FXUS62 KGSP 221949 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 249 PM EST SAT DEC 22 2012 .SYNOPSIS... DRY HIGH PRESSURE WILL DRIFT OFFSHORE LATE SUNDAY. A SURFACE LOW WILL MOVE WEST OF THE MOUNTAINS ON MONDAY. A STRONGER LOW WILL FOLLOW A SIMILAR TRACK ON TUESDAY. HIGH PRESSURE FROM CANADA WILL SETTLE IN ON FRIDAY BRINGING SLIGHTLY COOLER TEMPERATURES. && .NEAR TERM /THROUGH SUNDAY/... AT 2 PM...TEMPERATURES EAST OF THE MTNS HAVE WARMED A LITTLE MORE THAN EXPECTED...WITH VALUES COMMON IN THE 50S EAST OF THE MTNS. DEWPOINTS REMAIN IN THE SINGLE DIGITS TO TEENS...RESULTING IN RH VALUES IN THE TEENS TO L20S. I WILL KEEP A FIRE DANGER STATEMENT IN EFFECT FOR THE NC PIEDMONT...FOOTHILLS...AND EAST FACING SLOPES UNTIL 6 PM. RECENT GOES...AND ONE MODIS...VISIBLE IMAGES INDICATED A THIN SNOWPACK ACROSS THE WESTERN UPSLOPE AREAS OF THE NC MTNS. AREA WEB CAMS THAT INSOLATION HAS MELTED THE SNOW ON ROADS...PARKING LOTS...AND SIDEWALKS. CLEAR SKY COVER...DECREASING WINDS...AND A DRY AIR MASS SHOULD RESULT IN STEADY COOLING AFTER SUNSET. HOWEVER...H85 TEMPS RISE SLIGHTLY OVERNIGHT...SUPPORTING A WEAK INVERSE LAPSE RATES. BY MORNING...TEMPERATURES MAY RANGE FROM THE L20S WITHIN THE MTNS VALLEYS TO UPPER 20S ACROSS THE RIDGES...FOOTHILLS...AND PIEDMONT. THE FREEZING TEMPERATURES SHOULD RESULT IN PATCHES OF BLACK ICE WHERE MELT WATER REMAINS ON THE ROAD. I WILL ISSUE A SPS TO HIGHLIGHT THE SLICK CONDITIONS FOR THE AREAS WITH SNOW COVER. ON SUNDAY...WEAK LOW PRESSURE BEGINS TO FORM OVER THE ARKLATX REGION...SUPPORTING RETURN FLOW ACROSS THE SOUTHERN APPALACHIANS. MILD LLVL THICKNESSES AND MORNING INSOLATION SHOULD RESULT IN STEADILY WARMING TEMPERATURES AFTER SUNRISE. A BLEND OF MOS INDICATES THAT HIGH TEMPERATURES ARE FORECAST TO RANGE FROM THE LOW TO MID 50S WITHIN THE MTN VALLEYS TO U50S EAST. DEWPOINTS MAY RISE THROUGH THE DAY ON SW WINDS...BUT RH VALUES MAY REMAIN AROUND CRITICAL VALUES DURING THE HEAT OF THE AFTERNOON. OTHERWISE...THE FORECAST WILL FEATURE INCREASING HIGH CLOUDS ORIGINATING FROM THE ARKLATX LOW. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... AS OF 210 PM SATURDAY...A SHORT WAVE WILL CROSS THE REGION LATE IN THE DAY ON MONDAY. LOW PRESSURE ASSOCIATED WITH THE WAVE WILL LIFT WELL WEST OF THE MOUNTAINS...BUT THE REGION WILL BE UNDER STRONG LLVL WARM ADVECTION. THE ECMWF...CANADIAN AND UKMET ALL HAVE WIDESPREAD QUARTER TO HALF INCH RAIN AMOUNTS OVER THE FORECAST AREA CHRISTMAS EVE. THE NAM IS A LITTLE DRIER...THOUGH THE SREF ALSO HAS CATEGORICAL POPS SOUTH OF I-40. I/VE INCREASED POPS TO LIKELY ACROSS THE FORECAST AREA DURING THE DAY ON MONDAY...WITH AN AREA OF CATEGORICAL POPS ACROSS THE SRN ESCARPMENT OF THE BLUE RIDGE. THIS IS AN INCREASE FROM WHAT WE HAD BEFORE...BUT BASED ON CURRENT TRENDS I/D IMAGINE IT/S STILL A LITTLE TOO LOW. THERE MAY BE SOME COOL AND DRY AIR TRAPPED IN THE NC MTN VALLEYS AT THE START OF THE PCPN EVENT MONDAY MORNING...BUT WITH WARM H8 TEMPS AND SKIES CLOUDING UP EARLY SUNDAY EVENING...I DON/T SEE WET-BULBS BEING LOW ENOUGH FOR ANYTHING OTHER THAN RAIN ON MONDAY. THE MAV MOS IS COOLER ON MONDAY OWING TO THE HEAVIER PCPN IN THAT MODEL...AND THAT/S WHAT I USED IN THE GRIDS...ALBEIT WITH A FEW TWEAKS. THE SFC FRONT IS LIKELY TO HANG UP OVER THE FOOTHILLS AND MOUNTAINS MONDAY NIGHT. I/M NOT SURE HOW MUCH CLEARING WE/LL ACTUALLY SEE...ESPECIALLY DOWN ACROSS UPSTATE SC AND NE GA. I DID GO WITH A PERIOD OF PARTIAL CLEARING LATE MONDAY AND MONDAY NIGHT...BUT CONFIDENCE IS CLEARING IS NOT HIGH. ON TUESDAY A STRONGER SHORT WAVE WILL LIFT ACROSS THE LOWER MS RIVER VALLEY. THE NAM LOOKS TOO WEAK WITH THIS FEATURE AND I/VE SIDED WITH THE GFS/ECWMF WHICH ARE ABOUT 10 MB DEEPER WITH THE SFC LOW THAN THE NAM. PARTIAL THICKNESSES ARE MUCH TOO WARM FOR ANYTHING OTHER THAN RAIN. THERE IS SOME MID-LEVEL FRONTOGENESIS THAT CROSSES THE FA WELL AHEAD OF THE WAVE TUE AFTN. THIS IS CAUSING QUITE A SPREAD IN THE ONSET TIME OF PCPN IN THE MODELS. I/VE GONE A LITTLE SLOWER THAN SOME OF THE NEIGHBORS...BUT THERE IS STILL QUITE A BIT OF QUESTION AS TO WHETHER WE CAN EEK OUT A DRY CHRISTMAS MORNING WITH THIS PATTERN. EVEN WITH A MILD AIRMASS...THE CLOUDY SKIES WILL HOLD MAX TEMPS AROUND NORMAL LEVEL FOR THE DAY. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... AS OF 110 PM SATURDAY...THE GLOBAL MODELS REMAIN IN GOOD AGREEMENT IN THE EVOLUTION OF A MILLER B SCENARIO ACROSS THE SOUTHEAST AND MID-ATLANTIC TUE NIGHT AND WEDNESDAY...WITH WIDESPREAD RAIN EXPECTED TO OVERSPREAD THE AREA BEGINNING CHRISTMAS EVENING. WITH THE PRIMARY SURFACE LOW TRACKING WEST OF THE APPALACHIANS...AND SYNOPTIC SURFACE HIGH IN AN UNFAVORABLE LOCATION FOR CLASSICAL COLD AIR DAMMING... WINTRY WEATHER DOES NOT APPEAR TO BE A MAJOR CONCERN. HOWEVER...THE LATEST RUNS OF THE ECMWF ARE SLIGHTLY MORE AGGRESSIVE WITH LOWERING THICKNESS VALUES IN RESPONSE TO IN SITU CAD DEVELOPMENT TUE NIGHT. IT IS NOT OUT OF THE QUESTION THAT TEMPS COULD DROP TO/BELOW FREEZING ALONG THE EASTERN ESCARPMENT AFTER PRECIP ONSET...AND BECOME LOCKED THERE FOR A FEW HOURS...AS IS SOMETIMES THE CASE WITH IN SITU EVENTS. A MENTION OF -FZRA WILL BE CARRIED ACROSS A VERY SMALL PORTION OF THE CWFA WED MORNING (MAINLY THE NRN MTNS AND FOOTHILLS). PRECIP IS EXPECTED TO END ACROSS THE AREA BY WED EVENING...THE ONLY EXCEPTION BEING ACROSS THE TENN BORDER COUNTIES...WHERE SCT/NUMEROUS ACCUMULATING NW FLOW SNOW SHOWERS SHOULD PERSIST THROUGH WED NIGHT INTO EARLY THURSDAY. A TRANSITION TO A MORE PHASED/HIGH AMPLIFIED FLOW IS EXPECTED BY THE END OF THE PERIOD...WITH A MAJOR/PROGRESSIVE LONG WAVE TROUGH EXPECTED TO TAKE SHAPE ACROSS THE CENTRAL CONUS BY THE END OF THE WEEK. THE GLOBAL MODELS SUGGEST THE ATTENDANT FRONTAL SYSTEM WILL BEGIN AFFECTING THE EASTERN STATES BY NEXT WEEKEND...AND SMALL POPS HAVE BEEN INCLUDED ACROSS OUR AREA BEGINNING EARLY SATURDAY MORNING. A GUIDANCE CONSENSUS SUGGESTS THERMAL PROFILES WILL ONCE AGAIN BE TOO WARM TO SUPPORT MUCH IN THE WAY OF WINTRY PRECIP OVER OUR AREA. HOWEVER...IF LIGHT PRECIP BEGINS AS EARLY AS SUGGESTED BY THE LATEST GUIDANCE...ENOUGH COLD AIR MAY REMAIN IN PLACE ACROSS PORTIONS OF THE HIGH TERRAIN TO SUPPORT A BRIEF PERIOD OF FREEZING RAIN. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... AT KCLT AND ELSEWHERE...NO CEILING OR VISIBILITY RESTRICTIONS THROUGH THE 18Z TAFS. THE MAIN CONCERN THROUGH THE FORECAST PERIOD WILL BE WIND DIRECTION AND SPEEDS. THE LATEST SFC ANALYSIS INDICATES THAT A LEE TROF WAS LOCATED OVER THE PIEDMONT OF THE CAROLINAS. THE TROF WILL LIKELY SUPPORT WSW WINDS EAST OF THE MTNS...WITH NNW WINDS AT KAVL AND KHKY. KHKY SHOULD BACK TO WSW LATER THIS AFTERNOON. SPEEDS EAST OF THE MTNS SHOULD FAVOR VALUES BETWEEN 5 TO 10 KTS. KAVL MAY REMAIN GUSTY UNTIL WINDS DECOUPLE TOWARD SUNSET. OVERNIGHT...A BROAD PRESSURE FIELD IS EXPECTED WITHIN THE LEE TROF...WINDS WILL BECOME AND REMAIN LIGHT TO VARIABLE TO CALM THIS EVENING AND OVERNIGHT. LITTLE CHANGE IN THE PATTERN EXPECTED SUNDAY...SPEEDS WILL FAVOR VALUES NEAR 5 KTS. A FEW HIGH CLOUDS MAY ARRIVE ACROSS THE WESTERN CAROLINAS BY LATE SUNDAY MORNING. OUTLOOK...AN ACTIVE PATTERN ON TAP FOR THE UPCOMING WEEK. THE NEXT SYSTEM IS EXPECTED TO BRING A QUICK SHOT OF CLOUDS/PRECIP ON MONDAY. THEN ANOTHER...STRONGER...SYSTEM IS EXPECTED TO AFFECT THE AREA TUESDAY NIGHT THRU WEDNESDAY. AN EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLE SHOWING THE PERCENTAGE OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED ISSUANCE CATEGORY IS AVAILABLE AT FOLLOWING LINK (USE LOWER CASE)... WWW.WEATHER.GOV/GSP/AVIATION/TABLES.HTM && .FIRE WEATHER... OWING TO THE LACK OF WIND ON SUNDAY WE ARE NOT PLANNING TO ISSUE A FIRE DANGER STATEMENT FOR ANY PARTS OF THE WESTERN CAROLINAS OR NORTHEAST GEORGIA. AND IN THE CASE OF NE GA...WHERE A FIRE DANGER STATEMENT CAN BE ISSUED JUST BASED ON MINIMUM RH AND FUELS...THE RH VALUES ARE NOT PREDICTED TO FALL TO CRITICAL LEVELS. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...PAT NEAR TERM...NED SHORT TERM...MCAVOY LONG TERM...JDL AVIATION...NED FIRE WEATHER...MCAVOY