FXUS62 KGSP 251532
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1032 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/...
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 /16Z 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...ARK/JAT
SHORT TERM...RWH
LONG TERM...JPT
AVIATION...JAT
