000 FXUS62 KGSP 251741 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 1241 PM EST WED NOV 25 2009 .SYNOPSIS... HIGH PRESSURE WILL GIVE AWAY TO AN ADVANCING COLD FRONT WHICH WILL ARRIVE ON THURSDAY. HIGH PRESSURE WILL BE IN CONTROL DURING THE WEEKEND AND INTO EARLY NEXT WEEK. ANOTHER COLD FRONT AND LOW PRESSURE WILL ARRIVE MONDAY NIGHT AND TUESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 10 AM...A WEAK COLD FRONT WAS ANALYZED JUST WEST OF THE APPALACHIANS...WITH VISIBLE SATELLITE IMAGERY SHOWING STUBBORN LOW CLOUDS ALONG AND EAST OF THE BNDRY. THE FRONT WILL PUSH THRU THE CWFA BY EARLY THIS EVENING...AS A H5 SHORTWAVE TROF CROSSES THE MTNS. DEEP DRY WLY FLOW WILL HELP SCOUR OUT THE CLOUDS GRADUALLY...AND ALLOW TEMPS TO WARM DUE TO DOWNSLOPING EAST OF THE MTNS. THERE WILL BE LLVL CAA THIS AFTN...BUT NOT VERY STRONG...SO ABOVE NORMAL TEMPS (ACTUALLY TEMPS A COUPLE DEGREES WARMER THAN WHAT THE 12Z THICKNESSES WOULD INDICATE) IS EXPECTED TODAY. ONLY CHANGES WILL BE TO TWEAK THE TIMING OF THE SKY CLEARING. OTHERWISE...FCST IN GOOD SHAPE. PREVIOUS DISCUSSION... 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 /18Z WEDNESDAY THROUGH MONDAY/... AT KCLT...SATELLITE IMAGERY AND METARS TO THE WEST OF THE TERMINAL INDICATE THAT THE MVFR CIGS SHOULD SCATTER OUT BY 19Z...LEAVING SOME LINGERING LIFTING CUMULUS AND BKN CIRRUS. WINDS WILL REMAIN LIGHT OUT OF THE SW THRU THIS EVENING...AND WILL LIKELY GO CALM OVERNIGHT. GUIDANCE IS IN DISAGREEMENT ON WHETHER THERE WILL BE GOOD ENUF CONDITIONS TO SUPPORT FOG DEVELOPMENT TOWARD DAYBREAK. FOR NOW...I HAVE ADDED A 6SM BR MENTION TO REFLECT A POTENTIAL IMPACT. OTHERWISE...VFR WITH A LIGHT NW WIND AFTER SUNRISE. WIND WILL SHIFT BACK TO SW BY AROUND 18Z THU. ELSEWHERE...STRATOCU IS SCATTERING OUT ALONG A LINE EXTENDING FROM KHKY...KEHO...KSPA. SO VFR CONDITIONS ARE EXPECTED THE REST OF THE AFTN AND INTO TONIGHT. BASED ON THE MODEL CONSENSUS...KAVL AND KHKY HAVE THE HIGHEST PROB OF FOG DEVELOPMENT LATE TONIGHT. SOME OF THE GUIDANCE DOES HAVE FOG DEVELOPMENT ACROSS THE UPSTATE. BUT WINDS ARE NOT EXPECTED TO DECOUPLE THERE. ANY FOG THAT DEVELOPS SHOULD QUICKLY BURN OFF BY LATE THU MORNING. OUTLOOK...ANOTHER COLD FRONT WILL BRING BREEZY NORTHWESTERLY WINDS ON THURSDAY NIGHT AND FRIDAY. THERE COULD BE BRIEF PERIODS OF RESTRICTIONS IN SHOWERS AT KAVL...MAINLY EARLY FRIDAY MORNING. OTHERWISE...VFR THROUGH SUNDAY. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...NONE. NC...NONE. SC...NONE. && $$ SYNOPSIS...JAT NEAR TERM...ARK/JAT SHORT TERM...RWH LONG TERM...JPT AVIATION...ARK