000 FXUS62 KGSP 251109 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 609 AM EST WED NOV 25 2009 .SYNOPSIS... HIGH PRESSURE WILL LINGER OVER THE REGION INTO WEDNESDAY. A COLD FRONT WILL CROSS THE AREA THURSDAY. HIGH PRESSURE WILL BE IN CONTROL DURING THE WEEKEND AND INTO EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... A SHORTWAVE TROUGH WILL CROSS THE SOUTHERN APPALACHIANS TODAY AS IT EXITS THE BASE OF A MEAN LONGWAVE THAT STRETCHES FROM THE GREAT LAKES TO THE GULF. WEAK ISENTROPIC UPGLIDE CONTINUE TO PRODUCE LOW CLOUD COVER AND DRIZZLE ACROSS MUCH OF THE AREA EARLY THIS MORNING. UPGLIDE WILL DIMINISH AS LOW LEVEL FLOW VEERS AHEAD OF AN APPROACHING COLD FRONT...ENDING DRIZZLE. THIS FRONT WILL CROSS THE AREA BY MIDDAY... SCOURING OUR LOW LEVEL MOISTURE. THE FRONT ITSELF LACKS GULF INFLOW...AND HAS VERY LIMITED MOISTURE...AND NO POPS WILL BE CARRIED. SKY COVER WILL RAPIDLY DECREASE TODAY...AND REMAIN LIMITED TONIGHT. MAXIMUM TEMPERATURES WILL WARM ABOVE NORMAL TODAY WITH THE LOSS OF CLOUD COVER AND WEAK WARM ADVECTION IN LIGHT SOUTH TO SOUTHWEST WINDS. MINIMUM TEMPERATURES WILL FALL TO AROUND NORMAL... DUE MAINLY TO THE LOSS OF CLOUD COVER AND LIGHT WINDS...AS COLD ADVECTION WILL BE RATHER WEAK...AND LOW LEVEL FLOW WILL VEER TO THE WEST AND ACQUIRE A DOWNSLOPE COMPONENT. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... AS OF 245 AM WED...GOOD MODEL AGREEMENT CONTINUES THIS RUN WITH THE UPPER FLOW PATTERN DURING THE PERIOD. A DEEP CLOSED LOW OVER THE MIDWEST THU MOVES EAST ACROSS THE GREAT LAKES AND OH VALLEY ON THU. THIS FEATURE WILL PUSH A REINFORCING COLD FRONT ACROSS THE AREA. MOISTURE WILL BE VERY LIMITED WITH ALONG THE BOUNDARY...BUT COLDER AIR WILL BEGIN TO FILTER IN FROM THE TOP DOWN THU AFTERNOON. THE STRONGEST UPPER FORCING WITH THE TROUGH AXIS SHOULD TRAVERSE THE AREA THU EVENING...BUT THIS WILL BE AHEAD OF THE MAIN INFLUX OF LOW LEVEL MOISTURE ON NW FLOW. HIGHS THU NEAR TO JUST ABOVE NORMAL. THE BULK OF THE PRECIPITATION IN NW UPSLOPE FLOW PRONE LOCATIONS SHOULD DEVELOP THU NIGHT AS SNOW LEVELS SLOWLY FALL INTO THE LOWER MTN VALLEYS. THE BEST COMBINATION OF STRONG NW FLOW...DEEP SFC BASED MOISTURE...AND THE COLDEST PROFILES WILL BE AFTER MIDNIGHT THU NITE AND UNTIL MID MORNING FRI. THE UPSLOPE MOISTURE WILL THEN STEADILY DIMINISH THROUGH THE DAY...LIKELY TAPERING OFF TO FLURRIES FRI NIGHT ACROSS THE NRN NC MTNS. WHILE QPF WILL NOT BE HIGH...A BLEND OF MDL AND HPC GUIDANCE SHOWS AS MUCH AS 0.20 INCHES OF LIQUID EQUIVALENT QPF ALONG THE TN BORDER THU NIGHT AND FRI THRU THE EVENT. THIS SEEMS IN LINE WITH THE PROGRESSIVE NATURE OF THE SYSTEM. NOT ALL OF THIS WILL FALL AS SNOW HOWEVER...ESPECIALLY AT THE THU AND FRIDAY AFTERNOONS AND IN THE VALLEYS. STILL...AN ADVISORY FOR LIGHT SNOW ACCUMULATIONS MAY WELL BE NEEDED FOR MUCH OF THE TN BORDER AREA AT SOME POINT THIS WEEK GIVEN THE POTENTIAL IMPACT ON POST HOLIDAY TRAVEL. A TIGHT PRESSURE GRADIENT WILL ALSO SET UP IN THE NW FLOW BEHIND THE DEPARTING LOW LATE THU NIGHT THROUGH FRI EVENING. BREEZY TO WINDY CONDITIONS WILL RESULT...WITH HIGH MTN LOCATIONS PROBABLY APPROACHING WIND ADVISORY CRITERIA. IT STILL APPEARS AS IF THE DEEPEST MIXING THROUGH THE PERIOD WILL BE UNABLE TO TAP INTO THE STRONGER WINDS ALOFT. WILL CONTINUE TO HIGHLIGHT BOTH THE SNOW AND WIND MTN THREATS IN THE HWO. DRY RIDGING SFC AND ALOFT WILL BUILD OVER THE FORECAST AREA FROM THE WEST ON SAT...AS THE PRESSURE GRADIENT STEADILY RELAXES. TEMPERATURES WILL REBOUND TO NEAR NORMAL VALUES AFTER WELL BELOW NORMAL LEVELS THU NITE THRU FRI NITE. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... AS OF 2 AM WEDNESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON SUNDAY WITH UPPER LVL RIDGING IN PLACE OVER THE REGION AND DEEP TROUGHING DEVELOPING OVER THE WESTERN CONUS. THE MODELS CONTINUE TO DIVERGE BEGINNING AROUND MONDAY WITH THE 00Z GFS STILL FAVORING A SPLIT FLOW PATTERN OVER THE SRN PLAINS WHILE THE ECMWF AND GEM FAVOR AN ELONGATED POSITIVELY TILTED UPPER TROUGH. SINCE THE LATER PORTION OF THE SYNOPTIC PATTERN REMAINS FAIRLY UNCERTAIN...I DID NOT DEVIATE MUCH FROM THE INHERITED GRIDS. SUNDAY SHOULD BE DRY WITH A SLIGHT CHANCE OF PRECIP INTRODUCED SUN NIGHT AND EARLY MON. I RAMPED POPS UP TO SOLID CHANCE FOR THE REST OF THE MEDIUM RANGE SINCE THE POSITION AND TRACK OF THE SFC LOW IS UNCLEAR. LOOKS LIKE ALL PRECIP SHOULD BE LIQUID WITH TEMPS REMAINING WELL ABOVE FREEZING EXCEPT SAT EVENING/SUN MORNING WHEN CONDITIONS ARE DRY. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/... AT KCLT...THE IFR CEILING AND MVFR FOG ARE EXPECTED TO PERSIST UNTIL A COLD FRONT SCOURS LOW LEVEL MOISTURE LATER THIS MORNING. BY LATE MORNING VFR IS EXPECTED...WITH CLOUDS BREAKING UP IN THE AFTERNOON BEHIND THE FRONT. THE LIGHT SOUTHWEST WIND WILL BACK TO THE SOUTH THIS AFTERNOON...THEN WILL BECOME LIGHT AND VARIABLE EARLY THURSDAY MORNING. DEW POINTS WILL BE FALLING THURSDAY MORNING...AND FOG IS NOT EXPECTED AT THIS TIME. ELSEWHERE...IFR TO LOW MVFR CEILINGS AND MVFR FOG WILL PERSIST UNTIL LATER THIS MORNING WHEN A COLD FRONT SCOURS LOW LEVEL MOISTURE. KAVL WILL HAVE LIFR FOG UNTIL MID MORNING...WHILE KGSP WILL REMAIN VFR. VFR CEILINGS AND VISIBILITY ARE EXPECTED AT ALL SITES BY AFTERNOON. LIGHT SOUTHWEST WINDS WILL VEER TO THE WEST THIS EVENING...EXCEPT AT KAVL WHERE A NORTH NORTHWEST WIND WILL PREVAIL. DEW POINTS WILL BE FALLING AT MOST SITES THURSDAY MORNING...AND DEW POINT DEPRESSIONS ARE MOST SUPPORTIVE OF FOG AT KAVL...WHERE MVFR WILL BE INTRODUCED. A WEAKER CASE COULD BE MADE FOR KHKY...BUT MODEL GUIDANCE DEW POINT DEPRESSIONS ARE IN GREATER DISAGREEMENT THERE THAN AT KAVL...AND FOR NO NO FOG WILL BE CARRIED. OUTLOOK...ANOTHER COLD FRONT WILL BRING BREEZY NORTHWESTERLY WINDS ON THURSDAY NIGHT AND FRIDAY...WITH A FEW RESTRICTIONS IN SHOWERS IN THE MOUNTAINS. OTHERWISE...VFR THROUGH SUNDAY. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...JAT NEAR TERM...JAT SHORT TERM...RWH LONG TERM...JPT AVIATION...JAT