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000
FXUS62 KGSP 061518
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1018 AM EST THU MAR 6 2014

.SYNOPSIS...
A COASTAL LOW WILL DEVELOP TO OUR SOUTH TODAY AND TRACK UP THE
SOUTHEAST COAST LATER TONIGHT AND FRIDAY. DRIER HIGH PRESSURE IS
THEN EXPECTED TO RETURN TO OUR REGION THIS WEEKEND AND PERSIST
THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 955 AM...DENSE CIRRUS SHIELD CONTINUES TO OVERSPREAD THE AREA
LATE THIS MORNING. CONSIDERING THAT TEMPS HAVE ONLY WARMED TO THE
MID 30S OR SO THUS FAR...THE MAX TEMP FORECAST IS IN JEOPARDY OF
BEING TOO WARM...ESP IN LIGHT OF LOW LEVEL CAA RESULTING FROM ONSET
OF COLD AIR DAMMING. WE HAVE BEGUN THE PROCESS OF STEPPING BACK THE
FORECAST THIS AFTERNOON...NOW THINKING THAT MOST LOCATIONS WILL ONLY
SEE HIGHS OF AROUND 40. THIS IS OF PARTICULAR INTEREST CONSIDERING
THE DRYNESS OF THE AIR MASS...AND ATTENDANT IMPACT UPON SURFACE WET
BULB TEMPS...WHICH ARE SUB-FREEZING ACROSS THE ENTIRE FORECAST AREA.
PRECIP ASSOCIATED WITH ONGOING NORTHERN GMEX CYCLOGENESIS REMAINS
POISED TO MOVE INTO OUR SOUTHERN ZONES THIS AFTERNOON. WE WILL
ADVERTISE PRECIP ONSET AS A MIX OF RA/SLEET AS IT OVERSPREADS THE
AREA FROM SOUTH TO NORTH THIS AFTERNOON INTO THIS EVENING...WITH NO
SIGNIFICANT ACCUMS ANTICIPATED ANYWHERE IN THE CWA THROUGH 00Z.

IN TERMS OF THE MAIN EVENT TONIGHT/EARLY FRIDAY...UNCERTAINTY STILL
REMAINS...AS THE 12Z NAM IS STICKING TO ITS GUNS IN DEVELOPING
TREMENDOUS WAA NORTH OF THE DEVELOPING SOUTHEAST COASTAL CYCLONE...
AND PUNCHING A STRONG WARM NOSE INTO OUR AREA THIS EVENING...
SUGGESTING PRIMARILY AN ICING CONCERN...ESP FOR AREAS FROM THE BLUE
RIDGE EAST ALONG THE I-40 CORRIDOR. HOWEVER...THIS SCENARIO IS NOT
SUPPORTED BY OTHER OPERATIONAL GUIDANCE...AND ONLY 1/3 OR SO OF THE
SREF ENSEMBLE MEMBERS. WHILE UNCERTAINTY REMAINS HIGH REGARDING THE
THERMAL STRUCTURE ABOVE THE SURFACE...BECOMING MORE CONVINCED THAT
STRONG/CLASSICAL CAD WILL BE ABLE TO SUPPORT AN EXTENDED PERIOD OF
FREEZING/SUB-FREEZING TEMPS IN THE CLIMATOLOGICALLY FAVORED AREAS
NEAR THE BLUE RIDGE...AND ALONG THE I-40 CORRIDOR IN THE PIEDMONT.
STRONGLY SUSPECT THAT THE ADVISORY WILL NEED AN UPGRADE FOR THE BLUE
RIDGE AREAS...AND WILL NEED TO CONSIDER AN UPGRADE ALONG THE I-40
CORRIDOR AS WELL. SINCE OUR WINDOW OF OPPORTUNITY FOR ADEQUATE LEAD
TIME IS RAPIDLY SHRINKING...THE PLAN IS TO MAKE FAIRLY QUICK
DECISIONS ONCE THE 12Z GFS TRICKLES IN.

AS OF DAYBREAK...QUIET ACROSS THE WESTERN CAROLINAS AND NORTHEAST
GEORGIA UNDER THICKENING MID/HIGH LEVEL CLOUDS. THE LEADING EDGE OF
THE PRECIP REMAINS WELL TO THE SOUTH OVER SRN GEORGIA.

WE HAVE BEEN WATCHING THE FCST DEVELOPMENT OF A CLOSED MID/UPPER LOW
OVER THE SOUTHEAST FOR THE LAST SEVERAL DAYS...AND THE MODELS HAVE
CONVERGED MORE OR LESS ON A SOLUTION...CLOSING OFF THE LOW THIS
MORNING OVER THE MS DELTA REGION...AS SEEN ON WATER VAPOR IMAGERY.
IN RESPONSE...A SURFACE LOW WILL SLOWLY ORGANIZE AND MOVE FROM THE
NORTHEAST GULF...ACROSS THE FL PENINSULA LATE TODAY...AND OFF THE
SOUTHEAST COAST TONIGHT. THE MID/UPPER LOW WILL SPREAD ALL MANNER OF
FORCING UP FROM THE SOUTH WITH DEEP GULF/ATLANTIC MOISTURE...SO
PRECIP LOOKS LIKE A SAFE BET. ONLY THE ONSET TIME IS IN DOUBT FOR
TODAY...AND THE TREND OF THE MODELS SUGGESTS THAT PRECIP WOULD
DEVELOP FROM S TO N THROUGHOUT THE DAY SUCH THAT WE BEGIN DRY AND
MOVE THE LEADING EDGE OF THE PRECIP CHANCES TO I-40 BY SUNSET. ALTHO
IT WILL BE WELL BELOW NORMAL TODAY...TEMPS WILL REMAIN WARM ENOUGH
INITIALLY THAT PRECIP SHOULD BE RAIN AT ONSET...PERHAPS MIXED WITH
SOME SLEET E OF THE MTNS...OR SNOW/SLEET OVER THE HIGHER TERRAIN.

THINGS GET INTERESTING TONIGHT AS PRECIP ENGULFS THE ENTIRE REGION.
THE GFS CONTINUES TO BE ON THE COOL SIDE OF THE GUIDANCE WITH MUCH
LOWER THICKNESSES...WHILE THERE IS GOOD AGREEMENT AMONG THE
NAM/ECMWF/CANADIAN/SREF POINTING MORE TOWARD MORE OF A SLEET/
FREEZING RAIN SCENARIO OVER THE NRN ZONES. ALTHO THE NAM/ECMWF IS
PREFERRED...THE FCST USES A BLEND OF THE NAM AND GFS IN ORDER TO
ACCOUNT FOR THE POSSIBILITY THAT PROFILES MIGHT BE COOLER
OVERNIGHT...THUS MORE OF A SNOW/SLEET POSSIBILITY OVER THE HIGHER
TERRAIN AND NC BLUE RIDGE. WHAT FALLS OUT OF THIS PROCESS IS A
COMPLEX ELEVATION DEPENDENT SNOW/SLEET SCENARIO OVER THE CENTRAL AND
NRN MTNS OF NC...THAT SHOULD CHANGE OVER TO FREEZING RAIN AND RAIN
AS THE WARM NOSE STRENGTHENS WITH WARM ADVECTION IN THE EASTERLY
ATLANTIC FLOW ON THE N SIDE OF THE LOW BY DAYBREAK. THE NC FOOTHILLS
AND NW PIEDMONT WOULD SEE PRECIP BECOMING SLEET IN THE
EVENING...THEN CHANGING OVER TO FREEZING RAIN IN THE EARLY MORNING
HOURS...AND EVENTUALLY RAIN AROUND DAYBREAK. ANOTHER GUIDANCE TREND
IS THE WETTER NAM SOLUTION...WHICH MIGHT RAISE PRECIP AMTS ENOUGH TO
WORRY ABOUT WARNING CRITERIA. AS CONSTRUCTED...THERE IS THE
POTENTIAL FOR UP TO TWO TENTHS OF ICE OVER PARTS OF THE NW
PIEDMONT...AND 2-3 INCHES OF SNOW OVER MAINLY THE HIGHER ELEVATIONS
OF THE CENTRAL/NRN MTNS OF NC. WILL ISSUE A WINTER WEATHER ADVISORY
FOR TONIGHT THROUGH NOON FRIDAY TO HANDLE THIS. THERE IS SOME RISK
THAT IF WARMER AIR DOES NOT COME IN AS MUCH AS EXPECTED THAT MORE
PRECIP OVER THE MTNS WOULD FALL AS SNOW/SLEET...AND THAT FREEZING
RAIN WOULD HANG ON LONGER OVER THE NW PIEDMONT...SO SOME ADJUSTMENTS
ON THE FLY MIGHT BE ANTICIPATED. ELSEWHERE...JUST A COLD RAIN FOR
METRO CHARLOTTE/UPSTATE SC/NE GEORGIA/AND THE SRN MTNS OF NC.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AT 300 AM EST THURSDAY...A CLOSED UPPER LOW WILL BE OVER S GA FRIDAY
MORNING. AN ASSOCIATED COASTAL SURFACE LOW WILL BE OFF THE SC
COAST...WITH A DEFORMATION ZONE WILL WRAPPED AROUND IT ACROSS
NC...UPSTATE SC AND N GA. THE NAM SHOWS STRONG EASTERLY ISENTROPIC
UPGLIDE ACROSS THE CAROLINAS AND NE GA THAT BACKS TO THE NE BY
MIDDAY...SUPPORTING ROBUST PRECIPITATION PRODUCTION. PRECIPITATION
WILL TRANSITION TO ALL RAIN VERY EARLY IN THE MORNING AS LOW LEVELS
WARM. BY AFTERNOON...LOW LEVEL FLOW WILL BE FROM THE NNE AND WEAK
DOWNGLIDE...ALTHOUGH MOISTURE REMAINS WITH THE PIVOTING...SLOW
MOVING DEFORMATION ZONE CENTERED OVER THE PIEDMONT...AND DECREASING
PRECIPITATION WILL CONTINUE INTO THE EVENING. HIGH TEMPERATURES WILL
BE SIGNIFICANTLY BELOW NORMAL...ESPECIALLY IN THE EAST WHERE LOWER
HEIGHTS...GREATER RAINFALL...AND MORE CLOUD COVER WILL EXIST.

THE SURFACE LOW WILL MOVE TO THE NC COAST BY FRIDAY EVENING...WHILE
A LOW AMPLITUDE UPPER RIDGE CROSSES TO LOWER MS RIVER VALLEY. CLOUD
COVER AND PRECIPITATION ASSOCIATED WITH THE DEFORMATION ZONE SHOULD
DEPART OUR AREA TO THE EAST BY AROUND MIDNIGHT...EVEN IN THE SLOWER
NAM SOLUTION. HIGH PRESSURE WILL BUILD IN FROM THE SW LATE SATURDAY
NIGHT...WITH CIRRUS SPILLING OVER THE APPROACHING UPPER RIDGE FROM A
TROUGH UPSTREAM.  LOW TEMPERATURES WILL RUN NEAR NORMAL.

BY SATURDAY MORNING THE UPPER RIDGE PROGRESSES TO THE SOUTHERN
APPALACHIANS WHILE THE COASTAL LOW MOVES UP THE GULF STREAM. THE
SURFACE RIDGE WEAKENS OVER OUR AREA AND A LEE TROUGH FORMS...WHILE A
COLD FRONT CROSSES THE OH RIVER VALLEY. HIGH TEMPERATURES WILL RUN
ABOVE NORMAL UNDER THE UPPER RIDGE.

THE UPPER RIDGE DEAMPLIFIES AND MOVES OFFSHORE ON SATURDAY...LEAVING
ZONAL FLOW ACROSS THE SOUTHEAST IN ITS WAKE. A STRONG SHORTWAVE
MOVING THROUGH A POSITIVELY TILTED UPPER TROUGH REACHES THE CENTRAL
APPALACHIANS AND TN VALLEY BY SUNDAY MORNING IN THE GFS AND ECMWF...
BUT ONLY APPROACHES THE OH VALLEY IN THE NAM. THE MODELS SHOW A COLD
FRONT MOVING INTO OUR AREA FROM THE NW SATURDAY NIGHT...BUT DIFFER
ON THE AMOUNT OF MOISTURE THAT ACCOMPANIES IT. LOW TEMPERATURES WILL
RUN ABOVE NORMAL UNDER CLOUDS COVER.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 215 AM THURSDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
SUNDAY WITH A LOW AMPLITUDE UPPER SHORTWAVE OVER THE FCST AREA AND A
NEARLY CUTOFF SOUTHERN STREAM UPPER TROF OVER THE EXTREME SW CONUS.
OVER THE NEXT 24 TO 48 HRS...THE PATTERN REMAINS FAIRLY ZONAL OVER
THE SE CONUS WHILE THE SOUTHERN STREAM TROF DRIFTS VERY SLOWLY
EASTWARD. BEYOND THIS POINT...THE LONG RANGE MODEL SOLUTIONS BEGIN
TO DIVERGE CONSIDERABLY WRT TO THE SYNOPTIC PATTERN EVOLUTION. THE
NEWER 00Z RUN OF THE GFS AMPLIFIES A BROAD UPPER TROF OVER THE GREAT
LAKES REGION ON WED AND EVENTUALLY DIGS THE TROF SOUTHWARD AND TO
OUR WESTERN FRINGE BY THE END OF THE MEDIUM RANGE...WHILE THE ECMWF
IS FASTER TO AMPLIFY THE TROF AND MOVE IT TO OUR DOORSTEP BY LATE
WED/EARLY THURS.

AT THE SFC..A WEAK AND DRY COLD FRONT IS EXPECTED TO MOVE THRU THE
CWFA EARLY SUN WITH HIGH PRESSURE MOVING IN BEHIND IT. HIGH PRESSURE
IS EXPECTED TO REMAIN OVER THE REGION THRU TUES WITH ANOTHER LOW
DEVELOPING TO OUR WEST LATE TUES/EARLY WED AND MOVING INTO THE CWFA
BY LATE WED/EARLY THURS. THE SPECIFIC TRACK AND PLACEMENT OF THE LOW
AS IT MOVES OVER THE REGION REMAINS AMBIGUOUS AT THIS POINT WITH
CONFIDENCE IMPROVING OVER THE NEXT FEW DAYS. FOR THE SENSIBLE
FCST...ONLY SLIGHT CHANCE POPS LINGER OVER THE NC MTS AT THE
BEGINNING OF THE MEDIUM RANGE AND TAPER OFF BY 00Z MONDAY. THE FCST
IS DRY UNTIL WE MOVE INTO LATE TUES WITH POPS RAMPING UP FROM SW TO
NE AND BECOMING SOLID CHANCE BY EARLY WED. PRECIP CHANCES PEAK LATE
WED INTO THURS AS THE LOW IS EXPECTED TO BE MOVING OVER THE FCST
AREA BY THAT TIME. TEMPS WILL START OUT ABOVE NORMAL ON SUN AND
LIKELY REMAIN ABOVE NORMAL THRU THE PERIOD.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
AT KCLT...VFR THROUGH AT LEAST EARLY AFTERNOON WITH THICKENING CLOUD
COVER AND GRADUALLY LOWERING CLOUD BASE. WIND WILL REMAIN NE AND
SHOULD STRENGTHEN AND BECOME GUSTY BY MID MORNING AS THE PRESSURE
GRADIENT INCREASES BETWEEN THE COOL HIGH TO THE NORTHEAST AND
DEVELOPING LOW PRESSURE OVER THE NORTHEAST GULF. FLIGHT CONDITIONS
GO DOWNHILL IN THE LATE AFTERNOON AND EARLY EVENING AS UPGLIDE
STRENGTHENS AND MOISTURE INCREASES ON THE NORTH SIDE OF THE LOW.
PRECIPITATION WILL DEVELOP AFTER 21Z WHICH WILL SERVE TO BRING THE
CEILING DOWN INTO THE MVFR RANGE. THERE SHOULD BE A DRY AND COLD
LAYER BETWEEN THE CLOUD BASE AND THE GROUND...AND IN THESE
SITUATIONS WE USUALLY SEE EITHER A BRIEF PERIOD OF SLEET OR AT LEAST
SOME SLEET MIXED WITH THE RAIN...SO THAT WAS INCLUDED IN A TEMPO
GROUP WHEN THE PRECIP BEGINS. STEADIER RAIN AND SLIGHTLY WARMER
TEMPS WILL ELIMINATE THE SLEET THREAT DURING THE EARLY EVENING. IFR
CONDITIONS ARE A SAFE BET DEVELOPING THURSDAY EVENING. WILL SHOOT
FOR 03Z FOR ONSET...BUT IT COULD BE SOONER THAN THAT. CANNOT RULE
OUT LOW IFR EARLY FRIDAY.

ELSEWHERE...A SIMILAR PROGRESSION...AT LEAST OVER THE UPSTATE SC TAF
SITES...EXCEPT FOR AN HOUR OR TWO EARLIER PERHAPS AS THE PRECIP AND
LOW CLOUDS MOVE UP/DEVELOP FROM THE S/SE. THE MTNS PRESENT A BIT
MORE OF A PROBLEM. THE PRECIP SHOULD SWITCH TO A PERIOD OF SLEET OR
SLEET/SNOW THROUGH THURSDAY EVENING...ESPECIALLY AT THE HIGH
ELEVATIONS AROUND KAVL. AS MID LEVELS WARM THIS SHOULD TRANSITION TO
FREEZING RAIN IN THE FRENCH BROAD VALLEY BEFORE DAYBREAK FRIDAY.

OUTLOOK...IFR/MVFR FLIGHT RESTRICTIONS AND PRECIPITATION COVERAGE
WILL CONTINUE INTO FRI MORNING...WITH PRECIP POSSIBLY LINGERING
THROUGH FRIDAY AFTN AS LOW PRESSURE PULLS AWAY ALONG THE EAST COAST.
THE BEST CHANCE OF FREEZING/FROZEN WILL BE FROM KAVL TO KHKY THROUGH
MIDDAY FRI. DRY HIGH PRESSURE AND IMPROVING CONDITIONS ARE EXPECTED
THROUGH SAT...WITH A DRY COLD FRONT CROSSING ON SUNDAY.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-15Z
KCLT       HIGH 100%     HIGH  92%     MED   67%     LOW   55%
KGSP       HIGH 100%     HIGH  92%     LOW   58%     MED   75%
KAVL       HIGH 100%     HIGH  94%     HIGH  83%     MED   75%
KHKY       HIGH 100%     HIGH  96%     MED   63%     MED   75%
KGMU       HIGH 100%     HIGH  86%     LOW   58%     MED   75%
KAND       HIGH  95%     MED   70%     MED   61%     MED   75%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE
HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE
FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO NOON EST
     FRIDAY FOR NCZ033-035>037-048>050-052-053-056-057-059-
     063>065-501>510.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JDL/PM
SHORT TERM...JAT
LONG TERM...JPT
AVIATION...PM