURNS TO OUR NORTH MAINLY ASSOCIATED WITH MID LEVEL CLOUD COVER...AND PRECIP IS NOT MAKING ITS WAY TO THE SURFACE...NOR IS IT EXPECTED TO AS THE FRONT CONTINUES TO SLIP ACROSS THE CWA THROUGH THE MORNING. STRATUS DECK IS EVIDENT ON IR IMAGERY BUILDING SOUTH BEHIND THE FRONT. EXPECT THESE LOWER CLOUDS TO BUILD ACROSS THE FORECAST AREA LATER THIS MORNING THEN REMAIN IN PLACE THROUGH THE DAY AND TONIGHT. WEAK HIGH PRESSURE IS EXPECTED TO BUILD ACROSS THE AREA TONIGHT...THOUGH MODEL RH FIELDS SHOW LITTLE IF ANY DISSIPATION OF THE STRATUS DECK. ASSUMING WE STAY CLOUDY OVERNIGHT...TEMPERATURES SHOULD STAY PROPPED UP INTO THE UPPER 20S TO LOW 30S DESPITE WINDS LIKELY GOING VERY LIGHT OR CALM. HOWEVER...IF WE DO SEE CLEARING...WILL HAVE TO MAKE HEFTY CHANGES TO OVERNIGHT LOWS WHICH COULD FALL 10+ DEGREES MORE THAN CURRENTLY FORECAST UNDER A STRONG RADIATIONAL COOLING SETUP. MONDAY... UPPER LOW DIGS FROM BRITISH COLUMBIA INTO THE PACIFIC NORTHWEST THIS PERIOD WHILE A LEAD WAVE KICKS EAST ACROSS THE NORTHERN PLAINS WITH SURFACE LOW UNDERGOING CYCLOGENESIS. ECMWF NO LONGER ADVERTISING SHORTWAVE EARLY MONDAY...WHICH IS IN LINE WITH OTHER MODEL SOLUTIONS THUS PULLED MENTION OF POPS MONDAY. BY MONDAY EVENING...H85 BAROCLINIC ZONE SETS UP FROM THE DAKOTAS INTO THE MID MISSISSIPPI VALLEY WITH A ZONE OF ISENTROPIC ASCENT FOCUSED JUST TO OUR WEST. STILL UNCERTAIN HOW FAR EAST THE PRECIP WILL EXTEND...BUT BEST CHANCES WILL BE IN THE NORTHWESTERN PORTIONS OF THE CWA AROUND ROCKFORD. PRECIP MAY START OFF AS RAIN SNOW MIX...BUT SHOULD TRANSITION TO ALL RAIN AS THE WARM AIR CONTINUES TO PUSH NORTHWARD. TEMPERATURES MAY RISE OVERNIGHT MONDAY NIGHT ACROSS PORTIONS IF NOT ALL OF THE CWA DEPENDING ON HOW QUICKLY THE WARM FRONT LIFTS ACROSS THE AREA. TUESDAY THROUGH WEDNESDAY... LONGWAVE TROUGH CONTINUES TO DEEPEN ACROSS THE WESTERN CONUS WITH DOWNSTREAM AMPLIFICATION OF THE RIDGE ACROSS THE CENTRAL CONUS. SURFACE LOW PROGGED TO TRACK FROM THE DAKOTAS INTO THE NORTHERN LAKES REGION THROUGH THE PERIOD WITH STRONG WARM ADVECTION AHEAD OF THE LOW WARMING H85 TEMPS TO AROUND 7-8C TUE/WED. 01/00Z EMCWF ACTUALLY THROWING A WRENCH INTO PREVIOUS FORECAST THINKING FOR THIS SYSTEM MIDWEEK...TRENDING MUCH FASTER AND MORE IN LINE WITH THE GFS. NOT QUITE READY TO BITE OFF ON THIS COMPLETELY AS OFTEN TIMES WITH CLOSED UPPER LOWS SLOWER MODEL SOLUTIONS TEND TO BE BETTER...AND WOULD NOT BE SURPRISED TO SEE THE GFS AND ECMWF TREND SLOWER IN THE NEXT COUPLE DAYS. TEMPERATURES ON WEDNESDAY A BIT TRICKY WITH BIG BUST POTENTIAL. SLIGHTLY FASTER OR SLOWER FROPA WILL RESULT IN A 15-20 DEGREE RANGE OF POSSIBLE TEMPERATURES. ECMWF CONTINUES TO BE AGGRESSIVE WITH TEMPERATURES AHEAD OF THE FRONT...SUGGESTING MID TO UPPER 50S ACROSS MUCH OF THE EASTERN HALF OF THE CWA EVEN WITH FASTER FROPA. THE GEM...WHICH IS SLOWER THAN THE GFS/ECMWF NOW SUGGESTING LOW TO MID 60S WEDNESDAY. TRENDED SLIGHTLY WARMER ACROSS THE EASTERN CWA WHICH WILL HAVE THE BEST LIKELIHOOD OF SEEING FULL WARMTH AHEAD OF THE FRONT. THURSDAY THROUGH SATURDAY... BY THURSDAY...H85 TEMPS SHOULD QUICKLY FALL TO AROUND -10C...THEN FURTHER COOL TO AROUND -15C TO -18C SATURDAY AS A COLD ARCTIC AIRMASS TRICKLES INTO THE REGION. BOTH THE GFS AND ECMWF INDICATE A SERIES OF WAVES LIFTING NORTHEAST ALONG THE FRONT CAUSING PRECIP NORTH OF THE FRONT AND POSSIBLY IMPACTING EASTERN PORTIONS OF THE CWA THURSDAY AND THURSDAY NIGHT. OTHERWISE...STRONG HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTHEAST WITH RIDGING IN PLACE FRIDAY INTO THE WEEKEND BRINGING MORE SETTLED AND COLD WEATHER...WITH HIGHS IN THE TEENS TO LOW 20S...AND SINGLE DIGIT LOWS FRIDAY AND SATURDAY. DEUBELBEISS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * MVFR CIGS LIKELY BY MID-DAY. POTENTIAL FOR MVFR CIGS TO LINGER INTO TONIGHT. RATZER //DISCUSSION...UPDATED 12Z... COLD FRONT HAS JUST MOVED THROUGH TERMINALS EARLY THIS MORNING AND WILL CONTINUE TO TRACK OFF TO THE SOUTHEAST TODAY. LIGHT WINDS LESS THAN 10 KT INITIALLY SHIFTING NNW EXPECTED TO BECOME NORTH OR NE LATER THIS MORNING. WITH THIS SWITCH TO NNE WINDS...CONCERN BECOMES LARGE AREA OF MVFR STRATUS OVER NORTHERN LAKE MICHIGAN WHICH MODEL GUIDANCE CONTINUES TO INDICATE WILL MOVE INTO THE TERMINALS BY MID-DAY. CEILINGS UPSTREAM RANGE FROM 1500-3500 FT CURRENTLY...THOUGH AREA OF 2500 FT STRATUS ALONG THE EAST SHORE OF THE LAKE APPEARS TO BE BUILDING SOUTHWEST SIMILAR TO MODEL FORECASTS AND IS EXPECTED INTO ORD/MDW AREA 16-18Z. WEAK HIGH PRESSURE DEVELOPS ACROSS THE AREA TONIGHT...MAINTAINING LIGHT NNE WINDS. LACK OF STRONG SUBSIDENCE OR STRONGER LOW LEVEL WINDS RAISES QUESTION OF HOW LONG MVFR DECK WILL HANG AROUND. MODELS DIFFER IN THEIR SOLUTIONS WHICH LOWERS CONFIDENCE. HAVE MAINTAINED MVFR CIGS THROUGH THE NIGHT WHICH MAY BE ON THE PESSIMISTIC SIDE. ONCE SURFACE HIGH PASSES AND WINDS VEER SOUTHEAST MONDAY MORNING...IT DOES APPEAR THAT LOWER CLOUDS SHOULD SCATTER...WHILE VFR CLOUDS INCREASE. RATZER //ORD AND MDW CONFIDENCE...UPDATED 12Z... * MEDIUM-HIGH CONFIDENCE IN MVFR CIG DEVELOPMENT BY MID-DAY. LOW CONFIDENCE IN CIG TRENDS TONIGHT. * HIGH CONFIDENCE IN WIND TRENDS. RATZER //OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z... MONDAY NIGHT...MVFR PROBABLE. CHANCE OF -RASN. TUESDAY INTO WEDNESDAY...MVFR CIGS POSSIBLE. CHANCE OF RAIN ESPECIALLY WEDNESDAY. THURSDAY...SLGT CHANCE OF SHSN WITH MVFR VSBY. OTHERWISE MAINLY VFR. FRIDAY AND SATURDAY...MAINLY VFR. RATZER && .MARINE... 252 AM CST MAIN MARINE FORECAST CONCERNS FOCUS ON DEVELOPMENT OF STRONG LOW PRESSURE OVER THE PLAINS MONDAY-TUESDAY...WHICH THEN IS EXPECTED TO LIFT NORTHEAST ACROSS THE NORTHERN LAKES ON WEDNESDAY. THERE CONTINUES TO BE SOME SPREAD IN MODEL SOLUTIONS WITH THE DEPTH... TRACK AND TIMING OF THE LOW. WEAK LOW PRESSURE WAS OVER LOWER MICHIGAN STATE EARLY THIS MORNING...WITH A COLD FRONT TRAILING ACROSS SOUTHERN LAKE MICHIGAN. THE LOW WILL CONTINUE TO TRACK EAST ACROSS THE EASTERN LAKES THROUGH THIS EVENING...WITH THE FRONT PUSHING SOUTHEAST OF LAKE MICHIGAN LATER THIS MORNING. WEAK HIGH PRESSURE RIDGING WILL THEN MOVE ACROSS THE WESTERN LAKES LATER TODAY/TONIGHT...DRIFTING SLOWLY OFF TO THE EAST ON MONDAY. WITH A RELATIVELY WEAK PUSH TO THE FRONT TODAY... WINDS WILL SHIFT TO THE NORTH AT GENERALLY LESS THAN 15 KT. FORECAST MODELS CONTINUE TO DEPICT AN AREA OF LOW PRESSURE DEVELOPING ACROSS THE HIGH PLAINS BY EARLY MONDAY...WHICH THEN DEEPENS ACROSS THE CENTRAL PLAINS MONDAY NIGHT. VARIOUS MODEL SOLUTIONS CONTINUE TO SHOW DIFFERENCES WITH THE EVOLUTION OF THIS LOW THROUGH MID-WEEK...THOUGH THERE IS SOME CONSENSUS IN LIFTING THE LOW NORTHEAST ACROSS THE NORTHERN GREAT LAKES WEDNESDAY. GENERALLY HAVE CONTINUED TO FOLLOW THE SLOWER SOLUTIONS OF THE ECMWF/GEM/UKMET WITH THIS SYSTEM...THOUGH WILL HAVE TO SEE SOME OF THE DIFFERENCES IRONED OUT BEFORE CONFIDENCE INCREASES IN DETAILS OF STRENGTH/TRACK AND TIMING. IT DOES APPEAR THAT THE POTENTIAL EXISTS FOR SOUTHEAST 30-35 KT WINDS AHEAD OF THE LOW LATE TUESDAY INTO WEDNESDAY...AND WEST GALES LATER WEDNESDAY INTO THURSDAY WITH THE PASSAGE OF THIS STORM. STILL 3-4 DAYS OUT SO WILL NOT HAVE ANY HEADLINES...THOUGH WILL MENTION POSSIBLE GALES IN FORECAST FOR THIS PERIOD. RATZER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 021131 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 531 AM CST MON DEC 2 2013 .DISCUSSION... 343 AM CST MAIN FORECAST CONCERNS FOCUS ON LIGHT PRECIP POTENTIAL AND MILDER TEMPERATURES TODAY THROUGH WEDNESDAY...THEN A SHARP SHIFT TO MUCH COLDER WEATHER LATE WEDNESDAY THROUGH THE WEEKEND AND BEYOND. IN THE NEAR TERM...A SERIES OF MINOR AMPLITUDE MID-LEVEL SHORT WAVES WILL RACE ACROSS THE REGION TODAY AND TONIGHT...IN FAST ZONAL WEST-EAST FLOW ALOFT. ONE SUCH WAVE WAS EVIDENT EXITING THE AREA EARLY THIS MORNING IN GOES VAPOR IMAGERY...WHILE ANOTHER WAS QUICKLY APPROACHING FROM THE CENTRAL AND NORTHERN PLAINS. A FEW WEAK RADAR RETURNS WERE NOTED ACROSS THE REGION THIS MORNING WITHIN ELEVATED BAROCLINIC ZONE...WITH AN ISOLATED SPRINKLE/FLURRY POSSIBLE IN A FEW SPOTS PRIOR TO SUNRISE. LOW LEVEL SOUTH-SOUTHWEST FLOW WILL INCREASE AS THE PLAINS SHORT WAVE APPROACHES THIS AFTERNOON...INCREASING ASCENT AND PRODUCING SOME ADDITIONAL LIGHT PRECIPITATION AS ELEVATED WARM FRONT BEGINS TO SHARPEN AND LIFT ACROSS THE AREA INTO TONIGHT. FORECAST SOUNDINGS AND THICKNESS FIELDS INDICATE THAT THERMAL PROFILES ARE PERHAPS MARGINAL PROFILES FOR LIQUID/WET SNOW THIS MORNING...BUT WARM/MOISTEN THIS AFTERNOON WITH LOW LEVEL WET BULBS CLIMBING ABOVE 0C AND 1000-850 MB THICKNESS INCREASING INTO THE 1310-1315 METER RANGE AND SUPPORTING MAINLY LIQUID/RAIN. SURFACE WARM FRONT LIFTS ACROSS THE CWA BY TUESDAY MORNING...EVENTUALLY BECOMING NEARLY STATIONARY ACROSS SOUTHERN WI OR ALONG THE IL/WI BORDER DURING THE DAY TUESDAY WITH ADDITIONAL LIGHT RAIN CHANCES MAINLY FAR NORTH. THIS WILL ALLOW TEMPS TO RISE INTO THE LOW-MID 40S MOST AREAS TODAY...WITH LOWS ONLY SETTLING BACK TO THE MID 30S-LOWER 40S TONIGHT AS THE WARM SECTOR LIFTS ACROSS THE AREA. 50S ARE EXPECTED IN MOST AREAS TUESDAY...WITH PERHAPS A FEW UPPER 40S RIGHT ALONG THE WI/IL BORDER. BIG QUESTIONS ARISE AS WE APPROACH MID-WEEK...WITH RESPECT TO THE EVOLUTION OF A LARGE UPPER TROUGH OVER MUCH OF THE NORTHERN/WESTERN CONUS. ECMWF/GEM/UKMET MODELS HAVE BEEN CONSISTENT IN MAINTAINING A SLOWER SOLUTION AND DEVELOPING THE MAIN SURFACE LOW ACROSS THE PLAINS AND LOWER MISSOURI VALLEY TUESDAY NIGHT...WHILE NCEP MODELS INCLUDING THE GFS/NAM/SREF DEEPEN AN UPPER LOW ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WITH AN ASSOCIATED DEEP SURFACE LOW TRACKING ACROSS THE NORTHERN GREAT LAKES TUESDAY NIGHT. THIS HAS A HUGE TEMPERATURE IMPACT ON THE MIDWEST...AS THE SLOWER SOLUTION WOULD ALLOW MILD TEMPERATURES TO CONTINUE INTO WEDNESDAY BEFORE A SHARP COLD FRONT BRINGS TEMPS CRASHING DOWN LATE WEDNESDAY/WEDNESDAY EVENING. GOING FORECAST HAS FAVORED THE SLOWER SOLUTION OVER THE PAST COUPLE OF DAYS...AND HPC CONTINUES TO PREFER THE EC/GEM/UK SLOWER SCENARIO AS WELL. WILL CONTINUE TO LEAN ON THE NON-U.S. MODEL CONSENSUS AT THIS TIME...THOUGH CONFIDENCE IS ADMITTEDLY LOW WITH SIGNIFICANT MODEL DIFFERENCES SHOWING UP AS CLOSE AS 36 HOURS INTO THE FORECAST RUN. THUS FORECAST HIGHS IN THE 40S/50S ARE IN THE FORECAST FOR WEDNESDAY...INSTEAD OF 30S AND FALLING SUCH AS INDICATED BY THE GFS AT THIS TIME. ONCE THE FRONT PASSES WEDNESDAY EVENING...COLDER AIR SURGES IN WITH TEMPS AROUND 20 DEGREES COLDER BY THURSDAY. STRONG SOUTHWEST FLOW ALOFT SLOWS THE PROGRESSION OF THE LOW LEVEL BAROCLINIC ZONE OFF TO OUR SOUTHEAST...KEEPING A LOW CHANCE POTENTIAL FOR SOME LIGHT SNOW ACROSS OUR FAR SOUTHEAST CWA THURSDAY AFTERNOON INTO FRIDAY AS A COUPLE OF WAVES RIDGE ALONG THE JET. A SECONDARY SURGE OF COLD AIR THEN ARRIVES THURSDAY NIGHT...WITH TEMPS A GOOD 8-10 DEGREES COLDER THAN THURSDAY. EVEN WITH NO SNOW COVER...SPRAWLING ARCTIC HIGH PRESSURE IS EXPECTED TO PRODUCE DAYTIME HIGHS ONLY IN THE UPPER TEENS TO LOWER 20S AS WE ENTER THE WEEKEND...WITH OVERNIGHT LOWS IN THE SINGLE DIGITS AND LOWER TEENS. AN APPROACHING SHORT WAVE LOOKS TO BRING A CHANCE OF SOME LIGHT SNOW TO THE AREA SUNDAY/SUNDAY NIGHT. RATZER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * VARIABLE VSBY EARLY THIS MORNING...WITH TEMPO MVFR CONDITIONS. * MVFR CIGS DEVELOPING THIS EVENING...DROPPING TO IFR WITH LIGHT RAIN AND DRIZZLE POSSIBLE. BMD //DISCUSSION...UPDATED 12Z... HIGH PRESSURE IS CENTERED JUST EAST OF THE TERMINALS THIS MORNING WITH LIGHT E/SE FLOW STARTING TO DEVELOP. THESE WINDS SHOULD PICK UP THROUGH THE DAY AS LOW PRESSURE DEVELOPS OFF TO OUR WEST. PATCHY FOG/BR HAS DEVELOPED OVERNIGHT...AND VSBY WILL LIKELY CONTINUE TO BE VARIABLE BETWEEN 4SM AND 7SM THROUGH DAY BREAK. THE EXCEPTION IS GYY WHICH HAS DROPPED TO IFR AND WILL LIKELY BOUNCE BETWEEN 1SM AND 3SM THROUGH DAYBREAK BEFORE IMPROVING. NO BIG CHANGES IN THE WEATHER THROUGH THE DAY TODAY WITH MODEST SOUTHEAST WINDS AND MID LEVEL VFR CLOUD COVER EXPECTED TIL AT LEAST MID EVENING. A WARM FRONT LIFTING NORTH TOWARDS THE AREA THIS EVENING AND TONIGHT WILL CAUSE CIGS TO LOWER...DROPPING TO MVFR MID EVENING...AND IFR LATE IN THE EVENING OR OVERNIGHT. ISENTROPIC ASCENT WILL LEAD TO SOME LIGHT RAIN DEVELOPING THIS EVENING...THOUGH MOISTURE IS FAIRLY SHALLOW...AND EVEN DRIES SOME IN THE MID LEVELS OVERNIGHT. RAIN MAY TRANSITION OVER TO LIGHT DRIZZLE BEFORE ENDING AS THE BEST ASCENT SHIFTS NORTH OF THE TERMINALS OVERNIGHT. BMD //ORD AND MDW CONFIDENCE...UPDATED 12Z... * MEDIUM CONFIDENCE IN VSBY TRENDS THIS MORNING. * HIGH CONFIDENCE IN WINDS AND VFR CONDITIONS AFTER DAYBREAK THROUGH EARLY TO MID EVENING. * MEDIUM TO HIGH CONFIDENCE IN CIG TRENDS THIS EVENING/TONIGHT...MEDIUM CONFIDENCE IN TIMING. * LOW TO MEDIUM CONFIDENCE IN PRECIP DETAILS/TIMING. BMD //OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z... TUESDAY NIGHT...MVFR PROBABLE. SLT CHC OF -RA. WEDNESDAY...MVFR POSSIBLE. CHANCE OF RAIN. THURSDAY THROUGH SATURDAY...VFR. SUNDAY...SLT CHC SNOW. BMD && .MARINE... 236 AM CST WHILE HIGH PRESSURE IS IN PLACE OVER LAKE MICHIGAN THIS MORNING PROVIDING LIGHT FLOW...LOW PRESSURE WILL BEGIN TO ORGANIZE ACROSS THE PLAINS TODAY WITH EASTERLY FLOW INCREASING THROUGHOUT THE DAY. MODELS INDICATE BY TUESDAY MORNING THE LOW SHOULD BE IN THE VICINITY OF THE MID MISSOURI VALLEY...BUT SOLUTIONS AMONGST THE VARIOUS GUIDANCE QUICKLY DIVERGE THEREAFTER WITH RESPECT TO STRENGTH... TRACK...AND TIMING OF THE LOW. ALL THIS RESULTS IN LOWER THAN AVERAGE FORECAST FOR THE DETAILS OF THE UPCOMING SYSTEM AS IT PASSES OVER THE GREAT LAKES REGION MIDWEEK. WHILE THE PICTURE WILL LIKELY BECOME MORE CLEAR IN THE NEXT 24 HOURS...FOR NOW THINK THAT SUB GALE SOUTHERLY WINDS ARE LIKELY TUESDAY NIGHT INTO WEDNESDAY...WITH STABLE CONDITIONS OVER THE LAKE LIMITING THE GUSTINESS OF THE FLOW. A BRIEF PERIOD OF GALES IS POSSIBLE IMMEDIATELY BEHIND THE FRONT WEDNESDAY EVENING/NIGHT...MAINLY OVER THE NORTH HALF OF THE LAKE. WINDS WILL REMAIN BREEZY OUT OF THE W/NE THURSDAY AND FRIDAY BEHIND THE FRONT WITH A STRONG HIGH BUILDING ACROSS THE NORTHERN PLAINS...BUT THE GRADIENT SHOULD RELAX ENOUGH FOR WINDS TO STAY BELOW GALES. BMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 081010 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 410 AM CST SUN DEC 8 2013 .DISCUSSION... 314 AM CST MAIN FORECAST CONCERN WILL BE SNOWFALL ACROSS PARTICULARLY THE NORTHERN PORTIONS OF THE FORECAST AREA TODAY. TODAY AND TONIGHT... HIGH PRESSURE IS IN PLACE ACROSS THE WESTERN LAKES REGION THIS MORNING AND WILL SHIFT EAST THROUGH THE DAY WITH RETURN FLOW DEVELOPING ACROSS THE AREA. VERY COLD AIRMASS REMAINS IN PLACE THOUGH EARLY THIS MORNING WITH TEMPS BOTTOMING OUT IN THE SINGLE DIGITS FOR MANY AREAS OUTSIDE THE URBAN HEAT ISLAND. LAKE MICHIGAN WATER TEMPERATURES ESTIMATED IN THE LOW TO MID 40S HAS LED TO OFFSHORE FLOW OVERNIGHT WITH A MESOLOW BEGINNING TO DEVELOP ACROSS THE SOUTHERN END OF LAKE MICHIGAN. LOCAL 8KM WRF SHOWS THIS FEATURE SHIFTING NORTHWEST INTO SE WI BY MID MORNING AS A SHORT SOUTHEAST FETCH DEVELOPS. VERY DIFFICULT TO PIN DOWN HOW WIDESPREAD THE LAKE EFFECT IMPACTS WILL BE...BUT BASED ON THE HIGH RES GUIDANCE WHICH IS BEST HANDLING THE SITUATION...APPEARS IMPACTS WILL MAINLY BE LIMITED TO PORTIONS OF LAKE COUNTY IL WHICH MAY SEE AROUND AN INCH BY EARLY AFTERNOON...THOUGH CANNOT RULE OUT LIGHT ACCUMULATIONS SOUTH INTO NORTHERN COOK COUNTY. A SOUTHERN STREAM H5 WAVE IS NOTED OVER THE GREAT BASIN AND WILL RACE EAST...LIFTING ACROSS THE MIDWEST TONIGHT. THERE WILL ONLY BE A WEAK SURFACE REFLECTION AS A LOW WILL MOVE NEAR DBQ THIS EVENING THEN NEAR SHEBOYGAN TONIGHT. THIS IS NOT A FAVORABLE TRACK FOR SEEING HEAVY SNOW...THOUGH STILL EXPECT LIGHT ACCUMULATIONS AS WE ARE WELL ENTRENCHED IN THE COLD AIR FOR WARM ADVECTION PRECIP TO FALL AS SNOW. MOISTURE AVAILABILITY THE BIG CONCERN...ESPECIALLY AS YOU HEAD INTO THE SOUTHERN CWA WHERE THE MOISTURE MAY BE TOO SHALLOW FOR INTRODUCTION OF ICE INTO THE COLUMN. BIGGEST CONCERN FOR LIGHT FREEZING DRIZZLE IS ACROSS EAST CENTRAL ILLINOIS AND NORTHWEST INDIANA. ACROSS THE NORTHERN PORTIONS OF THE CWA...EXPECT FAIRLY EFFICIENT DENDRITE PRODUCTION...ESPECIALLY TOWARDS THE BEGINNING OF THE EVENT WHEN A DEEP DGZ IS NOTED IN THE SOUNDINGS. COULD BE LOOKING AT 20-25:1 SLR ACROSS NORTH/NORTHWEST COUNTIES IN THE CWA. BLENDED TOWARDS NAM/GFS QPF AND WITH EXPECTED SLR...DID NOT REALLY COME OUT WITH ANY BIG CHANGES IN EXPECTED SNOW TOTALS FROM PREVIOUS FORECAST. STILL APPEARS 1 TO 3 INCHES POSSIBLE NORTH OF THE I-88 CORRIDOR...UP TO 2 INCHES SOUTH TO THE I-80 CORRIDOR. SOUTH OF I-80...A DUSTING IF ANY ACCUMULATION EXPECTED... WITH THE MAIN CONCERN BEING FREEZING DRIZZLE. MONDAY AND TUESDAY... HIGH PRESSURE WILL BUILD ACROSS THE MID MISSISSIPPI VALLEY WHICH WILL RESULT IN DRY WEATHER ACROSS THE AREA...BUT A CLIPPER SYSTEM PUSHING ACROSS THE NORTHERN LAKES REGION WILL RESULT IN BREEZY CONDITIONS AS A TIGHT GRADIENT DEVELOPS BETWEEN THESE FEATURES AND A REINFORCING SHOT OF COLD AIR CLIPS THE AREA. H85 TEMPS AROUND -16C WILL PUSH INTO NORTHERN ILLINOIS MONDAY NIGHT. WITH OVERNIGHT LOWS IN THE LOW TO MID SINGLE DIGITS...WIND CHILLS MONDAY NIGHT ARE EXPECTED TO FALL WELL BELOW ZERO...WITH AROUND -15 POSSIBLE WEST OF THE FOX RIVER VALLEY...JUST SHY OF ADVISORY CRITERIA. WEDNESDAY THROUGH FRIDAY... NORTHWEST FLOW IN PLACE WEDNESDAY AND MODELS IN DECENT AGREEMENT ADVERTISING A POTENT UPPER LEVEL WAVE DIGGING INTO THE MID TO UPPER MISSISSIPPI VALLEY. MODELS DEVELOP VERY LIGHT QPF WITH THIS SYSTEM...BUT TEND TO STRUGGLE IN SUCH COLD AIRMASSES. BUMPED UP POPS SLIGHTLY WEDNESDAY AS THIS TYPE OF SETUP CAN OFTEN PRODUCE "SURPRISE" QUICK BUT LIGHT SNOW ACCUMULATIONS. BEHIND THIS SYSTEM...HIGH PRESSURE BUILDS BACK ACROSS THE AREA WITH NO RELIEF IN SIGHT FROM THE WELL BELOW NORMAL TEMPERATURES UNTIL POSSIBLY LATE IN THE WEEK. GFS SHOWS A MODEST UPPER LEVEL RIDGE BUILDING OVER THE AREA ALLOWING TEMPS TO REBOUND...BUT DOESNT HAVE MUCH SUPPORT FROM OTHER MODELS OR GEFS MEAN WHICH KEEPS THE RIDGE AXIS FARTHER WEST...SO WHILE TEMPERATURES MAY MODERATE SOME...STILL LOOKING AT BELOW NORMAL. DEUBELBEISS && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * LAKE EFFECT CLOUDINESS AND POSSIBLE FLURRIES EARLY THIS MORNING * CHANCE OF SNOW LATE THIS MORNING INTO EARLY AFTERNOON * SNOW DEVELOPING LATE THIS AFTERNOON AND CONTINUING INTO THIS EVENING * HIGHEST PROBS OF IFR SNOW APPEAR TO BE 22/23Z SUN THROUGH AROUND 03Z MONDAY IZZI //DISCUSSION...UPDATED 09Z... VERY LIGHT REFLECTIVITY SHOWING UP STREAMING WEST OFF LAKE MICHIGAN BUT VERY WEAK RETURNS INDICATIVE OF ONLY A FEW FLURRIES AT WORST. GIVEN NO SIGNS OF AN INCREASE IN INTENSITY THINK THE THREAT OF ANY LAKE EFFECT SNOW BEYOND A FEW FLURRIES THIS MORNING IS MINIMAL AT THE TERMINALS. RADAR DATA INDICATES THAT SNOW IS FALLING ALOFT...BUT EVAPORATING AROUND 9K FT MSL WITH ABOUT A 5K FT INTERVENING DRY LAYER. RUC MODEL FORECAST SOUNDINGS SUGGEST THAT VERY DRY EXISTS BELOW 8K FT AGL AND WILL BE SLOW TO SATURATE WITH MAJORITY OF THIS FIRST WAVE OF LIFT REMAINING ALL VIRGA. GIVEN WSR-88D VWP DATA INDICATING SMALLER DRY LAYER THAN MODEL FORECASTS...AM CONCERNED THAT THERE COULD BE A PERIOD OF SNOW LATE THIS MORNING INTO THE EARLY AFTERNOON. THINKING THE PROBABILITY OF THIS OCCURRING IS AROUND 40 PERCENT...SO KEPT IT OUT OF THE DETERMINISTIC TAF FORECAST BUT WILL NEED TO WATCH RADAR TRENDS CLOSELY. STILL LOOKS LIKE THE MOST LIKELY PERIOD OF SNOW IS BETWEEN 22/23Z THROUGH AROUND 03Z WITH AT LEAST PERIODIC IFR PROBABLE. IZZI UPDATED 06Z... HIGH END MVFR CIGS COULD SPREAD WEST OFF OF LAKE MICHIGAN AND INTO ORD/MDW PRIOR TO SUNRISE AS GRADIENT FLOW GRADUALLY BECOMES MORE EASTERLY. SOME POTENTIAL DOES EXIST FOR -SHSN...BUT BETTER THREAT LOOKS TO REMAIN EAST OF ORD/MDW SO HAVE MAINTAINED THE DRY TAF AND WILL CLOSELY MONITOR TRENDS THE NEXT FEW HOURS. VIRGA SHOULD BEGIN OVER THE REGION LATER THIS MORNING AS SNOW ATTEMPTS TO DEVELOP BUT SUBLIMATES BEFORE REACHING THE GROUND. HAVE OPTED TO BEGIN FLURRIES IN THE TAFS MIDDAY...BUT STEADIER/HEAVIER SNOW EXPECTED TO HOLD OFF UNTIL LATE AFTERNOON INTO EARLY EVENING. STILL APPEARS AS THOUGH CHICAGO TERMINALS WILL BE ON THE SOUTH EDGE OF THE HEAVIER SNOWFALL...BUT A FEW HOUR LONG PERIOD WITH AT LEAST PERIODIC IFR VSBY IN -SN SEEMS LIKE A DECENT BET EARLY SUNDAY EVENING. SNOW SHOULD TAPER OFF TO FLURRIES OR PERHAPS A VERY FREEZING SNIZZLE FOR BRIEF TIME BEFORE ENDING MID-LATE EVENING SUNDAY. WINDS THROUGH SUNDAY MORNING WILL BE RATHER SQUIRRELLY AT THE CHICAGO METRO TERMINALS AS MESOLOW OVER SOUTHERN LAKE MICHIGAN DEVELOPS AND TRACKS NORTHWEST ACROSS FAR SOUTHERN PORTIONS OF THE LAKE. MESOLOW SHOULD DISSIPATE BY MID-LATE MORNING SUNDAY ALLOWING FOR SYNOPTIC E TO SE WINDS TO LOCK IN AROUND 10-15KT THROUGH SUNDAY AFTERNOON. IZZI //ORD AND MDW CONFIDENCE...UPDATED 06Z... * LOW CONFIDENCE REGARDING POTENTIAL MVFR CIGS EARLY THIS MORNING * MEDIUM CONFIDENCE ANY LAKE EFFECT -SHSN WILL REMAIN EAST OF TERMINALS THIS MORNING * LOW CONFIDENCE IN FLURRY/VERY LIGHT SNOW POTENTIAL MIDDAY TODAY THRU MID AFTERNOON * MEDIUM-HIGH CONFIDENCE IN MOST SIGNIFICANT SNOW OCCURRING VERY LATE THIS AFTERNOON INTO EARLY SUNDAY EVENING. * MEDIUM-HIGH CONFIDENCE IN AT LEAST PERIODIC IFR CIGS DURING HEIGHT SNOW * LOW CONFIDENCE IN WIND DIRECTION THROUGH MID MORNING...THEN HIGH CONFIDENCE IN WIND FORECAST THIS AFTERNOON INTO TONIGHT IZZI //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY...IFR/MVFR CIGS IMPROVING TO VFR. TUESDAY THROUGH FRIDAY...MAINLY VFR WITH MVFR POSSIBLE WEDNESDAY. MDB && .MARINE... 415 PM CST WINDS ON LAKE MI WILL CONTINUE TO GRADUALLY SUBSIDE AS A RIDGE OF HIGH PRESSURE FROM SD TO IA MOVES E ACROSS THE MIDWEST AND INTO THE GREAT LAKES REGION. DURING SUN WINDS WILL BECOME SE AND WILL BE INCREASING AS THE LOW CONTINUES TO MOVE E TO THE ST. LAWRENCE VALLEY AND LOW PRESSURE MOVES E FROM THE SOUTHERN HIGH PLAINS. THE LOW DEEPENS AS IT TURNS NE SUNDAY...TRAVELING FROM THE LOWER MO VALLEY TO LAKE SUPERIOR...AND THEN NNE INTO ONTARIO SUN NIGHT. A COLD FRONT TRAILING FROM THIS LOW WILL PUSH E ACROSS LAKE MI DURING OVERNIGHT SUN AND MON MORNING. FOLLOWING THE COLD FRONTAL PASSAGE WINDS ON THE N PORTIONS OF THE LAKE ARE LIKELY TO INCREASE TO GALE FORCE. THE LOW CONTINUES OFF TO NEAR JAMES BAY BY MON WHILE ANOTHER HIGH MOVES E ACROSS THE PLAINS. THE HIGH SETTLES OVER THE SOUTHERN PLAINS MON NIGHT WHILE LOW PRESSURE MOVES SE TO WESTERN LAKE SUPERIOR. WITH THE LOW CONTINUING TO THE E ON TUE ANOTHER COLD FRONT WILL MOVE ACROSS THE LAKE WITH GALES LIKELY ACROSS MUCH OR ALL OF THE LAKE MON INTO MON NIGHT. THERE IS ALSO LIKELY TO BE FREEZING SPRAY ON MUCH OF LAKE DURING THE GALES. A SMALL CRAFT ADVISORY MAY BE NEEDED ON MON WITH BRISK WINDS BEHIND THE FIRS COLD FRONT. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...NOON SUNDAY TO 10 PM MONDAY. SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT MONDAY TO 10 PM MONDAY. GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567- LMZ669-LMZ868-LMZ870...10 AM MONDAY TO 11 PM MONDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 310938 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 338 AM CST TUE DEC 31 2013 .DISCUSSION... 332 AM CST WE FITTINGLY CLOSE A WET AND ACTIVE WEATHER YEAR ACROSS THE CHICAGO AND ROCKFORD AREAS WITH MORE ACTION IN THE FORM OF ACCUMULATING SNOWFALL. THIS SNOW FROM MID TO LATE AFTERNOON THROUGH EARLY WEDNESDAY IS THE FIRST OF SEVERAL FORECAST CHALLENGES. HAVE EXPANDED THE GOING WINTER WEATHER ADVISORY FOR THIS EVENT A TIER OF COUNTIES FURTHER SOUTH AND STARTED IN THE ROCKFORD AREA JUST A TAD EARLIER. NEXT COMES TWO CHALLENGES FROM WEDNESDAY AFTERNOON THROUGH THURSDAY DISCERNING SYNOPTIC SNOW POSSIBILITY ACROSS THE REGION AS MODEL GUIDANCE BECOMES MORE CONSISTENT...AS WELL AS THE LIKELY LAKE EFFECT POTENTIAL AND JUST HOW ROBUST AND WHERE THAT MAY BE. QUITE A BIT OF DIFFERENCES STILL WITH THE LATTER. FINALLY TEMPERATURES FROM THURSDAY NIGHT INTO NEXT WEEK OFFER SOME PERIODS WHERE ROOM FOR IMPROVEMENT FROM MODEL GUIDANCE COULD BE QUITE LARGE. THE SYSTEM THAT BROUGHT A QUICK ONE HALF TO ONE INCH OF SNOW ACROSS THE AREA MONDAY EVENING IS ON ITS WAY OUT EARLY THIS MORNING. WE ALONG WITH THE EASTERN TWO-THIRDS OF THE U.S. ARE NOW FIRMLY ESTABLISHED AT THE BASE OF THE HUDSON BAY VORTEX WITH A CENTER THAT IS AT AN EYE-OPENING 484DM 500MB HEIGHT...IN OTHER WORDS WELL ESTABLISHED AND THE MAJOR CONTRIBUTOR FOR KEEPING ACTIVE NORTHWEST FLOW. NEXT IN THE SERIES OF VORT MAXS OVER WESTERN ND IS EVOLVING SOUTHEAST IN THE RIGHT ENTRANCE OF A 130KT JET. THIS WILL PERTURBATE ALONG A WELL-SAMPLED SHARP MID TO LOW- LEVEL BAROCLINIC ZONE. CLOUDS AHEAD OF THIS HAVE ALREADY BLOSSOMED ON EARLY MORNING SATELLITE AS FAR EAST AS SOUTHERN MN AND IA...A SIGN OF THE WARM AIR ADVECTION AND FRONTOGENETIC CIRCULATION ALREADY AT WORK AHEAD OF THE SHORT WAVE...AND AN INDICATION BY AFTERNOON THAT PRECIP MAY EXPAND QUICKER ACROSS THE AREA THAN EARLIER THOUGHT. WITH THE CLOUDS MOVING IN AND THE SURFACE WARM FRONT DEVELOPING SOUTH OF THE CWA...TEMPERATURES WILL STRUGGLE TO CLIMB MUCH TODAY WITH HIGHS IN THE LOWER TO MID TEENS FOR MANY LOCATIONS NORTH OF I-80. THIS AFTERNOON THROUGH WEDNESDAY MORNING...MODEL GUIDANCE REMAINS IN STRONG AGREEMENT WITH PRECIP EXPANDING FAIRLY QUICKLY EASTWARD ACROSS THE AREA DURING THE MID-AFTERNOON THROUGH SUNSET...AND HAVING A CONCISE FOCUS ALONG THE MID-LEVEL BAROCLINIC ZONE. DIFFERENCES ON GREATEST QPF PLACEMENT DO EXIST ON THE COUNTY SCALE WHICH UNFORTUNATELY IMPACT TOTAL SNOWFALL BY A DECENT AMOUNT. HAVE LEANED A LITTLE FURTHER SOUTH FOR THE MAXIMUM SNOWFALL THAN PREVIOUS FORECAST AND FROM WHAT THE MEAN OF THE 31.00 GUIDANCE WOULD INDICATE. HAVE DONE SO AS THE MID-LEVEL FRONTOGENETIC CIRCULATION AND GREATEST MOISTURE CONVERGENCE IS A LITTLE BIT SOUTH OF WHERE THE OUTPUT QPF IS...AND REALLY THOSE FACTORS SHOULD BE THE MAIN CONTRIBUTORS FOR SNOW PLACEMENT. IN ADDITION...CROSS SECTIONS CONTINUE TO INDICATE SOMEWHAT TRANSIENT NEGATIVE EPV ABOVE THE FRONTOGENESIS...BUT ITS LOCATION ON THE NAM AND GFS IS MORE SO BETWEEN I-88 AND I-80. ITS CERTAINLY SOMETHING THAT IS TRICKY TO GET THAT DETAILED ABOUT...BUT WITH IT BEING 12-24 HOURS OUT...MAKING A STRONG ATTEMPT TO. SO FEEL MODESTLY COMFORTABLE WITH THE HEAVIEST AXIS OF FORECAST SNOW CENTERED NEAR I-88 AND A SHARP GRADIENT SOUTH OF THERE...WHICH IS COMMON WITH THESE PATTERNS AND WELL-INDICATED IN HIGH RES WRF AND ARW GUIDANCE. THE GRADIENT SHOULD BE MUCH LESS SHARP TO THE NORTH. FOR SNOWFALL AMOUNTS...HAVE INCREASED THEM IN THE MAXIMA AREA DUE TO BOTH HIGHER QPF /NAMELY THIS EVE/ AND SLIGHTLY HIGHER SNOW RATIOS. WHILE MOISTURE VALUES ARE ONLY 2 G/KG...THE COLUMN LOOKS TO REMAIN SATURATED AND SUSTAINED FOR 9-12 HRS...WITH CONTINUED 700-925MB MOISTURE TRANSPORT THROUGH 06Z...AND BE EFFICIENT ALONG THE ELEVATED THERMAL BOUNDARY. THE DGZ REMAINS AT OR VERY CLOSE TO BEING SIGNIFICANTLY DEEP...AND LOOKING AT CROSSHAIR PROJECTIONS HAVE OMEGA SLICING INTO THAT ESPECIALLY DURING THE EVE. IT ALSO LOOKS LIKE THERE MAY BE SOMEWHAT OF A LULL IN THE WIND FIELD IN THE LOW-LEVELS ESPECIALLY DURING THE EVE...WHICH MAY PREVENT FLAKE FRAGMENTING FOR A PERIOD. WOULD NOT BE SURPRISED TO SEE SOME AREAS HAVE 3-5 INCHES BY MIDNIGHT...WITH TOTALS THROUGH WEDNESDAY MORNING OF 5-7 INCHES ALONG THE MAXIMUM STRIPE WHICH IS LIKELY TO BE NARROW. THE GENERAL 3-6 INCHES WORKS WELL FOR MUCH OF THE ADVISORY AREA. THE CITY OF CHICAGO SHOULD BE IN THE AXIS FOR THE HIGHER SNOWFALL AMOUNTS. ANY LAKE ENHANCEMENT CONTINUES TO LOOK SOMEWHAT MARGINAL GIVEN SHALLOW CLOUD DEPTHS OFF THE LAKE BOUNDARY LAYER. RATES SHOULD BECOME PRETTY LIGHT IN MOST AREAS AFTER 09Z INTO WEDNESDAY MORNING. THE ADVISORY END TIME STILL LOOKS GOOD THOUGH...WITH LIKELY POPS IN MANY OF THOSE AREAS TO START OUT WEDNESDAY MORNING. WEDNESDAY AFTERNOON THROUGH THURSDAY NIGHT...LOOKING BACK AT MODEL DETERMINISTIC AND ENSEMBLE /SREF AND GEFS/ RUNS THROUGH THE PAST 24-36 HOURS...THERE IS A PRONOUNCED TREND OF A MORE SOUTHERLY SOLUTION WITH THE INFLUENCE OF THE UPPER TROUGH THAN DEPICTED PRIOR WITH GUIDANCE. CONTINUE TO LEAN TOWARD GLOBAL GUIDANCE...BASICALLY AN EC AND GFS BLEND FOR THE SYNOPTIC SCALE. SUCH AS PREVIOUS SHIFT INCHED DOWN POPS ACROSS NORTH CENTRAL IL. AS THE 850MB LOW TAKES SHAPE TO THE SOUTHEAST...IMPROVED FORCING WITH POSSIBLY DEVELOPING DEFORMATION ACROSS THE SOUTHEAST FORECAST AREA WEDNESDAY NIGHT STILL PROVIDE LIKELY POPS. SNOWFALL AMOUNTS DO NOT LOOK TO BE TOO OUT OF HAND WITH THIS...AND MAINLY SOUTH OF CHICAGO WITH THE SYNOPTIC FORCING. BELIEVE THAT THE GFS IS MORE IN LINE WITH THE LAKE EFFECT POTENTIAL AND HAVING JUST GLANCED AT HIGH RES MODELS SUCH AS THE NAM...SREF...AND LOCAL ARW TO GET A FEEL FOR WHAT COULD OCCUR ON THE MESOSCALE...ALL SHOW LAKE EFFECT PARAMETERS THAT ARE SUFFICIENT FOR SNOW INTO NORTHEAST IL LATE WEDNESDAY NIGHT INTO THURSDAY...AND NORTHWEST IN ON THURSDAY AFTERNOON AND NIGHT. TOUGH TO TELL HOW ROBUST THOUGH AND IF CONVERGENCE WILL BE FOCUSED AND STATIONARY. SO HAVE LIKELY POPS WITH THIS FEATURE IN LAKE ADJACENT COUNTIES AND COORDINATED WITH WFO MKX AND THE WPC WINTER WEATHER DESK FOR AN INITIAL 1-3 INCHES POSSIBLE WITH THIS LAKE EFFECT FORCING. AS IT SHIFTS FROM EASTERN WI INTO NORTHEAST IL A SUFFICIENTLY LONG FETCH AND A DEEPENING CLOUD DEPTH...AROUND 10KFT LAKE INDUCED INDICATED AT THIS TIME...ARE FORECASTED BASED ON LAKE MODIFIED AIR. THE SURFACE HIGH...GREATER THAN 1035MB ON GUIDANCE...STILL LOOKS TO EXPAND INTO NORTH CENTRAL IL BY LATE THU NIGHT SETTING THE STAGE FOR A BITTERLY COLD NIGHT. THE TEMPS WOULD BE FAVORED TO DROP AROUND THE NEGATIVE DOUBLE DIGITS GIVEN THE FRESH SNOW PACK AND THE FORECAST 850MB AND 925MB TEMPS...IF INDEED THE SKY CAN CLEAR. MTF FRIDAY THROUGH MONDAY...A LONGWAVE TROUGH WILL BE SWINGING EASTWARD ACROSS THE LOWER GREAT LAKES AND ST. LAWRENCE VALLEY FRIDAY MORNING WITH A LOWER AMPLITUDE UPPER FLOW IN PLACE ACROSS THE CENTRAL AND WESTERN U.S. ANOTHER TROUGH DOES LOOK TO BE COMING ONSHORE OVER THE PACIFIC NORTHWEST AND BRITISH COLUMBIA WHILE BROAD AND FAIRLY LOW AMPLITUDE RIDGING TRANSLATES EASTWARD OVER THE UPPER MIDWEST AND WESTERN GREAT LAKES. STRONG SURFACE HIGH PRESSURE IS EXPECTED TO BE MOVING EASTWARD ACROSS MISSOURI WITH A RIDGE AXIS QUICKLY CROSSING THE LOCAL AREA FRIDAY MORNING. ANY LINGERING LAKE EFFECT SNOW SHOULD BE EAST OF THE AREA BY THIS TIME PROVIDED THE RIDGE ARRIVES IN THE MORNING. WINDS WILL THEN QUICKLY SHIFT TO THE SOUTH AND INCREASE IN SPEED AS SEVERAL AREAS OF LOW PRESSURE STRETCHING FROM THE CANADIAN PRAIRIES TO THE NORTHERN PLAINS TRACK EASTWARD. THE UPPER RIDGING WILL PUSH WARMER AIR ALOFT WHILE THE STRONG SOUTHERLY WINDS BRING WARMER LOW LEVEL AIR IN AS WELL. RIGHT NOW THERE IS GOOD AGREEMENT ON H85 TEMPS WARMING TO AROUND 0C BY EARLY SATURDAY WITH H92 TEMPS SEVERAL DEGREES COLDER. THIS COMBINATION OF WAA AND STRONG SOUTH WINDS SHOULD RESULT IN WARMING TEMPS FRIDAY NIGHT AND A RELATIVELY MILDER SATURDAY. THE LIMITING FACTOR WILL LIKELY BE THE RENEWED SNOW PACK. LOCAL CLIMO OF SIMILAR H85 AND H92 TEMPS WITH AT LEAST AN INCH OF SNOW COVER SHOWS MEDIAN HIGH TEMP VALUES IN THE LOW TO MID 30S WHICH MAY BE ON THE WARM SIDE GIVEN THE ANTICIPATED DEEPER SNOW BUT THIS COOLING COULD BE OFFSET BY THE GUSTY SOUTH WINDS...THOUGH THEY WILL LIKELY HAVE A TRAJECTORY FROM AN EXTENSIVE SNOW FIELD TO THE SOUTH. WILL STICK ON THE LOWER END OF THE POSSIBILITIES FOR NOW...ESPECIALLY GIVEN THE COLD HIGHS FROM FRIDAY...WHICH WILL LIKELY ONLY BE IN THE TEENS. A CONSOLIDATED SURFACE LOW OR TROUGH WILL PASS NORTH OF THE AREA SATURDAY EVENING DRAGGING A COLD FRONT THROUGH THE CWA LATE SATURDAY AFTERNOON OR EARLY SATURDAY EVENING FLIPPING WINDS TO THE NORTHWEST. AN UPPER TROUGH AXIS WILL ALSO SWING ACROSS BRINGING A PUSH OF COLDER AIR IN SATURDAY NIGHT THOUGH THE UPPER FLOW STAYS FAIRLY LOW AMPLITUDE SO MID LEVEL TEMPS SHOULD NOT FALL TOO MUCH. SPREAD IN POTENTIAL SCENARIOS INCREASES GOING INTO NEXT MONDAY-TUESDAY...WITH GOOD GENERAL AGREEMENT ON AT LEAST SOME AMPLIFICATION OF AN UPPER TROUGH BUT MEDIUM RANGE GUIDANCE HAS SHOWN A WIDE RANGE OF POSSIBILITIES FROM A COOL DOWN SIMILAR TO WHAT WE ARE CURRENTLY SEEING TO ONE THAT IS MARKEDLY COLDER. MDB && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * VERY LIGHT SNOW CONTINUING FOR A COUPLE OF HOURS WITH JUST SOME FLURRIES INTO THE PREDAWN HOURS. * MVFR/HIGH END IFR VISIBILITY BECOMING VFR BY 08Z. * LIGHT SNOW SPREADING W TO E ACROSS THE ORD AND MDW AREA MID AFTERNOON RESULTING IN MVFR CONDITIONS THEN QUICKLY INCREASING IN INTENSITY WITH CONDITIONS DETERIORATING TO IFR...WITH SOME PERIODS OF LIFR POSSIBLE THROUGH MID EVENING. * SNOW CONTINUING INTO THE OVERNIGHT THOUGH SHOULD BE OF LESSER INTENSITY. * WINDS GENERALLY NO MORE THAT 8-12KT FROM THE WNW-WSW TODAY AND FIRST PART OF THE EVENING THEN BECOMING N-NNE THOUGH STILL REMAINING FAIRLY LIGHT. TRS //DISCUSSION...UPDATED 06Z... SHORT WAVE TROUGH CONTINUES TO MOVE QUICKLY E ACROSS IL LATE THIS EVENING AND WILL BE E OF THE LOCAL AREA BY 08Z. NEXT SYSTEM THAT WAS OVER B.C AND THE PAC NW COAST MIDDAY MON HAD ADVANCED TO MT AND WY BY WITH MID LEVEL CLOUDS REACHING SW MN...FAR NW IA...AND NE NEB BY LATE EVENING. A LITTLE FURTHER UPSTREAM LOWER THOUGH STILL VFR CIGS ALONG WITH SOME LIGHT SNOW HAD SPREAD OVER PORTIONS OF THE DAKOTAS. BY 01/00Z THIS DISTURBANCE IS PROGGED TO MOVE TO OVER THE UPPER MS AND MID MO VALLEY AREAS...WITH A WING OF INCREASINGLY STRONG LOWER AND MID LEVEL WINDS AHEAD OF THE SHORT WAVE SPREADING FROM S MN AND N IA ESE ACROSS TO SW WI AND NW IL BY 18Z AND AS FAR E AND SOUTHERN LOWER MI AND NW OH BY 00Z. THE TROUGH SLOWS LATER TODAY AND TONIGHT WITH MODELS HOLDING IT STILL TO THE W OF THE AREA THROUGH WED. WITH THE FIRST SURGE OF WARM ADVECTION A SUSTAINED PERIOD OF DEEP ISENTROPIC LIFT FROM THE LOWER LEVELS THROUGH THE MID LEVELS DEVELOPS WITH A BAROCLINIC ZONE OVER NORTHERN IL. THE LIFT INCREASES OVERHEAD LATE THIS AFTERNOON AND INTO THIS EVENING... RESULTING IN INCREASING SNOWFALL RATES AND A DETERIORATION TO IFR...POSSIBLY LIFR AT TIMES DURING THE HEAVIER SNOWFALL. THE WARM AIR ADVECTION CONTINUES LATE THIS EVENING AND INTO THE OVERNIGHT BUT WEAKENING SOME THOUGH STILL EXPECT LIGHT SNOW TO PERSIST. AS WE GET INTO THE OVERNIGHT HOURS SNOWFALL IS ANTICIPATED TO RE- INTENSIFY AGAIN FOR A PERIOD AS THE UPGLIDE INCREASES AGAIN DUE TO AN 850HPA LOW...THOUGH WEAKENING WITH TIME...CROSSES THE MS RIVER AND MOVE ACROSS NORTHERN IL. TRS //ORD AND MDW CONFIDENCE...UPDATED 03Z... * HIGH CONFIDENCE IN OVERALL TRENDS. * MEDIUM CONFIDENCE IN TIMING OF ONSET OF LIGHT SNOW AND PERIODS OF INCREASED SNOWFALL RATE AND RESULTING MVFR AND IFR. TRS //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY THROUGH THURSDAY...SNOW LIKELY. MVFR WITH PERIODS OF IFR AND OCCASIONAL LIFR. FRIDAY AND SATURDAY...VFR. SUNDAY...CHANCE OF SNOW. MVFR POSSIBLE. RATZER && .MARINE... 245 PM CST A LARGE AREA OF HIGH PRESSURE EXTENDS FROM WISCONSIN THROUGH EAST TEXAS WHILE WEAK LOW PRESSURE OVER THE UPPER MISSOURI VALLEY TRACKS THROUGH IOWA THIS EVENING. BRISK WEST WINDS WILL PERSIST OVER THE LAKE TONIGHT AND THROUGH TOMORROW. A WEAK LOW THAT HAS BEEN SITTING OVER THE EASTERN UPPER PENINSULA OF MICHIGAN WILL MOVE OFF TO THE EAST AS WELL. ANOTHER ARCTIC HIGH WILL BUILD OUT OF CANADA AND INTO THE UPPER MISSISSIPPI VALLEY TUESDAY EVENING...THEN SPREAD ACROSS THE UPPER GREAT LAKES WEDNESDAY. THIS WILL SET UP A PERIOD OF NORTHEAST TO EAST WINDS FOR WEDNESDAY THROUGH THURSDAY. YET ANOTHER LOW IS EXPECTED TO DEVELOP IN THE SOUTH HIGH PLAINS WEDNESDAY...DEEPENING AS IT MOVES ARKANSAS WEDNESDAY NIGHT AND TENNESSEE THURSDAY. AS THE LOW MOVES INTO THE MID ATLANTIC COAST BY FRIDAY MORNING AND HIGH PRESSURE BUILDS INTO THE NORTHERN PLAINS THURSDAY AND SPREADS ACROSS THE MIDDLE MISSISSIPPI VALLEY THURSDAY NIGHT...WINDS WILL BACK THROUGH NORTH TO NORTHWEST. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011...2 PM TUESDAY TO 10 AM WEDNESDAY. WINTER WEATHER ADVISORY...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014- ILZ020-ILZ022...4 PM TUESDAY TO 10 AM WEDNESDAY. IN...WINTER WEATHER ADVISORY...INZ001-INZ002...4 PM TUESDAY TO 10 AM WEDNESDAY. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 011000 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 400 AM CST WED JAN 1 2014 .DISCUSSION... 349 AM CST A HAPPY NEW YEAR FROM THE NWS CHICAGO FAMILY TO YOURS. FORECASTING INTO 2014...OUR CONCERNS CENTER ON THE ONGOING ACTIVE PATTERN WITH THE SNOW LIKELIHOOD INCREASING...OR RE-INCREASING WE SHOULD SAY...THROUGH LATE THIS MORNING INTO THE AFTERNOON ACROSS NORTHERN IL AND THEN GRADUALLY MOVING SOUTH LATE IN THE DAY INTO TONIGHT FOR THOSE AREAS SOUTH OF I-80 THAT REALLY HAVE NOT SEEN MUCH SNOW IN THE PAST 24 HOURS. THE LAKE EFFECT POTENTIAL ON THE HEELS OF THIS SNOW CONTINUES TO LOOK SIMILAR. WE HAVE EXPANDED THE WINTER WEATHER ADVISORY TO INCLUDE THE REST OF THE FORECAST AREA THIS AFTERNOON INTO TONIGHT. OTHERWISE ANY HEADLINE CHANGES WERE JUST MASSAGING THE TIMES SOMEWHAT. THE NEW YEARS EVE DISTURBANCE HAS EXITED EAST ALONG THE ELEVATED STATIONARY FRONT. THIS PRODUCED 2 TO 4 INCHES ALONG AND NORTH OF I-88...WITH A SWATH OF 4 TO 6 INCHES ACROSS CENTRAL AND SOUTHERN LAKE IL...PARTS OF MCHENRY...AND FAR NORTHERN COOK COUNTIES. STRONG ENERGY WITH AN UPPER JET DIVING INTO THE ROCKIES CONTINUES TO ROUND THE MASSIVE HUDSON BAY POLAR VORTEX. WITH THIS ENERGY...HEIGHT FALLS ARE EVOLVING INTO THE CENTRAL PLAINS WITH ELEVATED WARM AIR ADVECTION AND LIKELY FRONTOGENETIC CIRCULATION LEADING TO RE-COOLING CLOUDS TOP AND SNOW DEVELOPING ACROSS PARTS OF IA AND FAR SOUTHERN WI AS OF 300 AM. THIS ACTIVITY SHOULD SEE A GRADUAL INCREASE IN COVERAGE AND EVOLUTION ESE INTO NORTH CENTRAL IL THIS MORNING...GIVEN THE PROGRESSION OF THE FORCING. MOST OF THE SNOW SHOULD REMAIN NORTH OF I-80 THROUGH NOON...WITH MORNING ACCUMULATIONS OF ONE HALF TO AN INCH OR SO ACROSS NORTHERN COUNTIES. WHILE NO LAKE EFFECT SHOWERS/ENHANCEMENT HAVE BEEN NOTED EARLY THIS MORNING...IT IS POSSIBLE TO BRIEFLY SEE SOME LAKE EFFECT SHOWERS INTO LAKE COUNTY BEFORE THE FLOW TURNS MORE EASTERLY REDUCING THE FETCH AND CONVERGENCE. DO NOT SEE TEMPERATURES CLIMBING MUCH ACROSS THE NORTH WITH THE NORTHEAST SURFACE LOW AND SNOW STARTING THIS MORNING. SO HAVE LOWERED SEVERAL DEGREES AND MAY NOT HAVE COME DOWN ENOUGH. THE EXCEPTION OF COURSE IS NEAR THE LAKE WHERE THE ONSHORE FLOW IS THAT OF A WARMER ONE AND HAVE KEPT GOING HIGHS SIMILAR THERE. THIS AFTERNOON AND EVE...WITH THE UPPER TROUGH DIGGING ACROSS THE PLAIN STATES IN RESPONSE TO THE AFOREMENTIONED ROCKIES JET...BROAD LIFT WILL INCREASE WITH A CONTINUED FOCUS FOR WEST-TO-EAST SWATH OF SNOW ALONG THE ELEVATED BAROCLINIC ZONE. THIS BOUNDARY...AND THE ASSOCIATED SNOW...SHOULD BE EASING ITS WAY SOUTHWARD THIS AFTERNOON AND EVE. SIMILAR TO YESTERDAY...WITH MOISTURE CONVERGENCE AND FRONTOGENESIS BEING TWO KEY ELEMENTS...IT IS ANTICIPATED THE SOUTHERN EDGE OF THE SNOW WILL BE A TIGHT GRADIENT THROUGH AT LEAST MID-AFTERNOON...AND HIGH RES GUIDANCE SUPPORTS THIS. AFTER THAT...WITH THE SURFACE LOW DEVELOPING TO OUR SOUTH AND ELEMENTS MORE SO OF A CYCLONE AT PLAY...THERE WILL BE A FEW FORCING PARAMETERS AT WORK AND THE SNOW SHOULD EXPAND ACROSS THE REMAINING SOUTHEAST FORECAST AREA. MODEL GUIDANCE IS IN PRETTY MODEST AGREEMENT WITH EVERYTHING THROUGH THIS EVE SO HAVE FOLLOWED THE NAM FOR SOME OF THE SPECIFICS. ELEVATED INSTABILITY REMAINS MARGINAL BUT AT LEAST SOME EXISTS...SO DO EXPECT SOME TEMPORARY MORE MODEST BANDS SIMILAR TO LAST EVE...BUT THESE SHOULD BE SOMEWHAT TRANSIENT. AGAIN WE WILL BE CLOSE TO A DEEP DENDRITIC GROWTH ZONE BUT JUST A LITTLE WARM FOR IDEAL EFFICIENCY...SO CONTINUE TO LEAN AROUND 15:1 FOR SNOW-TO-LIQUID RATIOS. HAVE FORECAST DAYTIME TOTALS TODAY NORTH OF I-80 AROUND 1.5 TO 3 INCHES...AND AROUND 3 SOUTH OF THERE FOR THIS AFTERNOON INTO TONIGHT. SOME HIGHER SWATHS ARE PROBABLE...JUST LIKE LAST EVE. WHILE IT IS A BIT BORDERLINE FOR TOTALS IN SOUTHERN AREAS...THERE COULD BE THE TRANSIENT MODEST RATES OF ONE HALF TO MAYBE THREE QUARTERS OF AN INCH PER HOUR...AND HAVE THUS FELT BETTER GOING WITH AN ADVISORY FOR THE REMAINDER OF THE AREA. THIS IS TIERED INTO DIFFERENT STARTING TIMES PER THE EVOLUTION OF THE EVENT AND NEIGHBORING WFO COLLABORATION. LATER TONIGHT THROUGH THURSDAY NIGHT...WITH CYCLOGENESIS CONTINUING ACROSS THE TENNESSEE/OHIO RIVER VALLEYS LATER TONIGHT INTO EARLY THURSDAY...THE OVERALL LOW-LEVEL WIND FIELD WILL VEER MORE TO NE/NNE ACROSS THE LAKE. THIS INTRODUCES THE LAKE EFFECT POTENTIAL INTO NORTHEAST IL...WITH BEST CHANCES FOR COOK COUNTY AND THE CITY OF CHICAGO LIKELY NOT ARRIVING UNTIL CLOSER TO DAYBREAK THU. INGREDIENTS REMAIN FAVORABLE WITH 1. MORE THAN ENOUGH LOW-LEVEL INSTABILITY DUE TO -17C 850MB TEMPS 2. CLOUD DEPTHS AROUND 10000 FT 3. SUPERSATURATED AND LOW DENDRITIC GROWTH AREA AT THE IMMEDIATE TOP OF THE UNSTABLE LAYER...AND 4. AT LEAST THE POTENTIAL FOR STRONG CONVERGENCE FOR REALIZATION OF THE MAXIMUM FETCH AND PRONOUNCED LAKE EFFECT BANDING. THE DURATION OF THESE PARAMETERS LOOK THE BEST FOR LAKE COUNTY IL AND NORTHERN COOK IL...JUST GIVEN THE LONGER DURATION FORECAST THERE BEFORE THE CONVERGENCE PIVOTS ITS WAY SOUTHEAST. THE PROBLEMATIC ASPECT OF IDEAL LAKE EFFECT SNOW INGREDIENTS CONTINUES THOUGH...WITH THE POTENTIAL FOR EXPLOSIVE RATES OVER A SMALL DISTANCE AND HOW FOCUSED THAT WILL BE. THESE RATES WHILE MORE FAVORED IN BANDS CAN BE FOUND IN JUST SHOWERS...WHICH AT LEAST LOOK LIKELY GIVEN THE VERY FAVORABLE THERMODYNAMIC SETUP. SO FELT COMFORTABLE LEAVING AT A WATCH RIGHT NOW. DID SHIFT THE LAKE COUNTY INDIANA WATCH TIMES A BIT AND DEBATED MOVING COOK TO 6 AM THU AS WELL...BUT LEFT A MIDNIGHT START TIME. DO FORESEE AT LEAST AN ADVISORY BEING NEEDED FOR THE WATCH AREA BASED ON FORECAST SNOWFALL AMOUNTS OF 2-5 INCHES...BUT AGAIN VARIABILITY COULD BE SIGNIFICANTLY HIGHER. THURSDAY NIGHT CONTINUES TO SHOW STRONG SIGNS OF BEING VERY COLD ACROSS NORTH CENTRAL IL. LOOKING AT A DPROG/DT OF BOTH THE NAM AND GFS LOW-LEVEL RH FIELDS...WHICH HAVE SHOWN DRIER AIR...AND JUST THE QUICKER PROGRESSION OF ANTICYCLONIC FLOW INTO THE AREA...HAVE FELT COMFORTABLE LOWERING TEMPS EVEN FURTHER...INTO THE 13-18 BELOW RANGE ACROSS NORTH CENTRAL IL. AGAIN FRESH SNOW PACK WILL HELP. UNCERTAINTY ACTUALLY INCREASES AS ONE HEADS EAST TOWARD CHICAGO BECAUSE THE CLEARING LINE MAY BE CLOSE YET STILL SOME WIND FLOW. NO MATTER WHAT...A VERY CHILLY FRIDAY MORNING. THE INVERSION IN PLACE GOING INTO FRIDAY SHOULD BE QUITE STRONG WITH LIGHT WIND FLOW AND THEN SIGNS OF WARM AIR ADVECTION CLOUDS MOVING IN TO NORTH CENTRAL IL...SO EVEN HAVE BUMPED DOWN FRI HIGHS A TAD THINKING THE DIURNAL RANGE MAY NOT BE MUCH AT ALL. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * WHEN/IF MVFR CEILINGS TEMPORARILY IMPROVE TO VFR LATE OVERNIGHT AND PREDAWN. * TIMING OF NEXT PERIOD OF ACCUMULATING SNOW TODAY AND ASSOCIATED IFR CONDITIONS. * TIMING OF LAKE EFFECT ENHANCEMENT TO SYNOPTIC SNOWFALL LATER THIS MORNING AND INTO THIS EVENING. TRS //DISCUSSION...UPDATED 08Z SNOW WAS DIMINISHING AND THEN ENDING FROM W TO E ACROSS THE LOCAL AREA LATE TONIGHT AS THE DISTURBANCE GENERATING THE SNOW WAS MOVING FROM JUST ABOUT OVERHEAD EASTWARD OVER S LAKE MI. BEHIND THE SHORT WAVE TROUGH SKY CONDITIONS WERE GENERALLY VFR...THOUGH THERE WERE SOME AREAS OF MVFR INCLUDING OVER/NEAR ORD & MDW. THE NEXT IN TRAIN OF FAST MOVING SHORT WAVES WAS MOVING ESE OVER THE CENTRAL PLAINS AND SPREADING SNOW FROM SD AND NEB TO FAR NW IA. DUE TO POOR HANDLING BY MODELS OF MULTIPLE SMALL FAST CLOSELY SPACED SHORT WAVES AM RELYING ON A ENSEMBLE MEAN AND MODEL CONSENSUS WHICH PLACE THE SHORT WAVE TROUGH OVER SOUTHERN WI AND NORTHERN IL AT 00Z. MODEL QPF PROGS HAVE FAIRLY GOOD AGREEMENT IN BRINGING MEASURABLE PRECIPITATION E ACROSS NORTHERN IL TO THE LOCAL AREA MID MORNING SO EXPECT A PERIOD OF IFR CONDITIONS BETWEEN THEN AND EARLY AFTERNOON. THROWN IN THERE I THE LAKE EFFECT WILD CARD. A NE LOW LEVEL FLOW OF VERY COLD AIR DOWN NORTHERN AND CENTRAL LAKE MI WILL BE QUITE FAVORABLE FOR A BAND OF LAKE EFFECT SNOW TO DEVELOP TODAY. THOUGH NOTHING ON RADAR OR IN METARS AS FAR AS LAKE EFFECT SNOW OCCURRENCE IS CONCERNED THE CLASSIC SIGN OF CONVERGENCE DEVELOPING DOWN THE OPEN WATERS OF THE LAKE IS SEEN...WITH NW WINDS ALONG THE W SHORE AND NE ON THE E SHORE. THE DEVELOPING LAKE EFFECT SNOW IS EXPECTED TO O PROGGED TO REACH INTO FAR SE WI AND FAR NE IL BY LATE MID MORNING BUT WITH TIME TODAY THE LOW LEVEL FLOW OVER THE FAR S PORTION OF THE LAKE IS PROGGED TO BE MORE NE TO ENE TODAY WHICH WOULD TEND TO HAVE THE TAIL END OF TH BAND SHIFTING FURTHER INLAND AND TO THE W OF ORD FOR THIS AFTERNOON. HOWEVER...GIVEN THE LARGE DIFFERENTIAL BETWEEN THE WATER AND THE AIR OF LAKE ADDITIONAL LAKE EFFECT SNOW SHOWERS ARE EXPECTED TO BE DEVELOPING THOUGH DUE TO SHORTER FETCH AND LIMITED DEPTH WILL NOT BE NEARLY AS VIGOROUS AS WITHIN THE MAIN LES BAND. TRS //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH CONFIDENCE IN WIND FORECAST. * MEDIUM CONFIDENCE IN ALL OTHER ELEMENTS. TRS //OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z... THURSDAY...SNOW LIKELY. PERIODS OF MVFR/IFR. FRIDAY...VFR. SATURDAY AND SUNDAY...VFR. SLIGHT CHANCE OF LIGHT SNOW AND MVFR. MONDAY...CHANCE OF SNOW SHOWERS. MVFR POSSIBLE. RATZER && .MARINE... 310 PM CST GENERALLY WESTERLY WINDS HAVE BEEN IN PLACE ACROSS THE LENGTH OF THE LAKE TODAY...AS HIGH PRESSURE HAS BEEN SITUATED TO THE WEST AND A TROUGH OF LOW PRESSURE HAS BEEN SLOW TO EXIT TO THE EAST. WITH THE SLOW MOVEMENT OF THIS TROUGH...A TIGHT GRADIENT HAS REMAINED WITH SPEEDS APPROACHING 30KT. WITH A CONTINUED EASTERLY MOVEMENT OF THIS TROUGH...ANTICIPATE SPEEDS TO FURTHER DIMINISH TONIGHT INTO EARLY WEDNESDAY BUT WITH SPEEDS TO START OFF TO 30 KT THIS AFTERNOON/EARLY EVENING. WESTERLY WINDS WILL TURN MORE NORTHERLY TONIGHT AND THEN TO THE NORTHEAST AND EAST ON WEDNESDAY...AS HIGH PRESSURE TO THE WEST/NORTHWEST MOVES EAST. ALTHOUGH WINDS WONT BE OVERLY STRONG ACROSS THE WHOLE LENGTH OF THE LAKE...DO EXPECT SPEEDS OF 15 TO 25 KT OVER THE SOUTHERN HALF OF THE LAKE ON WEDNESDAY. AN EAST/NORTHEAST ORIENTATION TO THE WIND WILL HELP TO CREATE HAZARDOUS CONDITIONS FOR SMALL CRAFT ACROSS THE NEARSHORE...ESPECIALLY AS WAVES BUILD DURING THE DAY. WITH A TROUGH OF LOW PRESSURE MOVING EAST JUST SOUTH OF THE REGION AND HIGH PRESSURE REMAINING TO THE WEST/NORTHWEST...EXPECT A NORTHEAST WIND TO SLOWLY TURN MORE NORTHERLY LATE WEDNESDAY NIGHT INTO THURSDAY...DIMINISHING INTO THURSDAY NIGHT AS HIGH PRESSURE MOVES OVER THE GREAT LAKES REGION. SOUTHERLY WINDS WILL BE ON THE INCREASE ONCE AGAIN FRIDAY...AS HIGH PRESSURE SHIFTS TO THE EAST AND LOW PRESSURE APPROACHES FROM THE WEST. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008- ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ020-ILZ022 UNTIL 6 PM WEDNESDAY. LAKE EFFECT SNOW WATCH...ILZ006-ILZ014...MIDNIGHT THURSDAY TO 4 PM THURSDAY. IN...LAKE EFFECT SNOW WATCH...INZ001...MIDNIGHT THURSDAY TO 4 PM THURSDAY. WINTER WEATHER ADVISORY...INZ001-INZ002 UNTIL 6 PM WEDNESDAY. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744- LMZ745...9 AM WEDNESDAY TO 4 PM THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 020957 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 357 AM CST THU JAN 2 2014 .DISCUSSION... 352 AM CST SNOW AND COLD ONCE AGAIN ARE THE REPETITIVE HEADLINES TO THIS FORECAST...AND IN FACT ARE THE HEADLINES THAT WE HAVE IN EFFECT. THERE ARE LAKE EFFECT SNOW HEADLINES FOR TODAY ACROSS NORTHEAST IL AND INTO NORTHWEST INDIANA TONIGHT...WITH SOME ADJUSTMENTS DONE FOR TIMING AS WELL AS ADDING COUNTIES FOR AN ADVISORY. A WIND CHILL ADVISORY HAS BEEN ISSUED FOR TONIGHT INTO FRIDAY MORNING FOR MUCH OF NORTH CENTRAL AND PARTS OF NORTHEAST IL. THE MASSIVE UPPER LEVEL TROUGH AND ITS EXPANSIVE COLD DEEP AIR /500MB TEMPS NEARING -40C IN THE GREAT LAKES REGION/ REMAIN ESTABLISHED OVER THE AREA. THIS IS EVEN SEEN ON THE HEMISPHERIC WATER VAPOR IMAGERY THIS MORNING WITH A VERY EVIDENT DEEP ROSBY WAVE CENTERED FROM HUDSON BAY TO GREENLAND AND EXTENDING ACROSS CENTRAL/EASTERN NORTH AMERICA. PRONOUNCED JET AND UPPER SHORT WAVE IS ROUNDING THE BASE OF THIS TROUGH ACROSS THE LOWER OHIO VALLEY EARLY THIS MORNING. THIS WAS THE MAIN CAUSE OF OUR SNOW YESTERDAY AND THAT HAS ALL BUT SHIFTED EAST OUT OF THE AREA EARLY THIS MORNING...SO WILL BE ABLE TO LET THE WINTER WEATHER ADVISORY END AT 6 AM. LOW PRESSURE OF 1013MB IS DEEPENING ACROSS TENNESSEE EARLY THIS MORNING AND THAT WILL FURTHER DO SUCH INTO THE MID-ATLANTIC BY EARLY EVE. WITH THE STRONG ARCTIC HIGH BUILDING INTO THE PLAINS...THIS OVERALL PRESSURE EVOLUTION WILL FAVOR GRADUALLY VEERING WINDS ACROSS THE LAKE. THIS SLOW VEERING WILL LIKELY HELP TO KEEP A MESOSCALE LOW PRESSURE TROUGH/CONVERGENCE AXIS INTACT ACROSS THE FAR WESTERN PART OF THE LAKE THROUGH THE MORNING. THIS AXIS EARLY THIS MORNING IS ABOUT 35 MILES INLAND ACROSS NORTHEAST IL...BUT WILL SHIFT BACK OUT TOWARD THE LAKE SHORE...LIKELY TOWARD MIDDAY AND BE THE FOCUS FOR THE HEAVIEST LAKE EFFECT SNOW AND A LIKELY COUPLE/FEW HOUR PERIOD OF VERY HEAVY RATES GIVEN THE VERY FAVORABLE PARAMETERS. THESE INCLUDE STRONG LAKE-INDUCED INSTABILITY IN EXCESS OF 500 J/KG...THIS INSTABILITY MAINLY COLLOCATED WITH SUPERSATURATION WITH RESPECT TO ICE AND WITHIN THE DENDRITIC GROWTH AREA...AND CLOUD DEPTHS OF 9-10KFT. ALL THIS HAS BEEN CONSISTENTLY SHOWN BY THE NAM AND LOCAL ARW. PRIOR TO THIS AXIS...GENERAL ONSHORE FLOW INTO NORTHEAST IL HAS ENOUGH INSTABILITY WITH IT TO BE DEVELOPING WIDESPREAD LAKE EFFECT SNOW SHOWERS THIS MORNING...AND THESE ACTUALLY EXTEND AS FAR WEST IN ILLINOIS AS ROCHELLE AND MENDOTA! A LONGER FETCH OF INSTABILITY IS GRADUALLY WORKING INTO LAKE COUNTY IL FROM THE NORTH AND BASED ON OBSERVATIONS OF LOWERING VISIBILITIES TO AT OR UNDER A MILE...ACCUMULATIONS OF AROUND ONE HALF INCH PER HOUR WILL SLOWLY SPREAD SOUTH. SO GIVEN THAT SNOW SHOWERS ARE ALREADY ONGOING WITH PARAMETERS ONLY BETTERING...SEE NO REASON SNOW SHOWERS WILL NOT STOP FOR NORTHEAST IL UNTIL THE FLOW TURNS OFFSHORE. THE HEAVIEST SNOW AGAIN WILL BE CONFINED TO NEAR THAT CONVERGENT AXIS AND USING OUR LOCAL 8KM ARW...THAT LOOKS TO LINE ITSELF INTO DOWNTOWN CHICAGO DURING THE EARLY TO MID AFTERNOON...BEFORE SHIFTING EASTWARD INTO NORTHWEST IN. THIS TIMING OF THE PROBABLE HEAVIEST RATES AND DURATION IN WHICH THEY LAST...WILL LIKELY BE DEPENDENT ON IF A MESOSCALE CIRCULATION CAN REMAIN INTACT OVER THE FAR SOUTHERN PART OF THE LAKE TOO...BASICALLY SLOWLY THAT EASTWARD PROGRESSION. THE LONGER THAT DOES SUCH...THE MORE PROBABLE THAT SOME CORRIDOR OF THE LAKE EFFECT WARNING WILL REALIZE 6 OR MORE...POSSIBLY EVEN 8-10 INCHES OF SNOW. THE CONVERGENCE BEGINS TO WEAKEN LATE THIS EVENING INTO NORTHWEST INDIANA AS IT CONTINUES TO PIVOT EAST...SO THAT RESULTS IN SNOW ENDING FROM WEST TO EAST ACROSS ADJACENT COUNTIES TO SOUTHERN LAKE MICHIGAN. MODEL GUIDANCE REMAINS IN STRONG AGREEMENT WITH ANTICYCLONIC FLOW IN THE LOW-LEVELS AND SUPPRESSION ALOFT DISSIPATING CLOUDS QUICKLY FROM WEST TO EAST ACROSS NORTHERN IL LATE THIS AFTERNOON AND THIS EVE. RADIATIONAL COOLING...HIGHLY ANOMALOUS COLD ATMOSPHERIC AIR...SLOWLY DECREASING FLOW...AND A FRESH SNOWPACK ALL LOOK TO STILL COLLOCATE FOR A VERY CHILLY NIGHT. HAVE MINS STILL IN THE -11 TO -18 ARENA ACROSS ALL OF NORTH CENTRAL IL. HAVE HOISTED A WIND CHILL ADVISORY AS WINDS WILL MAINTAIN ENOUGH FLOW TO MAKE IT DANGEROUS FOR ANY PROLONGED EXPOSE SKIN. FOR THIS WEEKEND WE CONTINUE TO WATCH A SYSTEM OF INTEREST. THE NEXT IN A SERIES OF COLD FRONTS IS EXPECTED TO PASS SATURDAY AFTERNOON WITH THE CHANCE FOR LIGHT SNOW. THE SLOWER EC HAS BEEN FOLLOWED WHICH KEEPS THIS CHANCE OF SNOW AREAWIDE MAINLY DURING THE LATE AFTERNOON AND NIGHT. AS THE NEXT UPPER TROUGH DEEPENS TO OUR WEST...MUCH LIKE YESTERDAY...THAT WILL ENHANCE THE BAROCLINIC ZONE OVER THE REGION POTENTIALLY PROVIDING FOR A FOCUS FOR SNOW LATER SATURDAY NIGHT INTO SUNDAY. DO HAVE SOME LIKELY POPS IN THE SOUTHEAST FORECAST AREA...BUT KNOWING THAT SHIFTS ARE INEVITABLE WITH THIS HAVE NOT TRIED TO GET TOO FANCY. AT THIS TIME IT APPEARS CHICAGO MAY BE GRAZED WITH THIS. MTF MONDAY THROUGH WEDNESDAY... MAJOR ARCTIC BLAST ARRIVES EARLY MONDAY MORNING...WITH THE LATEST GUIDANCE SHOWING NO SIGNS OF BACKING OFF ON THE DANGEROUSLY COLD LOWS AND HIGH TEMPS FOR THE THE MON/TUE TIME FRAME. ENSEMBLES FOR OVER A WEEK NOW HAVE INDICATED AN ARCTIC BLAST ARRIVING FOR THE START OF NEXT WEEK...AND THIS CONTINUES TO BE THE THEME. THE 500MB TROUGH AXIS ARRIVES OVER THE GREAT LAKES REGION MON...AND WITH WEAK RIDGING OVER THE WESTERN ATLANTIC OCEAN STRETCHING NORTH THROUGH THE CANADIAN MARITIME. THIS RIDGING WILL LIKELY SLOW THE FORWARD PROGRESSION TO THE TROUGH AXIS...ALLOWING IT TO LINGER LONGER OVER THE GREAT LAKES INTO TUE. THEN HEADING INTO WED THE RIDGING OVER THE WESTERN ATLANTIC BEGINS TO PUSH EAST...WHICH WILL ALLOW FOR A RELATIVELY MORE FLUID ATMOSPHERE AND THE TROUGH AXIS WILL DRIFT EAST/NORTHEAST TOWARDS NEW ENGLAND. AS PREVIOUSLY NOTED ABOUT THE COLD AIR...ENSEMBLES FOR NUMEROUS DAYS HAVE BEEN PAINTING A HIGH CONFIDENCE THAT AT 850MB TEMPS BY EARLY MON WILL BE ARND -24 TO -28 DEG C...WITH A POCKET OF -30 DEG C JUST NORTH OF THE FORECAST AREA INTO CENTRAL/NORTHERN WISC. WITH THE SLOW FORWARD PROPAGATION TO THE MID-LVL TROUGH...THIS WILL LIKELY KEEP THE POTENT THERMAL TROUGH OVERHEAD INTO TUE. CLOSER TO THE SFC RIDGING IS EXPECTED TO PUSH IN BEHIND THE ARCTIC FRONTAL BOUNDARY AND PROVIDE RELATIVELY LITTLE IN THE WAY OF PRECIP TO THE FORECAST AREA MON/TUE. UNFORTUNATELY WITH HOW COLD TEMPS WILL BE ALOFT AND A THICK BLANKET OF SNOW...SFC TEMPS WILL EASILY HOLD WELL BELOW ZERO FOR HIGHS BOTH MON/TUE. AT THIS TIME HIGH TEMPS MAY STRUGGLE ON BOTH DAYS TO REACH -5 DEG F...WITH POSSIBLY A FEW LOCATIONS IN OUR WESTERN CWFA STRUGGLING TO REACH -10 DEG C MON AFTN. DEPENDING ON CLOUD COVER...OVERNIGHT LOWS COULD EASILY APPROACH RECORD LOWS AT -15 TO -20 DEG F IN THIS TIMEFRAME. THE COMBINATION OF DANGEROUSLY COLD SFC TEMPS...AND A GRADIENT PRODUCING BREEZY CONDITIONS...WILL SET THE STAGE FOR WIND CHILL VALUES LIKELY TO EXCEED -30 BELOW AND POSSIBLY APPROACH -40 DEG MON NGT. THE GRADIENT SLACKENS FOR TUE NGT...HOWEVER WIND CHILL VALUES WILL ONCE AGAIN APPROACH -20 TO -30 DEG F. THEN TOWARDS THE MIDDLE OF NEXT WEEK THE TROUGH AXIS PIVOTS EAST...WITH FLOW TURNING SOUTH/SOUTHWEST AND ADVECTING MUCH WARMER AIR INTO THE REGION. ENSEMBLES HAVE CONTINUED TO INDICATE RELATIVELY HIGH CONFIDENCE IN THE LONGER TERM PERIODS...WITH A MID-LVL TROUGH DIGGING INTO THE SOUTHERN PLAINS AND POSSIBLY LEADING TO YET ANOTHER ACTIVE PERIOD OF WEATHER FOR THE MIDDLE OF NEXT WEEK. CONFIDENCE IN TEMPS MON/TUE...HIGH. CONFIDENCE IN WIND CHILL VALUES MON/TUE...HIGH. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * LIGHT TO MODERATE LAKE EFFECT SNOW INTO THE AFTERNOON WITH BRIEF PERIODS OF HEAVIER SNOW AND IFR CIGS/VSBYS. * NORTHEAST WINDS BECOMING NORTH-NORTHEAST BY MORNING THEN NORTH- NORTHWEST BY AFTERNOON. LENNING //DISCUSSION...UPDATED 06Z... LARGER SCALE SWATH OF SNOW HAS MOSTLY SLID SOUTH OF THE ORD/MDW AREA BUT A BROAD LAKE EFFECT BAND IS SUPPORTING CONTINUED LIGHT SNOW WITH BLOWING SNOW. EXPECT THIS BAND TO PERSIST INTO THE MORNING AND LIKELY INTENSIFY AT TIMES WHILE GRADUALLY SHIFTING FROM THE ILLINOIS SIDE TO THE INDIANA END AS WINDS BACK FROM NORTHEAST TO NORTH NORTHEAST. THE PEAK PERIOD FOR MORE INTENSE SNOWFALL AT THE ORD/MDW TERMINALS STILL APPEARS TO BE TOWARD DAYBREAK INTO THE MORNING HOURS BEFORE ACTIVITY DROPS SOUTH. AS PER THE PREVIOUS DISCUSSION...MODERATE TO HEAVY SNOW IS POSSIBLE WITH 1/2 TO POTENTIALLY 1/4SM VSBY AT TIMES...WITH SEVERAL INCHES OF ACCUMULATION DEPENDING ON HOW LONG THE BAND IS OVERHEAD. LENNING //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH CONFIDENCE OF ACCUMULATING LAKE EFFECT SNOW PERSISTING INTO THE AFTERNOON. MEDIUM CONFIDENCE ON ENDING TIME AROUND 21-22Z. * MEDIUM TO HIGH CONFIDENCE OF SEEING PERIODS OF IFR VSBYS. LOWER CONFIDENCE OF LIFR TODAY. * HIGH CONFIDENCE IN WIND TRENDS BECOMING NORTHWEST THIS AFTERNOON. LENNING //OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z... FRIDAY...VFR. SATURDAY...SNOW SHOWERS ARRIVE AFTERNOON...MVFR/IFR LIKELY. SUNDAY...CHANCE SNOW SHOWERS AND MVFR/IFR. MONDAY AND TUESDAY...BREEZY AND VFR...SOME MVFR POSSIBLE MONDAY. MDB && .MARINE... 326 AM CST MAIN CONCERN IS STRONG LOW PRESSURE PASSING NORTH OF THE LAKES FRIDAY NIGHT. LATEST MODELS CONTINUE THE TREND OF INCREASING WINDS AND GUSTS FRIDAY NIGHT...SO ELECTED TO REPLACE THE GALE WATCH WITH A STORM WATCH. REGARDLESS OF THE EXACT TRACK AND STRENGTH OF THE LOW...FEEL FAIRLY CONFIDENT OF SEEING AT LEAST A PERIOD OF STORM FORCE GUSTS...BUT NOT QUITE CONFIDENT ENOUGH YET TO GO WITH THE WARNING. THESE STORM FORCE WINDS WOULD BE PRECEEDED BY GALES FRIDAY AFTERNOON AND FOLLOWED BY GALES SATURDAY...BUT WILL CARRY JUST A STORM WATCH FOR THE ENTIRE PERIOD TO AVOID COMPLICATING THE HEADLINES. IN THE NEARSHORE...GALES LIKELY WILL DEVELOP LATE FRIDAY INTO SATURDAY DURING THE SAME PERIOD AS THE STORM FORCE WINDS IN THE OPEN WATERS. SMALL CRAFT ADVISORIES CURRENTLY IN EFFECT DO LOOK LIKE THEY CAN BE DROPPED FOR A SHORT TIME EARLY ON FRIDAY BEFORE CONDITIONS RAPIDLY INCREASE AGAIN. TO DRAW ATTENTION TO THE SHORT BREAK BEFORE THE NEW SYSTEM APPROACHING FRIDAY...AND TO AVOID RUNNING THE HEADLINES TOGETHER...ELECTED TO HOLD OFF ON ISSUING A GALE WATCH AT THIS TIME BUT DID MENTION IT IN THE FORECAST TEXT. LENNING && .LOT WATCHES/WARNINGS/ADVISORIES... IL...LAKE EFFECT SNOW WARNING...ILZ006-ILZ014 UNTIL 3 PM THURSDAY. WINTER WEATHER ADVISORY...ILZ013-ILZ022-ILZ023-ILZ032-ILZ033- ILZ039 UNTIL 6 AM THURSDAY. IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL MIDNIGHT FRIDAY. WINTER WEATHER ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 6 AM THURSDAY. LM...GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868- LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM FRIDAY TO 4 PM SATURDAY. SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 4 AM FRIDAY. SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 9 AM FRIDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 100537 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1137 PM CST THU JAN 9 2014 .DISCUSSION... 816 PM CST RADAR MOSAIC SHOWS CONTINUED LIGHT SNOW ACROSS MUCH OF THE EASTERN CWA FROM NEAR PONTIAC NORTHEAST TO THE NORTHERN CHICAGO METRO. WARM ASCENT CONTINUES ABOVE WITH ADDITIONAL ASCENT LOOKING TO BE PROVIDED BY AN ELONGATED AREA OF CYCLONIC VORTICITY TRAILING A SHORTWAVE DEPARTING TO THE EAST. ASCENT AHEAD OF SUBTLE WAVE MOVING INTO WEST CENTRAL IL MAY ALSO BE PLAYING A ROLE. RECENT AIRCRAFT SOUNDINGS AND FORECAST RAP SOUNDINGS SHOW THE TOP OF THE MOIST LAYER NEAR -10C SUPPORTING NEEDLE AND COLUMN LIKE CRYSTALS. MAINLY NEEDLES APPEAR TO BE FALLING AT THE OFFICE AT THE MOMENT. THIS FINER CRYSTAL STRUCTURE SUGGESTS MINIMAL ACCUMULATION BUT A COATING TO A TENTH OR TWO IS IS LIKELY UNTIL THIS BETTER ORGANIZED SNOW BAND DEPARTS...WHICH SHOULD OCCUR IN THE NEXT FEW HOURS. HAVE INCREASED POPS FOR THE NEXT FEW HOURS AND ADDED SOME MINIMAL ACCUMULATION TO THE GRIDS. GIVEN THE SNOW FALLING...FREEZING DRIZZLE LOOKS TO HOLD OFF UNTIL LATER THIS EVENING AS THE SNOW DEPARTS AND COLUMN MOISTURE BECOMES MORE SHALLOW LEADING TO A LOWER PERCENTAGE OF ICE IN THE CLOUDS...BUT THIS STILL LOOKS TO BE PATCHY IN COVERAGE IF IT OCCURS. OTHERWISE VSBY LOOKS TO BE REDUCED IN MIST WHICH MAY BE ENOUGH TO PROVIDE SOME SLICK SPOTS ON SOLID SURFACES INTO THE OVERNIGHT BUT DENSE FREEZING/ACCUMULATING FOG IS NOT EXPECTED AT THIS TIME. MDB //PREV DISCUSSION... 339 PM CST MAIN FORECAST CHALLENGES/CONCERNS ARE WITH LIGHT SNOW OR LIGHT FREEZING DRIZZLE POTENTIAL LINGERING INTO THIS EVENING...POTENTIAL FOR FREEZING RAIN OR FREEZING DRIZZLE ONCE AGAIN FRIDAY MORNING...AND THEN A CONTINUED WARM UP WITH ALL RAIN LIKELY FRIDAY AFTERNOON THROUGH EARLY SATURDAY MORNING. CONCERNS IN THE NEAR TERM REMAIN WITH ONGOING LIGHT SNOW...AS WELL AS A TRANSITION TO EITHER LIGHT SNOW OR LIGHT FREEZING DRIZZLE LATE THIS AFTERNOON INTO THE EARLY EVENING. LATEST RADAR IMAGERY DEPICTING ONLY LIGHT RETURNS ON RADAR...WITH SURFACE OBS STILL REPORTING ALL SNOW ACROSS THE AREA. THIS SNOW HAS BEEN IN RESPONSE TO A SHORT WAVE TROUGH LIFTING EAST/NORTHEAST ACROSS THE REGION...AS WELL AS A WAA WING SWINGING A SWATH PRECIP ACROSS MAINLY THE SOUTHEAST TWO THIRDS OF THE CWA. AN OVERALL DIMINISHING TREND AS BEEN OBSERVED THIS PAST HOUR AND EXPECT THIS TO CONTINUE LATE THIS AFTERNOON...AS WITH THIS WEAK FORCING FURTHER WEAKENING WHILE SHIFTING EAST OUT OF THE AREA. SNOWFALL THIS PAST AFTERNOON HAS BEEN FROM A DUSTING UP TO A HALF INCH...VIA REPORTS FROM FACEBOOK/TWITTER...AND WOULD EXPECT AT MOST A COUPLE OF TENTHS OF AN INCH OF ADDITIONAL SNOWFALL THIS AFTERNOON. ALTHOUGH THERE STILL REMAINS CONCERNS FOR A TRANSITION OVER TO FREEZING DRIZZLE LATE THIS AFTERNOON...CONCERNS FOR ANY LONG DURATION/PREVAILING FREEZING DRIZZLE ARE BEGINNING TO LESSEN. AS DEEPER MOISTURE CONTINUES TO STREAM OVER THE REGION...PRECIP TYPE REMAINS ALL SNOW AT THIS HOUR. THROUGH THE 00Z TIME FRAME IT DOES APPEAR THAT THIS DEEPER MOISTURE IS LOSS...BUT STILL ON THE LOWER THRESHOLD FOR CRYSTALS TO BE PRESENT AND THUS FOR SNOW FOR MOST AREAS. 00Z AND BEYOND...CONTINUED LOSS OF THIS MOISTURE WILL OCCUR AND ITS DURING THIS TIME FRAME THAT I THINK THERE WILL BE THE POTENTIAL FOR LIGHT FREEZING DRIZZLE. ALTHOUGH...LATEST GUIDANCE IN FAIR AGREEMENT WITH THE BETTER LIFT/OMEGA IN THE LOWER LEVEL MOIST LAYER TO BEGIN SHIFTING EAST OF THE CWA ALSO DURING THIS TIME. SO DO FEEL THAT THERE IS STILL POTENTIAL FOR LIGHT FREEZING DRIZZLE THIS EVENING...THINK ITS A SMALL WINDOW FOR THIS OPPORTUNITY BEFORE ALL LIFT DEPARTS. HAVE TRENDED THE GRIDS THIS WAY FOR THIS EVENING...BUT DID LEAVE PATCHY FREEZING DRIZZLE IN OVERNIGHT FOR MOST AREAS. LATEST SATELLITE IMAGERY/OBSERVATIONS DEPICTING LOW LEVEL MOISTURE STILL WORKING ITS WAY NORTH ACROSS THE REGION. IN THE HIGHLY SATURATED LOWER LEVELS...CONCERNED THAT THIS PATCHY LIGHT FREEZING DRIZZLE COULD STILL OCCUR. AM NOT EXPECTING MUCH IN TERMS OF ICE ACCUMULATION...BUT CANNOT RULE OUT ISOLATED SLIPPERY CONDITIONS TO DEVELOP. TEMPERATURES LATE THIS AFTERNOON/EARLY EVENING WILL BE OUR LOWS FOR THE NIGHT...AS STRONG WAA CONTINUES TONIGHT WITH RISING TEMPS EXPECTED TONIGHT INTO FRIDAY MORNING. DESPITE WARMING TEMPS THROUGH EARLY FRIDAY MORNING...SURFACE TEMPS WILL STILL BE AT OR JUST BELOW FREEZING THROUGH MID LATE MORNING. ASCENT WILL BE ON THE INCREASE ON FRIDAY AS A STRONG MID/UPPER LEVEL TROUGH SHIFTS EAST ACROSS THE CENTRAL PLAINS. WITH THERMAL PROFILES DURING THIS TIME SUPPORTIVE OF ALL LIQUID...AM STILL CONCERNED THAT A BRIEF PERIOD OF FREEZING RAIN COULD OCCUR. THE QUESTIONS WILL BE IF FORCING/PRECIP RETURNS SOON ENOUGH BEFORE TEMPS RISE ABOVE FREEZING. ALTHOUGH DO FEEL THAT THIS BETTER PRECIP AXIS WONT ARRIVE UNTIL TEMPS RISE AT OR ABOVE FREEZING BY THIS MID LATE MORNING PERIOD. IF FREEZING RAIN DOES OCCUR...IT SHOULD BE A NARROW TIME FRAME WITH THE WEST/SOUTHWEST AREAS IN A MORE PREFERRED LOCATION IN THE MORNING...AND POSSIBLY FOR THE FAR NORTHWEST CWA THROUGH MID DAY. CONTINUED WARMING CONTINUES INTO THE AFTERNOON WITH ALL RAIN THEN OCCURRING FRIDAY AFTERNOON INTO FRIDAY NIGHT FOR ALL AREAS...WITH THREE QUARTERS OF AN INCH TO ONE INCH POSSIBLE AREA WIDE. LATEST TRENDS HAVE BEEN FOR A QUICKER TRANSITION BACK TOWARDS SNOW LATE FRIDAY NIGHT INTO EARLY SATURDAY MORNING...WITH ALL SNOW LIKELY THEN SATURDAY BEFORE THIS PRECIP EXITS. ALTHOUGH ANY LINGERING SNOW SHOULD BE ON THE LIGHT SIDE...AND DONT ANTICIPATE ANY ADDITIONAL SNOW ACCUMULATION. RODRIGUEZ && .HYDROLOGY... ALSO OF INTEREST THIS FORECAST CONTINUE TO BE WITH HYDROLOGIC ISSUES...WITH A WARMER AND MORE MOIST AIR MASS MOVING NORTH ACROSS THE REGION TONIGHT THROUGH FRIDAY. THIS WILL ALLOW FOR A TRANSITION TO ALL RAIN BY MID DAY FRIDAY...CONTINUING INTO EARLY SATURDAY MORNING. RAINFALL TOTALS OF THREE QUARTERS OF AN INCH TO ONE INCH ARE POSSIBLE AREA WIDE FROM FRIDAY AFTERNOON THROUGH EARLY SATURDAY MORNING. CONCERNS WITH THE WARM UP...RAINFALL...FROZEN GROUND WITH CURRENT SNOWPACK IN PLACE COULD ALL RESULT IN RISES IN AREA RIVERS/STREAMS/CREEKS AS WELL AS POTENTIAL FOR FLOODING AND ICE JAM FLOODING. CONFIDENCE IS NOT TOO HIGH WITH REGARDS TO THE EXTENT OF THE SNOWMELT...NONETHELESS...THE PREVIOUSLY MENTIONED CONCERNS WARRANT CONTINUED CLOSE MONITOR OF THIS SITUATION INTO THE WEEKEND. FOR MORE INFORMATION ON THIS FLOOD POTENTIAL SEE THE HYDROLOGIC OUTLOOK ISSUED EARLIER THIS AFTERNOON...ESF. RODRIGUEZ && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * IFR CIGS LIKELY TREND DOWN TO LIFR OVERNIGHT OR EARLY FRI AM * VLIFR/DENSE FOG POSSIBLE FRIDAY MORNING INTO THE EARLY AFTERNOON * RAIN DEVELOPS LATE FRIDAY AFTERNOON AND CONTINUES THROUGH MID EVENING FRIDAY...SOME MINOR IMPROVEMENTS TO CIGS/VSBY LIKELY WITH THE RAIN IZZI //DISCUSSION...UPDATED 06Z... WARM FRONT WILL LIFT NORTHWARD ACROSS THE REGION FRIDAY WITH A PRETTY STRONG SURGE OF MOIST AND FAIRLY MILD AIR MOVING UP INTO THE AREA OVER A DENSE SNOW PACK. ALREADY HAVE WIDESPREAD LIFR CIGS UPSTREAM HEADING INTO THE AREA AND ANTICIPATE CONDITIONS TO LIKELY TO CONTINUE TO DETERIORATE THROUGH THE NIGHT AND PROBABLY FRIDAY MORNING AS WELL. SUSPECT THAT IF ANYTHING THESE TAFS ARE OPTIMISTIC WITH REGARDS TO CIGS/VSBY WITH AT LEAST SOME POTENTIAL FOR DENSE FOG AND VV001 DEVELOPING FRIDAY MORNING...BUT RELUCTANT TO TREND THAT LOW YET DUE TO LACK OF CONFIDENCE. ALSO CONCERNED THAT SOME FZDZ COULD DEVELOP FOR A TIME FRIDAY MORNING BEFORE TEMPERATURES RISE ABOVE FREEZING...BUT FORECAST SOUNDINGS SUGGEST FAIRLY SHALLOW MOIST LAYER UNTIL CLOSER TO MIDDAY BY WHICH TIME TEMPS SHOULD BE ABOVE FREEZING. IF DZ MATERIALIZES SOONER THAN EXPECTED THEN A PERIOD OF FZDZ WOULD BE POSSIBLE FRIDAY MORNING. STEADY RAIN DEVELOPS LATE FRIDAY AFTERNOON LIKELY MIXING OUT THE LOWEST CIGS WITH SOME IMPROVEMENT IN CONDITIONS AT THAT TIME...BUT LIKELY TO REMAIN IFR. RAIN SHOULD TAPER OFF TO MORE OCNL -SHRA OR -DZ LATER FRIDAY EVENING INTO THE OVERNIGHT WITH IFR PROBABLY CONTINUING. IZZI //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH CONFIDENCE IN IFR OR LOWER CONDITIONS THROUGH FRIDAY EVENING * LOW CONFIDENCE IN POTENTIAL FOR VLIFR IN DENSE FOG FRIDAY * HIGH CONFIDENCE IN TIMING OF ONSET OF STEADIER RAIN +/- AN HOUR OR SO * LOW CONFIDENCE IN POTENTIAL FOR FZDZ FRIDAY MORNING IZZI //OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z... 00Z... SATURDAY...GUSTY WEST WINDS WITH A CHANCE OF -SN WITH IFR/MVFR POSSIBLE EARLY. VFR/WX NIL OVERNIGHT. SUNDAY...GUSTY SOUTH WINDS. VFR/WX NIL EARLY. SLIGHT CHANCE OF RAIN OR SNOW WITH MVFR POSSIBLE OVERNIGHT. MONDAY...VFR/WX NIL. TUESDAY...SLIGHT CHANCE OF SNOW. MVFR POSSIBLE. WEDNESDAY...VFR/WX NIL. KJB && .MARINE... 219 PM CST BROAD SURFACE RIDGE ALONG THE EASTERN SEABOARD STRETCHES FROM QUEBEC SOUTH THROUGH THE CAROLINAS...WITH AN INFLUENCING REMAINING ACROSS THE WESTERN GREAT LAKES THIS AFTERNOON. THE LARGEST INFLUENCE HAS BEEN THE LACK OF A GRADIENT...WHICH HAS RESULTED IN WINDS BEING MUCH LIGHTER THAN EARLIER ANTICIPATED. THUS HAVE SLOWED THE WIND SPEEDS DOWN...AND ALSO HAS RESULTED IN WINDS REMAINING MORE SOUTHEASTERLY. A BOUNDARY WAS LIFTING NORTH ACROSS THE OHIO VALLEY...AND WILL LIKELY REACH THE SOUTHERN PORTIONS OF THE LAKE OVERNIGHT THEN ALLOW WINDS TO TURN MORE SOUTHERLY FOR THE LAKE. OVERNIGHT INTO FRIDAY GUIDANCE CONTINUES TO SUGGEST THE LACK OF A GRADIENT WILL REMAIN WEST OF LAKE MICHIGAN...THEN THE CHANNEL OF BETTER WINDS WILL EVENTUALLY SLIDE EAST/SOUTHEAST ACROSS THE LAKE FRIDAY AFTERNOON/EVENING. SFC FLOW WILL REMAIN SOUTHERLY...WITH SPEEDS GENERALLY AROUND 20 TO 30 KT. AT THIS TIME IT APPEARS HAZARDOUS WINDS FOR SMALL CRAFT WILL DEVELOP AROUND THIS TIME AS WELL. THEN THE FOCUS FOR THE WEEKEND WILL BE ON A DEVELOPING LOW PRESSURE SYSTEM THAT IS EXPECTED TO DEVELOP ACROSS THE SOUTHERN PLAINS...WHICH WILL EVENTUALLY LIFT NORTHEAST ACROSS LATE SATURDAY MORNING. THE GRADIENT WILL TIGHTEN SATURDAY EVENING...POSSIBLY BRINGING SOME OCCASIONAL GUSTS TO 30 KT. THEN THE GRADIENT BEGINS TO SLACKEN OFF THROUGH EARLY SUNDAY. YET ANOTHER LOW PRESSURE SYSTEM IS EXPECTED TO SLIDE EAST ACROSS THE UPPER MIDWEST SUN AFTN...WITH THE GRADIENT TIGHTENING YET AGAIN FOR LAKE MICHIGAN. CURRENT FORECAST GUIDANCE INDICATES THE POSSIBILITY OF OCCASIONAL GALE FORCE GUSTS FOR THE OPEN WATERS SUN LATE AFTN/EVE. THE PATTERN REMAINS RELATIVELY ACTIVE FOR EARLY NEXT WEEK...WITH ANOTHER LOW PRESSURE SYSTEM POISED TO SLIDE SOUTHEAST FROM THE UPPER MIDWEST INTO THE GREAT LAKES. THE GRADIENT WILL ONCE AGAIN TIGHTEN...WITH WINDS EVENTUALLY TURNING WEST/NORTHWESTERLY TUE NGT/WED. THE AMOUNT OF ICE REMAINS HIGH ACROSS NEARSHORE WATERS AS SEEN IN WEBCAMS AND SATELLITE IMAGERY. THUS WAVES WILL BE OMITTED FROM THE NEARSHORE FORECAST. BEACHLER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 262352 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 552 PM CST MON JAN 26 2015 .UPDATE... 542 PM CST FREEZING DRIZZLE HAS BECOME MORE WIDESPREAD OVER MUCH OF NORTHERN ILLINOIS. LATEST SATELLITE IMAGERY AND SOUNDING DATA INDICATE THAT CLOUD DEPTH HAS DECREASED OVER THIS AREA...TO THE POINT WHERE ICE CRYSTAL PRODUCTION IN THE CLOUD LAYER HAS DIMINISHED...AS DRIER AIR ALOFT IS OVERSPREADING THE AREA. A LIGHT GLAZING OF ICE IS LIKELY OVER THE AREA TONIGHT...MAKING TRAVEL HAZARDOUS ON UNTREATED ROADS. A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR THIS AREA. KREIN && .SHORT TERM... 258 PM CST TONIGHT THROUGH TUESDAY... WEAK CLIPPER HAS PRODUCED SOME LIGHT SNOW ACROSS NORTHERN IL THIS AFTERNOON. LATEST RADAR IMAGERY SUGGESTS THE BACK EDGE OF THE PRECIP BEGINNING TO WORK EAST ALONG I-39. WITH CONSIDERABLE DRY AIR AT THE SFC...NOT ALL PRECIP HAS BEEN ABLE TO REACH THE SFC. THE SLIGHTLY STEADIER SNOW WAS LOCATED ACROSS FAR NORTHEAST IL...MAINLY OVER LAKE/MCHENRY COUNTIES. MOST HI-RES GUIDANCE INDICATES THE LIFT/OMEGA WILL QUICKLY DISSIPATE ARND 00Z...WHICH SUGGESTS WE MAY BE ABLE TO END THE LIGHT SNOW EARLIER. IT IS POSSIBLE THAT WITH SOME WEAK LLVL CONVERGENCE THAT SOME FLURRIES/LGT SNOW MAY LINGER TO 3Z...BUT THIS IS A LOW CONFIDENCE SCENARIO. THE OTHER LINGERING CONCERN IS THE POSSIBILITY FOR PATCHY FZDZ. WITH THE LACK OF GOOD SATURATION...THINK AT MOST THIS WILL END UP AS A PATCHY FZDZ. CLOUDS WILL LIKELY REMAIN LOCKED IN THRU THE OVERNIGHT PERIOD...DESPITE THE CLEAR SKIES THIS AFTN ACROSS CENTRAL IOWA. THE LACK OF MIXING WILL PERSIST THRU TUE MORNING...ANTI-CYCLONIC FLOW WILL STEADILY MIX IN DRY AIR TUE MIDDAY. THIS MAY PROVIDE SOME BREAKS IN THE CLOUD COVER BY EARLY AFTN. LLVL FLOW WILL TURN NORTHEASTERLY...WHICH COULD HOLD TEMPS IN THE LOW 30S. IF CLOUDS CAN THIN EARLIER IN THE DAY...TEMPS MAY BE ABLE TO WARM AN ADDTL DEGREE OR TWO GIVEN THE LACK OF SNOW PACK. SFC RIDGE WILL BE OVERHEAD TUE NGT...WITH DRY CONDS PERSISTING. TEMPS SHUD EASILY RADIATE INTO THE MID-TEENS. BEACHLER && .LONG TERM... 258 PM CST WEDNESDAY THROUGH MONDAY... MID-LVL RIDGING WILL SLIDE EAST ACROSS THE CENTRAL PLAINS WED...WITH A ROBUST MID-LVL THERMAL RIDGE OF 10 TO 14 DEG C LIFTING NORTHEAST INTO A PORTION OF THE MID-MISSOURI VALLEY. THIS WILL LIKELY SET THE STAGE FOR POTENTIALLY A MILD WED AFTN/EVE...AS TEMPS COULD WARM INTO THE UPR 30S TO POSSIBLY THE LOW 40S ALONG THE SOUTHERN CWFA. LLVL MOISTURE WILL BE SLOW TO ADVECT NORTH...HOWEVER GUIDANCE SUGGESTS THAT AS THE BETTER MID-LVL VORT ARRIVES PRECIP SHIELD WILL INCREASE. EQUALLY LATE WED NGT/EARLY THUR A DRY SLOT IS BEING PROGGED TO DEVELOP. WITH THE LACK OF STRONG LLVL FORCING...IT IS POSSIBLE THAT PARCELS REMAIN SMALL MORE IN THE FORM OF DRIZZLE. WILL MAINTAIN A RAIN/SNOW MIX...BUT FEELING IS THAT ENOUGH WARM AIR WILL BE IN PLACE TO PUSH THIS OVER TO LGT RAIN. 500MB PATTERN TRIES TO TRANSITION TOWARDS QUASI-ZONAL. THIS WILL PROVIDE A RELATIVELY ACTIVE SETUP TOWARDS THE UPCOMING WEEKEND. THE MID-WEEK SHORTWAVE WILL SLIDE EAST BY THUR NGT...WITH LIKELY A DRY END TO THE WEEK. TEMPS WILL BE MILD AGAIN THUR...THE CHALLENGE IS HOW WARM. CURRENT THINKING IS THAT WITH FROPA LIKELY IN THE MORNING THUR THAT MAX TEMPS MAY OCCUR PRIOR TO DAYBREAK...MAINLY IN THE UPR 30S. POSSIBLY ARND 40 IN THE SOUTHERN CWFA. THEN WITH COLD AIR ADVECTING IN FROM THE NORTHWEST...TEMPS WILL STEADILY COOL THUR AFTN INTO THE LOW/MID 30S. DRY AIR MOVES IN THUR NGT WITH SFC RIDGING AND SHUD REMAIN IN PLACE THRU MUCH OF FRI. BEACHLER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 22Z... * MAINLY VFR LIGHT SNOW INTO THIS EVENING...WITH PERIODIC MVFR VISIBILITY IN STEADIER SNOW. * SNOW TAPERING THIS EVENING AND POSSIBLY TRANSITIONING TO OR MIXING WITH FREEZING DRIZZLE. * IFR CIGS EXPECTED LATE THIS EVENING...WITH IFR/MVFR VSBY POSSIBLE. RC //DISCUSSION...UPDATED 18Z... SHEARED UPPER LEVEL DISTURBANCE IS HELPING TO DRIVE AN AREA OF SNOW ACROSS ILLINOIS AND WISCONSIN EARLY THIS AFTERNOON. THIS SNOW IS EXPECTED TO MOVE INTO THE CHICAGO AREA OVER THE NEXT COUPLE HOURS. INITIALLY DRY LOW/MID LEVELS WILL TAKE THEIR TIME TO SATURATE AS THE RADAR RETURNS MOVE OVERHEAD...PRECIPITATION INITIALLY EVAPORATING IN THE DRY AIR...BUT THEN EXPECT CONDITIONS TO DETERIORATE TO MVFR WITH TEMPO IFR VSBY IN ANY MODERATE BURSTS OF SNOW. ACCUMULATIONS ARE EXPECTED TO BE FAIRLY MINIMAL...A DUSTING TO AROUND HALF AN INCH OR SO. PRECIPITATION SHOULD BEGIN TO TAPER LATE THIS AFTERNOON OR EARLY THIS EVENING AS UPPER LEVEL RIDGING BEGINS TO BUILD OVERHEAD SUPPRESSING THE DEEPER MOISTURE. ON THE OTHER HAND...PERSISTENT LOW LEVEL CONVERGENCE NEAR THE SURFACE TROUGH MAY RESULT IN WEAK ASCENT LATER INTO THE EVENING WHICH WOULD SUPPORT A FEW FLURRIES...OR POSSIBLY DRIZZLE AT TIMES AS SOUNDINGS INDICATE LOSS OF ICE IN THE COLUMN LATER THIS EVENING AS DRY AIR BUILDS DOWN IN THE UPPER LEVEL SUBSIDENCE. SOUTH WINDS THIS AFTERNOON SHOULD BACK AROUND TO THE NORTHEAST OVERNIGHT. BMD //ORD AND MDW CONFIDENCE...UPDATED 22Z... * MEDIUM-HIGH IN SNOW TRENDS AND VSBY IMPACTS. * LOW-MEDIUM IN PRECIP END TIME THIS EVENING AND THAT SNOW MAY CHANGE TO OR MIX WITH FZDZ AT SOME POINT LATE THIS EVENING. * MEDIUM IN CIG/VSBY TRENDS LATE THIS EVENING INTO THE OVERNIGHT. RC //OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z... TUESDAY NIGHT...MAINLY VFR. WEDNESDAY...MAINLY VFR DURING THE DAY. CHANCE OF RAIN/SNOW AT NIGHT WITH MVFR/IFR POSSIBLE. THURSDAY...CHANCE OF LIGHT SNOW. MVFR LIKELY/IFR POSSIBLE. FRIDAY...MAINLY VFR. SATURDAY...CHANCE OF SNOW/MVFR CIGS. SUNDAY...MVFR CIGS POSSIBLE. RATZER && .MARINE... 216 PM CST LOW PRESSURE OVER THE UPPER MIDWEST WILL DROP SOUTH TOWARDS THE TENNESSEE VALLEY TODAY AND TONIGHT...BUT WEAKENING WHILE DOING SO. THIS WEAKENING TREND ALONG WITH HIGH PRESSURE BUILDING ACROSS THE CENTRAL GREAT LAKES TONIGHT WILL HELP MAINTAIN OVERALL LIGHTER WINDS IN PLACE. THIS WILL CONTINUE ON TUESDAY AND TUESDAY NIGHT AS THE CENTER OF THE HIGH PASSES OVER THE LAKE. THIS HIGH WILL THEN SHIFT TO THE EAST WEDNESDAY INTO WEDNESDAY NIGHT AS LOW PRESSURE SHIFTS EAST THROUGH THE CENTRAL PLAINS. EXPECT SOUTHERLY WINDS TO INCREASE OUT AHEAD OF THE LOW DURING THIS PERIOD...AND ESPECIALLY WEDNESDAY NIGHT WHEN SPEEDS APPROACHING 30KT WILL BE OBSERVED. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...FREEZING RAIN ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010- ILZ011-ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 6 AM TUESDAY. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240939 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 339 AM CST TUE FEB 24 2015 .SHORT TERM... 335 AM CST THROUGH WEDNESDAY... THERE ARE SEVERAL MAINLY MINOR WINTRY WEATHER CONCERNS THIS FINAL WEEK OF METEOROLOGICAL WINTER...WHICH WILL CONTINUE TO FEEL MORE LIKE MID-WINTER FOR THE MOST PART. FOR THE IMMEDIATE SHORT TERM...UPPER LEVEL NORTHWEST FLOW OVER THE GREAT LAKES REGION WILL BE CARVED INTO BY A DIGGING JET STREAK AND ASSOCIATED TROPOSPHERIC FOLD...WHICH ORIGINATED WELL NORTH OF THE ARCTIC CIRCLE JUST 18-24 HOURS AGO. THE SURFACE REFLECTION AHEAD OF THIS IS A DEEPENING 992MB LOW IN FAR NORTHERN ONTARIO EARLY THIS MORNING...WHICH IS INDUCING A TIGHTENING PRESSURE GRADIENT AND GUSTY SOUTHWEST WINDS FOR THE FORECAST AREA THIS MORNING AND TURNING MORE WEST THIS AFTERNOON. GUSTS OF 30 TO 35 MPH LOOK TO EASILY BE SUPPORTED. THE WEST WINDS THIS AFTERNOON ACTUALLY WILL BE A WARMING WIND AS THIS CLIPPER-LIKE WARM SECTOR DRIVES A NARROW CORRIDOR OF DOWNSLOPED PACIFIC AIR INTO THE AREA...SO HIGHS OF AROUND 30 DEGREES ACTUALLY SHOULD BE REACHED NEAR OR JUST AFTER SUNSET. THE SYSTEM COLD FRONT WILL THEN DRIVE TEMPERATURES DOWN LATER THIS EVENING INTO OVERNIGHT WITH LOWS IN THE SINGLE DIGITS. AS FOR THE CHANCES OF SNOW TODAY...WHILE THE GREATEST FORCING CONTINUES TO BE NORTHEAST OF THE AREA...WITH SUCH A WELL-DEFINED VORTICITY MAXIMA THESE SITUATIONS OFTEN PRODUCE AT LEAST SOME SNOW SHOWERS IN THE WINDOW WHERE DEEP ENOUGH SATURATION CAN OCCUR. THAT FAVORED CORRIDOR IS REALLY THE NORTHEAST FORECAST AREA...OR FAR NORTHEAST ILLINOIS AND FAR NORTHWEST INDIANA INCLUDING THE CHICAGO METRO. SO HAVE TIMED THE MAIN INCREASE IN HOURLY FORECAST POPS WITH THE DEEPEST LIFT...TAKING INTO ACCOUNT HIGH-RES ENSEMBLE SOLUTIONS SUCH AS THE HOPWRF AND SSEO. THIS LOOKS TO BE WITHIN THE 11 AM TO 2 PM RANGE IN THE CITY OF CHICAGO. THE VERY NARROW FORCING WINDOW AND LOW-LEVEL DRY AIR LIKELY WILL LIMIT THE INTENSITY OF ANY SNOW SHOWERS...HOWEVER THE CONCURRENT GUSTY WINDS MAY STILL AID IN VISIBILITY COMING DOWN BRIEFLY BUT SHARPLY. ELSEWHERE SOME FLURRIES ARE POSSIBLE BUT THE BIGGEST STORY TODAY WILL BE THE GUSTY WINDS BUT STILL MILDER TEMPERATURES. AS FOR THE DAY WEDNESDAY...COLD AIR ADVECTION WILL LESSEN BUT GRADUALLY CONTINUE IN THE LOWER TROPOSPHERE THROUGH AT LEAST MIDDAY. WITH SOME INCREASING CLOUDS BY AFTERNOON...ONLY SEE TEMPERATURES REACHING INTO THE 15 TO 20 RANGE...AROUND 20 DEGREES BELOW NORMAL HIGHS. MTF && .LONG TERM... 335 AM CST WEDNESDAY NIGHT THROUGH MONDAY... AN ANOMALOUSLY COLD CORE UPPER LOW OVER SOUTHERN CA EARLY THIS MORNING WILL BY WEDNESDAY BE MOVING ACROSS TX AND INTO THE LOWER MISSISSIPPI VALLEY...BRINGING THAT REGION RARE LATE WINTRY PRECIP. AS THIS HAS BECOME CLEARER IN GUIDANCE...IT HAS SEEMED TO SLOW A NORTHERN STREAM SHORT WAVE AND KEEP IT FURTHER NORTH AS IT DIGS AROUND THE MASSIVE EASTERN NORTH AMERICAN TROUGH. THIS MEANS MORE INFLUENCE FOR OUR AREA ON WEDNESDAY NIGHT AND AS SUCH HAVE INCREASED LIGHT SNOW CHANCES MAINLY FOR AREAS ALONG AND SOUTH OF I-80 IN ILLINOIS. WHILE THIS SNOW SHOULD BE LIGHT AS THE WAVE IS DAMPENING QUICKLY...GIVEN SOME DEPTH TO THE SNOW GROWTH ZONE IT IS POSSIBLE LOCATIONS AROUND PONTIAC AND PERU COULD END UP WITH AN INCH OF NEW SNOW THROUGH THURSDAY MORNING. ON THE MESOSCALE WEDNESDAY NIGHT INTO THURSDAY...THE LOW-LEVEL FLOW PATTERN AND THERMAL PROFILES STILL LOOK TO BE SUPPORTIVE OF LAKE EFFECT SNOW POTENTIAL. EQUILIBRIUM LEVELS ARE FORECAST TO RAISE TO AROUND 7000 FT OR SO WITH GLOBAL AND REGIONAL MODELS BOTH INDICATING AT LEAST TEMPORARY CONVERGENT SIGNATURE IN THE LOW-LEVEL WIND FIELD. ONE POTENTIAL ISSUE WITH THIS IS THAT THERE WAS EXTENSIVE ICE EVIDENT IN NEARSHORE AREAS AND FOR QUITE A FEW MILES BEYOND ON YESTERDAYS NOAA AND NASA POLAR ORBITING SATELLITE IMAGERY. WHILE MUCH OF THIS MAY NOT BE DEEP...IT SHOULD DAMPEN THE LAKE INDUCED INSTABILITY SOME. SO WHILE HAVE SOME LIKELY SNOW SHOWERS MENTIONED IN LAKE-SIDE COUNTIES LATE WEDNESDAY NIGHT AND THURSDAY...IT MAY BE SOMEWHAT LIGHT AS THE CLOUD DEPTHS THIN BY THE TIME THEY REACH SHORE. OBVIOUSLY ONLY LIGHT SNOW WITH TEMPERATURES AROUND 10 DEGREES OR SO CAN CAUSE SOME ISSUES DURING A HIGH TRAFFIC TIME...SO THAT WILL HAVE TO BE WATCHED FOR THURSDAY MORNING. IN ADDITION...THURSDAY CERTAINLY LOOKS CHILLY THOUGH CONFIDENCE ON HOW COLD IS SOMEWHAT LOW AS CLOUDS WITH THE SYNOPTIC WAVE AND LAKE EFFECT CLOUDS COULD LINGER ALL DAY. AT THIS TIME...DO HAVE A HIGHS FORECAST NEAR DAILY RECORD LOWS FOR THAT DAY WHICH ARE 10 IN CHICAGO AND 11 IN ROCKFORD. FINALLY...AS WE HEAD INTO MARCH...WE CONTINUE TO SEE MODEL GUIDANCE PROVIDE A VERY SHORT RESPITE IN THE RELENTLESS DEEP NORTHERLY FLOW. THIS LOOKS TO BE TIMED JUST RIGHT TO HAVE ENERGY FROM THE SOUTHWEST U.S. ABLE TO BEND THE FLOW MORE SOUTHWESTERLY AHEAD OF IT AND LIKELY BRING MOISTURE RETURN FOR PRECIP IN THE MIDDLE OF THE COUNTRY. STILL SOME MAJOR DIFFERENCES AND WOULD NOT BE SURPRISED TO SEE SOME LATITUDE SHIFT WITH THIS JUST GIVEN THE MODEST TEMPORARY PATTERN SHIFT. THE RETURN OF MOISTURE TRANSPORT LOOKS TO BE ON THE HEELS OF THE COLD AIR MASS SO WILL STILL LEAN MORE TOWARD SNOW FOR PRECIPITATION TYPE INCLUDING INTO SUNDAY. WHILE HAVE SOME LIKELY WORDING FOR THIS IN THE FORECAST...CONFIDENCE ON THE TIMING AND INTENSITY OF ANY SNOW IS STILL QUITE LOW GIVEN THIS PATTERN. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * LOW LEVEL WIND SHEAR THROUGH 14-15Z. * STRONG/GUSTY SOUTHWEST WINDS TOWARDS DAYBREAK AND THROUGH THE DAY * CHANCE OF BRIEF SNOW SHOWER OR FLURRY WITH MVFR VSBY OR BRIEF IFR * PERIOD OF MVFR CIGS TUESDAY AFTERNOON. KMD //DISCUSSION...UPDATED 09Z... STRONG LOW LEVEL JET IS DEVELOPING AND WINDS WITHIN A COUPLE THOUSAND FT OF THE GROUND WILL INCREASE TO 45 KT+. AIRCRAFT SOUNDINGS BEFORE 7Z WERE SHOWING 35-40 KT IN THE 1500-2000 FT LAYER. THE STRONGER PRESSURE GRADIENT IS OVER NORTH CENTRAL AND NORTHWEST ILLINOIS THUS GUSTS ARE GENERALLY UNDER 20 KT AND INFREQUENT CLOSER TO LAKE MICHIGAN. AFTER SUNRISE WINDS WILL INCREASE FURTHER WITH OCNL GUSTS TO OR SLIGHTLY ABOVE 30KT POSSIBLE MID MORNING TUES INTO THE EARLY AFTERNOON. THUS WITH THE INCREASING SURFACE WINDS LOW LEVEL WIND SHEAR CONCERNS SHOULD EASE. A POTENT BUT COMPACT UPPER LEVEL DISTURBANCE WILL GRAZE THE AREA LATER THIS MORNING AND SHOULD BE ENOUGH TO SQUEEZE OUT A BRIEF SNOW SHOWER OR FLURRY BUT SHALLOW DEPTH OF MOISTURE WOULD SUGGEST THREAT IS LIMITED AND WOULD BE SHORT DURATION IF IT DID OCCUR. UPSTREAM OBSERVATIONS ARE GENERALLY FLURRIES WITH MVFR VSBYS...WITH INFREQUENT IFR VSBY. HAVE REPLACED THE PROB30 WITH A TEMPO AS THE SIGNAL IS STILL THERE FOR A BRIEF FLURRY/SHOWER. HOWEVER WENT WITH 3SM VSBY. NOT THAT IFR VSBY IS NOT POSSIBLE...BUT CONFIDENCE IN THAT IS NOT HIGH AS TO HOW LONG THAT WOULD LAST. BEHIND THE COLD FRONT STRONG COLD ADVECTION WILL LIKELY WILL TO A PERIOD OF MVFR CIGS IN THE AFTERNOON...THOUGH IT SHOULD NOT LAST TOO LONG. WINDS THEN EASE LATER TONIGHT AND EXPECT SOME CLEARING TONIGHT AND LIGHTER NW WINDS. KMD //ORD AND MDW CONFIDENCE...UPDATED 09Z... * LOW-MEDIUM CONFIDENCE IN LLWS * MEDIUM-HIGH CONFIDENCE IN WINDS * MEDIUM CONFIDENCE IN SNOW POTENTIAL AND ASSOCIATED VSBY ...MEDIUM-HIGH IN TIMING IF IT OCCURS. * MEDIUM CONFIDENCE IN MVFR CIGS...LOW IN HOW LONG IT LASTS. KMD //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...VFR. THURSDAY...CHANCE OF MVFR CIGS. FRIDAY...VFR. SATURDAY...VFR. SAT NIGHT AND SUNDAY...CHANCE OF SNOW/IFR. IZZI && .MARINE... 157 AM CST LOW PRESSURE CENTERED JUST SOUTH OF HUDSON BAY WILL SLOWLY MOVE SOUTHEAST TOWARDS JAMES BAY TONIGHT...WHILE WEAKENING SOME...BUT ITS ASSOCIATED PRESSURE TROUGH WILL PASS OVER THE LAKE. MEANWHILE...STRONG HIGH PRESSURE FROM THE SOUTHERN PLAINS INTO THE OHIO VALLEY WILL SLOWLY SHIFT EAST OVER THE ATLANTIC COAST TODAY. ALREADY SEEING SOME GALE FORCE SOUTHERLY WINDS AND EXPECT THAT TO INCREASE IN COVERAGE EARLY THIS MORNING. THE BULK OF THE TROUGH AXIS WILL SHIFT EAST OF THE LAKE THIS AFTERNOON BRINGING A BRIEF LULL IN SPEEDS BEFORE THE COLD FRONT MOVES IN AND STRONG COLD ADVECTION DRIVES SOME ADDITIONAL NW GALES THIS AFTERNOON AND EVENING. THE STRONGEST WINDS LOOK TO BE THROUGH THE MORNING. HIGH PRESSURE BUILDS EAST OF THE CANADIAN ROCKIES TONIGHT THEN SPREADS INTO THE UPPER MIDWEST ON THURSDAY...CREATING A PERIOD OF NORTHERLY WINDS DOWN THE LAKE AS BITTERLY COLD AIR FILTERS BACK IN. THE HIGH WILL THEN PASS JUST SOUTH OF THE LAKE ON FRIDAY BEFORE SHIFTING TO THE EASTERN LAKES BY SATURDAY MORNING. WINDS TURN BACK SOUTHWESTERLY AS THIS OCCURS. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...HEAVY FREEZING SPRAY WARNING...LMZ080-LMZ261-LMZ362-LMZ364- LMZ366-LMZ563-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675- LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 10 PM TUESDAY. GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868- LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 10 PM TUESDAY. GALE WARNING...NEARSHORE WATERS UNTIL 3 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 261220 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 620 AM CST THU FEB 26 2015 .SHORT TERM... 345 AM CST THROUGH TONIGHT... THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR IMPACTS. THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING. THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON. WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS. THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA. HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN EFFECT. AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW. FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT THIS POINT THE FORECAST IS SLIGHTLY WARMER. FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE. MTF && .LONG TERM... 331 AM CST FRIDAY AFTERNOON THROUGH WEDNESDAY... AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY. HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE -5 TO -20 RANGE. THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE AFTERNOON. LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT. THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY. BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER. MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH. BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY CROSS THE AREA. KMD && .CLIMATE... 345 AM CST TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER: ROCKFORD... TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920 FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014 SATURDAY FEB 28TH LOW: -7 IN 1962 SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962 CHICAGO... FRIDAY FEB 27TH LOW: -6 IN 1897 SATURDAY FEB 28TH LOW: 0 IN 1884 MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 12Z... * IFR/LIFR SNOW SHOWERS THROUGH MID TO LATE MORNING. POSSIBLY BRIEF 1/4SM TO 1/2SM VISIBILITY...WITH HIGHER PROBABILITY AT MDW. * NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST LATE THIS MORNING OR EARLY THIS AFTERNOON. * MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL VISIBILITY IN HEAVIER SNOW SHOWERS. //DISCUSSION...UPDATED 12Z... LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING. THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY DICTATING THAT. SO CONFIDENCE ON THAT IS LOW. BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK TONIGHT. //ORD AND MDW CONFIDENCE...UPDATED 12Z... * HIGH IN SNOW SHOWERS THROUGH AT LEAST 16Z AT ORD AND THROUGH THE MORNING AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY AT MDW...LOW-MEDIUM AT ORD. * HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH 15Z. LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST. * MEDIUM-HIGH ON CIGS. //OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z... FRIDAY NIGHT...VFR. SOUTHWEST WINDS. SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH WINDS. SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS. MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH WINDS. TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS. WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS. MTF && .MARINE... 259 AM CST THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE. HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST. LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE EXTENDED FORECAST TO HAVE MUCH CONFIDENCE. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY. IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY. LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 272338 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 538 PM CST FRI FEB 27 2015 .SHORT TERM... 157 PM CST THROUGH TONIGHT... QUIET CONDITIONS TO PREVAIL THIS AFTERNOON INTO TONIGHT AS HIGH PRESSURE DOMINATES THE REGION. SHEARED OUT SHORTWAVE WILL SHIFT EAST THROUGH THE REGION TONIGHT...WHILE UPSTREAM ENERGY OVER THE CENTRAL PLAINS LIFTS EAST/NORTHEAST THROUGH THE MID MISSISSIPPI VALLEY. THIS WILL HELP PROVIDE AN INCREASE IN MID/HIGH LEVEL CLOUD COVER TONIGHT...MAINLY ACROSS THE SOUTHEASTERN HALF OF THE CWA. THIS MOISTURE WILL REMAIN FAIRLY PROGRESSIVE WITH THE THICKER MOISTURE LIKELY EXITING BY EARLY SATURDAY MORNING...BUT WITH PARTLY CLOUDY TO POSSIBLY CLOUDIER SKIES FOR A TIME TONIGHT. MADE MINOR CHANGES TO FORECAST LOWS TONIGHT WITH SUBZERO TEMPS LIKELY ONCE AGAIN. HOWEVER...DONT FEEL THEY WILL BE AS COLD AS THIS MORNING BUT DO THINK SOME PLACES COULD APPROACH 10 BELOW. WINDS SHOULD RAPIDLY DROP OFF THIS EVENING AND ALTHOUGH WIND CHILLS WILL FALL TO AROUND 15 BELOW ZERO ONCE AGAIN TONIGHT...WONT BE LOW ENOUGH FOR ANY HEADLINES AT THIS TIME. RODRIGUEZ && .LONG TERM... 309 PM CST MAIN CONCERNS ARE WITH ACCUMULATING SNOW SATURDAY NIGHT THROUGH SUNDAY AND THEN A MESSY...STRONGER STORM SYSTEM MONDAY NIGHT INTO WEDNESDAY. HYDRO ISSUES ARE POSSIBLE ON TUESDAY FOR AT LEAST A PORTION OF THE CWA. SATURDAY... DAY WILL START OUT QUIET AND COLD WITH HIGH PRESSURE RIDGE AXIS OVERHEAD. AFTER EARLIER MID/HIGH CLOUDS IN MORNING PASS TO EAST... CLOUDS WILL THEN INCREASE IN THE AFTERNOON AS ISENTROPIC ASCENT BEGINS IN EARNEST. A LEAD MID LEVEL WAVE IN BROAD WEST-SOUTHWEST FLOW AT 500 MB COULD GENERATE SOME LIGHT SNOW IN LATE AFTERNOON IN THE FAR SOUTHWEST CWA...WHICH I INCLUDED SLIGHT POPS FOR. HIGH TEMPS SHOULD REACH THE LOWER-MID 20S THANKS TO STRONG NEARLY MARCH SUN AND WARM ADVECTION ALOFT...THOUGH A FEW TYPICALLY COLD SPOTS COULD BE HELD IN THE UPPER TEENS. SATURDAY NIGHT THROUGH SUNDAY... GUIDANCE IS IN GOOD AGREEMENT IN THE SYNOPTIC PATTERN OF BROAD LONGER DURATION ISENTROPIC ASCENT...BUT THERE ARE DIFFERENCES IN THE DETAILS...INCLUDING TIMING AND WHERE CUTOFF OF ACCUMULATING SNOW IS IN THE REGION. THERE WAS A SUBTLE TREND SOUTHWARD ON GFS/ECMWF WITH 12Z RUNS...AS WELL AS GEFS ENSEMBLE MEAN. FOCUS REMAINS ON SOUTHERN/SOUTHEAST CWA WITH BEST ACCUMS BY LATE SUNDAY. LEAD WAVE COULD BRING SOME LIGHT SNOW OR FLURRIES SATURDAY EVENING...ESPECIALLY SOUTHERN CWA...WITH LITTLE IF ANY ACCUMULATION. TIMING DIFFERENCES CREEP IN AFTER MIDNIGHT...BUT DID HEDGE DURING THIS PERIOD TOWARD SLIGHTLY FASTER ECMWF BECAUSE FORCING FOR SNOW MAINLY SOUTH OF I-80 CAN BE IMPLIED BY CONTINUED WARM ADVECTION WHICH SHOULD ENABLE COLUMN TO SATURATE. 1 TO 2 INCHES OF ACCUMULATION ARE POSSIBLE MAINLY SOUTH OF IL AND KANKAKEE RIVERS BY DAYBREAK SUNDAY. HAVE SOME CONCERN ON SUNDAY WITH HOW SHARP NORTHERN CUTOFF OF PRECIP WILL BE. DID NOT MAKE BIG CHANGES TO PREVIOUS FORECAST POPS...BUT LOWERED SNOW AMOUNTS IN NORTHERN TIER OF COUNTIES TO 1 TO 2 INCHES...WHICH COULD BE GENEROUS. WAA/ISENTROPIC ASCENT PATTERN WILL BRING A MOIST AIR MASS TO THE SOUTHERN CWA...WITH PWAT VALUES NEAR OR JUST OVER .7 INCHES. DECENT MOISTURE...WITH ROUGHLY HALF INCH PWATS...SHOULD MAKE IT UP TO CHICAGO AREA. FORECAST SOUNDINGS INDICATE DECENT MID LEVEL LAPSE RATES AS WELL IN THE SOUTHERN CWA...AND TIGHTENING THERMAL GRADIENT SHOULD YIELD STEADY LIGHT TO MODERATE SNOWFALL RATES. TEMPERATURES NEAR OR SLIGHTLY OVER 30 DEGREES WILL BRING SNOW RATIOS DOWN CLOSER TO AVERAGE AND HIGH MARCH SUN ANGLE MAY MAKE IT TOUGH FOR SNOW TO ACCUMULATE READILY ON WELL TREATED/HEAVILY TRAVELED ROADWAYS. OVERALL...SNOW AMOUNTS BY LATE SUNDAY FOR THE REMAINDER OF THE CWA LOOK TO FALL INTO 1 TO 3 INCH/LOCALLY 4 INCH RANGE ALONG I-88/I-90 CORRIDOR...2 TO 4 INCHES NEAR AND A BIT SOUTH OF I-80 AND 4 TO 6 INCHES SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. THERE COULD BE LOCALIZED AMOUNTS JUST OVER 6 INCHES IN FAR SOUTHEAST CWA...BUT LONGER DURATION AND LIGHT WINDS SHOULD MITIGATE IMPACTS. WILL LIKELY NEED A WINTER WEATHER ADVISORY FOR AT LEAST PART OF THE CWA SOUTH OF INTERSTATE 80 NONETHELESS. SUNDAY NIGHT AND MONDAY... EXPANSIVE HIGH PRESSURE WILL SETTLE OVER THE REGION SUNDAY NIGHT...WITH SKIES BECOMING PARTLY CLOUDY TO MOSTLY CLEAR AFTER MIDNIGHT. AIR MASS IS NOT ALL THAT COLD ALOFT...BUT STRONG INVERSION AND DIMINISHING WINDS AS HIGH NOSES IN SHOULD ENABLE CHILLY TEMPERATURES...ESPECIALLY IN TYPICAL COLD SPOTS. HAVE REMAINED CONSERVATIVE WITH LOWS FOR NOW...BUT WOULDNT BE SURPRISED IF LOCATIONS SUCH AS RPJ DIP BELOW ZERO. DEEP SOUTHWESTERN TROUGH WILL BRING RAPID MID LEVEL HEIGHT RISES AND INCREASING WARM ADVECTION DURING THE AFTERNOON...BUT LIMITED MIXING THROUGH MID DAY UNDER INFLUENCE OF HIGH PRESSURE SHOULD LIMIT TEMPS TO THE UPPER 20S TO AROUND 30. MONDAY NIGHT THROUGH FRIDAY... AFOREMENTIONED DEEP WESTERN TROUGH WILL RESULT IN STRONG SURFACE LOW MOVING NEAR OR OVER AREA ON TUESDAY. FAIRLY COMPLEX UPPER PATTERN DUE TO ANOMALOUS TROUGH EJECTING FROM SOUTHWEST AND DIFFERENCES ON GUIDANCE ON TRACK OF SURFACE AND MID/UPPER FEATURES AS WELL AS PHASING OF ALL THE PIECES. AIR MASS SHOULD START OUT COLD ENOUGH FOR SNOW MONDAY NIGHT...BUT THEN STRONG SOUTHWEST FLOW ALOFT SHOULD QUICKLY WARM COLUMN ABOVE FREEZING BY OR DURING TUESDAY MORNING. WONDERING IF AT LEAST NORTHERN HALF OF CWA COULD SEE A FRONT END OF ACCUMULATING SNOW...FOLLOWED BY QUICK TRANSITION TO MIX THEN PLAIN RAIN EVERYWHERE. UNSEASONABLY MOIST AIR MASS ADVECTING IN...ALONG WITH DEWPOINTS POSSIBLY APPROACHING OR EXCEEDING 40 DEGREES FOR A TIME TUESDAY INTO THE EARLY EVENING SOUTH OF I-80...ALONG WITH STEADY RAIN...COULD RESULT IN HYDROLOGIC ISSUES DUE TO FROZEN AND SNOW COVERED GROUND...AND ICED OVER RIVERS. WITH THIS SYSTEM STILL FAR OUT...THIS PERIOD NEEDS TO BE CLOSELY MONITORED FOR VARIETY OF POTENTIALLY SIGNIFICANT IMPACTS. STILL CAN SEE A WAY OUT FOR A MORE WINTRY SCENARIO OR ON THE OTHER HAND...HYDRO ISSUES FOR THE ENTIRE AREA IF SYSTEM TRACKS FARTHER NORTH. COLDER AIR WILL FILTER BACK IN AND CHANGE LINGERING PRECIP TO SNOW TUESDAY NIGHT...FOLLOWED BY A BLAST OF ARCTIC AIR WEDNESDAY INTO THURSDAY. POSSIBLE LARGE SCALE PATTERN CHANGE TO ZONAL PACIFIC FLOW COULD BRING MUCH MILDER WEATHER BY NEXT WEEKEND. RC && .CLIMATE... TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER: ROCKFORD... FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014 SATURDAY FEB 28TH LOW: -7 IN 1962 SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962 CHICAGO... SATURDAY FEB 28TH LOW: 0 IN 1884 && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * LIGHT SNOW COULD DEVELOP SATURDAY EVENING IZZI //DISCUSSION...UPDATED 00Z... WEATHER NIL THROUGH DAY SATURDAY. NEXT SYSTEM WILL APPROACH THE AREA SATURDAY NIGHT POTENTIALLY RESULTING IN LIGHT SNOW DEVELOPING SATURDAY EVENING DURING THE FINAL 6 HOUR FORECAST PERIOD AT O'HARE. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * LOW-MEDIUM CONFIDENCE IN SATURDAY EVENING SNOW * HIGH CONFIDENCE IN EVERYTHING ELSE IZZI //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY...IFR LIKELY WITH PERIODS OF LIGHT SNOW. MONDAY...VFR. TUESDAY...RAIN...FREEZING RAIN...OR SNOW. IFR PROBABLE. WEDNESDAY...MVFR CIGS POSSIBLE. THURSDAY...CHANCE OF MVFR CIGS EARLY. IZZI && .MARINE... 157 PM CST LARGE HIGH PRESSURE SITUATED JUST SOUTH OF THE LAKE THIS AFTERNOON WHILE LOW PRESSURE IS OVER HUDSON BAY. THIS IS ALLOWING FOR GENERALLY WESTERLY WINDS OVER THE LAKE IN THE 10 TO 20 KT RANGE. THIS HIGH WILL SLIDE TO THE EAST TONIGHT INTO SATURDAY...WITH WINDS BECOMING MORE SOUTHWEST OVERNIGHT AND WHILE WINDS SLIGHTLY INCREASE TO THE 15 TO 25 KT RANGE FOR A BRIEF PERIOD. A PERIOD OF SOUTHERLY WINDS WILL OCCUR ON SATURDAY AND SATURDAY NIGHT WITH 10 TO 20 KT RANGE INCREASING BACK UP TO THE 15 TO 25 KT RANGE. GENERALLY LIGHTER FLOW EXPECTED OVER THE LAKE TO END THE WEEKEND...BEFORE WINDS INCREASE ONCE AGAIN OUT OF THE WEST/NORTHWEST SUNDAY NIGHT INTO MONDAY. RODRIGUEZ && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 060831 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 331 AM CDT WED MAY 6 2015 .SHORT TERM... 329 AM CDT THROUGH THURSDAY... NUMEROUS CHALLENGES TO OPEN UP TODAY WITH A WARM FRONTAL BOUNDARY DRAPED ACROSS CENTRAL ILLINOIS AND DENSE FOG IN PLACES. OBSERVATIONS AND WEBCAM IMAGERY INDICATE WIDESPREAD 3/4SM OR LESS VISIBILITY ACROSS THE AREA...WITH SOME LOCATIONS UNDER 1/4SM OF A MILE. AS OF 330 AM...THIS IS NOT WIDESPREAD ENOUGH TO EXPAND THE ADVISORY BUT WILL CERTAINLY HIGHLIGHT IN SPS AND GRAPHICAST GOING INTO THE MORNING COMMUTE. PATCHES OF GOES EXPERIMENTAL CLOUD THICKNESS DATA WHERE AVAILABLE BETWEEN HIGHER CLOUDS AND AMDAR DATA INDICATE A CLOUD DEPTH OF AROUND 700-1000 FT...WITH THE LATTER INDICATING A SHARP INVERSION OF AROUND 15F IN THAT DEPTH. WITH THE SYNOPTIC AREA NORTH OF THE WARM FRONT FAVORED...DO NOT ENVISION THE FOG RAPIDLY DISSIPATING NORTH OF I-80 THIS MORNING. WILL INCLUDE MENTION IN FORECAST GRIDS THROUGH MID TO LATE MORNING. THE MOST VULNERABLE AREA FOR DENSE FOG THROUGH THE MORNING WILL BE NEAR THE LAKE SHORE INCLUDING DOWNTOWN CHICAGO. WILL CONTINUE THE ADVISORY FOR THIS AREA AS IS. THE CLOUDS ARE EXPECTED TO ERODE/ADVECT NORTH LATE THIS MORNING INTO EARLY AFTERNOON...BUT ONSHORE FLOW WILL CONTINUE INTO LAKE ADJACENT COUNTIES. THE SURFACE WARM FRONT WILL ADVANCE NORTHWARD IN RESPONSE TO THE UPPER LOW LIFTING NORTH ACROSS THE EASTERN ROCKIES REGION. IT WILL NOT BE ENOUGH TO SHUNT THE LAKE EFFECT COOLING IN IMMEDIATE NORTHEAST ILLINOIS TODAY...SO A DECENT TEMPERATURE DIFFERENCE WILL OCCUR AGAIN IN THE AREA. HIGHS POSSIBLY REMAINING BELOW 60 WILL BE SEEN ALONG THE IMMEDIATE LAKE SHORE...TO MID TO UPPER 70S NORTH OF I-88...TO MID 80S SOUTH OF I-80. THE MID 80S ARE IMPRESSIVE FOR THIS EARLY IN MAY...BUT VERIFIED YESTERDAY UPSTREAM WITH 14C AT 850MB AND 21C AT 925MB ON THE 00Z ILX SOUNDING...AND WIDESPREAD OBSERVED MID 80S IN CENTRAL IL. THE SYNOPTIC WARM FRONT WHILE BECOMING SOMEWHAT LOOSELY DEFINED IN THE WIND FIELD MAY BE ENOUGH WITH THE LAKE BREEZE TO PROVIDE A SOURCE OF LIMITED BUT POOLED INSTABILITY AND CONVERGENCE ACROSS NORTH CENTRAL IL INTO THE NORTHWEST CHICAGO METRO. CONTINUE WITH THE SLIGHT CHANCE OF AN AFTERNOON SHOWER OR STORM THERE...THOUGH WILL DEPEND ON JUST HOW QUICKLY THE CLOUDS DEPART. COVERAGE SHOULD BE LIMITED IF ANY CAN DEVELOP. TONIGHT WILL POTENTIALLY SEE SOME FOG AGAIN FOR LAKESIDE AREAS AND FAR NORTHERN IL...THOUGH THE WARM FRONT IS EXPECTED TO SHIFT WINDS SOUTHERLY BEFORE DAYBREAK THURSDAY. THIS WILL LEAD TO A LIKELY WARMING OVERNIGHT IN LAKE ADJACENT AREAS. THURSDAY WILL SEE THE LOW-LEVEL THERMAL RIDGE ESTABLISHED OVER THE AREA AND STRONGER LOW-LEVEL FLOW AS PRESSURE FALLS SPREAD EASTWARD IN THE UPPER MIDWEST. THE 850MB TEMPERATURES OF 14C WITH DEEP ENOUGH MIXING TO THAT LEVEL ARE EXPECTED ACROSS THE ENTIRE FORECAST AREA WITH NO LAKE ADJACENT COOLING. COMPARED TO 24 HOURS AGO...THERE IS A STRONGER SIGNAL FOR SOME CLOUDS...BOTH CIRRUS AND SOME DIURNAL CUMULUS. HOWEVER...AT LEAST LOWER 80S STILL LOOK LIKE A SOLID BET...WITH MID 80S FAVORED IF CLOUDS ARE NOT TOO THICK OR PERSISTENT. MTF && .LONG TERM... 329 AM CDT THURSDAY NIGHT THROUGH TUESDAY... TO BE ISSUED SHORTLY. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * LIFR/IFR CIGS AND IFR TO MVFR VSBY THROUGH THE MID MORNING THEN IMPROVING TO VFR. * EAST WINDS LESS THAN 10 KT. * VFR HAZE AND PERHAPS MVFR FOG THIS EVENING AND TONIGHT. JEE //DISCUSSION...UPDATED 06Z... NORTHEAST TO EAST FLOW CONTINUES TO BRING COOLER AIR OFF OF THE LAKE AND OVER THE TERMINALS. THE LOW CIGS AND FOG WILL CONTINUE THROUGH THE MID MORNING. MAY SEE A FEW HOURS OF IMPROVEMENT BUT NOT EXPECTING WIDESPREAD IMPROVEMENT TO VFR UNTIL 15/16Z. NEAR TERM GUIDANCE IS ALL SUGGESTING ORD AND MDW WILL REMAIN MORE EAST THAN SOUTHEAST TODAY...SO WENT WITH EAST WINDS LESS THAN 10 KT. A LAKE BREEZE SHOULD PUSH OVER GARY TURNING THE WINDS NORTH TO NORTHEAST AROUND NOON. RFD WILL HAVE SOUTHEAST TO SOUTH WINDS OVER 10 KT THIS AFTERNOON AND THEN EXPECTING SOUTHEAST WINDS ACROSS THE BOARD THIS EVENING LESS THAN 10 KT. MAY SEE ANOTHER ROUND OF FOG TONIGHT AT THE TERMINALS OUTSIDE OF MDW AND ORD. FOR NOW JUST HAVE MVFR FOG. JEE //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM-HIGH CONFIDENCE IN WHEN CIGS AND VSBY IMPROVE TO VFR. * MEDIUM-HIGH CONFIDENCE IN WINDS BEING EAST ALL DAY AND LESS THAN 10 KT. * MEDIUM CONFIDENCE IN CIGS AND VSBY THIS EVENING. * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS. JEE //OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z... THURSDAY...VFR. SOUTH WINDS. FRIDAY...CHANCE TSRA/MVFR. SOUTH-SOUTHWEST WINDS. SATURDAY...CHANCE TSRA/MVFR. NORTHEAST WINDS. SUNDAY...CHANCE TSRA/MVFR. EAST-NORTHEAST WINDS. MONDAY...CHANCE TSRA/MVFR. SOUTHEAST WINDS BECOMING NORTHWEST LATE. RATZER && .MARINE... 223 AM CDT THE STATIONARY FRONT IS OVER CENTRAL ILLINOIS AND IT WILL LIFT AS A WARM FRONT THROUGH TONIGHT. HAVE MEDIUM CONFIDENCE IN HOW QUICKLY IT WILL ADVANCE AND HAVE MEDIUM-HIGH CONFIDENCE THAT THE DENSE FOG WILL STAY PUT UNTIL THE WARM FRONT MOVES THROUGH. THEREFORE EXTENDED THE DENSE FOG ADVSY THROUGH 10PM CDT THIS EVENING. IF THE FRONT IS SLOWER THAN FORECAST...THE DENSE FOG COULD ALSO PERSIST LONGER. EAST WINDS BECOME SOUTH BEHIND THE FRONT TONIGHT AND INCREASE TO 15-25 KT OVER THE NORTHERN HALF OF THE LAKE THURSDAY NIGHT. A LOW OVER NORTHEAST CANADA DRAGS A COLD FRONT ACROSS THE LAKE FRIDAY NIGHT INTO SATURDAY. WINDS BECOME NORTH TO 20 KT BEHIND THE FRONT. THE NEXT LOW PRESSURE SYSTEM MOVES OVER THE LAKE EARLY NEXT WEEK BUT GUIDANCE DIFFERS ON IF THE LOW WILL MOVE OVER THE LAKE OR SOUTH OF THE LAKE. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...DENSE FOG ADVISORY...ILZ006-ILZ014 UNTIL 11 AM WEDNESDAY. IN...NONE. LM...DENSE FOG ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745- LMZ777-LMZ779 UNTIL 11 PM WEDNESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 140538 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 1238 AM CDT SUN JUN 14 2015 .SHORT TERM... 248 PM CDT THROUGH SUNDAY... FOR THE REMAINDER OF THE AFTERNOON AND INTO THE EARLY EVENING...THE MAIN FOCUS WILL BE DIURNAL CONVECTION. CELLS HAVE INITIALLY BEEN DEVELOPING OVER THE SOUTHERN PORTIONS OF THE CWA THAT WERE NEVER UNDER DENSE CLOUD COVER THIS MORNING...GENERALLY SOUTH OF A DIFFUSE WARM FRONT. THROUGH THE DAY...DIFFERENTIAL HEATING HAS MORE SHARPLY DEFINED THE WARM FRONT AS IT HAS LIFTED TO THE NORTH. THE WARM FRONT HAS PUSHED NORTH INTO SRN WI EXCEPT FOR A SMALL PORTION OF FAR NWRN IL WHICH IS STILL UNDER SOME DENSER LAYERED CLOUD COVER. HOWEVER...BEFORE TOO LONG...THE ENTIRE AREA WILL BE UNDER WARM...MOIST UNSTABLE AIR MASS. LATEST SFC OBS SHOW THAT TEMPERATURES HAVE BEEN ABLE TO RISE INTO THE MIDDLE 80S ACROSS MUCH OF THE AREA AND LATEST SPC MESO ANALYSIS INDICATES A BAND OF MUCAPE IN EXCESS OF 3000 J/KG GENERALLY SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS AND THIS IS THE AREA THAT HAS SEEN THE INITIAL CONVECTION. PWATS OF 1.75 INCHES OVER THIS REGION WILL BE CONDUCIVE TO LOCALLY HEAVY RAINFALL WITH THESE THUNDERSTORMS WHILE SOME OF THE STRONGER STORMS WILL HAVE THE POTENTIAL TO PRODUCE SOME SMALL HAIL AS WELL. OVER THE NEXT FEW HOURS...INSTABILITY WILL CONTINUE TO SPREAD NORTH OVER THE REMAINDER OF THE CWA AND HAVE GONE WITH LIKELY POPS FOR THE LATE AFTERNOON AND EARLY EVENING HOURS. WHILE COVERAGE MAY BE MORE SCT THAN WIDESPREAD THAN WOULD NORMALLY EXPECTED WITH HIGHER POPS...FEEL THAT THE LIKELY POPS ARE JUSTIFIED SINCE MANY LOCATIONS SHOULD SEE AT LEAST PASSING THUNDERSTORMS WITH THE POTENTIAL TO PRODUCE HEAVY RAIN AND SMALL HAIL. THERE WILL BE AN INCREASING SEVERE POTENTIAL AS STRENGTHENING MID LEVEL FLOW MAY ACT TO ORGANIZE SOME STORMS INTO SHORT LINES OR CLUSTERS...WITH THE POTENTIAL TO PRODUCE LOCALLY STRONG...DAMAGING WINDS AND SMALL HAIL. BY LATE THIS EVENING...WEAK LOW PRESSURE OVER THE IS EXPECTED TO CROSS THE MIDDLE MISSISSIPPI VALLEY AND THEN PROCEED NORTHEAST ACROSS SRN WI AND CENTRAL LAKE MICHIGAN. THE LOW WILL DRAG A WEAK COLD FRONT ACROSS THE REGION. AT SUNSET...THE DIURNAL ASPECT OF THE CONVECTIVE ACTIVITY WILL BEGIN TO DIMINISH AND THEN WEAK CONVERGENCE ALONG A FRONT EXTENDING FROM SERN IOWA TO ERN IOWA WILL BE THE PRIMARY FOCUSING MECHANISM FOR CONTINUED CONVECTIVE ACTIVITY OVERNIGHT. WHILE MUCH OF THE THUNDER WILL BE FOCUSED INVOF THE FRONTAL BOUNDARY...THERE WILL STILL BE ENOUGH LINGERING INSTABILITY AHEAD OF THE COLD FRONT SHOULD BE SUFFICIENT TO KEEP SCT SHRA/TSRA POSSIBLE OVERNIGHT. FOR SUNDAY...THE FRONTAL BOUNDARY WILL STALL OUT ALONG THE IL-WI BORDER AND EXTEND WEST TO A DEVELOPING LOW OVER THE CENTRAL PLAINS. THIS WILL KEEP THE CWA UNDER A WARM/MOIST AIRMASS. SINCE THE FRONT WILL REMAIN NORTH AND WEST OF THE CWA...TEMPERATURES SHOULD BE ABLE TO REACH INTO THE LOW TO MIDDLE 80S WITH DEWPOINTS IN THE LOWER 70S. THE LATEST SPC DAY 2 OUTLOOK KEEPS THE ENTIRE CWA UNDER A SLIGHT RISK FOR SEVERE THUNDERSTORMS. FORECAST WIND PROFILES SHOW UNIDIRECTIONAL WINDS THROUGH THE ATMOSPHERIC LAYER WITH LITTLE IN THE WAY OF DIRECTIONAL SHEAR EXCEPT THROUGH THE SFC-925MB LAYER. AT LEAST INITIALLY...THE GREATEST SEVERE THREAT WILL BE FOR LOCALLY DAMAGING WINDS...THOUGH WITH INCREASING INSTABILITY THROUGH THE AFTERNOON...A GREATER POTENTIAL FOR LARGE HAIL WILL BE POSSIBLE...ESPECIALLY OVER THE WRN PORTIONS OF THE CWA...CLOSER TO THE NEAR-STATIONARY FRONTAL BOUNDARY. KREIN && .LONG TERM... 147 PM CDT SUNDAY NIGHT THROUGH SATURDAY... THE UPPER AIR PATTERN TO START THE PERIOD WILL BE CHARACTERIZED BY HIGH PRESSURE OVER THE SOUTHEASTERN UNITED STATES. A WEAK THOUGH SEMI- PERSISTENT TROUGH OVER THE CENTRAL PLAINS WITH GENERALLY ZONAL FLOW OVER THE REGION...AND MORE AMPLIFIED FLOW IN CANADA. IMPULSES IN THE WSW UPPER FLOW PATTERN LOOK TO CONTINUE CHANCES FOR SHOWERS AND THUNDERSTORMS OVERNIGHT AND EVEN INTO MONDAY. ON MONDAY...A TRAILING COLD FRONT FROM THE MORE ACTIVE FLOW IN CANADA WILL GET A BIT OF A PUSH SOUTHEAST FROM HIGH PRESSURE IN THE UPPER MIDWEST. THERE WILL LIKELY BE QUITE A BIT OF CLOUD COVER AROUND FROM CONVECTION IN THE REGION WHICH WILL LIMIT INSTABILITY...BUT AS THE COLD FRONT MOVES SOUTHEASTWARD MODEST UNIDIRECTIONAL SHEAR OVER THE AREA WILL SUPPORT A CHANCE FOR LOCALLY DAMAGING WINDS AND POSSIBLY SOME LARGE HAIL. THE SURFACE TROUGH IN NORTHEAST IOWA WILL DRIFT SOUTHWARD..AND WITH HIGH PRESSURE SHIFTING EAST OVER NORTHERN WISCONSIN...THE COLD FRONTAL BOUNDARY LOOKS TO SHIFT TO THE SOUTHERN CWA MONDAY NIGHT INTO TUESDAY AS COOL NORTHEAST ONSHORE FLOW FILTERS BACK INTO NORTHEAST ILLINOIS AND FAR NORTHWEST INDIANA. THE MONDAY NIGHT INTO EARLY TUESDAY TIME FRAME OFFERS THE BEST CHANCE FOR A DRY PERIOD FOR MANY AREAS. UNFORTUNATELY WITH THE WSW FLOW ALOFT...HIGH PRESSURE PARKED OVER THE SOUTHEAST...THE FRONTAL BOUNDARY WILL NOT CLEAR THE AREA AND LIKELY LAY OUT OVER THE SOUTHERN CWA. WE NEVER RID OUR AREA OF THE HIGHER PWAT AIRMASS...WHICH WILL KEEP OUR SOUTHERN AREAS SUSCEPTIBLE TO OCCASIONAL HEAVY RAINFALL PRODUCING STORMS...ESPECIALLY EASTERN ILLINOIS INTO NORTHWEST INDIANA WHERE THE GROUND IS ALREADY SATURATED...RIVERS IN FLOOD OR BANKFULL...AND WHERE IT TAKES LITTLE TO KEEP URBAN AND SMALL STREAM FLOODING A PROBLEM. AT THIS POINT THE HEAVY RAINFALL AXIS MAY REMAIN JUST SOUTH AND EAST...BUT WILL BEAR WATCHING. ANOTHER ATTEMPT TO SHOVE THE BOUNDARY SOUTHWARD COMES LATE WEDNESDAY NIGHT AND THURSDAY WHICH COULD BE A DRIER PERIOD AS WELL...BUT ACTIVE ZONAL FLOW LEAVES THE REGION SUSCEPTIBLE FOR SHOWERS AND STORMS THROUGH WEEKS END. KMD && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * TEMPORARY TSRA THROUGH EARLY OVERNIGHT THEN SHRA LINGERING UNTIL OR A LITTLE AFTER SUNRISE. BRIEF IFR PROBABLE IN TSRA. * VARIABLE CIGS BUT A PERIOD OF LOWER MVFR SEEMS PROBABLE AT THE END OF THE RAIN...11Z-16Z OR SO THIS MORNING...WITH IFR POSSIBLE IN THAT TIME. * POTENTIAL FOR MORE TSRA ANYTIME FROM MID-AFTERNOON THROUGH THE NIGHT...SO LOW CONFIDENCE ON SPECIFIC TIMING. COVERAGE APPEARS MOST FAVORED JUST SOUTH OF THE TAF SITES / SOUTHERN TRACON AREA. //DISCUSSION...UPDATED 06Z... AN UPPER DISTURBANCE MOVING ACROSS NORTHERN IL THROUGH DAYBREAK WILL CONTINUE SHOWERS WITH STORMS LIKELY ENDING/FADING IN COVERAGE BY AFTER 08Z. TEMPORARY IFR VISIBILITY AND CIGS HAVE BEEN OBSERVED IN SOME OF THE HEAVIER STORMS. AFTER THE SHOWERS END TEMPORARILY...SOMETIME NEAR OR JUST AFTER DAYBREAK...THERE IS A FAVORED TIME FOR LOWER CIGS AND SOME OF THIS MAY BE IN THE IFR CATEGORY...ESPECIALLY AT RFD. PROFILES ARE MORE SUPPORTIVE OF LOW CIGS THAN FOG...BUT GIVEN ALL THE RAINFALL...AT LEAST LIGHT FOG WILL PROBABLY BE SEEN AFTER SUNRISE. THE FRONT THAT HELPED TO SPARK MUCH OF THE STORM ACTIVITY ON SATURDAY WILL STILL BE LOOSELY DEFINED OVER THE AREA INTO TODAY...WITH AMPLE MOISTURE REMAINING. DURING PEAK DESTABILIZATION IN THE MID-LATE AFTERNOON...AT LEAST SCATTERED STORMS ARE FAVORED IN THE CENTRAL TO NORTHERN IL AND IN REGION. GOING FORWARD INTO SUNDAY NIGHT...SUPPORT FOR AT LEAST SOME SHOWERS AND STORMS WILL CONTINUE...MAYBE EVEN WITH AN UPTICK LATE INTO EARLY MONDAY MORNING AS THE NEXT UPPER DISTURBANCE APPROACHES. //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM-HIGH IN TSRA END TIME EARLY THIS MORNING. MEDIUM IN SHRA END TIME THIS MORNING. * MEDIUM IN PERIOD OF LOWER END MVFR CIGS BUT LOW ON HOW FAR THEY WILL DROP AND DURATION. * LOW-MEDIUM IN ADDITIONAL SHRA/TSRA AT THE TERMINALS MID- AFTERNOON INTO TONIGHT. LOW ON SPECIFIC TIMING AND DURATION. * MEDIUM-HIGH IN WINDS LESS THAN 10KT OUTSIDE OF STORMS...LOW IN WIND DIRECTION HOWEVER. //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY THROUGH FRIDAY...PERIODIC CHANCES OF SHRA/TSRA WITH ASSOCIATED BRIEF IFR VSBY IN TSRA. MOSTLY VFR OUTSIDE OF STORMS. MTF/IZZI && .MARINE... 147 PM CDT HIGH PRESSURE REMAINS IN CONTROL IN THE SOUTHEAST UNITED STATES...WITH LOW PRESSURE OVER CENTRAL CANADA...AND A WEAK PRESSURE TROUGH EXTENDING FROM IOWA TO CENTRAL MICHIGAN. THE CANADIAN LOW WILL DEEPEN SOME AND SLOWLY DRIFT TOWARD HUDSON BAY SUNDAY THEN SLOWLY MOVE NORTHEAST THROUGH MID WEEK. HIGH PRESSURE IN THE CANADIAN ROCKIES WILL MOVE TO THE UPPER MIDWEST BY MONDAY AFTERNOON...SHOVING THE PRESSURE TROUGH SOUTHWARD AND PUSHING A COLD FRONT SOUTHWARD ACROSS THE LAKE MONDAY NIGHT. THE HIGH MOVES OVER THE NORTHERN HALF OF THE LAKE TUESDAY...THEN EASTWARD ON WEDNESDAY. A LOW PRESSURE TROUGH EXTENDING FROM THE CENTRAL PLAINS NORTHWARD INTO CENTRAL CANADA WILL GRADUALLY SHIFT EAST TOWARD THE LAKE LATE IN THE WEEK. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 070909 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 409 AM CDT TUE JUL 7 2015 .SHORT TERM... 330 AM CDT THROUGH THURSDAY... MAIN FORECAST CONCERNS/CHALLENGES IN THE NEAR TERM ARE WITH PRECIP TRENDS THROUGH MIDDAY WITH PRECIP LIKELY LINGERING ACROSS THE SOUTHEAST HALF OF THE CWA...AND THEN WITH MUCH COOLER TEMPS EXPECTED TODAY. LATEST RADAR IMAGERY DEPICTING PRECIP STILL PERSISTING OVER MUCH OF THE AREA THIS MORNING WITH HEAVIER SHOWERS AND ISOLATED THUNDER CONFINED PRIMARILY TO THE SOUTHEAST THIRD OF THE CWA...ALONG AND SOUTH OF INTERSTATE 80. THIS BETTER DEVELOPMENT IS OCCURRING SOUTH OF THE FRONT EARLY THIS MORNING WHERE HIGH MOISTURE CONTENT AIR CONTINUES TO BE TRANSPORTED NORTHEASTWARD. ALTHOUGH INSTABILITY IS LIMITED WITH THE HIGHEST INSTABILITY JUST SOUTH OF THE CWA...HIGH PWAT AIR IN EXCESS OF TWO INCHES REMAINS SITUATED OVER MUCH OF THE REGION. THIS IS ALLOWING FOR CONTINUED HEAVY DOWNPOURS WITH THE STRONGER PRECIP...WITH HIGH INSTANTANEOUS PRECIP RATES STILL NOTED ON DUAL POL. HOWEVER...THESE HEAVIER SHOWERS REMAIN FAIRLY PROGRESSIVE AND CONTINUE TO STEADILY LIFT NORTHEAST THROUGH THE REGION. LOOKING UPSTREAM...IT WOULD APPEAR THAT PRECIP WILL LIKELY MOVE OVER MUCH OF THE CWA THROUGH THE 12-14Z TIME FRAME WITH SHORT TERM GUIDANCE SUPPORTING THIS...BUT WITH THE HEAVIER RAIN AND ISOLATED THUNDER PUSHING FURTHER SOUTH THROUGHOUT THIS TIME. CONDITIONS SHOULD BE DRY FOR MUCH OF THE CWA BY MIDDAY...AND ESPECIALLY BY EARLY AFTERNOON. THIS WILL BE SUPPORTED WITH MUCH DRIER AND COOLER AIR ADVECTING ACROSS THE REGION POST FROPA EARLY THIS MORNING. EARLY MORNING SURFACE ANALYSIS WOULD PUT THE FRONT ACROSS A MENDOTA TO STREAMWOOD...TO LAKE FOREST LINE ACROSS NORTHERN ILLINOIS. OVER THE NEXT TWO TO THREE HOURS...THIS FRONT WILL CONTINUE THROUGH REMAINING AREAS IN NORTHERN ILLINOIS WITH REMAINING AREAS IN EAST CENTRAL ILLINOIS AND NORTHWEST INDIANA NOT OBSERVING FROPA UNTIL CLOSER TO MID MORNING. BEHIND THIS FRONT...NORTHERLY WINDS ARE RAMPING UP RATHER QUICKLY WHILE TEMPS FALL TO THE LOWER 60S. THIS WILL SET THE STAGE FOR A RATHER COOL AND BREEZY DAY TODAY WITH WELL BELOW NORMAL TEMPS EXPECTED FOR ALL AREAS. AREAS ACROSS NORTH CENTRAL ILLINOIS MAY OBSERVE SOMEWHAT OF A RECOVERY THROUGH MIDDAY...AS CLOUDS BEGIN TO SCATTER OUT. BY THIS AFTERNOON AND ESPECIALLY THIS EVENING AND OVERNIGHT...DRY CONDITIONS LIKELY IN PLACE WITH FRONT WELL SOUTH OF THE CWA AND WITH MORE ZONAL FLOW IN PLACE ACROSS THE REGION. TONIGHT THROUGH EARLY WEDNESDAY MORNING WILL BE DRY BUT THEN TURN ATTENTION TOWARDS SHORTWAVE ENERGY LIFTING NORTHEAST THROUGH THE CENTRAL PLAINS. THIS ENERGY AND ASSOCIATED SURFACE REFLECTION WILL LIFT TO THE MID MISSISSIPPI VALLEY ON WEDNESDAY...WITH ASSOCIATED PRECIP SPREADING NORTHWARD OUT AHEAD OF IT. DO BRING CHANCE POPS BACK OVER THE SOUTHERN HALF OF THE CWA ON WEDNESDAY AND DID KEEP MENTION OF SLIGHT CHANCE THUNDER AS WELL. HOWEVER...BEST INSTABILITY LOOKS TO BE SITUATED TO THE SOUTH OF THE CWA DURING THIS TIME AND AM NOT OVERLY EXCITED ABOUT THUNDER DURING THIS TIME. BEST CHANCES FOR PRECIP FOR THE CWA WILL ARRIVE WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING WITH THE APPROACH OF THIS SYSTEM. HOWEVER...GUIDANCE DOES VARY WITH PLACEMENT/TRACK OF THIS SYSTEM...BUT WITH AREAS SOUTH OF INTERSTATE 88 HAVING THE BETTER CHANCES OF OBSERVING PRECIP. INCREASING MOISTURE/INSTABILITY OUT AHEAD OF A STRENGTHENING LLJ SHOULD ALLOW FOR BETTER CHANCES FOR THUNDER. RODRIGUEZ && .LONG TERM... 330 AM CDT FRIDAY THROUGH MONDAY... THE EXTENDED PERIOD CONTINUES TO LOOK WARMER AND MORE ACTIVE...WITH CHANCES FOR THUNDER THROUGHOUT MUCH OF THE PERIOD. THIS WILL BEGIN ON FRIDAY WITH FAIRLY ENERGETIC FLOW RIDING ALONG RISING HEIGHTS ACROSS THE REGION WITH A GOOD WARM/MOIST ADVECTION PUSH...WITH AT LEAST SCATTERED THUNDERSTORM DEVELOPMENT LIKELY. THUNDERSTORM DEVELOPMENT APPEARS TO BE LIKELY AGAIN FRIDAY NIGHT INTO SATURDAY...WHILE STRONG LLJ PUMPS HIGHER MOISTURE CONTENT AIR OVER THE REGION. THUNDERSTORMS MAY LINGER SATURDAY MORNING...BUT SHOULD PUSH NORTH OF THE CWA THROUGH EARLY AFTERNOON. WITH THIS LIKELY OCCURRING...ABOVE NORMAL TEMPS ARE EXPECTED SATURDAY...WITH SIMILAR TEMPS EXPECTED SUNDAY. RODRIGUEZ && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * OCCASIONAL RAIN/DRIZZLE THROUGH DAYBREAK. * NORTHWEST WINDS QUICKLY FLIP TO NORTHEAST AROUND DAYBREAK AND INCREASE WITH GUSTS TO 22KT POSSIBLE THROUGH EARLY AFTERNOON. * MVFR CIGS THROUGH EARLY TUE...WITH OCCASIONAL IFR PROBABLE THROUGH AROUND 12-13Z. KMD //DISCUSSION...UPDATED 06Z... MORE ORGANIZED SHOWER AND THUNDERSTORM ACTIVITY IS NOW ALONG A LINE FROM KPNT TO KIKK AND NORTHEAST OF KGYY...WITH OCCASIONAL LIGHTER THOUGH AT TIMES MODERATE RAIN DRIFTING THROUGH NORTHEAST AND NORTH CENTRAL ILLINOIS. MEANWHILE...COLD FRONT IS KNOCKING AT THE DOOR OF KRFD WITH A RAPID SHIFT TO NORTH-NORTHWEST WINDS EXPECTED SOON. THIS SHOULD COME TO THE CHICAGOLAND TERMINALS CLOSER TO 9Z. LIGHTER WINDS AHEAD OF THE FRONT AND A VERY MOIST AIR MASS SUCH THAT MVFR CIGS SHOULD BEGIN TO MATERIALIZE IN THE NEXT HOUR OR TWO. IFR MAY BRIEFLY AS WELL IN THE NEXT FEW HOURS...THOUGH MVFR SHOULD BE MORE PREVAILING. WINDS WILL FLOP OVER TO NORTHEAST JUST AFTER DAYBREAK AND REMAIN ELEVATED THROUGH THE DAY. SKIES SHOULD SCATTER OUT DURING THE LATE MORNING HOURS. NORTHEAST WINDS REMAIN ABOVE 10 KT THROUGH THE EARLY EVENING. KMD //ORD AND MDW CONFIDENCE...UPDATED 09Z... * HIGH IN OCCASIONAL RAIN...MEDIUM ON END TIMING. HIGH THAT THUNDER WILL REMAIN TO THE SOUTH OF THE TERMINALS. * HIGH IN WIND DIR/SPEED. * HIGH IN CIGS DIPPING TO MVFR CONDS...BUT LOW ON HOW LONG ANY IFR LASTS. MEDIUM ON DURATION OF MVFR CIGS. KMD //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...CHANCE OF SHRA SLIGHT CHANCE OF TSRA. THURSDAY THROUGH SUNDAY...PERIODIC CHANCES FOR SHOWERS AND THUNDERSTORMS. BEACHLER && .MARINE... 250 AM CDT LOW PRESSURE PASSING OVER SOUTHERN LAKE MICHIGAN WILL CONTINUE OFF TO THE NORTHEAST THIS MORNING...ALLOWING A COLD FRONT TO CLEAR THE SOUTHERN TIP OF THE LAKE JUST AFTER DAYBREAK. WAVES WILL QUICKLY BUILD ON THE SOUTHERN HALF/THIRD OF THE LAKE AS THIS OCCURS...REACHING 7-8 FT ON THE INDIANA SHORELINE...MAYBE A TOUCH LOWER ON THE ILLINOIS SHORELINE. EXPANSIVE HIGH PRESSURE OVER THE UPPER MIDWEST WILL BUILD EAST ACROSS THE CENTRAL GREAT LAKES...BECOMING CENTERED OVER NORTHERN LAKE MICHIGAN WEDNESDAY. SEVERAL LOWS WILL CONTINUE TO PROGRESS SOUTH AND EAST OF THE LAKE THROUGH FRIDAY. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...BEACH HAZARDS STATEMENT...ILZ014...9 AM TUESDAY TO 4 AM WEDNESDAY. BEACH HAZARDS STATEMENT...ILZ006...9 AM TUESDAY TO 7 PM TUESDAY. IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...9 AM TUESDAY TO 4 AM WEDNESDAY. LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 7 PM TUESDAY. SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL 4 AM WEDNESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 230738 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 238 AM CDT SUN AUG 23 2015 .SHORT TERM... 232 PM CDT TONIGHT THROUGH SUNDAY... FOR THE REMAINDER OF THE AFTERNOON AND THROUGH TONIGHT...EXPECT BREEZY BUT GENERALLY QUIET CONDITIONS AS HIGH PRESSURE CENTERED OVER THE ERN GREAT LAKES VERY SLOWLY BUILDS TO THE EAST AND DEEPENING LOW PRESSURE OVER NWRN MN CONTINUES TO LIFT TO THE NORTHEAST AND A TRAILING COLD FRONT EXTENDS SOUTH TO THE TX PANHANDLE. TODAY WILL LIKELY BE THE WARMEST DAY FOR THE NEXT WEEK AS A MUCH COOLER AIRMASS FILTERS ACROSS THE REGION AFTER THE COLD FRONT PUSHES ACROSS THE REGION. AS OF 2PM THIS AFTERNOON...TEMPERATURES HAVE RISEN INTO THE UPPER 70S TO LOWER 80S AND MUCH OF THE REGION SHOULD SEE TEMPS HIT THE LOWER 80S. HOWEVER...WINDS TURNING SELY ALONG LAKE MICHIGAN HAS KEPT THE ILLINOIS LAKEFRONT MUCH COOLER WITH HIGHS TOPPING OUT IN THE LOWER TO MIDDLE 70S AND HAVE BEEN DROPPING THROUGH THE AFTERNOON. FOR SATURDAY NIGHT AND SUNDAY...MAIN CONCERN WILL FOCUS ON THE COLD FRONT APPROACHING THE REGION FROM THE WEST. THE VARIOUS MODELS ARE IN RELATIVELY GOOD AGREEMENT ON THE PROGRESSION AND TIMING OF THE FRONT...AND EXPECT IT TO CROSS THE MS RIVER INTO WRN IL BY THE PRE- DAWN HOURS AND THEN STEADILY MARCH ACROSS THE AREA THROUGH THE DAY. WHILE THERE ARE SOME MODEL DISCREPANCIES ON THE ASSOCIATED QPF FIELDS FROM THE MODELS...THERE IS GENERAL AGREEMENT ON A PERIOD OF SHOWERS TO ACCOMPANY THE FRONT. THERE IS SOME QUESTION AS TO HOW MUCH THUNDER MAY DEVELOP SINCE THE STRONGEST UPPER LEVEL FORCING WILL BE WELL TO THE NORTH AS THE ASSOCIATED UPPER LOW SHOULD BE IN SWRN ONTARIO BY THE TIME THAT THE FRONT REACHES THE AREA. ALSO...THE TIMING OF ONSET OF PCPN INTO THE CWA WILL BE AT A RELATIVELY UNFAVORABLE TIME AND THE FRONT SHOULD PUSH INTO NWRN INDIANA BY AROUND NOON. SO...WHILE THE HOURLY POP GRIDS MAY BE A BIT BROAD-BRUSHED...HAVE CONFINED ANY TS MENTION TO LIKELY OR CATEGORICAL POP AREAS INVOF THE FRONTAL BOUNDARY AND TO LOCATIONS GENERALLY NORTH OF I-80. WITH THE UPPER LOW SITTING OVER SWRN ONTARIO THROUGH THE DAY...PERSISTENT COLD ADVECTION WILL SET UP UNDER NWLY FLOW ALOFT...AND EXPECT THAT TEMPS SUNDAY WILL LIKELY PEAK BY MID DAY AND THEN REMAIN STEADY OR GRADUALLY DROP OFF THROUGH THE AFTERNOON. HIGHS FOR SUNDAY SHOULD BE IN THE MIDDLE TO UPPER 70S...WITH ONLY BENTON COUNTY HAVING A CHANCE TO HIT THE 80F MARK AS THAT AREA WILL BE THE LATEST TO SEE THE FROPA. KREIN && .LONG TERM... 232 PM CDT SUNDAY NIGHT THROUGH SATURDAY... THE MAIN TREND FOR THE LONGER TERM FORECAST PERIOD WILL BE FORE BELOW NORMAL TEMPERATURES WITH LITTLE OPPORTUNITY FOR ANY PCPN. THE LONGER RANGE GUIDANCE IS IN GOOD GENERAL AGREEMENT THROUGH THE LONG TERM FORECAST PERIOD AND GENERAL FORECAST CONFIDENCE IS HIGHER THAN AVERAGE. THE UPPER LEVEL PATTERN IS SETTING UP WITH INCREASING AMPLITUDE AND LITTLE PROGRESSION. THE MAIN UPPER LOW IS EXPECTED TO SLOWLY TRACK FROM SWRN ONTARIO SUNDAY NIGHT TO ERN QUEBEC BY WEDNESDAY NIGHT...BEFORE SLOWLY LIFTING TO THE NORTHEAST THROUGH QUEBEC WEDNESDAY NIGHT AND THURSDAY. BROAD UPPER TROUGHING WILL PERSIST OVER THE ERN CONUS AS UPPER RIDGING BUILDS OVER THE WRN CONUS WITH AXIS OF THE UPPER RIDGE REMAINING OVER THE ROCKIES THROUGH WEDNESDAY NIGHT. THIS WILL KEEP THE LOCAL AREA UNDER COLD ADVECTION THROUGH A DEEP LAYER OF THE ATMOSPHERE AND NWLY FLOW ALOFT. THERE IS ALSO SOME INDICATION OF WEAK SHORTWAVE RIDGING ACROSS THE UPPER MS VALLEY AND WRN GREAT LAKES. THIS WOULD HELP TO FOCUS THE TRACK OF ANY SHORTWAVE ENERGY DROPPING OUT OF CANADA IN THE NWLY FLOW ALOFT. SO...EXPECT DRY CONDITIONS FROM SUNDAY NIGHT THROUGH AT LEAST THURSDAY NIGHT. WITH LITTLE CHANGE TO THE LARGER SCALE PATTERN...THERE WILL ALSO BE LITTLE CHANGE TO THE TEMPERATURE TREND THROUGH THE PERIOD...WITH HIGHS REMAINING WELL BELOW NORMAL...IN THE LOWER TO MIDDLE 70S THROUGH THURSDAY. THE LONG RANGE GUIDANCE IS SUGGESTING THAT THE NEXT CHANCE FOR ANY PCPN WILL NOT BE UNTIL LATE NEXT WEEK. THE INTERESTING THIS IS THAT THE SHORTWAVE WHICH PROVIDE THE MAIN FORCING FOR ANY ACTIVITY IS CURRENTLY SOUTH OF THE ARIZONA/NEW MEXICO BORDER AS CAN BE SEEN IN THE LATEST SATELLITE IMAGERY OVER NRN OLD MEXICO. AND WHAT IS EVEN MORE INTERESTING...THE OPERATIONAL RUNS OF BOTH THE GFS AND ECMWF SIMILARLY INITIALIZE THIS SYSTEM AND ARE NOT ALL THAT DIFFERENT ON TRACKING IT WESTWARD THROUGH NRN MEXICO AND THEN TURNING NWD AS IT TRACKS AROUND THE PERIPHERY OF THE UPPER HIGH CENTERED OVER THE FOUR CORNERS AREA. THE GFS/ECMWF INDICATE THAT THIS FEATURE SHOULD HELP SUPPRESS THE NRN EXTENT OF THE UPPER RIDGE AS IT TURNS SOUTHEAST... AND DROPS THROUGH THE CNTRL PLAINS ON FRIDAY. WITH THE SUPPRESSION OF THE RIDGE...THERE WILL ALSO BE A BETTER OPPORTUNITY FOR NORTHERN STREAM ENERGY TO BEGIN TO TAKE A MORE SOUTHERLY TRACK THROUGH THE NRN PLAINS/UPPER MS VALLEY AND INTO THE WRN GREAT LAKES. SO...SHOULD THIS RATHER UNUSUAL SCENARIO PAN OUT...THERE SHOULD BE INCREASING CHANCES FOR PCPN AS WELL AS A RETURN TO MORE SEASONABLY NORMAL TEMPERATURES BY THE END OF THE LONG RANGE FORECAST PERIOD. KREIN && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * TWO-THREE HOUR PERIOD OF SCATTERED SHRA THIS MORNING WITH BRIEF MVFR LIKELY IN ANY SHRA. ISOLATED TSRA POSSIBLE. * WEST WINDS GUSTING AROUND 25 KT LATE THIS MORNING AND AFTERNOON. //DISCUSSION...UPDATED 06Z... THE AXIS OF SHOWERS WITH EMBEDDED STORMS WILL CONTINUE TO SHIFT EAST ACROSS THE MISSISSIPPI RIVER EARLY THIS MORNING WITH A LIKELY GENERAL WANING IN INTENSITY THROUGH DAYBREAK. AT LEAST SCATTERED SHOWERS ARE EXPECTED TO MAKE IT INTO NORTHERN ILLINOIS WITH POSSIBLY ISOLATED THUNDER GIVEN THE AMOUNT OF DYNAMIC FORCING COMPENSATING FOR DIMINISHING INSTABILITY. ANY TERMINAL SHOULD SEE THE AXIS OF SHOWERS PASS WITHIN TWO TO POSSIBLY THREE HOURS. PATCHES OF MVFR CIGS ARE POSSIBLE IN ADVANCE OF THE SHOWERS AND LIKELY UNDER ANY AREA OF SHOWERS THAT HOLD TOGETHER INTO THE REGION. THE COLD FRONT WILL MOVE EASTERLY RIGHT BEHIND THE SHOWERS AND TURN WINDS WESTERLY DURING THE LATE MORNING. SPEEDS WILL BECOME GUSTY WITH THE WIND SHIFT AND PERSIST THROUGH THE AFTERNOON. SOME CUMULUS IS ANTICIPATED DURING THE AFTERNOON BUT AT VFR HEIGHT. //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM-HIGH IN SHRA TIMING AND MEDIUM IN SHRA HOLDING TOGETHER TO ORD. LOW IN ANY TSRA OCCURRING. * HIGH IN WINDS. //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY AND TUESDAY...VFR. WEST WINDS...GUSTY ON MONDAY WEDNESDAY AND THURSDAY...VFR. LIGHT EASTERLY WINDS. FRIDAY...VFR. LIGHT WESTERLY WINDS. MTF/IZZI && .MARINE... 236 AM CDT A SOMEWHAT ACTIVE PERIOD OF THE LAKE EARLY THIS WEEK IS A SIGN OF THE BEGINNING OF A SEASON CHANGE AS WE ROUND OUT METEOROLOGICAL SUMMER. A DEEP LOW JUST NORTH OF INTERNATIONAL FALLS MINNESOTA EARLY THIS MORNING WILL INCH EASTWARD TODAY AND TONIGHT. AN ASSOCIATED COLD FRONT WILL MOVE EAST ACROSS THE LAKE EARLY THIS AFTERNOON WITH SOME SHOWER ACTIVITY. AHEAD OF THIS FRONT SOUTHERLY WINDS MAY BRIEFLY TOUCH GALE FORCE ACROSS THE FAR NORTH. BEHIND THE FRONT...WESTERLY WINDS WILL BE IN THE 25 KT TO 30 KT ARENA THIS AFTERNOON THROUGH MONDAY EVENING ACROSS MUCH OF THE NORTHERN AND CENTRAL PARTS OF THE LAKE. SMALL CRAFT ADVISORY CRITERIA WINDS WILL BE REACHED BY EARLY AFTERNOON ACROSS THE ILLINOIS AND INDIANA NEARSHORES...WITH WAVES BUILDING INTO TONIGHT ACROSS INDIANA SHORES AS WEST-NORTHWEST WINDS CONTINUE. THE WINDS ON MONDAY WILL BRING SMALL CRAFT CRITERIA WINDS AGAIN FOR BOTH NEARSHORES WITH EVEN HIGHER WAVES ALONG THE INDIANA SHORE. THE HIGHER WAVES WILL CONTINUE INTO TUESDAY. ONE OTHER ITEM TO NOTE IS A MARGINAL POSSIBILITY OF EARLY SEASON WATERSPOUTS ACROSS MAINLY NORTHERN AND WESTERN PARTS OF THE LAKE ON MONDAY AFTERNOON THROUGH TUESDAY. INDICES FOR INSTABILITY AND CONVECTIVE CLOUD DEPTHS ARE FORECASTED TO BE FAIRLY CLOSE TO THAT RANGE AND SOME GUIDANCE SHOWS A SUBTLE SURFACE TROUGH MOVING OVER THE LAKE SOMETIME MONDAY NIGHT INTO TUESDAY MORNING THAT COULD PROVIDE A FOCUS. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM SUNDAY TO 9 PM SUNDAY. SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM SUNDAY TO 7 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 232130 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 330 PM CST MON NOV 23 2015 .SHORT TERM... 204 PM CST THROUGH TUESDAY... SHORT TERM FOCUS IS ON POTENTIAL FOR FOG DEVELOPMENT AND TEMPERATURE TRENDS ASSOCIATED WITH FOG/OCCASIONAL CLOUDS. A SURFACE TROUGH HAS CLEARED THE AREA...ASSOCIATED WITH A FAST MOVING SHEARED OUT SHORTWAVE. BRIEF EARLIER REPORTS OF GRAUPEL/SNOW HAVE EXITED TO THE EAST THIS AFTERNOON. SKIES WILL CONTINUE TO CLEAR BEHIND THIS DISTURBANCE THROUGH THE AFTERNOON AND EVENING. EXPECT A QUICK DROP IN TEMPERATURES THIS EVENING IN THE CLEAR SKY REGIME HIGH PRESSURE SLIDES EAST. WITH ELEVATED DEWPOINTS AND WEAKENING WINDS WITH SOME MINOR SNOWMELT MOISTENING THE LOWER ATMOSPHERE...SEVERAL PIECES OF GUIDANCE SUGGEST FOG DEVELOPMENT OVERNIGHT. HAVE NOT HIT THINGS AS HARD AS SOME GUIDANCE INDICATES...AS THERE ARE A FEW AREAS OF CLOUDS TO MONITOR TONIGHT INTO TUESDAY THAT MAY LIMIT THE EXTENT...THUS THE PATCHY MENTION. THE FIRST AREA IN THE PLAINS ARE HIGHER CLOUDS THAT WILL DRIFT THROUGH OVERNIGHT INTO TUESDAY ASSOCIATED WITH A DAMPENING SHORTWAVE IN WESTERLY FLOW ALOFT. THERE IS ALSO AN AREA OF LOWER CLOUDS OVER MN AND N CENTRAL WI THAT MAY DRIFT CLOSE TO NORTHERN ILLINOIS AS WELL...BUT WITH THE RIDGE AXIS BUILDING IN...THERE IS THE TENDENCY FOR THESE CLOUDS TO SLOW THEIR PROGRESSION SOUTHWARD. ON TUESDAY...AFTER THE HIGH CLOUDS SHIFT EAST...EXPECT A SEASONABLY COOL DAY AS THE THERMAL RIDGE BUILDS OVERHEAD. EXPECT CLEARING SKIES AND READINGS IN THE MID TO UPPER 30S IN THE SNOWPACK...WITH 40S EXPECTED SOUTHWEST WHERE SNOWPACK IS THIN/MELTING AND UPPER 30S TO LOW 40S WERE ACHIEVED TODAY. SE WINDS INCREASE IN THE AFTERNOON. KMD && .LONG TERM... 326 PM CST TUESDAY NIGHT THROUGH MONDAY... THE HOLIDAY STILL LOOKS LIKE A RAINY AND/OR DRIZZLY ONE FOR MOST OF THE FORECAST AREA. BEING AT THREE TO FOUR DAYS OUT FROM THE EVENT THERE OF COURSE REMAINS DEGREES OF UNCERTAINTY...BUT FOR THIS EVENT IT APPEARS TO BE MAINLY TIMING OF START OF THE MODERATE RAIN AND THUS OVERALL DURATION...WHICH IMPACTS RAINFALL AMOUNTS. ITS PROBABLE A PERIOD OF FOG AND DRIZZLE WILL PRECEDE THE WIDESPREAD RAIN AND JUST HOW EARLY THAT ARRIVES ON THE MAIN TRAVEL DAY OF WEDNESDAY...OR IF IT ARRIVES YET BY THAT TIME...IS STILL QUITE UNCERTAIN. THE UPPER LEVEL PATTERN WILL BECOME MORE SOUTHWESTERLY ALOFT BY TUESDAY NIGHT AND MORE SO WEDNESDAY AS A POSITIVELY TILTED TROUGH DEFINES ITSELF FROM SOUTHERN CANADA THROUGH THE WESTERN PART OF THE UNITED STATES. WHILE MOIST ADVECTION WILL NOT BE PARTICULARLY STRONG YET TUESDAY NIGHT...THERE WILL BE A SIMILAR CONCERN FOR PATCHES OF FOG/STRATUS AS THERE IS TONIGHT AS BOUNDARY LAYER MOISTURE INCREASES AIDED BY A DAY OF GRADUALLY MORE MELT. WHILE WINDS WILL BE ON THE INCREASE...WHEN IT COMES TO ADVECTION TYPE FOG POTENTIAL...WIND SPEEDS MATTER LESS. LOW-LEVEL ISENTROPIC SURFACES SHOW MOISTURE RAPIDLY INCREASING FROM THE WEST WEDNESDAY AND THEN WEDNESDAY NIGHT WHICH WOULD INDICATE STRATUS/FOG AND LIKELY AREAS OF DRIZZLE AT SOME POINT. CONFIDENCE ON THIS OCCURRING IS FAIRLY HIGH GIVEN THE PATTERN BUT AS FOR WHAT TIME ON WEDNESDAY OR WEDNESDAY NIGHT...THAT REMAINS LOW. THE FOG POTENTIAL IS EVEN MORE CHALLENGING TO ASSESS AT THIS POINTS. CURRENT DEW POINTS ABOVE FREEZING ARE ALREADY UP TO CENTRAL MISSOURI AND AS THEY EXPAND RAPIDLY INTO THE AREA ON WEDNESDAY...SNOW MELT WILL INCREASE AND SHOULD REALLY TAKE OFF BY LATER WEDNESDAY AFTERNOON AND NIGHT WHEN DEW POINTS OF 40 PLUS ARE PROJECTED TO ADVECT INTO AND REMAIN OVER THE AREA. FOG...SOME OF IT POSSIBLY DENSE...WOULD BE LIKELY OVER AND NORTH OF SOME OF THE DEEPER REMAINING SNOW COVER. FOR US THAT IS MAINLY NORTHERN ILLINOIS PART NORTH OF I-88...BUT WITH THE COOLER DAMP GROUND ELSEWHERE WE MAY END UP SEEING IT AREA WIDE. AS ANOMALOUSLY HIGH MOISTURE VALUES OF THE 95TH PLUS PERCENTILE FOR LATE NOVEMBER STREAM NORTH AHEAD OF THE TROUGH...THE NORTHERN STREAM JET REMAINS PROGRESSIVE AND WILL PUSH THE TROUGH TOWARD AND THROUGH THE AREA ON FRIDAY. MODELS HAVE TRENDED STRONGER WITH THE SURFACE HIGH BEHIND THE SYSTEM AND THUS SLIGHTLY MORE PROGRESSIVE WITH THE DEVELOPING COLD FRONT ON FRIDAY. THE 12Z EC REMAINS A TAD SLOWER BECAUSE IT HAS A MORE WELL-DEFINED WAVE DEVELOP ALONG THE FRONT...AND HAVE LEANED THE FORECAST CLOSER TO THAT. THE KEY WITH THAT IS THIS SOLUTION IS THAT MODERATE RAIN WOULD LIKELY NOT PUSH INTO THE EASTERN FORECAST AREA...EAST OF I-55...UNTIL THANKSGIVING NIGHT. DRIZZLE MAY STILL OCCUR DURING THE DAY IN THAT AREA. THE LONGER RAIN POTENTIAL AND HIGHER QPF IS STILL MOST FAVORED OVER NORTH CENTRAL AND NORTHEAST ILLINOIS...WHICH OF COURSE IS THE AREA WITH THE HIGHER SNOW COVER. THE CURRENT FORECAST OF QPF IN OUR NORTHWEST AREA IS AROUND AN INCH AND A HALF...AND THAT IS NOT TO THE POINT WHERE WE WOULD EXPECT MUCH FOR NON-RIVER FLOODING IMPACTS. THIS IS BECAUSE THE MELT SHOULD PERCOLATE INTO THE GROUND GIVEN THE FREEZING LAYER IN THE LAYER IS VERY SHALLOW. SEE THE HYDROLOGY DISCUSSION BELOW FOR MORE ON THE DETAILS OF RIVER IMPACTS. DESPITE THE CLOUDS AND RAIN...LOW-LEVEL WARM ADVECTION WILL BRING A MILD THANKSGIVING WITH HIGHS CLOSE TO 50 NORTH AND SEVERAL DEGREES ABOVE 50 PRESENTLY FAVORED ACROSS THE THEN NEAR SNOW COVER-FREE SOUTH. ON THE BACKSIDE OF THE SYSTEM...COLD ADVECTION WILL LIKELY LEAD TO STEADY OR FALLING TEMPERATURES ON FRIDAY. THIS COULD BRING A LIGHT MIX OR LIGHT SNOW BEFORE THE SYSTEM ENDS. THERE IS THE POTENTIAL FOR SOME LAKE EFFECT SNOW SHOWERS INTO FAR NORTHWEST INDIANA FRIDAY NIGHT...BUT OVERALL THE PARAMETERS ARE NOT INDICATED TO BE GREAT WITH SHALLOW INVERSION HEIGHTS YIELDING MARGINAL CLOUD DEPTHS THAT DO NOT PERSIST LONG. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * MVFR VIS IN BR LATE TONIGHT THROUGH EARLY TOMORROW MORNING. KREIN //DISCUSSION...UPDATED 18Z... WITH HIGH PRESSURE SETTLING TOWARD THE GULF COAST AND WEAK LOW PRESSURE MOVING ACROSS THE UPPER GREAT LAKES...WINDS HAVE BECM WLY ACROSS THE AREA. WITH A WEAK PRESSURE GRADIENT AND A PATCH OF MID CLOUD ACROSS THE REGION...THERE IS LITTLE IN THE WAY OF DEEP LAYER MIXING...SO EXPECT THAT WLY WINDS WILL PERSIST ACROSS THE REGION WITH SPEEDS BELOW 10KT. PER LATEST SATELLITE TRENDS...THE PATCH OF MID CLOUD SHOULD MOVE EAST OF THE TERMINALS THIS AFTERNOON... LEAVING MOSTLY CLEAR SKIES UNTIL EARLY THIS EVENING WHEN A MID LEVEL IMPULSE BRINGS INCREASING MID AND HIGH CLOUD. THE GREATEST CONCERN...AND THE AREA OF GREATEST UNCERTAINTY WILL BE CIG/VIS TRENDS OVERNIGHT. LATEST GUIDANCE SUGGESTS THAT THERE IS A GREATER CHANCE FOR LESSER CLOUD COVER AND A GREATER CHANCE FOR LOWER VIS DEVELOPMENT AS WARMER AIR ADVECTS ACROSS THE FRESH SNOW COVERING THE GROUND. HAVE TRENDED A BIT CONSERVATIVE FOR NOW...WITH MVFR VIS FOR LATE TONIGHT AND INTO EARLY TOMORROW MORNING. HOWEVER...IF THERE IS MORE RADIATIONAL COOLING BEFORE THE WARM ADVECTION SETS UP...THERE IS CHANCE THAT VIS COULD DROP LOWER. KREIN //ORD AND MDW CONFIDENCE...UPDATED 20Z... * MEDIUM CONFIDENCE IN CIG/VIS TRENDS THROUGH THIS EVENING. * LOW TO MEDIUM CONFIDENCE IN CIG/VIS TRENDS OVERNIGHT. * HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS. KREIN //OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z... TUESDAY NIGHT...MVFR/IFR STRATUS OR FOG IS POSSIBLE. SOUTHEAST WINDS. WEDNESDAY...CHC RAIN AND FOG OVERNIGHT. MVFR. SOUTH WINDS WITH GUSTS UP TO 20 KT. THURSDAY...RAIN. IFR FOG LIKELY...LIFR PSBL. SOUTH WINDS GUSTING UP TO 25 KT. FRIDAY...RAIN BCMG RASN DURING THE DAY. DRY OVERNIGHT. IFR/LIFR PSBL EARLY BCMG MVFR. NORTH WINDS GUSTING TO 25 KT. SATURDAY...VFR. NORTH WINDS BCMG WEST OVERNIGHT. SUNDAY...SCHC RASN OVERNIGHT. WEST WINDS BCMG EAST. JEE && .MARINE... 212 PM CST HIGH PRESSURE WILL SPREAD OVER THE LAKE TONIGHT...RESULTING IN A CONTINUED DECREASE IN WAVES. WINDS SHIFT TO SOUTH-SOUTHEAST LATER TUESDAY IN RESPONSE TO A LOW PRESSURE TROUGH IN THE PLAINS. EVENTUALLY A SURFACE LOW WILL FORM OVER SOUTHERN ONTARIO THAT WILL SHIFT WINDS SOUTHERLY AND LIFT A WARM FRONT OVER THE LAKE. WINDS MAY APPROACH 30 KT DURING THIS TIME. ON THURSDAY ANOTHER SURFACE TROUGH WILL ORGANIZE IN THE PLAINS AND EXTEND TO THE NORTHERN TIP OF LAKE MICHIGAN. MEANWHILE STRONG HIGH PRESSURE WILL BUILD INTO THE UPPER MIDWEST. THESE FEATURES WILL LEAD TO A STRONG COLD FRONT MOVING SOUTHWARD ACROSS THE LAKE ON FRIDAY WITH A DRAMATIC SHIFT TO AT LEAST INITIALLY GUSTY NORTHERLY WINDS...GENERALLY AROUND 30 KT THOUGH POSSIBLY A TAD HIGHER RIGHT WITH THE FRONT. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240010 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 710 PM CDT FRI OCT 23 2015 .SHORT TERM... TONIGHT AND SATURDAY... 247 PM...FORECAST CONCERNS INCLUDE PRECIP DURATION TONIGHT/ SATURDAY MORNING...SLIGHT CHANCE OF THUNDER THEN STRONG/GUSTY WINDS SATURDAY. LOW PRESSURE OVER THE CENTRAL PLAINS WILL MOVE NORTHEAST TO THE NORTHERN GREAT LAKES REGION BY SATURDAY AFTERNOON. FIRST UPPER WAVE ROTATING NORTHEAST WILL MOVE ACROSS THE AREA LATE THIS AFTERNOON THRU THIS EVENING WITH PERIODS OF SHOWERS. CURRENTLY NO THUNDER WITH ACTIVITY MOVING INTO NORTHWEST IL. INSTABILITY LOOKS MARGINAL FOR THUNDER BUT MAINTAINED SLIGHT CHANCE MENTION. AS THIS FIRST WAVE DEPARTS LATE THIS EVENING OR EARLY SATURDAY MORNING. PRECIP COVERAGE SHOULD DECREASE BUT WITH LOW LEVELS SATURATED BY THAT TIME...ITS POSSIBLE PRECIP MAY TRANSITION TO DRIZZLE. HOWEVER... MAINTAINED JUST SHOWER MENTION FOR NOW. AS THE MAIN COLD FRONT MOVES ACROSS THE AREA SATURDAY MORNING...THERE WILL LIKELY BE ANOTHER BAND OF AT LEAST SCATTERED SHOWERS. ALSO POSSIBLE THERE COULD BE ENOUGH INSTABILITY FOR ISOLATED THUNDER DURING THIS TIME PERIOD. THE PASSAGE OF THE FRONT WILL THEN END THE CHANCE OF PRECIP. WINDS WILL TURN MORE SOUTHERLY THIS EVENING AND LIKELY BE GUSTY AT TIMES...BUT WINDS WILL SHIFT WESTERLY BEHIND THE COLD FRONT SATURDAY MORNING AND QUICKLY INCREASE DURING THE LATE MORNING. STILL SOME DIFFERENCES BETWEEN THE MODELS...BUT FORECAST SOUNDINGS WOULD SUGGEST THE POTENTIAL FOR GUSTS INTO THE 30-35 MPH RANGE THRU MUCH OF THE AFTERNOON...BEFORE WINDS DIMINISH QUICKLY WITH SUNSET. HIGH TEMPS HAVE SO FAR ONLY REACH THE UPPER 50S/LOWER 60S OVER MUCH OF THE NORTHERN CWA TODAY...BUT THESE MAY ACTUALLY GO UP A FEW DEGREES LATER THIS EVENING/OVERNIGHT AS WARMER AND MORE MOIST AIR ADVECTS INTO THE AREA. TEMPS MAY QUICKLY RISE AHEAD OF THE FRONT SATURDAY MORNING...THEN STEADY TO EVENTUALLY SLOWLY FALLING TEMPS ARE EXPECTED SATURDAY AFTERNOON. CMS && .LONG TERM... 310 PM CDT SATURDAY NIGHT THROUGH FRIDAY... RELATIVELY QUIET WEATHER IS EXPECTED FOR THE BEGINNING OF THE LONGER TERM FORECAST PERIOD. FOLLOWING THE PASSAGE OF THE COLD FRONT EARLIER SATURDAY...HIGH PRESSURE WILL BUILD ACROSS THE REGION AND REMAIN THE DOMINANT FEATURE INTO EARLY NEXT WEEK. EVEN FOLLOWING THE PASSAGE OF THE COLD FRONT...TEMPERATURES THROUGH EARLY NEXT WEEK SHOULD BE NEAR OR A LITTLE ABOVE NORMAL...WITH HIGHS IN THE UPPER 50S TO LOWER 60S AND LOWS IN THE UPPER 30S TO LOWER 40S...EXCEPT THE URBANIZED AREAS OF THE CHICAGO METRO AREA WHICH WILL REMAIN IN THE MIDDLE TO UPPER 40S. THE MAIN CONCERN FOR THE EXTENDED FORECAST PERIOD WILL FOCUS ON WHAT HAPPENS WITH THE REMNANTS OF HURRICANE PATRICIA. THE LONGER RANGE MODELS ARE IN GENERAL AGREEMENT ON THE TREND OF THE PROGRESSION OF THE SYSTEM...LIFTING THE REMNANTS OF THE TROPICAL SYSTEM INTO NERN MEXICO...THOUGH THE SYSTEM BECOMES MORE DIFFUSE AS IT CROSSES THE MOUNTAINOUS REGIONS OF NRN MEXICO...AND THUS...THE LOCATION OF THE REMNANT UPPER LEVEL VORT MAX BECOMES LESS CERTAIN AS IT ENTERS A REGION WHERE IT CAN BEGIN TO INTERACT WITH THE MID-LATITUDE FLOW PATTERN. HOWEVER...THE GENERAL IDEA IS THAT SOME REMNANTS OF THE TROPICAL SYSTEM WILL PHASE WITH A SRN STREAM SHORTWAVE TRACKING THROUGH TX AND STRENGTHEN OVER THE NWRN GULF COAST REGION MONDAY. THE GENERAL TREND OF THE LONGER RANGE GUIDANCE IS FOR THE RESULTANT UPPER LOW TO REMAIN OVER THE NWRN GULF COAST UNTIL THE NEXT LONGWAVE TROUGH MOVES OUT OF THE ROCKIES...LIFTING THE SYSTEM NEWD BY EARLY TUESDAY. BEYOND TUESDAY...THE FATE OF THE TROPICAL SYSTEM REMAIN UNCERTAIN. THE GFS AND THE ECMWF...WHILE EXHIBITING TIMING AND AMPLITUDE DIFFERENCES IN THE UPPER LEVEL FLOW PATTER...GENERALLY AGREE ON EMPHASIZING NRN STREAM ENERGY DIGGING OUT OF THE NRN/CNTRL ROCKIES AND QUICKLY SHUNTING THE TROPICAL SYSTEM QUICKLY TO THE EAST. THIS SCENARIO WOULD SUGGEST THAT THE TROPICAL SYSTEM WOULD HAVE LESS OF AN IMPACT ON THE LOCAL AREA...AND THAT MUCH OF THE PCPN EXPECTED FOR MIDWEEK WILL BE MORE ASSOCIATED WITH THE NRN STREAM SHORTWAVE ENERGY WITH LESS OF AN IMPACT FROM THE TROPICAL SYSTEM. HOWEVER...GIVEN THE GENERAL CONSENSUS OF THE LONGER RANGE GUIDANCE ON THE NRN STREAM PATTERN...FEEL CONFIDENT ENOUGH TO MAINTAIN THE HIGHER POPS FOR TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...BUT QPF AMOUNTS ARE STILL A BIG QUESTION MARK. KREIN && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 00Z... * STEADY SHOWERS END THIS EVENING...MVFR VSBY AND BRIEF IFR VSBY POSSIBLE * CIGS BUILDING DOWN TO MVFR AND PROBABLY IFR TONIGHT * GUSTY WEST WINDS SATURDAY IZZI //DISCUSSION...UPDATED 00Z... UPPER LEVEL DISTURBANCE BRINGING RAIN TO THE AREA NOW WITH STEADIER RAIN LIKELY TO END BY MID EVENING. RAIN WILL MOISTEN THE ATMOSPHERE AND HIGHER DEWPOINTS WILL SURGE IN TONIGHT WHICH SHOULD ALLOW FOR IFR CIGS TO DEVELOP AND PROBABLY SOME DRIZZLE AS WELL. CONFIDENCE IS LOW OVERNIGHT IN CIGS/VSBY TRENDS...WITH SOME POTENTIAL FOR IFR CIGS TO PERSIST OR EVEN BUILD DOWN. CONVERSELY...VFR CIGS UPSTREAM COULD SURGE IN BEHIND THE WARM FRONT AND CLEAR THINGS OUT. REALLY LOW CONFIDENCE IN HOW THINGS WILL PLAY OUT...SO MADE NO CHANGES TO GOING TAFS FOR NOW AND WILL CONTINUE WITH IFR FORECAST OVERNIGHT INTO SATURDAY MORNING. COLD FRONT WILL MOVE THROUGH SATURDAY MORNING WITH QUICKLY IMPROVING CIGS BEHIND THE FRONT BY MID-LATE MORNING SATURDAY. WINDS WILL BECOME SOUTHWEST AND GUSTY BEHIND THE FRONT GRADUALLY VEERING TO WEST THEN WEST-NORTHWEST SATURDAY AFTERNOON WITH OCNL GUSTS UP TO 30KT POSSIBLE. IZZI //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH CONFIDENCE IN PRECIP TRENDS * LOW CONFIDENCE IN CIGS/VSBY TONIGHT INTO SATURDAY MORNING * MEDIUM-HIGH CONFIDENCE IN WINDS IZZI //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY AND MONDAY...VFR. TUESDAY AND WEDNESDAY...CHANCE OF RAIN/IFR. THURSDAY...VFR/MVFR PROBABLE. IZZI && .MARINE... 310 PM CDT RELATIVELY ACTIVE WEATHER EXPECTED INTO SATURDAY NIGHT. LOW PRESSURE OVER THE ERN DAKOTAS WILL LIFT NORTHEAST THROUGH WISCONSIN AND ACROSS THE UPPER PENINSULA OF MICHIGAN TOMORROW AFTERNOON WHILE DEEPENING AND DRAGGING A COLD FRONT ACROSS THE LAKE. WINDS WILL STRENGTHEN TO ARND 30KT AND BECOME SLY AHEAD OF THE FRONT...WITH SOME GALE FORCE GUSTS POSSIBLE TONIGHT OVER THE NRN PORTIONS OF THE LAKE IN A ZONE OF STRONG PRESSURE FALLS AHEAD OF THE APPROACHING LOW WHILE IT DEEPENS. WINDS SHOULD SHIFT TO WLY AND THEN NWLY BEHIND THE FRONT. AGAIN...SOME NWLY GALE FORCE GUSTS WILL BE POSSIBLE SATURDAY EVENING IN A ZONE OF STRONG PRESSURE RISES AS THE LOW LIFTS OFF TO THE NORTHEAST AND HIGH PRESSURE BUILDS IN FROM THE WEST. CONDITIONS WILL QUIET DOWN SUNDAY AND INTO EARLY NEXT WEEK AS HIGH PRESSURE BUILDS ACROSS THE LAKES. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 7 PM SATURDAY. SMALL CRAFT ADVISORY...LMZ742-LMZ743-LMZ744-LMZ745...7 AM SATURDAY TO 4 AM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240318 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 918 PM CST MON NOV 23 2015 .SHORT TERM... 204 PM CST THROUGH TUESDAY... SHORT TERM FOCUS IS ON POTENTIAL FOR FOG DEVELOPMENT AND TEMPERATURE TRENDS ASSOCIATED WITH FOG/OCCASIONAL CLOUDS. A SURFACE TROUGH HAS CLEARED THE AREA...ASSOCIATED WITH A FAST MOVING SHEARED OUT SHORTWAVE. BRIEF EARLIER REPORTS OF GRAUPEL/SNOW HAVE EXITED TO THE EAST THIS AFTERNOON. SKIES WILL CONTINUE TO CLEAR BEHIND THIS DISTURBANCE THROUGH THE AFTERNOON AND EVENING. EXPECT A QUICK DROP IN TEMPERATURES THIS EVENING IN THE CLEAR SKY REGIME HIGH PRESSURE SLIDES EAST. WITH ELEVATED DEWPOINTS AND WEAKENING WINDS WITH SOME MINOR SNOWMELT MOISTENING THE LOWER ATMOSPHERE...SEVERAL PIECES OF GUIDANCE SUGGEST FOG DEVELOPMENT OVERNIGHT. HAVE NOT HIT THINGS AS HARD AS SOME GUIDANCE INDICATES...AS THERE ARE A FEW AREAS OF CLOUDS TO MONITOR TONIGHT INTO TUESDAY THAT MAY LIMIT THE EXTENT...THUS THE PATCHY MENTION. THE FIRST AREA IN THE PLAINS ARE HIGHER CLOUDS THAT WILL DRIFT THROUGH OVERNIGHT INTO TUESDAY ASSOCIATED WITH A DAMPENING SHORTWAVE IN WESTERLY FLOW ALOFT. THERE IS ALSO AN AREA OF LOWER CLOUDS OVER MN AND N CENTRAL WI THAT MAY DRIFT CLOSE TO NORTHERN ILLINOIS AS WELL...BUT WITH THE RIDGE AXIS BUILDING IN...THERE IS THE TENDENCY FOR THESE CLOUDS TO SLOW THEIR PROGRESSION SOUTHWARD. ON TUESDAY...AFTER THE HIGH CLOUDS SHIFT EAST...EXPECT A SEASONABLY COOL DAY AS THE THERMAL RIDGE BUILDS OVERHEAD. EXPECT CLEARING SKIES AND READINGS IN THE MID TO UPPER 30S IN THE SNOWPACK...WITH 40S EXPECTED SOUTHWEST WHERE SNOWPACK IS THIN/MELTING AND UPPER 30S TO LOW 40S WERE ACHIEVED TODAY. SE WINDS INCREASE IN THE AFTERNOON. KMD && .LONG TERM... 326 PM CST TUESDAY NIGHT THROUGH MONDAY... THE HOLIDAY STILL LOOKS LIKE A RAINY AND/OR DRIZZLY ONE FOR MOST OF THE FORECAST AREA. BEING AT THREE TO FOUR DAYS OUT FROM THE EVENT THERE OF COURSE REMAINS DEGREES OF UNCERTAINTY...BUT FOR THIS EVENT IT APPEARS TO BE MAINLY TIMING OF START OF THE MODERATE RAIN AND THUS OVERALL DURATION...WHICH IMPACTS RAINFALL AMOUNTS. ITS PROBABLE A PERIOD OF FOG AND DRIZZLE WILL PRECEDE THE WIDESPREAD RAIN AND JUST HOW EARLY THAT ARRIVES ON THE MAIN TRAVEL DAY OF WEDNESDAY...OR IF IT ARRIVES YET BY THAT TIME...IS STILL QUITE UNCERTAIN. THE UPPER LEVEL PATTERN WILL BECOME MORE SOUTHWESTERLY ALOFT BY TUESDAY NIGHT AND MORE SO WEDNESDAY AS A POSITIVELY TILTED TROUGH DEFINES ITSELF FROM SOUTHERN CANADA THROUGH THE WESTERN PART OF THE UNITED STATES. WHILE MOIST ADVECTION WILL NOT BE PARTICULARLY STRONG YET TUESDAY NIGHT...THERE WILL BE A SIMILAR CONCERN FOR PATCHES OF FOG/STRATUS AS THERE IS TONIGHT AS BOUNDARY LAYER MOISTURE INCREASES AIDED BY A DAY OF GRADUALLY MORE MELT. WHILE WINDS WILL BE ON THE INCREASE...WHEN IT COMES TO ADVECTION TYPE FOG POTENTIAL...WIND SPEEDS MATTER LESS. LOW-LEVEL ISENTROPIC SURFACES SHOW MOISTURE RAPIDLY INCREASING FROM THE WEST WEDNESDAY AND THEN WEDNESDAY NIGHT WHICH WOULD INDICATE STRATUS/FOG AND LIKELY AREAS OF DRIZZLE AT SOME POINT. CONFIDENCE ON THIS OCCURRING IS FAIRLY HIGH GIVEN THE PATTERN BUT AS FOR WHAT TIME ON WEDNESDAY OR WEDNESDAY NIGHT...THAT REMAINS LOW. THE FOG POTENTIAL IS EVEN MORE CHALLENGING TO ASSESS AT THIS POINTS. CURRENT DEW POINTS ABOVE FREEZING ARE ALREADY UP TO CENTRAL MISSOURI AND AS THEY EXPAND RAPIDLY INTO THE AREA ON WEDNESDAY...SNOW MELT WILL INCREASE AND SHOULD REALLY TAKE OFF BY LATER WEDNESDAY AFTERNOON AND NIGHT WHEN DEW POINTS OF 40 PLUS ARE PROJECTED TO ADVECT INTO AND REMAIN OVER THE AREA. FOG...SOME OF IT POSSIBLY DENSE...WOULD BE LIKELY OVER AND NORTH OF SOME OF THE DEEPER REMAINING SNOW COVER. FOR US THAT IS MAINLY NORTHERN ILLINOIS PART NORTH OF I-88...BUT WITH THE COOLER DAMP GROUND ELSEWHERE WE MAY END UP SEEING IT AREA WIDE. AS ANOMALOUSLY HIGH MOISTURE VALUES OF THE 95TH PLUS PERCENTILE FOR LATE NOVEMBER STREAM NORTH AHEAD OF THE TROUGH...THE NORTHERN STREAM JET REMAINS PROGRESSIVE AND WILL PUSH THE TROUGH TOWARD AND THROUGH THE AREA ON FRIDAY. MODELS HAVE TRENDED STRONGER WITH THE SURFACE HIGH BEHIND THE SYSTEM AND THUS SLIGHTLY MORE PROGRESSIVE WITH THE DEVELOPING COLD FRONT ON FRIDAY. THE 12Z EC REMAINS A TAD SLOWER BECAUSE IT HAS A MORE WELL-DEFINED WAVE DEVELOP ALONG THE FRONT...AND HAVE LEANED THE FORECAST CLOSER TO THAT. THE KEY WITH THAT IS THIS SOLUTION IS THAT MODERATE RAIN WOULD LIKELY NOT PUSH INTO THE EASTERN FORECAST AREA...EAST OF I-55...UNTIL THANKSGIVING NIGHT. DRIZZLE MAY STILL OCCUR DURING THE DAY IN THAT AREA. THE LONGER RAIN POTENTIAL AND HIGHER QPF IS STILL MOST FAVORED OVER NORTH CENTRAL AND NORTHEAST ILLINOIS...WHICH OF COURSE IS THE AREA WITH THE HIGHER SNOW COVER. THE CURRENT FORECAST OF QPF IN OUR NORTHWEST AREA IS AROUND AN INCH AND A HALF...AND THAT IS NOT TO THE POINT WHERE WE WOULD EXPECT MUCH FOR NON-RIVER FLOODING IMPACTS. THIS IS BECAUSE THE MELT SHOULD PERCOLATE INTO THE GROUND GIVEN THE FREEZING LAYER IN THE LAYER IS VERY SHALLOW. SEE THE HYDROLOGY DISCUSSION BELOW FOR MORE ON THE DETAILS OF RIVER IMPACTS. DESPITE THE CLOUDS AND RAIN...LOW-LEVEL WARM ADVECTION WILL BRING A MILD THANKSGIVING WITH HIGHS CLOSE TO 50 NORTH AND SEVERAL DEGREES ABOVE 50 PRESENTLY FAVORED ACROSS THE THEN NEAR SNOW COVER-FREE SOUTH. ON THE BACKSIDE OF THE SYSTEM...COLD ADVECTION WILL LIKELY LEAD TO STEADY OR FALLING TEMPERATURES ON FRIDAY. THIS COULD BRING A LIGHT MIX OR LIGHT SNOW BEFORE THE SYSTEM ENDS. THERE IS THE POTENTIAL FOR SOME LAKE EFFECT SNOW SHOWERS INTO FAR NORTHWEST INDIANA FRIDAY NIGHT...BUT OVERALL THE PARAMETERS ARE NOT INDICATED TO BE GREAT WITH SHALLOW INVERSION HEIGHTS YIELDING MARGINAL CLOUD DEPTHS THAT DO NOT PERSIST LONG. MTF && .HYDROLOGY... 340 PM CST A RAIN ON SNOW MELT SCENARIO IS SHAPING UP OVER THE REGION WEDNESDAY NIGHT THROUGH EARLY FRIDAY. OBSERVERS ON MONDAY MORNING RECORDED SNOW WATER EQUIVALENT VALUES OF MAINLY 0.9 TO 1.3 ACROSS FAR NORTHERN ILLINOIS WITHIN THE DEEPEST SNOW COVER. WEATHER PARAMETERS FAVORABLE FOR RAPID SNOW MELT ARE SET TO MOVE ACROSS THE REGION LATER WEDNESDAY WITH RAIN FURTHER SPEEDING THAT UP ON THANKSGIVING. AMOUNTS OF OVER AN INCH ARE LIKELY ACROSS ESPECIALLY NORTHERN ILLINOIS...AND IT IS NOT IMPOSSIBLE TO HAVE TWO INCH AMOUNTS GIVEN THE PARAMETERS. THE FROZEN SOIL DEPTH IS VERY SHALLOW AND WOULD LEAN TOWARD THAT NOT REALLY IMPACTING PERCOLATION OF THE RAIN/MELT. WITH STREAMFLOW VALUES RUNNING HIGHER THAN NORMAL FOR SOME STREAMS AND RIVERS THANKS TO THE WET PAST FOUR WEEKS...THERE IS CONCERN FOR SOME STREAMS TO POTENTIALLY RISE INTO FLOOD STAGE. HAVE CONTINUED ESF AT THIS TIME WITH DETAILS IN SPECIFIC RAINFALL AMOUNTS AND TIMING TO BE REFINED AS THE EVENT APPROACHES. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 03Z... * HIGH POTENTIAL FOR FOG TO PRODUCE MVFR VIS LATE TONIGHT AND TUESDAY MORNING...LOCAL IFR OR EVEN LIFR CONDITIONS LIKELY MAINLY WEST OF ORD/MDW. RATZER //DISCUSSION...UPDATED 03Z... FOG HAS DEVELOPED AT KRFD IN THE PAST HOUR...WITH IFR VSBY OF 2SM AT 03Z. FOG MOST LIKELY TO FORM/THICKEN WHERE WINDS HAVE GONE CALM AND TEMPS HAVE QUICKLY TANKED ACROSS NORTH CENTRAL IL. HAVE AMENDED RFD TAF TO INCLUDE TEMPO LIFR VSBY LATE TONIGHT/EARLY TUESDAY...AND WILL CONTINUE TO MONITOR TRENDS FARTHER EAST FOR THE NEED TO LOWER CHI TERMINALS AS WELL. RATZER PREVIOUS DISCUSSION FROM 00Z... LOW PRESSURE PASSING THROUGH THE NORTHERN GREAT LAKES REGION WAS TRAILING A WEAK PACIFIC COLD FRONTAL TROUGH ACROSS THE TERMINALS LATE THIS AFTERNOON...WITH A SHIFT TO LIGHT WEST WINDS AND A SLIGHT INCREASE IN LOW LEVEL MOISTURE. WEAK SURFACE HIGH PRESSURE RIDGE WILL SPREAD EAST ACROSS THE AREA LATE TONIGHT AND EARLY TUESDAY...ALLOWING WINDS TO BECOME LIGHT/VARIABLE EARLY TUESDAY...THEN EAST-SOUTHEAST LATER IN THE DAY AND GRADUALLY INCREASING TO 6-10 KT DURING THE AFTERNOON/EVENING. SKIES HAVE GENERALLY CLEARED ACROSS THE IMMEDIATE FORECAST AREA AT THIS TIME...THOUGH PATCHY MID-HIGH CLOUDS WERE NOTED UPSTREAM AND WILL SPREAD ACROSS THE AREA OVERNIGHT IN RESPONSE TO AN UPPER JET STREAK AND DEVELOPING WEAK MID-LEVEL WARM ADVECTION. PRIMARY CONCERN HOWEVER IS FOR FOG DEVELOPMENT AS WINDS LIGHTEN IN VICINITY OF THE APPROACHING SURFACE RIDGE COMBINED WITH SHALLOW LOW LEVEL MOISTURE. FORECAST SOUNDINGS INDICATE LIMITED DEPTH TO SATURATED LAYER...WITH WRF-BASED GUIDANCE SHOWING STRONGEST SIGNAL FOR FOG BUT ALSO USUALLY VERY MOIST-BIASED IN BOUNDARY LAYER. OTHER GUIDANCE...INCLUDING WRF MET MOS DOES NOT DEPICT WIDESPREAD DENSE FOG. THUS HAVE MAINTAINED PREVIOUS IDEA OF 3-5SM VISIBILITY WITH LOWEST VALUES WEST AT RFD/DPA AND HIGHER END AT MORE URBAN ORD/MDW...THOUGH WILL HAVE TO MONITOR OBS TRENDS THIS EVENING FOR POTENTIAL OF GREATER LOW VISIBILITY THREAT. RATZER //ORD AND MDW CONFIDENCE...UPDATED 03Z... * MEDIUM-LOW IN EXTENT/VISIBILITY IMPACTS IN FOG. MEDIUM IN CIG TRENDS AND HIGH IN WINDS. RATZER //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...MVFR/IFR FOG POSSIBLE ESPECIALLY WEDNESDAY NIGHT WITH LIGHT RAIN OR DRIZZLE DEVELOPING. THURSDAY...IFR LIKELY/LIFR POSSIBLE FOG WITH RAIN AND DRIZZLE LIKELY. FRIDAY...MVFR LIKELY WITH RAIN...POSSIBLY MIXING WITH SNOW BEFORE ENDING BY EVENING. SATURDAY...VFR. SUNDAY...MVFR POSSIBLE. SLIGHT CHANCE OF LIGHT SNOW. RATZER && .MARINE... 212 PM CST HIGH PRESSURE WILL SPREAD OVER THE LAKE TONIGHT...RESULTING IN A CONTINUED DECREASE IN WAVES. WINDS SHIFT TO SOUTH-SOUTHEAST LATER TUESDAY IN RESPONSE TO A LOW PRESSURE TROUGH IN THE PLAINS. EVENTUALLY A SURFACE LOW WILL FORM OVER SOUTHERN ONTARIO THAT WILL SHIFT WINDS SOUTHERLY AND LIFT A WARM FRONT OVER THE LAKE. WINDS MAY APPROACH 30 KT DURING THIS TIME. ON THURSDAY ANOTHER SURFACE TROUGH WILL ORGANIZE IN THE PLAINS AND EXTEND TO THE NORTHERN TIP OF LAKE MICHIGAN. MEANWHILE STRONG HIGH PRESSURE WILL BUILD INTO THE UPPER MIDWEST. THESE FEATURES WILL LEAD TO A STRONG COLD FRONT MOVING SOUTHWARD ACROSS THE LAKE ON FRIDAY WITH A DRAMATIC SHIFT TO AT LEAST INITIALLY GUSTY NORTHERLY WINDS...GENERALLY AROUND 30 KT THOUGH POSSIBLY A TAD HIGHER RIGHT WITH THE FRONT. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240721 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 221 AM CDT SAT OCT 24 2015 .UPDATE... 827 PM CDT FOR EVENING UPDATE.. RELATIVELY MINOR ADJUSTMENTS TO GOING FORECAST...MAINLY TO REFINE TIMING AND SPACIAL COVERAGE OF MORE SOLID RAIN/SHOWER AXIS CURRENTLY OVER NORTHEAST IL. DECREASED POPS A BIT WEST WHERE MORE ORGANIZED PRECIP HAS PASSED...AND DRIZZLE/OCCASIONAL LIGHTER SHOWERS EXPECTED REMAINDER OF THE NIGHT. 00Z ANALYSIS INDICATES AN UPPER TROUGH OVER THE UPPER MIDWEST...WITH SURFACE LOW PRESSURE LOCATED OVER SOUTHWEST MINNESOTA AND A WARM FRONT EXTENDING SOUTHEAST FROM THE SURFACE LOW INTO CENTRAL IL. A LEAD SHORT WAVE TROUGH AND ENHANCED 35-40 KT SOUTHERLY LOW LEVEL FLOW IN 925-850 MB LAYER HAS SPREAD AN AXIS OF RAIN/SHOWERS ACROSS THE AREA SINCE LATE AFTERNOON...WITH PWAT /LOW-LEVEL MOIST CONVERGENCE AXIS AND STRONGEST MOISTURE TRANSPORT NOW LIFTING ACROSS NORTHEAST IL AND LAKE MICHIGAN AS OF 01Z. HIGH RES GUIDANCE (HRRR-EXP) HANDLING TRENDS NICELY...INDICATING MORE ORGANIZED SHOWERS WILL CONTINUE TO PUSH EAST/NORTHEAST INTO WESTERN LOWER MICHIGAN... NORTHWEST INDIANA AND FAR EAST CENTRAL ILLINOIS OVER THE NEXT FEW HOURS. FARTHER WEST...GOES IR/WATER VAPOR IMAGERY DEPICTS DRY SLOT SPREADING ACROSS MO/EASTERN IA AND SOUTHWEST WI...ATOP RELATIVELY MILD/MOIST LOW LEVELS. THUS MORE ORGANIZED RAIN/SHOWERS WILL LIKELY DIMINISH SOMEWHAT AND FOCUS ACROSS AREAS EAST OF THE I-55 AND EVENTUALLY I-57 CORRIDORS LATER TONIGHT...WHILE LOW CLOUDS/PATCHY FOG...OCCASIONAL DRIZZLE AND ISOLATED LIGHTER SHOWERS WILL REPLACE THE HEAVIER RAINS FROM THE WEST. HAVE UPDATED HOURLY POP/WX GRIDS TO ADD DETAIL REFLECTING THESE TRENDS...AND HAVE REMOVED THUNDER MENTION WITH NO LIGHTNING OBSERVED OVER THE PAST SEVERAL HOURS AND RELATIVELY POOR MID-LEVEL LAPSE RATES. AS MAIN UPPER TROUGH AXIS APPROACHES FROM THE WEST TOWARD MORNING GUIDANCE DOES INDICATE A NARROW LINE OF SHOWERS COINCIDENT WITH THE ADVANCING SURFACE COLD FRONT. LAPSE RATES ALOFT LOOK TO BE MORE FAVORABLE FOR ISOLATED THUNDER AT THAT TIME...THOUGH SHOWER COVERAGE OVERALL LOOKS TO BE A FAIRLY NARROW LINE AND THUNDER MORE ISOLATED THAN THAT. OTHERWISE...EXCEPT FOR SOME ADJUSTMENTS BASED ON SFC TEMP TRENDS... NO SIGNIFICANT CHANGES TO GOING FORECAST WHICH IS GENERALLY ON TRACK. RATZER && .SHORT TERM... TONIGHT AND SATURDAY... 247 PM...FORECAST CONCERNS INCLUDE PRECIP DURATION TONIGHT/ SATURDAY MORNING...SLIGHT CHANCE OF THUNDER THEN STRONG/GUSTY WINDS SATURDAY. LOW PRESSURE OVER THE CENTRAL PLAINS WILL MOVE NORTHEAST TO THE NORTHERN GREAT LAKES REGION BY SATURDAY AFTERNOON. FIRST UPPER WAVE ROTATING NORTHEAST WILL MOVE ACROSS THE AREA LATE THIS AFTERNOON THRU THIS EVENING WITH PERIODS OF SHOWERS. CURRENTLY NO THUNDER WITH ACTIVITY MOVING INTO NORTHWEST IL. INSTABILITY LOOKS MARGINAL FOR THUNDER BUT MAINTAINED SLIGHT CHANCE MENTION. AS THIS FIRST WAVE DEPARTS LATE THIS EVENING OR EARLY SATURDAY MORNING. PRECIP COVERAGE SHOULD DECREASE BUT WITH LOW LEVELS SATURATED BY THAT TIME...ITS POSSIBLE PRECIP MAY TRANSITION TO DRIZZLE. HOWEVER... MAINTAINED JUST SHOWER MENTION FOR NOW. AS THE MAIN COLD FRONT MOVES ACROSS THE AREA SATURDAY MORNING...THERE WILL LIKELY BE ANOTHER BAND OF AT LEAST SCATTERED SHOWERS. ALSO POSSIBLE THERE COULD BE ENOUGH INSTABILITY FOR ISOLATED THUNDER DURING THIS TIME PERIOD. THE PASSAGE OF THE FRONT WILL THEN END THE CHANCE OF PRECIP. WINDS WILL TURN MORE SOUTHERLY THIS EVENING AND LIKELY BE GUSTY AT TIMES...BUT WINDS WILL SHIFT WESTERLY BEHIND THE COLD FRONT SATURDAY MORNING AND QUICKLY INCREASE DURING THE LATE MORNING. STILL SOME DIFFERENCES BETWEEN THE MODELS...BUT FORECAST SOUNDINGS WOULD SUGGEST THE POTENTIAL FOR GUSTS INTO THE 30-35 MPH RANGE THRU MUCH OF THE AFTERNOON...BEFORE WINDS DIMINISH QUICKLY WITH SUNSET. HIGH TEMPS HAVE SO FAR ONLY REACH THE UPPER 50S/LOWER 60S OVER MUCH OF THE NORTHERN CWA TODAY...BUT THESE MAY ACTUALLY GO UP A FEW DEGREES LATER THIS EVENING/OVERNIGHT AS WARMER AND MORE MOIST AIR ADVECTS INTO THE AREA. TEMPS MAY QUICKLY RISE AHEAD OF THE FRONT SATURDAY MORNING...THEN STEADY TO EVENTUALLY SLOWLY FALLING TEMPS ARE EXPECTED SATURDAY AFTERNOON. CMS && .LONG TERM... 310 PM CDT SATURDAY NIGHT THROUGH FRIDAY... RELATIVELY QUIET WEATHER IS EXPECTED FOR THE BEGINNING OF THE LONGER TERM FORECAST PERIOD. FOLLOWING THE PASSAGE OF THE COLD FRONT EARLIER SATURDAY...HIGH PRESSURE WILL BUILD ACROSS THE REGION AND REMAIN THE DOMINANT FEATURE INTO EARLY NEXT WEEK. EVEN FOLLOWING THE PASSAGE OF THE COLD FRONT...TEMPERATURES THROUGH EARLY NEXT WEEK SHOULD BE NEAR OR A LITTLE ABOVE NORMAL...WITH HIGHS IN THE UPPER 50S TO LOWER 60S AND LOWS IN THE UPPER 30S TO LOWER 40S...EXCEPT THE URBANIZED AREAS OF THE CHICAGO METRO AREA WHICH WILL REMAIN IN THE MIDDLE TO UPPER 40S. THE MAIN CONCERN FOR THE EXTENDED FORECAST PERIOD WILL FOCUS ON WHAT HAPPENS WITH THE REMNANTS OF HURRICANE PATRICIA. THE LONGER RANGE MODELS ARE IN GENERAL AGREEMENT ON THE TREND OF THE PROGRESSION OF THE SYSTEM...LIFTING THE REMNANTS OF THE TROPICAL SYSTEM INTO NERN MEXICO...THOUGH THE SYSTEM BECOMES MORE DIFFUSE AS IT CROSSES THE MOUNTAINOUS REGIONS OF NRN MEXICO...AND THUS...THE LOCATION OF THE REMNANT UPPER LEVEL VORT MAX BECOMES LESS CERTAIN AS IT ENTERS A REGION WHERE IT CAN BEGIN TO INTERACT WITH THE MID-LATITUDE FLOW PATTERN. HOWEVER...THE GENERAL IDEA IS THAT SOME REMNANTS OF THE TROPICAL SYSTEM WILL PHASE WITH A SRN STREAM SHORTWAVE TRACKING THROUGH TX AND STRENGTHEN OVER THE NWRN GULF COAST REGION MONDAY. THE GENERAL TREND OF THE LONGER RANGE GUIDANCE IS FOR THE RESULTANT UPPER LOW TO REMAIN OVER THE NWRN GULF COAST UNTIL THE NEXT LONGWAVE TROUGH MOVES OUT OF THE ROCKIES...LIFTING THE SYSTEM NEWD BY EARLY TUESDAY. BEYOND TUESDAY...THE FATE OF THE TROPICAL SYSTEM REMAIN UNCERTAIN. THE GFS AND THE ECMWF...WHILE EXHIBITING TIMING AND AMPLITUDE DIFFERENCES IN THE UPPER LEVEL FLOW PATTER...GENERALLY AGREE ON EMPHASIZING NRN STREAM ENERGY DIGGING OUT OF THE NRN/CNTRL ROCKIES AND QUICKLY SHUNTING THE TROPICAL SYSTEM QUICKLY TO THE EAST. THIS SCENARIO WOULD SUGGEST THAT THE TROPICAL SYSTEM WOULD HAVE LESS OF AN IMPACT ON THE LOCAL AREA...AND THAT MUCH OF THE PCPN EXPECTED FOR MIDWEEK WILL BE MORE ASSOCIATED WITH THE NRN STREAM SHORTWAVE ENERGY WITH LESS OF AN IMPACT FROM THE TROPICAL SYSTEM. HOWEVER...GIVEN THE GENERAL CONSENSUS OF THE LONGER RANGE GUIDANCE ON THE NRN STREAM PATTERN...FEEL CONFIDENT ENOUGH TO MAINTAIN THE HIGHER POPS FOR TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...BUT QPF AMOUNTS ARE STILL A BIG QUESTION MARK. KREIN && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * SCATTERED SHOWERS AND DRIZZLE DIMINISHING OVERNIGHT. * MVFR CIGS PERSISTING THROUGH MUCH OF THIS MORNING BUT POSSIBLY LASTING INTO THE AFTERNOON AND EVENING. A CHANCE FOR IFR THROUGH DAYBREAK. * CHANCE FOR VERY BRIEF RAIN SHOWERS IN THE 14Z-16Z WINDOW OR SO. * WINDS BECOMING WESTERLY AND GUSTY BY MIDDAY. //DISCUSSION...UPDATED 06Z... DEEPENING LOW PRESSURE HAS USHERED A WARM FRONT NORTHWARD ACROSS THE AREA VERY EARLY THIS MORNING. THIS HAS AIDED IN CIGS RISING AS WINDS TURN SOUTH-SOUTHWEST. GIVEN THE LOW TEMPERATURE-DEW POINT SPREADS THOUGH...THERE REMAINS POTENTIAL FOR SOME PATCHY IFR CIGS...ESPECIALLY TOWARD RFD THROUGH THIS MORNING. WITHIN THE WARM SECTOR SPREADING ACROSS TAF SITES...ISOLATED SHOWERS AND PATCHES OF DRIZZLE ARE EVIDENT IN RADAR MOSAIC AND SOME OBS...BUT THESE SHOULD BECOME LESS IN COVERAGE AFTER 08Z-09Z. JUST AHEAD OF THE COLD FRONT LATER THIS MORNING...NAMELY DURING THE 14Z-16Z WINDOW...THERE ARE INDICATIONS FOR A NARROW AXIS OF CONVECTIVE SHOWERS ALONG THIS FEATURE. HAVE INCLUDED A VCSH IN THE TAF FOR NOW...THOUGH THE DURATION OF ANY SHOWER WOULD LIKELY BE BRIEF GIVEN THE NARROW WIDTH OF FORCING. BEHIND THIS COLD FRONT THE WESTERLY WINDS WILL SHARPLY INCREASE WITH GUSTS TO NEAR 30 KT ANTICIPATED THROUGH THE AFTERNOON. CIGS WILL PROBABLY LIFT SOME ALTHOUGH UPSTREAM OBSERVATIONS INDICATE SKIES REMAINING BROKEN AT OR JUST ABOVE MVFR...WHICH THE COLD AIR ADVECTION SHOULD SUPPORT. CLOUDS ARE CURRENTLY FAVORED TO LAST INTO THIS EVENING AS WIND GUSTS GRADUALLY DIMINISH. //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH IN PRECIP TRENDS. * LOW-MEDIUM IN CIGS REMAINING MVFR. * MEDIUM-HIGH IN WINDS //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY AND MONDAY...VFR. TUESDAY AND WEDNESDAY...CHANCE OF RAIN/IFR. THURSDAY...VFR/MVFR PROBABLE. MTF/IZZI && .MARINE... 220 AM CDT AN ACTIVE DAY TODAY OVER LAKE MICHIGAN FOLLOWED BY A POTENTIALLY ACTIVE MIDDLE OF NEXT WEEK. LOW PRESSURE WILL MOVE EAST-NORTHEAST OVER THE UPPER PENINSULA OF MICHIGAN DURING MIDDAY. THE PRESSURE GRADIENT AHEAD OF THIS SHOULD SUPPORT SMALL CRAFT ADVISORY CRITERIA WINDS IN THE ILLINOIS AND INDIANA NEARSHORES BY DAYBREAK. WINDS WILL SHIFT FROM THE WEST-NORTHWEST ACROSS THE ENTIRE LAKE BY MIDDAY AS THE SYSTEM COLD FRONT SWEEPS EASTWARD ACROSS THE LAKE. AS THAT OCCURS...WIND GUSTS SHOULD REACH 30 KT. THE NORTHERN HALF TO THIRD OF THE LAKE IS IN A FAVORED QUADRANT OF THE SYSTEM TO GET A PERIOD OF NORTHWEST GALES...THOUGH THIS COULD BE SOMEWHAT SHORT IN DURATION /2-4 HOURS/. HAVE OPTED TO ISSUE A GALE WARNING FOR A WINDOW DURING THE MIDDLE AFTERNOON TO EARLY THIS EVE AROUND THIS TIME. WINDS SHOULD EASE AS THE EVENING AND OVERNIGHT UNFOLD AS THEY TURN MORE TOWARD DUE NORTH. HIGH PRESSURE WILL PASS OVER THE LAKE DURING SUNDAY AFTERNOON AND NIGHT. LONG RANGE MODEL GUIDANCE CONTINUES TO INDICATE A LARGE SYSTEM IN THE MIDDLE OF THE COUNTRY DURING TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. THE PATTERN IS CONDUCIVE FOR THIS TO OCCUR ALTHOUGH THE DETAILS IN THE GUIDANCE WILL INEVITABLY SHIFT SOME. DEPENDING ON THE EXACT LOW TRACK...A PERIOD OF GALES IS POSSIBLE...LIKELY MORE FAVORED ON THE BACKSIDE OF THE SYSTEM...WHICH WOULD BE IN THE WEDNESDAY NIGHT AND/OR THURSDAY TIME FRAME AT THIS VANTAGE POINT. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 7 PM SATURDAY. SMALL CRAFT ADVISORY...LMZ742-LMZ743-LMZ744-LMZ745...7 AM SATURDAY TO 4 AM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240751 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 151 AM CST TUE NOV 24 2015 .SHORT TERM... 204 PM CST THROUGH TUESDAY... SHORT TERM FOCUS IS ON POTENTIAL FOR FOG DEVELOPMENT AND TEMPERATURE TRENDS ASSOCIATED WITH FOG/OCCASIONAL CLOUDS. A SURFACE TROUGH HAS CLEARED THE AREA...ASSOCIATED WITH A FAST MOVING SHEARED OUT SHORTWAVE. BRIEF EARLIER REPORTS OF GRAUPEL/SNOW HAVE EXITED TO THE EAST THIS AFTERNOON. SKIES WILL CONTINUE TO CLEAR BEHIND THIS DISTURBANCE THROUGH THE AFTERNOON AND EVENING. EXPECT A QUICK DROP IN TEMPERATURES THIS EVENING IN THE CLEAR SKY REGIME HIGH PRESSURE SLIDES EAST. WITH ELEVATED DEWPOINTS AND WEAKENING WINDS WITH SOME MINOR SNOWMELT MOISTENING THE LOWER ATMOSPHERE...SEVERAL PIECES OF GUIDANCE SUGGEST FOG DEVELOPMENT OVERNIGHT. HAVE NOT HIT THINGS AS HARD AS SOME GUIDANCE INDICATES...AS THERE ARE A FEW AREAS OF CLOUDS TO MONITOR TONIGHT INTO TUESDAY THAT MAY LIMIT THE EXTENT...THUS THE PATCHY MENTION. THE FIRST AREA IN THE PLAINS ARE HIGHER CLOUDS THAT WILL DRIFT THROUGH OVERNIGHT INTO TUESDAY ASSOCIATED WITH A DAMPENING SHORTWAVE IN WESTERLY FLOW ALOFT. THERE IS ALSO AN AREA OF LOWER CLOUDS OVER MN AND N CENTRAL WI THAT MAY DRIFT CLOSE TO NORTHERN ILLINOIS AS WELL...BUT WITH THE RIDGE AXIS BUILDING IN...THERE IS THE TENDENCY FOR THESE CLOUDS TO SLOW THEIR PROGRESSION SOUTHWARD. ON TUESDAY...AFTER THE HIGH CLOUDS SHIFT EAST...EXPECT A SEASONABLY COOL DAY AS THE THERMAL RIDGE BUILDS OVERHEAD. EXPECT CLEARING SKIES AND READINGS IN THE MID TO UPPER 30S IN THE SNOWPACK...WITH 40S EXPECTED SOUTHWEST WHERE SNOWPACK IS THIN/MELTING AND UPPER 30S TO LOW 40S WERE ACHIEVED TODAY. SE WINDS INCREASE IN THE AFTERNOON. KMD && .LONG TERM... 326 PM CST TUESDAY NIGHT THROUGH MONDAY... THE HOLIDAY STILL LOOKS LIKE A RAINY AND/OR DRIZZLY ONE FOR MOST OF THE FORECAST AREA. BEING AT THREE TO FOUR DAYS OUT FROM THE EVENT THERE OF COURSE REMAINS DEGREES OF UNCERTAINTY...BUT FOR THIS EVENT IT APPEARS TO BE MAINLY TIMING OF START OF THE MODERATE RAIN AND THUS OVERALL DURATION...WHICH IMPACTS RAINFALL AMOUNTS. ITS PROBABLE A PERIOD OF FOG AND DRIZZLE WILL PRECEDE THE WIDESPREAD RAIN AND JUST HOW EARLY THAT ARRIVES ON THE MAIN TRAVEL DAY OF WEDNESDAY...OR IF IT ARRIVES YET BY THAT TIME...IS STILL QUITE UNCERTAIN. THE UPPER LEVEL PATTERN WILL BECOME MORE SOUTHWESTERLY ALOFT BY TUESDAY NIGHT AND MORE SO WEDNESDAY AS A POSITIVELY TILTED TROUGH DEFINES ITSELF FROM SOUTHERN CANADA THROUGH THE WESTERN PART OF THE UNITED STATES. WHILE MOIST ADVECTION WILL NOT BE PARTICULARLY STRONG YET TUESDAY NIGHT...THERE WILL BE A SIMILAR CONCERN FOR PATCHES OF FOG/STRATUS AS THERE IS TONIGHT AS BOUNDARY LAYER MOISTURE INCREASES AIDED BY A DAY OF GRADUALLY MORE MELT. WHILE WINDS WILL BE ON THE INCREASE...WHEN IT COMES TO ADVECTION TYPE FOG POTENTIAL...WIND SPEEDS MATTER LESS. LOW-LEVEL ISENTROPIC SURFACES SHOW MOISTURE RAPIDLY INCREASING FROM THE WEST WEDNESDAY AND THEN WEDNESDAY NIGHT WHICH WOULD INDICATE STRATUS/FOG AND LIKELY AREAS OF DRIZZLE AT SOME POINT. CONFIDENCE ON THIS OCCURRING IS FAIRLY HIGH GIVEN THE PATTERN BUT AS FOR WHAT TIME ON WEDNESDAY OR WEDNESDAY NIGHT...THAT REMAINS LOW. THE FOG POTENTIAL IS EVEN MORE CHALLENGING TO ASSESS AT THIS POINTS. CURRENT DEW POINTS ABOVE FREEZING ARE ALREADY UP TO CENTRAL MISSOURI AND AS THEY EXPAND RAPIDLY INTO THE AREA ON WEDNESDAY...SNOW MELT WILL INCREASE AND SHOULD REALLY TAKE OFF BY LATER WEDNESDAY AFTERNOON AND NIGHT WHEN DEW POINTS OF 40 PLUS ARE PROJECTED TO ADVECT INTO AND REMAIN OVER THE AREA. FOG...SOME OF IT POSSIBLY DENSE...WOULD BE LIKELY OVER AND NORTH OF SOME OF THE DEEPER REMAINING SNOW COVER. FOR US THAT IS MAINLY NORTHERN ILLINOIS PART NORTH OF I-88...BUT WITH THE COOLER DAMP GROUND ELSEWHERE WE MAY END UP SEEING IT AREA WIDE. AS ANOMALOUSLY HIGH MOISTURE VALUES OF THE 95TH PLUS PERCENTILE FOR LATE NOVEMBER STREAM NORTH AHEAD OF THE TROUGH...THE NORTHERN STREAM JET REMAINS PROGRESSIVE AND WILL PUSH THE TROUGH TOWARD AND THROUGH THE AREA ON FRIDAY. MODELS HAVE TRENDED STRONGER WITH THE SURFACE HIGH BEHIND THE SYSTEM AND THUS SLIGHTLY MORE PROGRESSIVE WITH THE DEVELOPING COLD FRONT ON FRIDAY. THE 12Z EC REMAINS A TAD SLOWER BECAUSE IT HAS A MORE WELL-DEFINED WAVE DEVELOP ALONG THE FRONT...AND HAVE LEANED THE FORECAST CLOSER TO THAT. THE KEY WITH THAT IS THIS SOLUTION IS THAT MODERATE RAIN WOULD LIKELY NOT PUSH INTO THE EASTERN FORECAST AREA...EAST OF I-55...UNTIL THANKSGIVING NIGHT. DRIZZLE MAY STILL OCCUR DURING THE DAY IN THAT AREA. THE LONGER RAIN POTENTIAL AND HIGHER QPF IS STILL MOST FAVORED OVER NORTH CENTRAL AND NORTHEAST ILLINOIS...WHICH OF COURSE IS THE AREA WITH THE HIGHER SNOW COVER. THE CURRENT FORECAST OF QPF IN OUR NORTHWEST AREA IS AROUND AN INCH AND A HALF...AND THAT IS NOT TO THE POINT WHERE WE WOULD EXPECT MUCH FOR NON-RIVER FLOODING IMPACTS. THIS IS BECAUSE THE MELT SHOULD PERCOLATE INTO THE GROUND GIVEN THE FREEZING LAYER IN THE LAYER IS VERY SHALLOW. SEE THE HYDROLOGY DISCUSSION BELOW FOR MORE ON THE DETAILS OF RIVER IMPACTS. DESPITE THE CLOUDS AND RAIN...LOW-LEVEL WARM ADVECTION WILL BRING A MILD THANKSGIVING WITH HIGHS CLOSE TO 50 NORTH AND SEVERAL DEGREES ABOVE 50 PRESENTLY FAVORED ACROSS THE THEN NEAR SNOW COVER-FREE SOUTH. ON THE BACKSIDE OF THE SYSTEM...COLD ADVECTION WILL LIKELY LEAD TO STEADY OR FALLING TEMPERATURES ON FRIDAY. THIS COULD BRING A LIGHT MIX OR LIGHT SNOW BEFORE THE SYSTEM ENDS. THERE IS THE POTENTIAL FOR SOME LAKE EFFECT SNOW SHOWERS INTO FAR NORTHWEST INDIANA FRIDAY NIGHT...BUT OVERALL THE PARAMETERS ARE NOT INDICATED TO BE GREAT WITH SHALLOW INVERSION HEIGHTS YIELDING MARGINAL CLOUD DEPTHS THAT DO NOT PERSIST LONG. MTF && .HYDROLOGY... 340 PM CST A RAIN ON SNOW MELT SCENARIO IS SHAPING UP OVER THE REGION WEDNESDAY NIGHT THROUGH EARLY FRIDAY. OBSERVERS ON MONDAY MORNING RECORDED SNOW WATER EQUIVALENT VALUES OF MAINLY 0.9 TO 1.3 ACROSS FAR NORTHERN ILLINOIS WITHIN THE DEEPEST SNOW COVER. WEATHER PARAMETERS FAVORABLE FOR RAPID SNOW MELT ARE SET TO MOVE ACROSS THE REGION LATER WEDNESDAY WITH RAIN FURTHER SPEEDING THAT UP ON THANKSGIVING. AMOUNTS OF OVER AN INCH ARE LIKELY ACROSS ESPECIALLY NORTHERN ILLINOIS...AND IT IS NOT IMPOSSIBLE TO HAVE TWO INCH AMOUNTS GIVEN THE PARAMETERS. THE FROZEN SOIL DEPTH IS VERY SHALLOW AND WOULD LEAN TOWARD THAT NOT REALLY IMPACTING PERCOLATION OF THE RAIN/MELT. WITH STREAMFLOW VALUES RUNNING HIGHER THAN NORMAL FOR SOME STREAMS AND RIVERS THANKS TO THE WET PAST FOUR WEEKS...THERE IS CONCERN FOR SOME STREAMS TO POTENTIALLY RISE INTO FLOOD STAGE. HAVE CONTINUED ESF AT THIS TIME WITH DETAILS IN SPECIFIC RAINFALL AMOUNTS AND TIMING TO BE REFINED AS THE EVENT APPROACHES. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * POTENTIAL FOR LOWER VIS IN FOG OVERNIGHT...ESPECIALLY WEST OF ORD/MDW. KJB //DISCUSSION...UPDATED 06Z... THE MAIN AVIATION WEATHER CONCERNS WILL BE THE POTENTIAL FOR PATCHY AREAS OF FOG THROUGH EARLY THIS MORNING...ESPECIALLY AT KRFD AND KDPA. SURFACE HIGH PRESSURE...CURRENTLY CENTERED OVER NORTHERN ILLINOIS WILL CONTINUE TO RESULT IN LIGHT AND VARIABLE WINDS ACROSS THE AREA THROUGH MID TO LATE MORNING. ASIDE FROM A DECK OF HIGH LEVEL CLOUDS...MAINLY OVER IOWA...SKIES HAVE REMAINED CLEAR TO PARTLY CLOUDY...AND THIS HAS ALLOWED TEMPERATURES TO RADIATE SIGNIFICANTLY ACROSS NORTH CENTRAL ILLINOIS. SOME SPOTTY AREAS OF DENSE FOG HAVE BEEN REPORTED FROM TIME TO TIME UNDER THIS HIGH...BUT OBSERVATIONAL TRENDS SUGGEST THAT THIS FOG IS NOT ONLY SPOTTY...BUT LIKELY FAIRLY SHALLOW AS WELL. WITH THIS IN MIND...WHILE SOME LOWER VISIBILITIES MAY DEVELOP ACROSS KRFD AND KDPA OVERNIGHT...IT APPEARS THAT THE LOWER VISIBILITIES WILL BE MORE OF A TEMPO CONDITION RATHER THAN PREVAILING. FOR THIS REASON I HAVE INCLUDED THE LOWEST VISIBILITIES IN TEMPO GROUPS THIS MORNING. FOG MAY HAVE A HARDER TIME DEVELOPING OVER THE MAIN TERMINALS TONIGHT...SO I HAVE ONLY CONTINUED THE MENTION OF 5-6 SM VISIBILITIES OVERNIGHT. OTHERWISE...IT APPEARS EAST-SOUTHEASTERLY WINDS WILL DEVELOP THROUGH THE AFTERNOON...AND CONTINUE THIS EVENING BEFORE TURNING SOUTH OVERNIGHT. KJB //ORD AND MDW CONFIDENCE...UPDATED 06Z... * LOW IN EXTENT/VISIBILITY IMPACTS IN FOG FOR THE MAIN TERMINALS. MEDIUM IN CIG TRENDS AND HIGH IN WINDS. KJB //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...MVFR/IFR FOG POSSIBLE ESPECIALLY WEDNESDAY NIGHT WITH LIGHT RAIN OR DRIZZLE DEVELOPING. THURSDAY...IFR LIKELY/LIFR POSSIBLE FOG WITH RAIN AND DRIZZLE LIKELY. FRIDAY...MVFR LIKELY WITH RAIN...POSSIBLY MIXING WITH SNOW BEFORE ENDING BY EVENING. SATURDAY...VFR. SUNDAY...MVFR POSSIBLE. SLIGHT CHANCE OF LIGHT SNOW. RATZER && .MARINE... 151 AM CST THE MAIN FORECAST CONCERN WILL BE WITH THE INCREASING POTENTIAL FOR A PERIOD OF SOUTHERLY GALES...ESPECIALLY OVER THE NORTHERN HALF OF LAKE MICHIGAN WENDESDAY INTO WEDNESDAY EVENING. LOW PRESSURE IS EXPECTED TO SHIFT RAPIDLY TO THE NORTHEAST ACROSS MINNESOTA AND INTO ONTARIO WEDNESDAY INTO WEDNESDAY NIGHT. STRONG PRESSURE FALLS AHEAD OF THIS FEATURE WILL LIKELY LEAD TO AN UPTICK IN SOUTHERLY WINDS OVER THE LAKE ON WEDNESDAY...WITH GALES OF 35 TO 40 KT POSSIBLE OVER NORTHERN HALF OF THE LAKE. WITH THIS IN MIND...WE WILL BE ISSUING A GALE WATCH TO COVER THIS POTENTIAL. A COLD FRONT IS EXPECTED TO SHIFT SOUTHEASTWARD DOWN LAKE MICHIGAN LATER ON THANKSGIVING AND INTO FRIDAY MORNING. ASIDE FROM A DECENT AMOUNT OF PRECIPITATION ASSOCIATED WITH THE FRONT...EXPECT WINDS TO INCREASE OUT OF THE NORTH IN ITS WAKE. A PERIOD OF 30 TO PERHAPS 35 KT WINDS LOOK LIKE A GOOD BET ON FRIDAY. ANOTHER WEATHER SYSTEM LOOKS TO TAKE AIM ON THE GREAT LAKES REGION LATER IN THE WEEKEND. THIS COULD AGAIN RESULT IN SOME STRONGER WINDS OVER THE LAKE INTO EARLY NEXT WEEK. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240817 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 317 AM CDT SAT OCT 24 2015 .SHORT TERM... 314 AM CDT THROUGH MONDAY NIGHT... MAIN FORECAST CONCERNS/CHALLENGES ARE WITH PRECIP TRENDS EARLY THIS MORNING THROUGH MIDDAY...AND WITH HOURLY TEMPS AS COOLER TEMPS ARRIVE LATER THIS MORNING BEHIND FROPA AND INCREASING WESTERLY WINDS. AS UPPER TROUGH AND SURFACE LOW REMAIN TO THE NORTHWEST EARLY THIS MORNING...STEADY STREAM OF SHORTWAVE ENERGY CONTINUES ACROSS THE REGION WHILE WARM/MOIST PUSH PERSISTS. THIS IS NOTED WITH STEADY OR INCREASING TEMPS WHILE SURFACE DEWPOINTS INCREASE INTO THE 60S FOR MOST LOCATIONS IN NORTHERN ILLINOIS AND NORTHWEST INDIANA...AS SURFACE WARM FRONT LIFTS TO THE NORTH OF THE CWA. LATEST RADAR IMAGERY DEPICTING RELATIVELY DRIER CONDITIONS ACROSS THE CWA AT THIS HOUR WITH THE BULK ANY SHOWERY ACTIVITY SHIFTING EAST/NORTHEAST NEAR IOWA AND WISCONSIN. THIS BETTER DEVELOPMENT IS CURRENTLY FOCUSED CLOSER TO SURFACE LOW AND COLD FRONT...WHERE BETTER LARGE SCALE ASCENT ASSOCIATED WITH UPPER TROUGH RESIDE. OUTSIDE OF A LIGHT AND BRIEF SHOWER HERE IN THE NEAR TERM ACROSS THE AREA...IT LOOKS AS IF THERE WILL BE A ONE TO TWO HOUR PERIOD WHEN MOST LOCATIONS STAY DRY. CURRENT SHOWERS TO THE WEST WILL THEN SHIFT ACROSS NORTH CENTRAL ILLINOIS IN THE 10-11Z TIME FRAME...BUT IT DOES APPEAR THAT COVERAGE WILL BE LOWER DURING THAT TIME AS THIS PRECIP SHIFTS EAST AWAY FROM THE STRONGER FORCING. HOWEVER...DO EXPECT SOME INCREASE IN SHOWER ACTIVITY THROUGH MID MORNING WITH THE ARRIVAL OF THE FRONT AND STRONGER LARGE SCALE ASCENT. ALTHOUGH I DO THINK THERE WILL BE AN INCREASE IN COVERAGE DURING THIS TIME AM NOT TOO CONFIDENT WITH THE EXTENT OF THIS INCREASE. SO DID INCREASE POPS TO HIGH CHANCE POPS FOR MOST LOCATIONS IN NORTHEAST ILLINOIS AND NORTHWEST INDIANA MID MORNING THROUGH MIDDAY...BUT COULD SEE SOME LATER REFINEMENT IN THE HOURLY TRENDS WHICH COULD SEE HIGHER POPS. WITH INSTABILITY REALLY LACKING THIS MORNING...HAVE LEFT OUT ANY MENTION OF THUNDER. AS THE FRONT SHIFTS EAST THROUGH THE CWA THROUGH MIDDAY...PRECIP WILL EXIT TO THE EAST WITH DRY CONDITIONS EXPECTED IN THE AFTERNOON. DID INCREASE CLOUD COVER FOR MUCH OF TODAY AS STRATUS EXPECTED TO LINGER OVER MUCH OF THE REGION...LIKELY NOT CLEARING UNTIL LATER THIS EVENING. A BREEZY DAY IS ALSO EXPECTED AS WESTERLY WINDS INCREASE BY MID TO LATE MORNING. WITH THIS FRONT PUSHING THROUGH TODAY...HIGH TEMPS WILL BE OBSERVED THIS MORNING AS FALLING TEMPS ARE EXPECTED INTO THE AFTERNOON. DRY AND COOL WEATHER WILL THEN BE OBSERVED THROUGH THE REMAINDER OF THE PERIOD. RODRIGUEZ && .LONG TERM... 314 AM CDT TUESDAY THROUGH FRIDAY... THE EXTENDED PERIOD WILL SEE A RETURN BACK TO WET WEATHER WITH RAIN CHANCES APPEARING LIKELY THROUGH MID WEEK. ALTHOUGH DIFFERENCES CONTINUE WITH TIMING/LOCATION OF THE LARGE SCALE PATTERN DURING THIS TIME...GUIDANCE STILL NARROWING IN ON HIGHER LIKELIHOOD OF PRECIP ACROSS THE REGION. THIS WILL INCLUDE AT LEAST REMNANT TROPICAL MOISTURE LIFTING NORTH ACROSS THE CONUS...AS A LONGWAVE TROUGH WORKS ITS WAY EAST THROUGH THE CENTRAL US. AT THIS TIME...TUESDAY NIGHT LOOKS TO BE THE WETTER PERIOD REGION WIDE. DID INCREASE POPS DURING THIS TIME BUT CAPPED THEM AT LIKELY POPS...OWING TO SOME SYSTEM EVOLUTION VARIABILITY. HAVE ALSO KEPT OUT ANY MENTION OF THUNDER...BUT THIS IS WORTH MONITORING WITH LATER FORECASTS. RODRIGUEZ && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * SCATTERED SHOWERS AND DRIZZLE DIMINISHING OVERNIGHT. * MVFR CIGS PERSISTING THROUGH MUCH OF THIS MORNING BUT POSSIBLY LASTING INTO THE AFTERNOON AND EVENING. A CHANCE FOR IFR THROUGH DAYBREAK. * CHANCE FOR VERY BRIEF RAIN SHOWERS IN THE 14Z-16Z WINDOW OR SO. * WINDS BECOMING WESTERLY AND GUSTY BY MIDDAY. //DISCUSSION...UPDATED 06Z... DEEPENING LOW PRESSURE HAS USHERED A WARM FRONT NORTHWARD ACROSS THE AREA VERY EARLY THIS MORNING. THIS HAS AIDED IN CIGS RISING AS WINDS TURN SOUTH-SOUTHWEST. GIVEN THE LOW TEMPERATURE-DEW POINT SPREADS THOUGH...THERE REMAINS POTENTIAL FOR SOME PATCHY IFR CIGS...ESPECIALLY TOWARD RFD THROUGH THIS MORNING. WITHIN THE WARM SECTOR SPREADING ACROSS TAF SITES...ISOLATED SHOWERS AND PATCHES OF DRIZZLE ARE EVIDENT IN RADAR MOSAIC AND SOME OBS...BUT THESE SHOULD BECOME LESS IN COVERAGE AFTER 08Z-09Z. JUST AHEAD OF THE COLD FRONT LATER THIS MORNING...NAMELY DURING THE 14Z-16Z WINDOW...THERE ARE INDICATIONS FOR A NARROW AXIS OF CONVECTIVE SHOWERS ALONG THIS FEATURE. HAVE INCLUDED A VCSH IN THE TAF FOR NOW...THOUGH THE DURATION OF ANY SHOWER WOULD LIKELY BE BRIEF GIVEN THE NARROW WIDTH OF FORCING. BEHIND THIS COLD FRONT THE WESTERLY WINDS WILL SHARPLY INCREASE WITH GUSTS TO NEAR 30 KT ANTICIPATED THROUGH THE AFTERNOON. CIGS WILL PROBABLY LIFT SOME ALTHOUGH UPSTREAM OBSERVATIONS INDICATE SKIES REMAINING BROKEN AT OR JUST ABOVE MVFR...WHICH THE COLD AIR ADVECTION SHOULD SUPPORT. CLOUDS ARE CURRENTLY FAVORED TO LAST INTO THIS EVENING AS WIND GUSTS GRADUALLY DIMINISH. //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH IN PRECIP TRENDS. * LOW-MEDIUM IN CIGS REMAINING MVFR. * MEDIUM-HIGH IN WINDS //OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z... SUNDAY AND MONDAY...VFR. TUESDAY AND WEDNESDAY...CHANCE OF RAIN/IFR. THURSDAY...VFR/MVFR PROBABLE. MTF/IZZI && .MARINE... 220 AM CDT AN ACTIVE DAY TODAY OVER LAKE MICHIGAN FOLLOWED BY A POTENTIALLY ACTIVE MIDDLE OF NEXT WEEK. LOW PRESSURE WILL MOVE EAST-NORTHEAST OVER THE UPPER PENINSULA OF MICHIGAN DURING MIDDAY. THE PRESSURE GRADIENT AHEAD OF THIS SHOULD SUPPORT SMALL CRAFT ADVISORY CRITERIA WINDS IN THE ILLINOIS AND INDIANA NEARSHORES BY DAYBREAK. WINDS WILL SHIFT FROM THE WEST-NORTHWEST ACROSS THE ENTIRE LAKE BY MIDDAY AS THE SYSTEM COLD FRONT SWEEPS EASTWARD ACROSS THE LAKE. AS THAT OCCURS...WIND GUSTS SHOULD REACH 30 KT. THE NORTHERN HALF TO THIRD OF THE LAKE IS IN A FAVORED QUADRANT OF THE SYSTEM TO GET A PERIOD OF NORTHWEST GALES...THOUGH THIS COULD BE SOMEWHAT SHORT IN DURATION /2-4 HOURS/. HAVE OPTED TO ISSUE A GALE WARNING FOR A WINDOW DURING THE MIDDLE AFTERNOON TO EARLY THIS EVE AROUND THIS TIME. WINDS SHOULD EASE AS THE EVENING AND OVERNIGHT UNFOLD AS THEY TURN MORE TOWARD DUE NORTH. HIGH PRESSURE WILL PASS OVER THE LAKE DURING SUNDAY AFTERNOON AND NIGHT. LONG RANGE MODEL GUIDANCE CONTINUES TO INDICATE A LARGE SYSTEM IN THE MIDDLE OF THE COUNTRY DURING TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. THE PATTERN IS CONDUCIVE FOR THIS TO OCCUR ALTHOUGH THE DETAILS IN THE GUIDANCE WILL INEVITABLY SHIFT SOME. DEPENDING ON THE EXACT LOW TRACK...A PERIOD OF GALES IS POSSIBLE...LIKELY MORE FAVORED ON THE BACKSIDE OF THE SYSTEM...WHICH WOULD BE IN THE WEDNESDAY NIGHT AND/OR THURSDAY TIME FRAME AT THIS VANTAGE POINT. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 7 PM SATURDAY. SMALL CRAFT ADVISORY...LMZ742-LMZ743-LMZ744-LMZ745...7 AM SATURDAY TO 4 AM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 240900 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 300 AM CST TUE NOV 24 2015 .SHORT TERM... 204 PM CST THROUGH TUESDAY... SHORT TERM FOCUS IS ON POTENTIAL FOR FOG DEVELOPMENT AND TEMPERATURE TRENDS ASSOCIATED WITH FOG/OCCASIONAL CLOUDS. A SURFACE TROUGH HAS CLEARED THE AREA...ASSOCIATED WITH A FAST MOVING SHEARED OUT SHORTWAVE. BRIEF EARLIER REPORTS OF GRAUPEL/SNOW HAVE EXITED TO THE EAST THIS AFTERNOON. SKIES WILL CONTINUE TO CLEAR BEHIND THIS DISTURBANCE THROUGH THE AFTERNOON AND EVENING. EXPECT A QUICK DROP IN TEMPERATURES THIS EVENING IN THE CLEAR SKY REGIME HIGH PRESSURE SLIDES EAST. WITH ELEVATED DEWPOINTS AND WEAKENING WINDS WITH SOME MINOR SNOWMELT MOISTENING THE LOWER ATMOSPHERE...SEVERAL PIECES OF GUIDANCE SUGGEST FOG DEVELOPMENT OVERNIGHT. HAVE NOT HIT THINGS AS HARD AS SOME GUIDANCE INDICATES...AS THERE ARE A FEW AREAS OF CLOUDS TO MONITOR TONIGHT INTO TUESDAY THAT MAY LIMIT THE EXTENT...THUS THE PATCHY MENTION. THE FIRST AREA IN THE PLAINS ARE HIGHER CLOUDS THAT WILL DRIFT THROUGH OVERNIGHT INTO TUESDAY ASSOCIATED WITH A DAMPENING SHORTWAVE IN WESTERLY FLOW ALOFT. THERE IS ALSO AN AREA OF LOWER CLOUDS OVER MN AND N CENTRAL WI THAT MAY DRIFT CLOSE TO NORTHERN ILLINOIS AS WELL...BUT WITH THE RIDGE AXIS BUILDING IN...THERE IS THE TENDENCY FOR THESE CLOUDS TO SLOW THEIR PROGRESSION SOUTHWARD. ON TUESDAY...AFTER THE HIGH CLOUDS SHIFT EAST...EXPECT A SEASONABLY COOL DAY AS THE THERMAL RIDGE BUILDS OVERHEAD. EXPECT CLEARING SKIES AND READINGS IN THE MID TO UPPER 30S IN THE SNOWPACK...WITH 40S EXPECTED SOUTHWEST WHERE SNOWPACK IS THIN/MELTING AND UPPER 30S TO LOW 40S WERE ACHIEVED TODAY. SE WINDS INCREASE IN THE AFTERNOON. KMD && .LONG TERM... 326 PM CST TUESDAY NIGHT THROUGH MONDAY... THE HOLIDAY STILL LOOKS LIKE A RAINY AND/OR DRIZZLY ONE FOR MOST OF THE FORECAST AREA. BEING AT THREE TO FOUR DAYS OUT FROM THE EVENT THERE OF COURSE REMAINS DEGREES OF UNCERTAINTY...BUT FOR THIS EVENT IT APPEARS TO BE MAINLY TIMING OF START OF THE MODERATE RAIN AND THUS OVERALL DURATION...WHICH IMPACTS RAINFALL AMOUNTS. ITS PROBABLE A PERIOD OF FOG AND DRIZZLE WILL PRECEDE THE WIDESPREAD RAIN AND JUST HOW EARLY THAT ARRIVES ON THE MAIN TRAVEL DAY OF WEDNESDAY...OR IF IT ARRIVES YET BY THAT TIME...IS STILL QUITE UNCERTAIN. THE UPPER LEVEL PATTERN WILL BECOME MORE SOUTHWESTERLY ALOFT BY TUESDAY NIGHT AND MORE SO WEDNESDAY AS A POSITIVELY TILTED TROUGH DEFINES ITSELF FROM SOUTHERN CANADA THROUGH THE WESTERN PART OF THE UNITED STATES. WHILE MOIST ADVECTION WILL NOT BE PARTICULARLY STRONG YET TUESDAY NIGHT...THERE WILL BE A SIMILAR CONCERN FOR PATCHES OF FOG/STRATUS AS THERE IS TONIGHT AS BOUNDARY LAYER MOISTURE INCREASES AIDED BY A DAY OF GRADUALLY MORE MELT. WHILE WINDS WILL BE ON THE INCREASE...WHEN IT COMES TO ADVECTION TYPE FOG POTENTIAL...WIND SPEEDS MATTER LESS. LOW-LEVEL ISENTROPIC SURFACES SHOW MOISTURE RAPIDLY INCREASING FROM THE WEST WEDNESDAY AND THEN WEDNESDAY NIGHT WHICH WOULD INDICATE STRATUS/FOG AND LIKELY AREAS OF DRIZZLE AT SOME POINT. CONFIDENCE ON THIS OCCURRING IS FAIRLY HIGH GIVEN THE PATTERN BUT AS FOR WHAT TIME ON WEDNESDAY OR WEDNESDAY NIGHT...THAT REMAINS LOW. THE FOG POTENTIAL IS EVEN MORE CHALLENGING TO ASSESS AT THIS POINTS. CURRENT DEW POINTS ABOVE FREEZING ARE ALREADY UP TO CENTRAL MISSOURI AND AS THEY EXPAND RAPIDLY INTO THE AREA ON WEDNESDAY...SNOW MELT WILL INCREASE AND SHOULD REALLY TAKE OFF BY LATER WEDNESDAY AFTERNOON AND NIGHT WHEN DEW POINTS OF 40 PLUS ARE PROJECTED TO ADVECT INTO AND REMAIN OVER THE AREA. FOG...SOME OF IT POSSIBLY DENSE...WOULD BE LIKELY OVER AND NORTH OF SOME OF THE DEEPER REMAINING SNOW COVER. FOR US THAT IS MAINLY NORTHERN ILLINOIS PART NORTH OF I-88...BUT WITH THE COOLER DAMP GROUND ELSEWHERE WE MAY END UP SEEING IT AREA WIDE. AS ANOMALOUSLY HIGH MOISTURE VALUES OF THE 95TH PLUS PERCENTILE FOR LATE NOVEMBER STREAM NORTH AHEAD OF THE TROUGH...THE NORTHERN STREAM JET REMAINS PROGRESSIVE AND WILL PUSH THE TROUGH TOWARD AND THROUGH THE AREA ON FRIDAY. MODELS HAVE TRENDED STRONGER WITH THE SURFACE HIGH BEHIND THE SYSTEM AND THUS SLIGHTLY MORE PROGRESSIVE WITH THE DEVELOPING COLD FRONT ON FRIDAY. THE 12Z EC REMAINS A TAD SLOWER BECAUSE IT HAS A MORE WELL-DEFINED WAVE DEVELOP ALONG THE FRONT...AND HAVE LEANED THE FORECAST CLOSER TO THAT. THE KEY WITH THAT IS THIS SOLUTION IS THAT MODERATE RAIN WOULD LIKELY NOT PUSH INTO THE EASTERN FORECAST AREA...EAST OF I-55...UNTIL THANKSGIVING NIGHT. DRIZZLE MAY STILL OCCUR DURING THE DAY IN THAT AREA. THE LONGER RAIN POTENTIAL AND HIGHER QPF IS STILL MOST FAVORED OVER NORTH CENTRAL AND NORTHEAST ILLINOIS...WHICH OF COURSE IS THE AREA WITH THE HIGHER SNOW COVER. THE CURRENT FORECAST OF QPF IN OUR NORTHWEST AREA IS AROUND AN INCH AND A HALF...AND THAT IS NOT TO THE POINT WHERE WE WOULD EXPECT MUCH FOR NON-RIVER FLOODING IMPACTS. THIS IS BECAUSE THE MELT SHOULD PERCOLATE INTO THE GROUND GIVEN THE FREEZING LAYER IN THE LAYER IS VERY SHALLOW. SEE THE HYDROLOGY DISCUSSION BELOW FOR MORE ON THE DETAILS OF RIVER IMPACTS. DESPITE THE CLOUDS AND RAIN...LOW-LEVEL WARM ADVECTION WILL BRING A MILD THANKSGIVING WITH HIGHS CLOSE TO 50 NORTH AND SEVERAL DEGREES ABOVE 50 PRESENTLY FAVORED ACROSS THE THEN NEAR SNOW COVER-FREE SOUTH. ON THE BACKSIDE OF THE SYSTEM...COLD ADVECTION WILL LIKELY LEAD TO STEADY OR FALLING TEMPERATURES ON FRIDAY. THIS COULD BRING A LIGHT MIX OR LIGHT SNOW BEFORE THE SYSTEM ENDS. THERE IS THE POTENTIAL FOR SOME LAKE EFFECT SNOW SHOWERS INTO FAR NORTHWEST INDIANA FRIDAY NIGHT...BUT OVERALL THE PARAMETERS ARE NOT INDICATED TO BE GREAT WITH SHALLOW INVERSION HEIGHTS YIELDING MARGINAL CLOUD DEPTHS THAT DO NOT PERSIST LONG. MTF && .HYDROLOGY...340 PM CST A RAIN ON SNOW MELT SCENARIO IS SHAPING UP OVER THE REGION WEDNESDAY NIGHT THROUGH EARLY FRIDAY. OBSERVERS ON MONDAY MORNING RECORDED SNOW WATER EQUIVALENT VALUES OF MAINLY 0.9 TO 1.3 ACROSS FAR NORTHERN ILLINOIS WITHIN THE DEEPEST SNOW COVER. WEATHER PARAMETERS FAVORABLE FOR RAPID SNOW MELT ARE SET TO MOVE ACROSS THE REGION LATER WEDNESDAY WITH RAIN FURTHER SPEEDING THAT UP ON THANKSGIVING. AMOUNTS OF OVER AN INCH ARE LIKELY ACROSS ESPECIALLY NORTHERN ILLINOIS...AND IT IS NOT IMPOSSIBLE TO HAVE TWO INCH AMOUNTS GIVEN THE PARAMETERS. THE FROZEN SOIL DEPTH IS VERY SHALLOW AND WOULD LEAN TOWARD THAT NOT REALLY IMPACTING PERCOLATION OF THE RAIN/MELT. WITH STREAMFLOW VALUES RUNNING HIGHER THAN NORMAL FOR SOME STREAMS AND RIVERS THANKS TO THE WET PAST FOUR WEEKS...THERE IS CONCERN FOR SOME STREAMS TO POTENTIALLY RISE INTO FLOOD STAGE. HAVE CONTINUED ESF AT THIS TIME WITH DETAILS IN SPECIFIC RAINFALL AMOUNTS AND TIMING TO BE REFINED AS THE EVENT APPROACHES. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 09Z... * POTENTIAL FOR LOWER VIS IN FOG THROUGH EARLY MORNING...ESPECIALLY WEST OF ORD/MDW. KJB //DISCUSSION...UPDATED 06Z... THE MAIN AVIATION WEATHER CONCERNS WILL BE THE POTENTIAL FOR PATCHY AREAS OF FOG THROUGH EARLY THIS MORNING...ESPECIALLY AT KRFD AND KDPA. SURFACE HIGH PRESSURE...CURRENTLY CENTERED OVER NORTHERN ILLINOIS WILL CONTINUE TO RESULT IN LIGHT AND VARIABLE WINDS ACROSS THE AREA THROUGH MID TO LATE MORNING. ASIDE FROM A DECK OF HIGH LEVEL CLOUDS...MAINLY OVER IOWA...SKIES HAVE REMAINED CLEAR TO PARTLY CLOUDY...AND THIS HAS ALLOWED TEMPERATURES TO RADIATE SIGNIFICANTLY ACROSS NORTH CENTRAL ILLINOIS. SOME SPOTTY AREAS OF DENSE FOG HAVE BEEN REPORTED FROM TIME TO TIME UNDER THIS HIGH...BUT OBSERVATIONAL TRENDS SUGGEST THAT THIS FOG IS NOT ONLY SPOTTY...BUT LIKELY FAIRLY SHALLOW AS WELL. WITH THIS IN MIND...WHILE SOME LOWER VISIBILITIES MAY DEVELOP ACROSS KRFD AND KDPA OVERNIGHT...IT APPEARS THAT THE LOWER VISIBILITIES WILL BE MORE OF A TEMPO CONDITION RATHER THAN PREVAILING. FOR THIS REASON I HAVE INCLUDED THE LOWEST VISIBILITIES IN TEMPO GROUPS THIS MORNING. FOG MAY HAVE A HARDER TIME DEVELOPING OVER THE MAIN TERMINALS TONIGHT...SO I HAVE ONLY CONTINUED THE MENTION OF 5-6 SM VISIBILITIES OVERNIGHT. OTHERWISE...IT APPEARS EAST-SOUTHEASTERLY WINDS WILL DEVELOP THROUGH THE AFTERNOON...AND CONTINUE THIS EVENING BEFORE TURNING SOUTH OVERNIGHT. KJB //ORD AND MDW CONFIDENCE...UPDATED 09Z... * LOW IN EXTENT/VISIBILITY IMPACTS IN FOG FOR THE MAIN TERMINALS. MEDIUM IN CIG TRENDS AND HIGH IN WINDS. KJB //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...MVFR/IFR FOG POSSIBLE ESPECIALLY WEDNESDAY NIGHT WITH LIGHT RAIN OR DRIZZLE DEVELOPING. THURSDAY...IFR LIKELY/LIFR POSSIBLE FOG WITH RAIN AND DRIZZLE LIKELY. FRIDAY...MVFR LIKELY WITH RAIN...POSSIBLY MIXING WITH SNOW BEFORE ENDING BY EVENING. SATURDAY...VFR. SUNDAY...MVFR POSSIBLE. SLIGHT CHANCE OF LIGHT SNOW. RATZER && .MARINE... 151 AM CST THE MAIN FORECAST CONCERN WILL BE WITH THE INCREASING POTENTIAL FOR A PERIOD OF SOUTHERLY GALES...ESPECIALLY OVER THE NORTHERN HALF OF LAKE MICHIGAN WENDESDAY INTO WEDNESDAY EVENING. LOW PRESSURE IS EXPECTED TO SHIFT RAPIDLY TO THE NORTHEAST ACROSS MINNESOTA AND INTO ONTARIO WEDNESDAY INTO WEDNESDAY NIGHT. STRONG PRESSURE FALLS AHEAD OF THIS FEATURE WILL LIKELY LEAD TO AN UPTICK IN SOUTHERLY WINDS OVER THE LAKE ON WEDNESDAY...WITH GALES OF 35 TO 40 KT POSSIBLE OVER NORTHERN HALF OF THE LAKE. WITH THIS IN MIND...WE WILL BE ISSUING A GALE WATCH TO COVER THIS POTENTIAL. A COLD FRONT IS EXPECTED TO SHIFT SOUTHEASTWARD DOWN LAKE MICHIGAN LATER ON THANKSGIVING AND INTO FRIDAY MORNING. ASIDE FROM A DECENT AMOUNT OF PRECIPITATION ASSOCIATED WITH THE FRONT...EXPECT WINDS TO INCREASE OUT OF THE NORTH IN ITS WAKE. A PERIOD OF 30 TO PERHAPS 35 KT WINDS LOOK LIKE A GOOD BET ON FRIDAY. ANOTHER WEATHER SYSTEM LOOKS TO TAKE AIM ON THE GREAT LAKES REGION LATER IN THE WEEKEND. THIS COULD AGAIN RESULT IN SOME STRONGER WINDS OVER THE LAKE INTO EARLY NEXT WEEK. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 250757 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 257 AM CDT TUE AUG 25 2015 .SHORT TERM... 248 AM CDT THROUGH WEDNESDAY... THE EXPANSIVE STACKED CLOSED LOW CONTINUES TO GYRATE ACROSS ONTARIO AND THE GREAT LAKES REGION. WHILE HEIGHTS AND PRESSURES ARE FILLING THERE REMAINS ANOMALOUSLY COOL AIR OVER THE REGION AS INDICATED BY THE 3C AT 850MB ON THE 00Z GRB SOUNDING LAST EVE /RIGHT AT A RECORD DAILY LOW IN THEIR 62-YEAR CLIMATOLOGY/. CLOUDS WITHIN THIS COLD ADVECTION REGIME HAD SPILLED INTO THE AREA LATE YESTERDAY. WITH THE ADVECTION SCHEME MORE NEUTRAL TODAY AND A LITTLE LESS VORTICITY STRENGTH OVERHEAD...EXPECT SOME LARGE HOLES IN THE CLOUDS THIS MORNING...POSSIBLY EVEN OUTRIGHT SUNNY. THERE SHOULD BE A NOTABLE DIURNAL RE-EXPANSION OF THE STRATOCUMULUS AS LAPSE RATES STEEPEN. CLOUDS SHOULD BE LESS PREVALENT TONIGHT WITH HEIGHT RISES AND WEAKENING CYCLONIC FLOW...BUT STILL SLOW TO CLEAR ESPECIALLY IN EASTERN AREAS. AS FLOW TURNS MORE NORTHERLY TONIGHT INTO WEDNESDAY MORNING...EARLY SEASON LAKE EFFECT CLOUDS SHOULD CONTINUE INTO PARTS OF NORTHWEST INDIANA. CLOUD DEPTHS ARE ONLY A FEW THOUSAND FEET BUT CONCEIVABLE SOME SPRINKLES OR LIGHT SHOWERS COULD OCCUR IN PORTER COUNTY. THE 00Z NAM INITIALIZED ABOUT 2C TOO WARM ACROSS THE GREAT LAKES REGION AT 850MB...WHICH SHOULD BE NEAR OR A LITTLE UNDER THE MIXING HEIGHT ONCE AGAIN TODAY. HAVE SLIGHTLY UNDERCUT A GUIDANCE BLEND FOR HIGHS TODAY WITH UPPER 60S FAR NORTH TO LOWER 70S ELSEWHERE. LOWS TONIGHT AGAIN WILL BE CHALLENGING DEPENDING ON THE RATE AT WHICH CLOUDS CLEAR...WHICH THEY LIKELY WONT IN SOME EASTERN LOCALES. NORTH CENTRAL ILLINOIS IS MOST SUSCEPTIBLE TO LOWS AROUND 50 DEGREES. HIGH PRESSURE WILL MOVE OVERHEAD BY WEDNESDAY AFTERNOON WITH DIMINISHING WINDS AND ONSHORE FLOW ESTABLISHING ITSELF FOR LAKE ADJACENT AREAS. OVER THE PAST WEEK...UPWELLING OF COOLER WATER HAS BROUGHT NEARSHORE WATER TEMPERATURES OFF OF NORTHEAST ILLINOIS DOWN TO THE UPPER 40S TO LOWER 60S AFTER PREVALENT UPPER 60S TO LOWER 70S DURING EARLY AUGUST. THIS COULD RESULT IN QUICK COOLING BEHIND THE WIND SHIFT ON WEDNESDAY AFTERNOON INTO THE MID OR POSSIBLY EVEN LOWER 60S FOR DOWNTOWN CHICAGO. MTF && .LONG TERM... 248 AM CDT WEDNESDAY NIGHT THROUGH MONDAY... HIGH PRESSURE CONTINUES ON THURSDAY WITH MODIFYING TEMPERATURES IN MOST PLACES OUTSIDE OF LAKE ADJACENT AREAS WHICH AGAIN ARE LIKELY TO HOLD MORE AROUND 70 OR DROP INTO THE MID-UPPER 60S DURING THE AFTERNOON. FRIDAY WILL SEE SOUTHERLY FLOW AS A SHORT WAVE APPROACHES FROM THE UPPER PLAINS WITH UPPER 70S FORECAST ACROSS MUCH OF THE AREA. THE UPPER FORCING WITH THIS SYSTEM PULLS AHEAD OF THE BETTER LOW-LEVEL MOIST RETURN FLOW BY LATER FRIDAY NIGHT WHEN THE 500MB WAVE IS FORECAST TO BE OVER THE AREA. AS THE WAVE DE-AMPLIFIES IN RESPONSE THE WEAKENING SURFACE BOUNDARY SLOWS ACROSS OR JUST SOUTH OF THE AREA THROUGH SATURDAY NIGHT AND POSSIBLY EVEN SUNDAY. OVERALL HAVE A CHANCE OF SHOWERS AND ISOLATED STORMS THROUGH THIS TIME. BEHIND THIS SYSTEM FOR NEXT WEEK...GLOBAL GUIDANCE AGREES ON ABOVE NORMAL HEIGHTS WITH AN UPPER RIDGE ACROSS THE PLAIN STATES INTO THE CANADIAN PRAIRIES. THIS LOOKS TO FAVOR TEMPERATURES NEAR OR ABOVE NORMAL FOR THE START OF METEOROLOGICAL AUTUMN AS THIS EXPANDS INTO OUR REGION...AND THIS IS SUPPORTED BY HIGHER CONFIDENCE OF SUCH IN THE CPC 6-10 DAY AND 8-14 DAY OUTLOOKS. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * NONE. JEE //DISCUSSION...UPDATED 06Z... HIGH PRESSURE OVER THE GREAT PLAINS WILL SHIFT EAST OVER THE WESTERN GREAT LAKES REGION THIS EVENING. AS SUCH WEST-NORTHWEST WINDS WILL INCREASE TO ARND 12 KT LATE THIS MORNING AND THEN WEAKEN AND BECOME NORTHWEST THIS AFTERNOON AND EVENING. WINDS WILL BECOME NORTH-NORTHWEST TONIGHT. THE BKN050 CLOUD DECK MAY SCATTER SLIGHTLY THIS MORNING BUT EXPECTING ANOTHER SIMILAR BKN VFR DECK TO FORM LATE THIS MORNING AND PERSIST THROUGH THE TAF TIME FRAME. JEE //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH CONFIDENCE IN ALL FORECAST ELEMENTS. JEE //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z... WEDNESDAY...VFR. NORTHWEST WINDS BECOMING NORTHEAST IN AFTERNOON. THURSDAY...VFR. EAST WINDS BECOMING SOUTH LATE. FRIDAY...MAINLY VFR. CHANCE OF RAIN/SLIGHT CHANCE OF THUNDER LATE. SOUTH WINDS. SATURDAY...MAINLY VFR. CHANCE OF RAIN/THUNDER. SOUTH WINDS BECOMING EAST. SUNDAY...VFR. EAST WINDS. BEACHLER && .MARINE... 248 AM CDT THE LOW OVER NORTHEAST ONTARIO WILL CONTINUE INTO NORTHERN QUEBEC BY WEDNESDAY MORNING WHILE HIGH PRESSURE OVER THE PLAINS WILL SPREAD OVER THE WESTERN GREAT LAKES WEDNESDAY EVENING. NORTHWEST WINDS TO 25 KT WILL DIMINISH OVER THE SOUTHERN END OF THE LAKE TODAY WHILE THE FAR NORTHERN END CONTINUES TO SEE 25 KT GUSTS THROUGH TONIGHT. WILL KEEP THE SMALL CRAFT ADVISORY AS IS FOR POINTS EAST OF GARY INDIANA AS WAVES WILL SUBSIDE TO BELOW SMALL CRAFT CRITERIA THIS AFTERNOON. WINDS DIMINISH ACROSS THE LAKE TO 15 KT OR LESS AND BECOME NORTH WEDNESDAY AFTERNOON. LIGHT AND VARIABLE WINDS THURSDAY BECOME SOUTHWEST TO 20 KT THURSDAY NIGHT AS THE HIGH SHIFTS EAST. A LOW PRESSURE SYSTEM EJECTS OVER THE CENTRAL PLAINS THURSDAY EVENING AND WEAKENS AS IT MOVES OVER THE CENTRAL MISSISSIPPI VALLEY SATURDAY MORNING. WINDS REMAIN LIGHT OVER THE LAKE AT 15 KT OR LESS WITH DIRECTIONS VARYING FROM SOUTH TO EAST FRIDAY THROUGH THE WEEKEND. JEE && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...BEACH HAZARDS STATEMENT...INZ002 UNTIL 10 PM TUESDAY. LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 PM TUESDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 270816 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 316 AM CDT TUE OCT 27 2015 .SHORT TERM... 316 AM CDT THROUGH TONIGHT... A CLASSIC MID TO LATE AUTUMN SYSTEM FOR MIDWEEK IS THE MAIN IMPACTING WEATHER AND HAD THE FOCUS OF THE FORECAST THIS MORNING. AS CAN BE THE CASE WITH AUTUMN CYCLONES...THE MAIN IMPACTS LOOK TO BE RAIN...STRONG WINDS...AND A SHARP TEMPERATURE DROP. SO NO HEADLINES AT THIS TIME THOUGH CANNOT RULE OUT A WIND ADVISORY FOR PART OF WEDNESDAY AFTERNOON AND EARLY EVENING. ALSO NOT A ZERO CHANCE FOR THE FIRST FLURRIES IN FAR NORTHERN ILLINOIS NEAR DAYBREAK THURSDAY...BUT AT THIS TIME THAT CHANCE IS LOW. A BETTER CHANCE EXISTS FOR SOME GRAUPEL IN WEDNESDAY AFTERNOON SHOWERS. THE PRIMARY CIRCULATION FROM...IN PART...ONCE HURRICANE PATRICIA HAS EASED ACROSS THE SOUTHEAST U.S...HOWEVER ITS SUBTROPICAL AIRMASS REMAINS AS SEEN ON SATELLITE AND LAST EVES RAOBS. MEANWHILE...A BROAD AMPLIFYING TROUGH ACROSS WESTERN CANADA INTO THE INTERMOUNTAIN U.S. HAS MULTIPLE LOW AMPLITUDE BUT STRONG SHORT WAVES ALL PROGRESSING EAST. THE OVERALL INFLUENCE OF THESE WILL BE TO DRAG THAT MOISTURE NORTHWARD TODAY TROUGH GRADUALLY STRENGTHENING ISENTROPIC LIFT. DRY AIR OVER THE REGION IN THE LOW- LEVELS...AS INDICATED BY EARLY MORNING AIRCRAFT SOUNDINGS AND SIMPLY SURFACE DEW POINTS IN THE MID 30S IN PLACES...WILL LIMIT SOME OF THE LEADING EDGE RAIN. HAVE GONE JUST A SHADE SLOWER THAN THE 3KM NCAR WRF ENSEMBLE FOR RAIN SPREADING NORTH TODAY...WHICH IS GENERALLY SUPPORTED BY OTHER HIGH-RES GUIDANCE. THE RAIN WILL LARGELY PERSIST ONCE IT STARTS THROUGH LATE TONIGHT WHEN A DRY SLOT STARTS TO MOVE OVER THE REGION. RAIN AMOUNTS THROUGH TONIGHT ARE FORECAST TO RANGE BASICALLY BETWEEN THREE QUARTERS OF AN INCH AND A LITTLE OVER AN INCH. THIS TIME OF YEAR SOMETIMES CAN SEE LEAVES IN DRAINS BECOME A LOCAL ISSUE...BUT OTHERWISE NO MAJOR IMPACTS BESIDES A SLOWER THAN NORMAL AFTERNOON COMMUTE. THIS RAIN COMBINED WITH INCREASING EASTERLY WINDS SHOULD RESULT IN TEMPERATURES SLIGHTLY FALLING ONCE RAIN STARTS AND THEN FLAT- LINING. EASTERLY WINDS WILL GUST TO 25-30 MPH THIS AFTERNOON WHILE AROUND 35 MPH NEAR THE SHORE...CERTAINLY GIVING A BITE TO THE AIR. WAVES RESULTING FROM THESE WINDS ARE EXPECTED TO REMAIN BELOW LAKESHORE FLOODING ADVISORY CRITERIA FOR THE CHICAGO SHORE...THOUGH STILL SOME OCCASIONAL WAVES TOWARD 10 FT MAY BE SEEN. MTF && .LONG TERM... 316 AM CDT WEDNESDAY THROUGH MONDAY... NUMERICAL GUIDANCE CONTINUES IN STRONG AND CONSISTENT AGREEMENT WITH RAPID CYCLOGENESIS ON WEDNESDAY...WHICH IS SUPPORTED BY THE WEATHER PATTERN DESPITE NOT THE STRONGEST OF SURFACE BAROCLINIC GRADIENTS. THE REAL IMPETUS TO THIS DEEPENING IS THE FINAL AND STRONGEST SHORT WAVE OVER NORTHERN MANITOBA THIS MORNING THAT WILL PHASE INTO THE SYSTEM. ITS PARENT JET STREAK OF OVER 130 KT WILL DROP SOUTHWARD AS THE WAVE AMPLIFIES WEDNESDAY MORNING AND A DEEP POTENTIAL VORTICITY ANOMALY IS FORECAST TO DEVELOP...WITH CORRELATING 200M HEIGHT FALLS DURING THE DAY WEDNESDAY. THIS WILL PROVIDE FOR DEEP CYCLOGENESIS ACROSS THE NORTHERN GREAT LAKES WITH NCEP MODELS AVERAGING 13MB/12HR SURFACE PRESSURE FALLS. THIS YIELDS VERTICALLY ALIGNED AND STRONG COLD ADVECTION IN THE COLUMN INTO OUR AREA BY MID-LATE WEDNESDAY AFTERNOON AS THE PRESSURES RISE RAPIDLY. HAVE FORECAST WESTERLY WIND GUSTS OF 35 MPH FOR MUCH OF THE TIME...BUT IN THE FEW HOURS FOLLOWING THE FRONT SOME GUSTS TO 45 MPH ARE POSSIBLE AND INDICATED BY ABOUT ONE QUARTER OF TOP MATCHING CIPS ANALOGS. WHILE SCATTERED SHOWERS ARE PROBABLE WEDNESDAY MORNING...THE COLD FRONT ITSELF IS LIKELY TO HAVE SOME CONVECTIVE SHOWERS ALONG AND NEAR IT BASED ON UNSTABLE FORECAST SOUNDINGS. GIVEN THE RAPID COOLING IN THE SHALLOW BUT CONVECTIVE CLOUD DEPTHS...IT IS POSSIBLE TO HAVE GRAUPEL WITH ANY SHOWERS THAT AFTERNOON. WRAPAROUND DEFORMATION WITH THE FULLY DEVELOPED CYCLONE LATE WEDNESDAY NIGHT IS LIKELY TO SEND SOME LOW CLOUDS OVER THE AREA FOR THURSDAY...AND THIS IS WHERE A SMALL CHANCE FOR SPRINKLES COULD BE SEEN THURSDAY MORNING...AND AGAIN AN OUTSIDE CHANCE OF SOME FLURRIES TOWARD ROCKFORD. AS WINDS START TO SETTLE AFTER A BLUSTERY THURSDAY...TEMPERATURES SHOULD DROP OFF QUICKLY THURSDAY NIGHT AND HAVE BUMPED DOWN FORECAST LOWS. THE MODEL TREND THE PAST 24 HOURS HAS SUPPORTED SHOWERS ON SATURDAY AND SATURDAY EVENING FOR THOSE THINKING ABOUT HALLOWEEN. HOWEVER...THIS IS FROM A SPLIT FLOW PATTERN BEHIND THE MIDWEEK SYSTEM AND A LOT OF THE RAIN COVERAGE WILL DEPEND ON HOW THE NORTHERN AND SOUTHERN STREAMS INTERACT...SO CONFIDENCE REMAINS LOW. TEMPERATURES ALSO DEPEND ON ANY RAIN AND COVERAGE BUT FOR RIGHT NOW FORECASTING HIGHS IN THE MID 50S...PRETTY CLOSE TO NORMAL. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * INCREASINGLY STRONG/GUSTY EASTERLY WINDS TODAY. * RAIN SPREADING NORTH ACROSS THE TERMINALS THIS AFTERNOON...CONTINUING FOR MOST OF TONIGHT. * STEADILY LOWERING CEILINGS/VIS LATER TODAY AND TONIGHT. RODRIGUEZ //DISCUSSION...UPDATED 06Z... GENERALLY QUIET IN THE NEAR TERM WITH ONLY HIGH LEVEL CLOUD COVER AND WITH A LIGHTER EASTERLY WIND IN PLACE...WHICH WILL LIKELY CONTINUE FOR THE REMAINDER OF THE EARLY MORNING PERIOD. WINDS WILL OBSERVE A STEADY INCREASE LATER THIS MORNING INTO THE AFTERNOON AS A DEVELOPING SYSTEM LIFTS NORTH TO THE AREA AND THEN HELPS SPREAD RAIN OVER MUCH OF THE REGION. AT THIS TIME...HAVE MADE LITTLE CHANGES TO PRECIP/VIS AND CEILING TRENDS LATER TODAY AND TONIGHT...BUT WITH AN EXTENDED PERIOD OF RAIN STILL LIKELY WITH LOWERING CEILINGS TO AT LEAST IFR. HAVE EXCLUDED ANY MENTION OF LIFR CEILINGS LATER TONIGHT...BUT WILL CONTINUE TO EVALUATE POSSIBLE INCLUSION IN THE NEXT FORECAST. CONDITIONS TO LIKELY REMAIN THE SAME TOWARDS EARLY WEDNESDAY MORNING...BUT WITH COVERAGE OF STEADIER RAIN POSSIBLY LOWERING DURING THIS TIME. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 06Z... * MEDIUM CONFIDENCE ON WIND SPEEDS/GUSTS THIS AFTERNOON/EVENING. * HIGH CONFIDENCE OF RAIN THIS AFTERNOON/TONIGHT...MEDIUM CONFIDENCE ON EXACT TIMING/DURATION. * HIGH CONFIDENCE OF LOWERING CEILINGS/VIS LATER TODAY AND TONIGHT...LOW MEDIUM ON EXACT TIMING AND HOW LOW THEY WILL FALL. RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z SUNDAY...UPDATED 00Z... WEDNESDAY...STRONG SOUTHWEST-WEST WINDS. IFR CIGS EARLY LIFTING TO MVFR. SCATTERED SHOWERS/POSSIBLY WITH GS IN AFTERNOON. THURSDAY...MVFR CIGS POSSIBLE. GUSTY WEST WINDS. FRIDAY...VFR. SATURDAY AND SUNDAY...CHANCE OF SHOWERS. PERIODIC MVFR CIGS PROBABLE...SMALLER CHANCE OF IFR. IZZI && .MARINE... 244 PM CDT IDEAL MARINE CONDITIONS TONIGHT WILL START TO DETERIORATE BY EARLY TUESDAY. AHEAD OF A LARGE EXTRA-TROPICAL SYSTEM... WINDS WILL INCREASE FROM THE EAST AND GUST OVER 20KT. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR SOUTHWEST LAKE MICHIGAN. STRONG WINDS WILL REMAIN IN PLACE AND INCREASE TUESDAY NIGHT AS LOW PRESSURE ADVANCES AND THE PRESSURE GRADIENT TIGHTENS. WINDS WILL SHIFT MORE SOUTHWESTERLY BEHIND THE LOW...BUT ADDITIONAL INSTABILITY ACROSS THE LAKE WILL LEAD TO INCREASED WIND THROUGH WEDNESDAY. AN UPPER LEVEL DISTURBANCE WILL CROSS THE REGION ON WEDNESDAY NIGHT...LEADING TO FURTHER COLD AIR ALOFT AND UNSTABLE LAKE CONDITIONS. THIS WILL COUPLE WITH A TIGHT PRESSURE GRADIENT TO CREATE WESTERLY GALES. WIND SPEEDS OVER 30KT WILL BE PREVALENT ACROSS MOST OF THE LAKE THROUGH THURSDAY. WINDS COME DOWN SIGNIFICANTLY AFTER THURSDAY NIGHT UNDER NORTHWEST FLOW. MM && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 AM TUESDAY TO 4 AM WEDNESDAY. SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 AM TUESDAY TO 10 PM WEDNESDAY. GALE WATCH...LMZ777-LMZ779...1 PM WEDNESDAY TO 4 PM THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 290835 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 335 AM CDT THU OCT 29 2015 .SHORT TERM... 331 AM CDT THROUGH TONIGHT... TODAY BRINGS ONE MORE DAY OF INFLUENCE FROM THE POTENT AUTUMN SYSTEM AND THIS WILL BE A WINDY AND COOL INFLUENCE WITH THE LOWEST DAYTIME TEMPERATURES OF THE AUTUMN THUS FAR. THE FORECAST FOCUS THEN SHIFTS TO SATURDAYS RAIN LIKELIHOOD WHICH CONTINUES TO INCREASE. WHILE THE RISK OF HIGH IMPACT WEATHER IS QUITE LOW...TRYING TO GET A HANDLE ON RAIN TIMING AND COVERAGE FOR THE TRICK-OR-TREAT DAY AND EVENING WAS OF FOCUS. THE CALENDAR THEN SHIFTS TO NOVEMBER AND THE SIGNAL FOR A WARM TO VERY WARM FIRST WEEK OF NEXT MONTH CONTINUES TO INCREASE. THE MASSIVE MATURE MID-LATITUDE CYCLONE LOOKS IMPRESSIVE ON MORNING GOES WATER VAPOR IMAGERY...WITH ITS CENTER ACROSS THE WESTERN GREAT LAKES AND ITS MOIST CONVEYOR BELT EXTENDING ALL THE WAY UP THE EASTERN SEABOARD TO NEAR JAMES BAY AND BACK AROUND INTO THE UPPER MISSISSIPPI VALLEY. THIS WRAPAROUND IS IN-SYNC WITH BROAD DEFORMATION AND LIFT...SUPPORTING SHOWERS TO NEAR THE STATE LINE AS OF 330 AM. LIGHT SNOW HAS BEEN OBSERVED AS FAR SOUTH AS ROCKTON ILLINOIS AS REPORTED ON SOCIAL MEDIA. AS THE DEFORMATION PIVOTS SLIGHTLY SOUTH OF EAST...SOME FORCING WILL CONTINUE TO CROSS SOUTH OF THE STATE LINE BY DAYBREAK. SO SOME MORNING FLURRIES OR A LIGHT MIX NORTH OF I-88 MAY BE SEEN FOR THE SEASONS FIRST. THE VORTICITY LOBE AIDING THESE SHOWERS ROTATES EAST BY LATE MORNING THOUGH THE ADVECTION OF MOISTURE FOR CLOUDS WILL ONLY STRENGTHEN. SO A CLOUDY DAY IS ON TAP DESPITE SOME SEEING SUNSHINE AT DAYBREAK. CANNOT RULE OUT SOME PATCHY SPRINKLES THIS AFTERNOON BUT THAT SHOULD BE IT AS CONVECTIVE CLOUD DEPTHS BECOME VERY SHALLOW. SOME LIGHT LAKE EFFECT RAIN SHOWERS MAY BE SEEN IN NORTHERN PORTER COUNTY LATE THIS AFTERNOON AND TONIGHT AS BOUNDARY LAYER FLOW TURNS MORE NORTHWESTERLY. THE PRESSURE GRADIENT AROUND THE 982MB LOW REMAINS VERY TIGHT OVER A LARGE DISTANCE FROM ITS EASTERN ONTARIO CENTER...INCLUDING OVER OUR FORECAST AREA. IN ADDITION...THE RATE OF RISING PRESSURES WILL INCREASE TODAY WITH A STRONG ISALLOBARIC COMPONENT AIDING SUSTAINED WIND SPEEDS. EXPECTING THESE TO BE 20 TO 25 MPH WITH 35 TO 40 MPH GUSTS THROUGH MUCH OF THE DAY. ADVECTION ON THESE WINDS BECOMES MORE NEUTRAL BY AFTERNOON...BUT STILL NOT EXPECTING MUCH OF A TEMPERATURE RECOVERY AT ALL GIVEN THE CLOUDS AND 850MB TEMPERATURES AROUND -3C. HAVE HIGHS MAINLY MID 40S NORTH TO UPPER 40S SOUTH. GIVE THE SHEER SIZE OF THIS SYSTEM...THE LOW CLOUDS EXTEND BACK TO THE NORTHWEST AS FAR AS SOUTHERN CANADA...SO CONTINUE TO TREND MORE PESSIMISTIC WITH ANY CLEARING THROUGH EARLY FRIDAY MORNING. IN RESPONSE...THE LOW TEMPERATURES TONIGHT SHOULD NOT DROP MUCH. IF WESTERN AREAS CAN SCATTER OUT LATE THE WINDS SHOULD BE RELAXED ENOUGH TO ALLOW THEM TO DROP QUICKLY TO AROUND 30. MTF && .LONG TERM... 331 AM CDT FRIDAY THROUGH WEDNESDAY... AN UPPER JET MAXIMUM IS FORECAST TO RIDE INTO THE PACIFIC NORTHWEST ON FRIDAY WITH ENERGY TRANSLATING BOTH INTO THE NORTHERN STREAM AND INTO AN EXISTING CLOSED NEAR THE CA/AZ BORDER. BOTH FEATURES PROGRESS EAST AND REMAIN DISTINCT BUT INCREASE IN INTENSITY ON SATURDAY. MOISTURE IS STEERED FAIRLY QUICKLY UP THE MISSISSIPPI RIVER VALLEY FROM THE COMBINED EFFECTS OF BOTH SYSTEMS. MODEL GUIDANCE IS IN GENERAL AGREEMENT WITH LATE FRIDAY NIGHT THROUGH MID- AFTERNOON SATURDAY BEING WET OVER THE AREA AS LIFT SHIFTS OVER THE AREA WITH A COMBINATION OF ISENTROPIC ASCENT...MOISTURE CONVERGENCE...AND A CHANNEL OF UPPER FORCING FOR RAIN. THE ECMWF CONTINUES TO BE A SHADE SLOWER THAN THE GFS AND HAVE LEANED THAT ROUTE. BUT IT STILL WOULD APPEAR IN AT LEAST MODEL SOLUTIONS...THAT GIVEN THE PROGRESSION OF THE SPLIT FLOWS THAT THE RAIN SHOULD COME TO AN ABRUPT WEST-TO-EAST END SOMETIME LATE SATURDAY OR SATURDAY EVENING. TEMPERATURES SHOULD NOT HAVE MUCH DIURNAL RANGE ON SATURDAY...LIKELY REMAINING AROUND 50 MUCH OF THE DAY. ANOTHER JET MAXIMUM RIDES SOUTHEASTWARD INTO THE WESTERN CONUS SHORE EARLY NEXT WEEK CARVING OUT A LARGE TROUGH IN THE WEST. UPSTREAM THIS WILL SUPPORT MILD CONDITIONS...ESPECIALLY WITH MODERATION ALREADY HAVING HAPPENED ON SUNDAY INTO MONDAY. WITH A BACKBUILDING RIDGE FORECAST ACROSS THE GULF OF MEXICO AND SOUTHEAST U.S...A CHANNEL OF VERY MILD 925MB-700MB TEMPERATURES ARE FORECAST TO EXPAND NORTHEAST OVER THE AREA. SOME OF THESE TEMPERATURES ARE NEAR RECORD LEVELS FOR THE TIME OF YEAR...BUT OBVIOUSLY THE CHALLENGE IS HOW DOES IT CORRESPOND TO SURFACE READINGS. LOOKING BACK AT NARR DATA FOR 925MB TEMPERATURES AT 13C OR HIGHER DURING THE FIRST HALF OF NOVEMBER...THESE DAYS HAVE RESULTED IN AN AVERAGE HIGH OF 69 AT CHICAGO. WHILE THE PATTERN LOOKS DRY AT LEAST TUESDAY INTO WEDNESDAY...THE WIND DIRECTION CURRENTLY FORECASTED IS MORE TOWARD DUE SOUTH. A SOUTHWEST DIRECTION WOULD BE THE MOST IDEAL TO REACH TEMPERATURES IN THE 70S...AND DUE SOUTH WINDS CAN DRAG UP STRATUS THIS TIME OF YEAR TOO. SO CONTINUE WELL ABOVE NORMAL IN THE FORECAST AND SLIGHTLY ABOVE A SMART MODEL BLEND. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * GUSTY WEST/SOUTHWEST WINDS THROUGH THIS AFTERNOON. * MVFR CEILINGS. RODRIGUEZ //DISCUSSION...UPDATED 06Z... SCATTERED CLOUDS WITH DRY CONDITIONS CURRENTLY ACROSS ALL THE TERMINALS EARLY THIS MORNING...BUT WITH SOME UPSTREAM PRECIP TRYING TO INCH CLOSER TO PRIMARILY RFD. AT THIS TIME...IT DOES APPEAR THAT THIS SHOULD STAY JUST TO THE NORTH OF RFD IN SOUTHERN WISCONSIN...BUT WILL CONTINUE TO MONITOR FOR THIS TO POSSIBLY/BRIEFLY IMPACT ONLY RFD. VFR CEILINGS WILL RETURN OVER THE NEXT SEVERAL HOURS WITH MVFR CEILINGS THEN RETURNING LATER THIS MORNING THROUGH TODAY. ANOTHER DAY OF WINDY CONDITIONS...AS WEST/SOUTHWEST WINDS GUST AROUND 30KT OR HIGHER THIS MORNING. WINDS WILL GRADUALLY TURN MORE NORTHWEST THIS AFTERNOON AND DIMINISH...FURTHER DIMINISH LATER THIS EVENING. RODRIGUEZ //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH WITH WIND SPEED/DIRECTION. * MEDIUM HIGH WITH CEILING TRENDS. RODRIGUEZ //OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z TUESDAY...UPDATED 00Z... 00Z... FRIDAY...VFR. CHANCE SHRA AFTER MIDNIGHT. SATURDAY...SHRA LIKELY. MVFR CIGS/VIS LIKELY. IFR POSSIBLE. SUNDAY...VFR. WX NIL. MONDAY...VFR. WX NIL. TUESDAY...VFR. WX NIL. KREIN && .MARINE... 224 PM CDT SURFACE LOW PRESSURE WILL CONTINUE TO STRENGTHEN TONIGHT AS IT MOVES TO THE TIP OF JAMES BAY BY DAYBREAK THURSDAY...THEN CONTINUE STRENGTHENING AS IT MOVES NORTHEAST THROUGH NORTHERN QUEBEC THURSDAY AND FRIDAY. THE LOWS COLD FRONT WILL PASS OVER THE LAKE TONIGHT...AND THIS WILL RESULT IN GALE FORCE WSW WINDS OVER THE LAKE. HIGH PRESSURE CURRENTLY OVER THE NORTHERN ROCKIES WILL ELONGATE AND EXTEND FROM THE CANADIAN PRAIRIES INTO THE CENTRAL PLAINS. THIS WILL TURN WINDS TO NORTHWEST LATER THURSDAY...THEN THE RIDGE AXIS WILL PASS OVER THE LAKE THURSDAY NIGHT. THIS WILL WEAKEN WINDS FAIRLY QUICKLY. THE HIGH WILL MOVE EAST THROUGH THE OHIO/TENNESSEE VALLEYS FRIDAY. A SERIES OF MODEST LOWS WILL PASS TO THE NORTH OF THE LAKE THROUGH THE MIDDLE OF NEXT WEEK...RESULTING IN AN EXTENDED PERIOD OF SSW WINDS. THIS WILL BUILD WAVES ALONG THE NORTHERN HALF OF THE LAKE. KMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777- LMZ779 UNTIL 9 PM THURSDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 210842 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 242 AM CST THU JAN 21 2016 .SHORT TERM... 242 AM CST THROUGH FRIDAY... BIGGEST CONCERN IN THE SHORT TERM IS WITH LAKE EFFECT POTENTIAL FRIDAY INTO FRIDAY EVENING. NOT MUCH CHANGE FROM PREVIOUS THINKING...STILL LOOKS LIKE A VERY MARGINAL SET-UP AND IF ANYTHING A BIT LESS FAVORABLE THAN YESTERDAY. SUSPECT THERE WILL INDEED BE ECHOS COMING IN OFF THE LAKE...BUT WITH TEMPS AT THE LAKE INDUCED EQUILIBRIUM LEVEL HARDLY SUPPORT OF ICE NUCLEI (AROUND -12C) AND SHALLOW CONVECTIVE CLOUD DEPTH THINKING THAT P-TYPE WILL BE MORE SNOW GRAIN AND/OR TINY FLAKES WHICH WILL BE DIFFICULT TO ACCUMULATE MUCH. TRICKY ONE WHAT TO DO WITH POPS AS THERE WILL LIKELY BE SOME LIGHT PRECIP AROUND...BUT UNLIKELY TO BE MEASURABLE SO HAVE MAINTAINED HIGH END CHANCE POPS AND WILL GO WITH SOME SORT OF CATEGORICAL COVERAGE WORDING. CLOUD COVER LOOKS TO BE THE RULE THROUGH FRIDAY...THOUGH THERE COULD BE SOME FILTERED SUNSHINE THROUGH THE HIGH CLOUDS TODAY. MODERATING TREND IN TEMPS WILL CONTINUE WITH HIGHS MID TO PERHAPS UPPER 20S TODAY AND UPPER 20S TO LOWER 30S FRIDAY. IZZI && .LONG TERM... 242 AM CST FRIDAY NIGHT THROUGH WEDNESDAY... BIG EAST COAST BLIZZARD WILL UNDOUBTEDLY GARNER MOST OF THE WEATHER ATTENTION THIS WEEKEND...HOWEVER OUR OWN LOCAL WEATHER EXCITEMENT WILL BE THE ANTICIPATED END TO OUR STREAK OF BELOW AVERAGE AND BELOW FREEZING WEATHER. UPPRE RIDGING AND WARM AIR ADVECTION WILL DEVELOP THIS WEEKEND AND EXPECT AT LEAST PARTIAL SUNSHINE...ESPECIALLY SUNDAY. DEVELOPING SOUTHERLY WINDS AND MINIMAL SNOW COVER MOST OF THE CWA SHOULD ALLOW TEMPS TO WARM NICELY INTO THE 30S. BLENDED MODEL GUIDANCE WOULD SUPPORT MID 30S FOR HIGHS SUNDAY...BUT WITH A STOUT SOUTHERLY FLOW AND 925MB TEMPS PROGGED TO APPROACH 0C THINK THAT 40F IS ATTAINABLE...ESPECIALLY OVER PORTIONS OF THE AREA THAT HAVE VERY LITTLE SNOW COVER. SHORTWAVE LOOKS TO AFFECT REGION MONDAY WITH MEDIUM RANGE MODELS STILL INDICATING WE WILL BE CLOSE TO THE RAIN SNOW LINE. ASSUMING PERFECT PROGS FROM THE MODELS AT THIS DISTANCE WOULD SUPPORT SOME RAIN SHOWERS PROBABLY CHANGING TO A BIT OF SNOW BEFORE ENDING MONDAY NIGHT...BUT AT THIS DISTANCE AND WITH SUCH A CHAOTIC AND HIGH AMPLITUDE FLOW IN OUR NECK OF THE HEMISPHERE ITS QUITE PLAUSIBLE THAT MODEL SOLUTIONS COULD WAVER AROUND A BIT BETWEEN NOW AND EARLY NEXT WEEK. IZZI && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 06Z... * NONE. KJB //DISCUSSION...UPDATED 06Z... A SURFACE RIDGE OF HIGH PRESSURE OVER THE AREA WILL CONTINUE TO PRODUCE A LIGHT WESTERLY WIND TODAY...GENERALLY AROUND 5 KT OR LESS. HOWEVER...BY EARLY THIS EVENING...WINDS SHOULD BEGIN TO SHIFT NORTHERLY...BUT WILL LIKELY REMAIN LIGHT UNTIL FRIDAY. THERE IS A POSSIBLY OF SOME FOG DEVELOPMENT OVERNIGHT...MAINLY AT KDPA AND KRFD. HOWEVER...ANY LOWER VSBYS THAT DEVELOP SHOULD IMPROVE BY MID TO LATE THIS MORNING. OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED UNTIL LATER THURSDAY NIGHT INTO FRIDAY...WHEN SOME MVFR CLOUDS WILL LIKELY DEVELOP OVER THE AREA. KJB //ORD AND MDW CONFIDENCE...UPDATED 06Z... * HIGH FOR ALL ELEMENTS. KJB //OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z... * FRIDAY...CHANCE OF LAKE EFFECT SNOW SHOWERS. MVFR/IFR POSSIBLE. GUSTY NORTHEAST WINDS. * SATURDAY...DRY/VFR. NORTHEAST WINDS. * SUNDAY...DRY. MVFR POSSIBLE. SOUTHWEST WINDS. * MONDAY...CHANCE OF RAIN/SNOW. MVFR LIKELY. IFR POSSIBLE. WESTERLY WINDS. * TUESDAY...CHANCE OF SNOW/MVFR. WESTERLY WINDS. && .MARINE... 115 AM CST SURFACE HIGH PRESSURE WILL CONTINUE TO RESULT IN GENERALLY LIGHT WESTERLY FLOW OVER THE LAKE TODAY. HOWEVER...ON FRIDAY AN AREA OF LOW PRESSURE IS EXPECTED TO TRACK FROM THE SOUTHERN MISSISSIPPI VALLEY EASTWARD OVER THE SOUTHEASTERN CONUS AS A SURFACE RIDGE OF HIGH PRESSURE BUILDS SOUTHWARD OVER THE UPPER GREAT LAKES. THESE TWO PRESSURE SYSTEMS WILL LIKELY RESULT IN A PERIOD OF 15 TO 25 KT NORTHERLY WINDS...ESPECIALLY OVER THE SOUTHERN END OF THE LAKE LATE FRIDAY INTO FRIDAY NIGHT. THIS COULD RESULT IN THE NEED FOR SMALL CRAFT ADVISORY FOR THE ILLINOIS AND INDIANA NEAR SHORES. ANOTHER PERIOD OF STRONGER WINDS LOOK TO DEVELOP OVER THE LAKE LATE SATURDAY NIGHT AND SUNDAY AS ANOTHER AREA OF LOW PRESSURE SHIFTS OVER THE UPPER GREAT LAKES REGION. SOUTHWEST WINDS UP AROUND 25 KT ARE POSSIBLE DURING THIS PERIOD. LOOKING AHEAD INTO EARLY NEXT WEEK IT APPEARS THAT ANOTHER AREA OF LOW PRESSURE COULD IMPACT THE GREAT LAKES REGION...AND THIS COULD LEAD TO ANOTHER PERIOD OF ENHANCED NORTHWESTERLY FLOW. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 221142 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 542 AM CST Tue Nov 22 2016 .SHORT TERM... 357 AM CST Today through Wednesday night... Main forecast focus in the short term period is with precip producing system which will move across the region later today through Wednesday. Early morning GOES water vapor imagery depicts a fairly vigorous mid-level short wave propagating across the southern Rockies. This wave is progged to lift northeast across the Plains and into the mid-Missouri Valley by evening while weakening, while additional energy rotates through the base of the upper trough into the region through Wednesday. Deep layer flow will veer southerly in advance of the upper trough today, increasing warm advection and isentropic ascent in the mid-upper levels and eventually saturating the column from the top downward across the area by tonight. While some light precip may begin to make its way to the surface across far western/northwestern IL late this afternoon, dry low level east-southeasterly flow will likely slow the eastward advance until the evening. This dry low-level air, with sub-freezing wet bulb temps will likely result in a brief period of sleet/snow/rain transition at onset, though surface temps should remain above freezing and forecast soundings indicate the entire column should saturate/warm above freezing across the area as steadier precip (changing to all rain) moves in overnight. Models continue to depict mid-level dry slot moving across the area early Wednesday morning which will likely taper the intensity of rain, though saturated conditions below about 700 mb combined with large scale ascent associated with the approach of the upper trough will likely result in persistent light rain or drizzle through the period. Far northwest and especially the far southeast counties of the cwa look to be on the edges of the dry slot and more apt to see steadier rain through much of the day Wednesday. Any lingering showers will end Wednesday evening as the upper trough axis moves east of the area, and subsidence develops beneath strong height rises in the wake of the departing system. Despite thickening mid-level clouds today, temperatures are expected to warm into the low-mid 40's across the area, and hold in the mid-upper 30's tonight. Moist low level south flow in advance of weakening surface low on Wednesday should push temps in to the upper 40's across southern parts of the cwa. Ratzer && .LONG TERM... 357 AM CST Thursday through Monday... After a dry Thanksgiving Day, a less-amplified, fast moving short wave will affect the region Thursday night into early Friday. Guidance does not produce much in the way of QPF with this feature, but forecast thermal fields and nighttime/early morning arrival do indicate the potential for a short period of mixed precip after midnight through just after sunrise. Soundings do indicate boundary layer wet-bulbs just above freezing which might help keep things wet rather than icy, but will have to continue to pay attention to trends with rain/snow mix for early Black Friday. Things dry out heading into the weekend, before another upper trough approaches Sunday. Medium-range models continue to have a tough time with the pattern by that time, with troughiness of various amplitude and timing into early next week. There is some agreement in overall lower heights and a long-wave trough setting up over the central CONUS however. Have indicated chance pops in the days 6-8 period, though confidence in details is rather low due to wide spread in model solutions. Ratzer && .AVIATION... For the 12Z TAFs... Southeast winds and primarily VFR conditions will prevail across the area this morning and this afternoon. There is some concern that some of the lake clouds could shift over the terminals this morning, particularly between 12Z and 15Z in which case there may be a window of high end MVFR (020-025). Otherwise expect southeast winds to pick up above 10 kt with a few gusts in the mid to high teens possible this afternoon. Low pressure will lift across the mid Missouri Valley this evening with a warm front lifting into northern Illinois. Initially dry low levels will take some time to saturate, and there is still a possibility of some sleet mixed in at precip onset as evaporative cooling occurs within this dry layer. Confidence remains a bit low in this, so will maintain a prob30 for sleet in the meantime. Once the column saturates though, have high confidence in rain late this evening and overnight. Cigs will continue to lower to low end MVFR late tonight with IFR probable as we head into Wednesday morning. As mid level dry slot punches into the area mid to late tomorrow morning, precip may taper to a drizzle at times, but expect periods of rain to continue beyond the current TAF period through mid to late evening when a trailing cold front will finally move across the terminals. BMD && .MARINE... 312 AM CST Ridge of high pressure over the area this morning is allowing light flow over most of Lake Michigan but expect southeast flow to increase across southern Lake Michigan initially as low pressure approaches the region over the next couple days. A small craft advisory will be needed for the Illinois nearshore zones by late this evening and remain in effect through Wednesday evening when the low center approaches far southern Lake Michigan. For the Indiana zones, off shore flow will help keep waves in check overnight but still expect winds to reach criteria by early Wednesday morning and persist into the afternoon. Winds will turn westerly behind the low on Thursday, then a secondary front will move across the region on Friday with west/northwest flow increasing back into the 20-25 kt range. BMD && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...MIDNIGHT Wednesday TO 3 PM Wednesday. Small Craft Advisory...LMZ743-LMZ744-LMZ745...6 AM Wednesday TO 3 PM Wednesday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 031741 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 1241 PM CDT Mon Apr 3 2017 .SHORT TERM... 245 AM CDT Through tonight... Bottom line upfront is it is going to rain today. Models have been struggling to come to a common solution in regard to how precip progresses today likely due to how the models are handling convection over the Gulf Coast. Luckily the latest runs appear to be merging on a single solution where the line of showers just north of I-88 continues north early this morning. Meanwhile the area of showers over central IL weakens as it moves over the southern forecast area (south of I-80). A new batch of showers increase in coverage from the late morning through the afternoon. I have high confidence in showers increasing in coverage through this afternoon, but medium confidence in how quickly it will occur. As my colleague put it, showers are over performing right now so logic would suggest they will continue to do so this afternoon. Therefore, have a more progressive trend, but summed the weather wording up with occasional showers this afternoon. Embedded thunderstorms are possible this afternoon and evening mainly south of I-80 closer to the surface low. Showers lift northeast with the low overnight. Expecting around 1-1.25 inches of rain to fall with locally higher amounts from thunderstorms. JEE && .LONG TERM... 245 AM CDT Tuesday through Sunday... More rain and possibly snow! A busy pattern continues with another big system and then a break in the action late this week. We should get a small break in precip Tuesday as the first low continues northeast. The GFS has a more substantial upper level vort wave that lingers over the region Tuesday morning. Therefore, the GFS has rainfall lingering into Tuesday morning. The NAM and ECMWF have the system exiting much quicker than the GFS so leaned toward their solutions. The ECMWF and NAM have good agreement with the path of the low Tuesday night and the GFS's low catches up with them Wednesday. All solutions feature a more southern track through downstate IL and central IN. The upper level trough is also impressive as it deepens and becomes negatively tilted Wednesday night into Thursday. So what does this mean? More rain spreads across the region Wednesday. Thinking the majority of thunderstorms will be south of the forecast area closer to the low, but could see a few thunderstorms along and south of I-80. Greater rainfall totals will likely be south of I-80. Rainfall totals from this system will vary from 0.5-1 inch north of I-80 to 1.5-1.75 inches south of I-80. Gusty north winds to 30 MPH are still expected. Interestingly, as cold air aloft filters over the region Wednesday night, expecting rain to transition over to snow. 850mb temps are below freezing and there is enough forcing aloft to suggest moderate, measurable snow is possible. Have medium-high confidence in snow occurring so kept a period of snow in the forecast Wednesday night, which may result in at least a few tenths of snow. Sticking snow all depends on snowfall rates given wet, warm ground. If snow comes down harder than forecast, accumulations could be greater than forecast. Gusty winds continue Thursday with gusts of 30-40 MPH. With such a cool pool aloft, lowered Thursday's high temps into the low 40s using a mixture of CONSRaw and local 925mb climatology. Have high confidence in temps being cooler than what SuperBlend had loaded in. Surface temps and forcing will play a key role in what type of precip falls Thursday. Right now have snow becoming rain as surface temps warm. Snow may continue longer than forecast if forcing creates snowfall rates so high that snow may overcome the surface warm layer. However, this far out, decided to play it safe and have snow turn over to rain with minimal accumulations. Lows Thursday night still look chilly in the low 30s. The synoptic precip will shift east Thursday night but models are suggesting that a lake effect snow band may form over NW IN which makes sense given strong north winds along the long fetch of the lake. High pressure and warmer air are still expected for late this week and the weekend. 60s are expected over the weekend, although models suggest another low may bring rain Sunday night. JEE && .HYDROLOGY... 245 AM CDT The first round of rain arrives today followed by another rain system Wednesday into Thursday. Plenty of deep layer moisture will be available to both of these storm systems, increasing the potential for significant rainfall amounts. For the first system, confidence is currently highest in rainfall amounts of 1 to 1.5 inches occurring across the area, with locally higher amounts around any thunderstorms that may develop this afternoon. For the mid to late week system, heavy rainfall is possible area wide depending on the track of the low pressure area. Confidence is increasing in regards to the track and timing of the second system, and current indicators suggest much of the area could see another 1 to 2 inches of additional rainfall. Given the saturated ground and ongoing minor river flooding from the March 30th event, these 2 heavy rain events will likely lead to areal flooding and renewed sharp river rises. JEE/Castro/Krein && .AVIATION... For the 18Z TAFs... Area of low pressure is currently near St Louis early this afternoon and is expected to lift near and just south of the Chicago Metro this evening. Showers are currently increasing out ahead of the low track over northern Illinois and northwest Indiana. Expect highest coverage around the terminals from mid to late this afternoon, with off and on precipitation the rest of the evening and overnight. Thunderstorms are most likely south of the terminals, except for GYY which will fall near the edge of the better instability that could support thunderstorms. Variable VFR/MVFR ceilings are expected in the very near term, over the next hour or two, but IFR probability increases through the afternoon and will likely be prevailing through the evening and overnight hours. As the surface low nears the region, expect winds to back from the ENE this afternoon to the NNW late this evening and eventually northwest overnight as the low starts to push east of the region. Because GYY will be closer to the low track, winds may become variable for several hours this evening before also turning northwest overnight. BMD && .MARINE... 221 AM CDT An active week for Lake Michigan remains highly likely due to two northeastward tracking low pressures, with the second probable to bring at least a period of higher end gales on/near Thursday. The first of the lows will reach the far southern tip of Lake Michigan by mid to late evening. Winds should turn north fairly quickly along the Illinois shore in the wake of this system by late evening, and then overnight along the Indiana shore. Wind speeds will increase with Small Craft Advisory conditions likely for a period Tuesday along the Indiana shore and possible early on the Illinois shore. Over the open waters, occasional gales are possible over the northern and central waters late tonight and Tuesday morning. The second system during midweek will be more potent as it will drag in cooler air and have a tight pressure gradient around it induced by it deepening concurrent with a strong high over the Plains states. The low is presently forecast on Wednesday night to move from near the Ozarks region to central Indiana and then more northeastward to Lake Erie during Thursday. Northeast winds will increase through Wednesday and to gales Wednesday evening, and then turn north with higher end gales likely on Thursday. There has been some indications of some storm force gusts of 50 kt over the southern half of the lake on Thursday, but confidence is still low on just how high above 40 kt gusts will reach. Given the preceding chop from tonight/Tuesday morning and then northerly gales, waves should build quite high and quickly Wednesday night along the Illinois and especially Indiana nearshores. Prevailing waves of 14+ feet are presently forecast for at least part of the northwest Indiana shore on Thursday. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO  FXUS63 KLOT 210757 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 257 AM CDT Wed Mar 21 2018 .SHORT TERM... 255 AM CDT Through Thursday Night... An impressive and large synoptic scale system from top to bottom continues to take shape in the Mid-Atlantic region this morning. The cold conveyor belt associated with this deepening system is wrapped over the Great Lakes into the Ohio River Valley, with 850mb temperatures on regional soundings last evening running around the 10th percentile for late March. This colder air above and into the boundary layer combined with clouds at least through midday will provide temperatures 5 to 10 degrees below normal for northern Illinois and northwest Indiana. The coolest values that will stay shy of 40 degrees look to be in lake adjacent counties. Winds will finally diminish and quickly late this afternoon and early this evening due to high pressure building in. Some lake effect clouds may linger into northwest Indiana. Lows of lower to mid 20s are forecast for much of the CWA. The light winds continue into Thursday with a lake breeze likely. Apart from this lake adjacent cooling, temperatures may rebound as much as to near 50 for highs, but that will depend on any high cloud thickness associated with a short wave dropping southeast over the Mississippi River Valley. MTF && .LONG TERM... 343 PM CDT Wednesday night through Tuesday... The focus for this period will be the potential for snow Friday night into Saturday morning. The end of the work week should be fairly quiet with low amplitude upper level NW flow in place. Upper heights begin to rise as an upper level ridge approaches the region. A weak vort max embedded in the NW flow will pass SW of the area Thu and shouldn't do much more than increase the cloud cover over the SWrn portion of the FA. A short wave is forecast to under cut the ridge for the end of the week. This system should pass well south of the area and has trended south early this week. The GFS and ECMWF have continued their southward trend with the new 12Z runs and if the GFS verifies, all but the extreme SWrn portion of the CWA will be dry. But the ECMWF is farther north and has precip across the entire CWA. Since temps aloft will be below freezing, p-types will be modulated based on SFC temps and due to Erly flow bringing in a steady supply of dry low level air in advance of this system, dew point depressions should be sizable and wet bulbs are forecast to be below freezing. This means that precip should quickly transition to snow late Friday night. The eventual amount of snow will depend on many things including onset timing...which has been steadily trending later and later. The slower the system gets means the less snow potential because more of the precip will occur during the day Sat when SFC temps will rise above freezing. Precip should exit the SErn zones Sat evng. The upper level ridge becomes re-established for the end of the wknd behind this system with the SFC ridge extending SW into the Midwest from the high centered across Quebec. Upper flow transitions to SW flow with the departing ridge as a long wave trough moves onshore along the West Coast. A short wave will get ejected from the SWrn US trough for early next week but with considerable differences in strength, timing and location it is much too early to be specific other than to say that there should be precip in the area somewhere in the Mon-Wed time frame. And with min temps near freezing, the p-type forecast could be tricky. 2% && .AVIATION... For the 06Z TAFs... Primary forecast concern for this period will continue to be winds. Winds which should remain generally northerly through the remainder of the night and through the daytime hours tomorrow. With an inverted trough extending from low pressure over the Upper Ohio Valley through north-central IL and a weak finer scale ridge along the west coast of Lake Michigan, wind direction will be a little difficult to pin down exactly if it will be a little west of north or a little east of north. At 06z, the dividing line between NNW and NNE is between ORD/DPA and MDW/GYY. Expect that there may be some variation to wind direction through the late morning hours when the low over the Upper Ohio Valley will begin to merge with the stronger low off of the Mid-Atlantic coast and a ridge of high pressure begins to build across the Mid Mississippi Valley. This will, ultimately, lead to a weaker pressure gradient over nrn IL/IN and set up the possibility for a lake breeze to develop, or perhaps, just some lake influence, leading to more of a true NE wind direction in the afternoon. In general, confidence in wind direction is only low-to-moderate through the morning hours. Through the late afternoon and evening hours, the ridge will build east across region, leading to a trend toward lgt/vrbl winds which should then persist through the overnight hours. Otherwise, the only other concern is some lingering mvfr cigs for the remainder of the overnight hours. Latest obs indicate the low-level clouds scattering, but there could still be brief periods of mvfr cigs. Otherwise, cloud cover will trend to operationally insignificant through the morning and then become skc for tomorrow night. && .MARINE... 343 PM CDT Small Craft Advisory continues into Wednesday evening across the nearshore waters of Lake Michigan. Gusty northeast winds to 30 knots into tonight will gradually weaken on Wednesday, and back to the north. High waves will linger into Wednesday afternoon for areas north of Calumet Harbor, and into the evening for areas to the east. May see another period of gusty winds and elevated waves this weekend, as low pressure passes by to the south of the area. JJW && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Small Craft Advisory...IN nearshore waters until 10 PM Wednesday. Small Craft Advisory...IL nearshore waters until 4 PM Wednesday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO