FXUS62 KRAH 222336 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 735 PM EDT FRI OCT 22 2010 .SYNOPSIS... COOL HIGH PRESSURE WILL BUILD DIRECTLY OVER NORTH CAROLINA TONIGHT...THEN SHIFT OFFSHORE AND RESULT IN A WARMER SOUTHWESTERLY FLOW SATURDAY INTO NEXT WEEK. && .NEAR TERM /THROUGH SATURDAY/... AS OF 240 PM FRIDAY... CLEAR SKIES AND CALM WIND UNDER HIGH PRESSURE WITH A DRY AIR MASS THROUGH THE AIR COLUMN. DIURNAL TEMPERATURE FALLS NEAR TO IN EXCESS OF 30 DEGREES... WITH LOW TEMPERATURES MID 30S MOST AREAS... AND NEAR 40 MORE URBAN AND SOUTH MOST LOCATIONS. FROST ISOLATED AT BEST WITH RELATIVE HUMIDITIES LESS THAN 85 PERCENT AT SUNRISE. WARMING CONTINUES WITH LOW LEVEL THICKNESSES RISING TO 1375 METERS OR HIGHER SATURDAY AFTERNOON. LIGHT SOUTHWEST BREEZES AS SURFACE HIGH EXITS INTO THE ATLANTIC. AFTERNOON HIGH TEMPERATURES IN THE MID 70S. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... AS OF 240 PM FRIDAY... CIRRUS LEVEL MOISTURE ON THE INCREASE SATURDAY NIGHT WITH OCCASIONAL BREEZES FROM THE SOUTHWEST. INFLUX OF NEAR SURFACE MOISTURE AS WELL... BUT PERHAPS NOT SIGNIFICANT UNTIL TOWARD DAWN. WE ARE SLIGHTLY ABOVE CLIMATOLOGICAL DIURNAL TEMPERATURE FALLS... AND ON THE LOW SIDE OF THICKNESS CLIMATOLOGY. LOW TEMPERATURES 45 TO 50... WITH A RISK OF BEING COOL IF LOW LEVEL MOISTURE IS MORE AGGRESSIVE. WELL MIXED BOUNDARY LAYER SUNDAY WITH A SOUTHWEST BREEZE NEAR TEN MPH. ENOUGH SUNSHINE TO REACH FULL SUN POTENTIAL TEMPERATURES. AFTERNOON HIGH TEMPERATURES IN THE UPPER 70S... SLIGHTLY COOLER NORTHWEST. GOOD WARM AND MOISTURE ADVECTION SUNDAY NIGHT. EXPECTING LOW STRATUS AND FOG MOST LOCATIONS BEFORE MIDNIGHT... WHICH WILL KEEP TEMPERATURES MILD AT UPPER 50S TO LOWER 60S. AIR MASS MOISTENS IN THE MID LAYERS WITH TIME...BUT CONTINUED OMISSION OF RAIN CHANCES SUNDAY NIGHT STILL JUSTIFIED. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 240 PM FRIDAY... OVERVIEW: ABOVE NORMAL UNCERTAINTY CONTINUES TO PLAGUE THE EXTENDED PORTION OF THE FORECAST...DUE TO A COMPLICATED UPPER LEVEL PATTERN PROGGED OVER THE LOWER 48 NEXT WEEK. MONDAY AND MONDAY NIGHT: ALTHOUGH ALL OF THE FORECAST MODELS ARE INDICATING A SHORTWAVE RIDGE MOVING OFFSHORE THE CAROLINAS/MID-ATLANTIC ON SUN/SUN NIGHT...WITH SOUTHWEST FLOW ALOFT OVER THE CAROLINAS ON MON/MON NIGHT... CONSIDERABLE DISAGREEMENT REMAINS W/REGARD TO THE EVOLUTION OF A SHORTWAVE TROUGH PROGGED TO APPROACH THE CAROLINAS OR MID-ATLANTIC MON/MON NIGHT. AT PRESENT...IT APPEARS THAT SHORTWAVE ENERGY MOVING ONSHORE THE PACIFIC COAST ON SAT WILL DIG SOUTHEASTWARD ALONG THE BACKSIDE OF A WEAKENING UPPER LOW OVER THE CENTRAL PLAINS SAT NIGHT/SUN...THEN TRACK EAST THROUGH THE DEEP SOUTH OR TN VALLEY SUN NIGHT/MON MORNING. THERE ARE DIFFERING SOLUTIONS W/REGARD TO THE TRACK AND AMPLITUDE OF THIS FEATURE...WHICH IS NO SURPRISE CONSIDERING A PATTERN OF SPLIT FLOW ALOFT OVER THE CONUS THIS WEEKEND...WITH IMPORTANT UPPER LEVEL FEATURES (THAT WILL AFFECT THE EVOLUTION OF THE AFOREMENTIONED SHORTWAVE) NOT MOVING ONSHORE THE PACIFIC COAST (BEING SAMPLED BY THE RAOB NETWORK) UNTIL SAT. AS SUCH...THE FORECAST FOR MON/MON NIGHT SHOULD COME INTO BETTER FOCUS BY SAT. AT THIS TIME...WILL CONTINUE CHANCE POPS (30-40%) FOR MON/MON NIGHT. GIVEN A SYNOPTIC PATTERN OF HIGH PRESSURE TO THE EAST AND LOW PRESSURE TO THE WEST...EXPECT SOUTHERLY FLOW/WARM ADVECTION AND ABOVE NORMAL TEMPS MON/MON NIGHT. HIGH/LOW TEMPS WILL HIGHLY DEPEND ON CLOUD COVER AND PRECIP. A BLEND OF GFS/NAM/ECMWF 1000-850 MB THICKNESSES GIVES 1390-1395 METERS MON AFT...SUGGESTING HIGHS IN THE LOWER 80S. HOWEVER...WITH A POSSIBILITY OF PERVASIVE CLOUD COVER AND PRECIP...WILL FCST HIGHS SEVERAL DEGREES COOLER...IN THE MID/UPPER 70S. EXPECT LOWS IN THE UPPER 50S TO LOWER 60S. A 10-15 KT SOUTHERLY BREEZE WITH GUSTS UP TO 20-25 KT WILL BE POSSIBLE MON AFTERNOON DEPENDING ON MIXING...GIVEN A RELATIVELY TIGHT MSLP GRADIENT. TUESDAY THROUGH FRIDAY: UNCERTAINTY FURTHER INCREASES IN THIS PORTION OF THE FORECAST. THE OVERALL PATTERN SUGGESTS PERSISTENT SW FLOW ALOFT OVER THE CAROLINAS...WITH PERSISTENT LOW LEVEL SOUTHERLY FLOW/WARM ADVECTION DUE TO A RELATIVELY TIGHT MSLP GRADIENT BETWEEN HIGH PRESSURE TO THE EAST AND LOW PRESSURE TO THE WEST. THIS TYPE OF PATTERN WOULD INDICATE ABOVE NORMAL TEMPERATURES (MODULATED PRIMARILY BY CLOUD COVER/PRECIP) WITH PRECIP CHANCES TIED TO ANY SHORTWAVES IN SW FLOW ALOFT AND PERHAPS DIURNAL SHOWERS ASSOC/W AN UNSEASONABLY MOIST AIRMASS AND WARM ADVECTION. WILL CONTINUE TO INDICATE A SLIGHT CHANCE (20%) OF SHOWERS TUE THROUGH FRIDAY. W/REGARD TO TEMPS...WILL FCST HIGHS GENERALLY IN THE UPPER 70S...WITH LOWS IN THE UPPER 50S TO LOWER 60S. IT SHOULD BE NOTED THAT THE GFS/ECMWF SHOW THICKNESSES REACHING UP TO ~1410 METERS ON WED/THU...WHICH COULD YIELD RECORD-BREAKING HIGHS IN THE MID 80S...DEPENDING ON THE AMOUNT OF CLOUD COVER AND WHETHER OR NOT THERE IS PRECIP. THE CURRENT RECORD HIGH FOR RDU IS 82F ON BOTH WED/27TH AND THU/28TH. -VINCENT && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... AS OF 735 PM FRIDAY... VFR CONDITIONS THROUGH THE 24 HR PERIOD. HIGH PRESSURE TO THE WEST WILL SLIDE OVERHEAD TONIGHT LEADING TO CLEAR SKIES AND NEAR CALM WINDS. WITH NORTHWESTERLY FLOW ALOFT.... A FEW RIPPLES IN WATER VAPOR IMAGERY FROM A MODIS SATELLITE PASS SUGGESTS SOME LIGHT CLEAR AIR TURBULENCE POSSIBLE...BUT OTHERWISE GOOD AVIATION WEATHER IN STORE. AS THE HIGH MOVES FURTHER EAST ON SATURDAY...LIGHT SOUTHWESTERLY WINDS WILL DEVELOP...BUT SKIES WILL REMAIN CLEAR. MOISTURE RETURN WITH SOUTHWESTERLY LOW LEVEL FLOW MAY LEAD TO MVFR VISIBILITY RESTRICTIONS SUNDAY MORNING. FOG AND STRATUS WILL BE MORE LIKELY ON SUNDAY NIGHT AND MONDAY MORNING. RAIN CHANCES WILL INCREASE MONDAY THROUGH WEDNESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM... SHORT TERM... LONG TERM...VINCENT AVIATION...BLS  FXUS62 KRAH 290804 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 300 AM EST WED DEC 29 2010 .SYNOPSIS... A GRADUAL WARM UP IS EXPECTED THE REMAINDER OF THIS WEEK INTO THE WEEKEND AS HIGH PRESSURE BUILDS OVER THE CAROLINAS AND THEN MOVES OFFSHORE. A COLD FRONT WILL CROSS THE AREA LATE IN THE WEEKEND. && .NEAR TERM / THROUGH TONIGHT/... AS OF 300 AM WEDNESDAY... THIN CIRRUS AHEAD OF A WEAK SYSTEM OVER THE SOUTHERN PLAINS WILL CONTINUE TO DRIFT OVERHEAD TODAY AS SHORTWAVE RIDGING ALOFT AND SURFACE HIGH PRESSURE SHIFT EAST ACROSS THE THE REGION. THE SURFACE HIGH PRESSURE RIDGE SHOULD LIE DIRECT OVER THE CWA BY 00Z THIS EVENING..THEN SHIFT TO THE COAST TONIGHT. GUIDANCE HAS STRUGGLED TO CAPTURE THE DEPTH OF MIXING WITH RELATIVELY WARM AIR ALOFT...AND THUS MOST STATISTICAL GUIDANCE HAS VERIFIED TOO COOL RECENTLY. HOWEVER MODELS INDICATE A WEAK LOW LEVEL THERMAL TROUGH SLIDING ACROSS THE AREA THIS AFTERNOON...WHICH MAY LIMIT WARMING TO ONLY A COUPLE DEGREES OVER TUESDAYS VALUES. BASED ON MODIS VISIBLE IMAGERY...SNOW COVER REMAINS GREATEST ALONG I-95 AND ACROSS THE WESTERN PIEDMONT...WITH LESS COVER ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS TO JUST SOUTH OF THE TRIANGLE. HAVE ADJUSTED HIGHS TO BE RELATIVELY COOLER IN WHATS LEFT OF THE SNOW COVER...WITH HIGHS OF 45-52. THE AFOREMENTIONED SHORTWAVE OVER THE SOUTHERN PLAINS WILL LIFT NORTHEAST THROUGH THE MS VALLEY REGION...DEAMPLIFYING AS IT ENCOUNTERS THE MID LEVEL RIDGE AXIS OVER THE SE. WHILE MID LEVEL MOISTURE IS FORECAST TO INCREASE LATE TONIGHT...THE LOWEST 10-12K FT LOOKS TO REMAIN QUITE DRY. QUITE A BIT OF SPREAD IN GUIDANCE FOR OVERNIGHT LOWS...SO HAVE GONE CLOSER TO WARMER MET GUIDANCE WITH INCREASING CLOUD COVER IN THE WEST...25-29 EAST TO WEST. && .SHORT TERM /THURSDAY THROUGH FRIDAY/... AS OF 300 AM WEDNESDAY... SHEARED OUT SHORTWAVE ENERGY WILL TOP THE MID LEVEL RIDGE AND CROSS VA THURSDAY. WITH A CONTINUED LACK OF LOW LEVEL MOISTURE...MODEL QPF MOST ROBUST OVER NORTHERN VA...HAVE KEPT THE FORECAST DRY FOR THURSDAY. SURFACE HIGH PRESSURE SHIFTING OFFSHORE WILL ALLOW SOUTHERLY RETURN FLOW TO DEVELOP LATE IN THE DAY AND BECOME BETTER ESTABLISHED ON FRIDAY....AS A DEEP UPPER TROUGH DEVELOPS OVER THE ROCKIES AND THEN EJECTS NE INTO THE MIDWEST. MID LEVEL CLOUD COVER WITH THE FIRST WAVE WILL MOVE EAST THURSDAY NIGHT...WITH MOSTLY CLEAR SKIES THURSDAY NIGHT GIVING WAY TO INCREASING LOW LEVEL MOIST WARM ADVECTION AND STRATUS LATE IN THE DAY FRIDAY AS A COLD FRONT ASSOCIATED WITH THE SECOND AND DEEPER SYSTEM MOVES EAST TO THE TN VALLEY REGION.. IN THIS WARM ADVECTION REGIME...TEMPS WILL CONTINUE TO REBOUND TO ABOVE NORMAL VALUES BY FRIDAY...WITH LOWS AROUND 30...HIGHS IN THE MID 50S. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 PM TUESDAY... FRIDAY AND FRIDAY NIGHT (NEW YEARS EVE): A SURFACE AND UPPER LEVEL RIDGE CENTERED DIRECTLY OVER THE CAROLINAS WILL BEGIN TO SHIFT OFFSHORE ON FRIDAY AS AN H5 TROUGH AMPLIFIES SOUTH/SE THROUGH THE INTERMOUNTAIN WEST/ROCKIES THU NIGHT... PROGRESSING EASTWARD TOWARD THE MS RIVER VALLEY FRI/FRI NIGHT. THIS WILL SET UP A SOUTHERLY RETURN FLOW ACROSS THE CAROLINAS ON FRIDAY...WITH 1000-850 MB THICKNESSES REBOUNDING TO ~1340 METERS 12Z FRI...FURTHER INCREASING TO ~1350 METERS FRI EVENING. THIS SHOULD YIELD HIGHS RANGING FROM THE MID/UPPER 50S TO LOWER 60S...DEPENDING ON CLOUD COVER...WHICH SHOULD BE INCREASING LATE IN THE DAY FRI IN ASSOC/W INCREASINGLY SW FLOW ALOFT AHEAD OF A FRONTAL ZONE MOVING INTO THE MS RIVER VALLEY. WILL FCST HIGHS RANGING FROM 56-61F (5-10F ABOVE NORMAL). EXPECT SKIES TO BECOME MOSTLY CLOUDY FRI NIGHT IN ASSOC/W STRENGTHENING WARM ADVECTION IN THE LOWER LEVELS AND MID/UPPER LEVEL CLOUD COVER MOVING DOWNSTREAM INTO THE CAROLINAS FROM PRECIP ALONG THE APPROACHING FRONTAL ZONE...WHICH WILL BE IN THE TN/OH VALLEY BY 12Z SAT. EXPECT RELATIVELY BALMY LOWS IN THE LOWER/MID 40S...WARMEST WEST/SW AND COOLEST EAST/NE. SATURDAY THROUGH SUNDAY NIGHT: AFOREMENTIONED FRONTAL ZONE IN THE TN/OH VALLEY 12Z SAT IS PROGGED TO SLOWLY PUSH EASTWARD ACROSS THE CAROLINAS LATE SAT EVENING THROUGH THE DAY SUNDAY. WHILE THE BEST SYNOPTIC FORCING WILL BE LOCATED WELL NORTH OF THE CAROLINAS...THE GFS/ECMWF CONTINUE TO SHOW 20-40 METER 12-HR HEIGHT FALLS OVER THE CAROLINAS SAT INTO SUN. THIS...ALONG WITH WEAK LOW LEVEL CONVERGENCE AND MOISTURE ASSOC/W SOUTHERLY RETURN FLOW SHOULD PROVIDE ENOUGH OF THE NECESSARY 'INGREDIENTS' FOR SHOWER ACTIVITY ALONG THE FRONTAL ZONE AS IT PUSHES SLOWLY EAST THROUGH THE AREA. THE GFS/ECMWF/GEM ALL SHOW 0.10-0.25" OF QPF OVER CENTRAL NC...PRIMARILY SAT NIGHT THROUGH SUNDAY AFTERNOON. NO CHANCE FOR THUNDER IS EXPECTED DUE TO WEAK DYNAMICS AND POOR LAPSE RATES. AT THIS TIME...WILL GO AHEAD AND INCREASE POPS ON SAT NIGHT/SUN TO 50%. EXPECT MOSTLY CLOUDY TO OVERCAST CONDITIONS ON BOTH SAT/SUN. EXPECT HIGH TEMPS 10-15F ABOVE NORMAL WITH CONTINUED SOUTHERLY RETURN FLOW AND WARM ADVECTION AHEAD OF THE APPROACHING FRONT...IN THE LOWER/MID 60S. LOCATIONS IN THE SANDHILLS/SE COASTAL PLAIN COULD SEE TEMPS INTO THE MID/UPPER 60S. DESPITE SHOWER ACTIVITY MOVING INTO THE AREA...LOWS SAT NIGHT SHOULD GENERALLY BE IN THE LOWER 50S OWING TO A RELATIVELY WARM/MOIST AIRMASS IN PLACE. HIGHS SUNDAY SOMEWHAT TRICKY...DEPENDING ON THE TIMING OF THE FRONTAL PASSAGE. AT THIS TIME...WILL SHOW HIGHS IN THE LOWER 50S N/NW AND LOWER 60S S/SE FOR SUN. EXPECT A COOLER/DRIER AIRMASS TO PUSH INTO THE AREA SUN NIGHT IN THE WAKE OF THE COLD FRONT...WITH LOWS CLOSER TO NORMAL FOR THIS TIME OF YEAR...IN THE UPPER 20S TO LOWER 30S. MONDAY THROUGH TUESDAY NIGHT: WILL TREND TOWARD THE 12Z ECMWF MODEL RUN FOR THE FORECAST EARLY NEXT WEEK...SHOWING HIGH PRESSURE BUILDING OVER THE AREA MON IN THE WAKE OF THE FRONT...SHIFTING OFFSHORE ON TUE...WITH DRY CONDITIONS. THE 12Z GFS TRIES TO GEN UP A WEAK COASTAL LOW MON/TUE...HOWEVER... THIS IS A PRETTY WEAK/SUBTLE FEATURE TO EXPECT THE MODEL TO HANDLE EVEN REMOTELY WELL AT THAT TIME RANGE. EXPECT TEMPS NEAR CLIMATOLOGY ON MON/TUE...WITH HIGHS NEAR 50F AND LOWS IN THE UPPER 20S TO LOWER 30S. -VINCENT && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 1225 AM WEDNESDAY... VFR CONDITIONS WILL PREVAIL THROUGH THE 24 HOUR TAF PERIOD. HIGH PRESSURE WILL CONTINUE TO BUILD OVERHEAD TODAY...RESULTING IN VFR CONDITIONS WITH LIGHT AND VARIABLE WINDS. HIGH THIN CLOUDINESS TODAY WILL BE THICKENING WEDNESDAY NIGHT AS AN UPPER WAVE MOVES EAST ACROSS THE OHIO VALLEY. CEILINGS WILL BOTTOM OUT AROUND 10 THOUSAND FEET ON THURSDAY. THERE IS ALSO CHANCE FOR A COUPLE OF HOURS OF IFR VISIBILITIES IN THE PREDAWN THURSDAY MORNING. IFR/LIFR VISBYS/CIGS WILL BE POSSIBLE THURSDAY NIGHT...BECOMING MORE LIKELY ON FRIDAY NIGHT INTO SATURDAY. A COLD FRONT WILL BE MOVING ACROSS THE AREA SATURDAY NIGHT...AND SHOWERS WILL BE POSSIBLE SATURDAY NIGHT AND SUNDAY WITH ASSOCIATED MVFR TO IFR CEILINGS AND VISIBILITIES. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...SMITH SHORT TERM...SMITH LONG TERM...VINCENT AVIATION...MLM