FXUS62 KGSP 040554
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1254 AM EST FRI DEC 4 2009
.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO NOSE IN FROM THE WEST INTO FRIDAY.
ANOTHER LOW PRESSURE SYSTEM WILL MOVE UP FROM THE GULF...CROSSING
THE REGION ON SATURDAY. BEHIND THIS SYSTEM...HIGH PRESSURE WILL
REBUILD OVER THE REGION AND REMAIN IN PLACE THROUGH EARLY NEXT WEEK.
&&
.NEAR TERM /THROUGH TODAY/...
LOW CLOUDS CONTINUE TO LINGER ALONG THE NW FACING ESCARPMENT OF THE
NC MTNS AS EXPECTED BUT SHOULD SLOWLY DIMINISH OVERNIGHT...WHILE
HIGH CLOUDS INCREASE LATE TONIGHT AHEAD OF APPROACHING SHORTWAVE.
FCST ON TRACK AND MADE ONLY MINOR ADJUSTMENTS TO TEMP/DP GRIDS FOR
THIS UPDATE.
PREVIOUS DISCUSSION...WATER VAPOR IMAGERY AND RUC HEIGHT FIELDS
PLACE AN UPPER VORTEX OVER NRN IA EARLY THIS AFTERNOON. OVER THE
SOUTHEAST...THE TRAILING EDGE OF A STRONG UPPER JET STREAK HAS BEEN
SLOWLY MIGRATING TOWARD THE SOUTHEAST COAST. THIS UPPER JETLET IS
EXPECTED TO BEGIN MOVING BACK TO THE NW AS THE TROUGH DEEPENS TO THE
WEST. THIS WILL COMBINE WITH IMPROVING UPPER DIVERGENCE THROUGH THE
NEAR TERM PERIOD TO ALLOW HIGH CLOUDS TO STEADILY LOWER AND THICKEN
THROUGH FRIDAY. HOWEVER...HIGH CLOUDS AND LINGERING NW FLOW MOISTURE
NEAR THE TN TONIGHT SHOULD BE SPARSE ENOUGH TO PERMIT FAIRLY CHILLY
OVERNIGHT TEMPS. MINS WILL RANGE FROM THE UPPER 20S TO LOWER 30S IN
THE MTNS OVERNIGHT...AND MID TO UPPER 30S ELSEWHERE.
ALONG WITH THE INCREASING HIGH CLOUDS FRIDAY...BRIEF ISENTROPIC LIFT
AT LOWER LEVELS MAY DEVELOP DURING THE MORNING HOURS. HOWEVER...THIS
SHOULD BE FAIRLY TRANSIENT AS THE 850 MB FLOW VEERS AND WEAKENS
BEFORE BACKING SHARPLY LATE IN THE DAY. WITH LOW LEVELS QUITE
DRY...NO PRECIPITATION IS ANTICIPATED THROUGH DAY. MAXES FRIDAY
SHOULD REACH INTO THE 40S MTNS AND 50S PIEDMONT...EXCEPT FOR CHILLY
30S ALONG THE HIGHER RIDGE TOPS.
&&
.SHORT TERM /TONIGHT THROUGH SUNDAY/...
AS OF 230 PM THURSDAY...MODELS IN GOOD AGREEMENT ON FAST-MOVING
LONGWAVE TROF...WITH AXIS SHIFTING FROM THE HIGH PLAINS TO THE
APPALACHIANS DURING THE SHORT TERM PERIOD. A VORT MAX IS DEPICTED ON
ALL THE OP MODELS...ROUNDING THE BASE OF THE TROF AS IT PROGRESSES
EWD ACRS THE TN VLY. AT THE SFC...A WEAK COASTAL LOW IS EXPECTED TO
QUICKLY TRACK FROM THE NRN GULF OF MEXICO TO WELL EAST OF THE OUTER
BANKS BY SATURDAY AFTN. COLD HIGH PRESSURE RIDGE AXIS WILL EXTEND
FROM THE LOWER MS VLY TO NEW ENGLAND.
BASED ON MODEL CONSENSUS...MAXIMUM SYNOPTIC LIFT IS PROGGED TO OCCUR
IN THE 06Z-18Z SAT TIME FRAME. LOOKING AT FGEN FORCING IN CROSS
SECTIONS FROM BOTH THE NAM AND GFS...IT DOES NOT LOOK LIKE THERE IS
THAT HIGH A LIKELIHOOD OF HEAVY SNOW BANDING. HOWEVER...ISENTROPIC
LIFT ON THE 295K SFC WILL BE STRONG AT THE TIME OF MAX Q-VECTOR
FORCING (AFOREMENTIONED TIME FRAME). ALSO...NAM/GFS IN DECENT
AGREEMENT ON NOMOGRAM SHOWING A RAIN/SNOW PTYPE EVENT WITH SNOW
LEVELS FALLING FROM 3500 FT EARLY SAT MORNING TO THE VALLEY FLOORS
BY EARLY AFTN. A BLEND OF HPC AND GFS QPF AND 12-1 SNOW/LIQUID
RATIOS RESULTS IN GENERALLY 2-4" OF SNOW FROM THE EASTERN SMOKIES TO
AVERY COUNTY. GUIDANCE SEEMS TO SHOW DECENT SNOW IN THE FRENCH BROAD
VALLEY. SO A WINTER STORM WATCH FOR HEAVY SNOW WILL BE ISSUED FROM
SWAIN/NRN JACKSON COUNTIES NORTH (INCLUDING BUNCOMBE) FOR FRIDAY
NIGHT THRU SATURDAY EVENING. THE SNOW SHOULD TAPER OFF RAPIDLY LATE
SAT AFTN INTO THE EVENING...AS THE VORT MAX EXITS THE CWFA TO THE
EAST.
TEMPS WERE A CHALLENGE...BUT A BLEND OF THE GUIDANCE MADE LITTLE
CHANGE TO INHERITED GRIDS. LOWS SATURDAY MORNING WILL BE IN THE
UPPER 20S TO MID 30S IN THE MTNS...AND UPPER 30S TO LOWER 40S
PIEDMONT. TEMPS WILL HOLD NEAR STEADY OR SLOWLY DROP SATURDAY...THEN
DROP INTO 20S SATURDAY NIGHT...AS SKIES BEGIN TO CLEAR AND STRONGER
CAA WORKS IN BEHIND THE SYSTEM. WITH WET ROADS ACROSS THE CWFA SAT
NGT...BLACK ICE STILL LOOKS LIKE A THREAT AND WILL CONTINUE TO BE
MENTIONED IN THE HWO.
SUNDAY...HIGH PRES QUICKLY BUILDS IN FROM THE WEST...WITH MOSTLY
SUNNY SKIES EXPECTED. TEMPS SHOULD REBOUND TO THE MID TO UPPER 40S
(LOWER 50S ACRS EXTREME SOUTHERN TIER). SO MUCH OF THE SNOW IN THE
VALLEYS SHUD MELT.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 200 PM THURSDAY...GLOBAL MODELS ARE IN SOLID AGREEMENT IN
DEPICTING A RELATIVELY LOW AMPLITUDE/ACTIVE/PROGRESSIVE PATTERN
DURING THE EARLY PART OF THE MEDIUM RANGE...TRANSITIONING TO MORE
AMPLIFICATION BY THE END OF THE PERIOD. THE NEXT STORM SYSTEM
APPEARS POISED TO TAKE AIM ON THE CWFA DURING MID-WEEK. ALTHOUGH
THEY DIFFER IN THEIR DETAILS...THE 12Z RUNS OF THE ECMWF AND GFS
DEPICT A MAJOR CYCLONE ORIGINATING FROM THE MISS VALLEY MOVING ACROSS
THE EASTERN CONUS ON WED/WED NIGHT...WITH WIDESPREAD PRECIPITATION
AFFECTING THE CAROLINAS DURING THIS TIME. DESPITE THE RATHER LARGE
DISCREPANCIES BETWEEN THE MODELS REGARDING THE PLACEMENT OF KEY
SYNOPTIC FEATURES...THIS DISPARITY WILL NOT HAVE A HUGE IMPACT UPON
THE SENSIBLE WEATHER. THEREFORE...LOW CHANCE POPS WILL BEGIN ACROSS
THE AREA EARLY TUE...TRANSITIONING TO SOLID CHANCES TUE NIGHT INTO
WED. ALTHOUGH THE ONSET OF ISENTROPIC LIFT MAY RESULT IN A BRIEF
PERIOD OF A PATCHY/LIGHT WINTRY MIX TUE MORNING...ESPECIALLY IN
SHELTERED MTN VALLEYS...ANY LIGHT PRECIP SHOULD TRANSITION TO LIQUID
QUICKLY DURING THE DAY TUESDAY.
CONDITIONS SHOULD BEGIN TO IMPROVE WED NIGHT...ALTHOUGH WRAP-AROUND
MOISTURE/NORTHWEST FLOW COULD RESULT IN UPSLOPE SNOW SHOWERS INTO
EARLY THURSDAY.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
KCLT...HKY...KAND AND KGMU...WINDS WILL BE LIGHT OUT OF THE N TO NNE
OVERNIGHT AND A LITTLE STRONGER OUT OF THE NE DURING THE DAY. HIGH
CLOUDS WILL GRADUALLY INCREASE...AND AT SOME POINT A SCT TO BKN DECK
SHOULD FORM UP AROUND 5KFT. THE TIMING OF THIS DECK VARIES QUITE A
BIT BETWEEN MODELS. I/VE STARTED SCT050 AT 15 UTC AND RUN IT THROUGH
THE REST OF THE PERIOD...BUT THERE IS A GOOD CHANCE THAT AT SOME
POINT IT WILL BECOME BKN.
KAVL...NNW WINDS WILL KEEP AN MVFR DECK OVER THE AIRFIELD THE REST
OF THE NIGHT. THE WINDS WEAKEN AFTER SUNRISE...AT WHICH TIME THE LOW
CLOUDS SHOULD RETREAT TO THE TN LINE. VFR CIGS WILL DEVELOP AGAIN
DURING THE AFTN. WINDS WILL BE OUT OF THE N THIS MORNING...BECOMING
VARIABLE IN THE AFTN.
FOR KGSP...WINDS SHOULD REMAIN VERY LIGHT OVERNIGHT WITH A GRADUAL
SHIFT TO THE NE AND A SLIGHT INCREASE IN INTENSITY IN THE 4-6KT
RANGE THROUGH FRI. MOSTLY CLEAR SKIES WILL GIVE WAY TO HIGH CLOUDS
BY MORNING WITH SCT VFR LOW TO MID CLOUDS DEVELOPING BY FRI
AFTERNOON.
OUTLOOK...MOISTURE AND LIFT WILL INCREASE RAPIDLY TONIGHT AND
SATURDAY WITH RESTRICTIONS DEVELOPING. SOME SNOW COULD DEVELOP AND
AFFECT KAVL LATE TNGT-SAT MRNG...WITH CHC RAIN OTHER TAF SITES.
CONDITIONS SHOULD IMPROVE QUICKLY SAT NIGHT INTO SUN AS DRY HIGH
PRESSURE BUILDS IN. VFR LIKELY MON-TUE.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER STORM WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING
FOR NCZ033-048>053-059.
SC...NONE.
&&
$$
SYNOPSIS...DEO
NEAR TERM...HG/RB
SHORT TERM...ARK
LONG TERM...JDL
AVIATION...JPT/MCAVOY
