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000
FXUS62 KGSP 140541
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1241 AM EST SAT DEC 14 2013

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE CAROLINA COAST LATER TONIGHT. A LOW
WILL MOVE ACROSS THE REGION FROM THE WEST ON SATURDAY BRINGING
WIDESPREAD PRECIPITATION AND COOL TEMPERATURES FOR THE WEEKEND. IN
THE WAKE OF THE FRONT...EXPECT ANOTHER HIGH TO MOVE BACK IN AND
BRING DRY WEATHER THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1240 PM...MID CLOUDS MOVING INTO THE AREA...BUT LOWER CLOUDS
AND PRECIP STILL A FEW HOURS AWAY. MADE UPDATES FOR CURRENT
CONDITIONS...BUT LEFT BULK OF THE FORECAST UNCHANGED.

AS OF 945 PM EST FRIDAY...THICK MID-LEVEL CLOUD COVER HAS CAUSED
TEMPERATURES TO STOP FALLING AND EVEN SLOWLY RISE IN SOME CASES. THE
LATEST NAM AND GFS RUNS ARE A LITTLE COLDER IN THE 12-15 UTC PERIOD.
HOWEVER...I WILL NOT EXPAND ICE ACCUMULATIONS OWNING TO THE PRESENT
WARM ANTECEDENT CONDITIONS.

AS OF 630 PM EST FRIDAY...HIGH CLOUDS CONTINUE TO THICKEN OVER THE
FORECAST AREA. THERE ARE SOME RADAR RETURNS APPROACHING THE NC
MTNS...BUT WITH UPSTREAM CLOUD BASES RANGING FROM 10-12KFT IT SHOULD
BE VIRGA AT LEAST THROUGH MIDNIGHT.

PREVIOUS DISCUSSION...
CIRRUS HAS BEGUN SPREADING INTO THE AREA AS EXPECTED...AND WILL
GRADUALLY INCREASE AND THICKEN THROUGH THE AFTERNOON...WITH MOSTLY
CLOUDY SKIES LIKELY ACROSS THE AREA BY MID-EVENING. MEANWHILE...
INCREASING ISENTROPIC LIFT/SOUTHERLY FLOW IS EXPECTED TO RESULT IN
STRATOCU OVERSPREADING MUCH OF THE AREA AFTER MIDNIGHT. THESE
FACTORS WILL ACT TO LIMIT DIURNAL COOLING...WITH MIN TEMPS EXPECTED
TO AVERAGE ABOUT A CATEGORY ABOVE NORMAL ACROSS THE BOARD. THIS WILL
HAVE CONSEQUENCES FOR P-TYPE CONSIDERATIONS AS PRECIP MOVES INTO THE
AREA BY DAYBREAK IN STRONG LOW-MID LEVEL UPGLIDE REGIME...ESPECIALLY
AS TEMPS ARE EXPECTED TO WARM QUICKLY ALOFT. THE 12Z NAM HAS COME IN
CONSIDERABLY WARMER AND SUPPORTING MUCH LESS WINTRY PRECIP ACROSS
THE MTNS THAN THE 06Z RUN...WHICH MAY BE A CONSEQUENCE OF ITS
STRONGER AND FARTHER NORTH SURFACE LOW. MEANWHILE...THE GFS LOOKS
QUITE SIMILAR TO THE 06Z NAM...ARGUING FOR A BRIEF PERIOD OF SNOW/
SLEET ACROSS THE NORTHERN MTNS...FOLLOWED BY SEVERAL HOURS OF FZRA
ALONG THE EASTERN ESCARPMENT.

WE HAVE OPTED TO STICK CLOSELY TO THE GFS...WITH PERHAPS A SLIGHT
NOD TO THE NAM. WHILE IN SITU CAD WILL DEVELOP IN RESPONSE TO PRECIP
FALLING INTO A DRY/COOL AIR MASS...A LACK OF STRONG COLD/DRY AIR
ADVECTION AT THE SURFACE WILL MAKE IT DIFFICULT TO LOCK TEMPS IN
MUCH BELOW FREEZING. A STRONG S/SE UPSLOPE FLOW ALOFT MAY PROVIDE
FOR A COOLING MECHANISM IN A NARROW CORRIDOR ALONG THE BLUE RIDGE
(PRIMARILY NORTH OF I-40)...BUT THIS IS USUALLY AN INADEQUATE
SUBSTITUTE FOR A STRONG BARRIER JET EVENT. WE ARE ALSO ANTICIPATING
THAT THE PRECIP EVENT WILL ENTAIL 4-6 HOURS OF MODERATE TO
OCCASIONALLY HEAVY RAIN...WHICH ADDS TO THE DIFFICULTY OF LOCKING IN
FREEZING TEMPS...OWING TO STRONG LATENT HEAT RELEASE OF FREEZING AT
THE SURFACE. FINALLY...ROAD TEMPS SHOULD BE QUITE WARM THANKS TO
TEMPS THAT ARE WELL INTO THE 40S THIS AFTERNOON...SO EVEN IF A FEW
HOURS OF FZRA ARE SEEN ALONG THE ESCARPMENT SATURDAY MORNING...
SIGNIFICANT TRAVEL PROBLEMS ARE UNLIKELY.

OTHERWISE...ALL AREAS WILL SEE 100 POPS AT SOME POINT ON SATURDAY.
STRONG DEEP LAYER FORCING SHOULD YIELD PRECIP AMOUNTS OF .5-1.0 INCH
IN MOST AREAS...ALTHOUGH LOCATIONS ALONG THE SOUTHERN ESCARPMENT MAY
SEE IN EXCESS OF AN INCH. WARM CONVEYOR BELT PRECIP SHOULD END FROM
WEST TO EAST FAIRLY QUICKLY SAT AFTERNOON...ALTHOUGH LOW CLOUDS AS
WELL AS DRIZZLE/-RA AND VERY COOL CONDITIONS WILL LINGER INTO AT
LEAST SAT EVENING.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
AS OF 210 PM FRI...0Z SUN...A MILLER B SYSTEM WILL LIKELY BE CENTERED
NORTH OF THE FORECAST AREA...NAM SLOWER THAN THE GFS AND ECMWF. RAIN
WILL LINGER ACROSS MOST OF THE FORECAST AREA SAT EVENING.
HOWEVER...DOWNSLOPE FLOW SHOULD DEVELOP AFTER MIDNIGHT...RESULTING
IN THE END OF ACCUMULATING RAINFALL ACROSS THE FOOTHILLS AND
PIEDMONT BY SUNDAY MORNING. COOL AND MOIST NORTHWEST WINDS WILL
DEVELOP ACROSS THE MTNS...SUPPORTING LIGHT UPSLOPE PRECIP ALONG THE
TN BORDER. MODERATE CAA SHOULD RESULT IN H85 TEMPERATURES FALLING
FROM 3C AT 6Z SUN TO -3 TO -5C BETWEEN 12-18Z SUNDAY. FORECAST
SOUNDINGS INDICATE THE MOST OF THE MOISTURE IS LIMITED TO THE LOWEST
2KFT...AND WELL BELOW THE LEVEL OF OPTIMAL SNOW GROWTH TEMPERATURES.
IN ADDITION...LLVL WINDS ARE SLOW TO VEER FROM THE NW...WITH SPEEDS
LIMITED TO 20-25 KTS. IN THIS
ENVIRONMENT...COUNTIES ALONG THE TN LINE SHOULD EXPERIENCE RAIN IN
THE EVENING...MIXING TO SN WITH PERIODS OF -FREEZING RAIN AND
DRIZZLE EARLY SUNDAY MORNING. PRECIP ACCUMULATION ASSOCIATED WITH
THE NW UPSLOPE WINDS WILL BE LIGHT. LOW TEMPERATURES SUNDAY SHOULD
RANGE FROM THE MID TO LOWER 30S ACROSS THE MTNS TO MID TO UPPER 30S
EAST.

LLVL MOISTURE AND WINDS WILL DECREASE THROUGH SUNDAY. HOWEVER...THE
SOUTHERN APPALACHIANS SHOULD EXPERIENCE CAA DURING THE MORNING...AND
NEUTRAL DURING THE AFTERNOON. MTN TEMPERATURES NEAR THE TN BORDER
COULD CONTINUE TO COOL THROUGH THE MORNING HOURS...THEN REMAIN
NEARLY STEADY DURING THE AFTERNOON. AREAS EAST OF THE
MTNS...CONDITIONS SHOULD REMAIN DRY...BREEZY...WITH HIGHS NEAR
NORMAL.

ON MONDAY...DRY HIGH PRESSURE SHOULD BUILD ACROSS THE DEEP SOUTH AS
A CLIPPER TRACKS OVER THE OHIO RIVER VALLEY. CONDITIONS ACROSS THE
CWA SHOULD REMAIN DRY...WEAK WINDS...AND NORMAL TEMPERATURES.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 1 PM EST FRIDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
TUESDAY WITH A LONGWAVE UPPER TROF OVER THE EASTERN CONUS AND UPPER
RIDGING OVER THE FAR WESTERN CONUS. OVER THE NEXT 24 HRS...THE UPPER
TROF IS EXPECTED TO AMPLIFY BRINGING CONSIDERABLE PVA JUST TO OUR
NORTH AND THEN QUICKLY LIFTING THE TROF AXIS TO OUR NE BY EARLY
THURSDAY. HEIGHTS THEN BEGIN TO GRADUALLY RISE AS AN UPPER RIDGE
BUILDS OVER THE GULF OF MEXICO AND REMAINS IN PLACE THRU NEW DAY 7.

AT THE SFC...DRY WEATHER AND NEAR SEASONAL TEMPERATURES ARE
ANTICIPATED THROUGH THE FCST PERIOD AS CANADIAN HIGH PRESSURE WILL
BE IN PLACE THRU FRIDAY. AS WE MOVE BEYOND DAY 7 AND INTO THE
WEEKEND...IT APPEARS THAT A LOW WILL DEVELOP TO OUR WEST OR NW AND
MOVE A COLD FRONT TO OUR DOORSTEP BY SUNDAY. AS SUCH...I INCREASE
POPS FROM SLIGHT TO SOLID CHANCE BY LATE FRIDAY WITH HIGHER CHANCES
ANTICIPATED ON SATURDAY.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIGHT WIND WITH LOWERING VFR CIGS BEFORE DAYBREAK.
CONDITIONS THEN DETERIORATE AFTER DAYBREAK WITH MVFR AND RAIN BY MID
MORNING THEN IFR AND RAIN BY NOON. KEPT THE LLWS IN THE TAF...BUT
CURRENT GUIDANCE SUGGESTS BEST CHC IN THE 17Z TO 20Z TIME FRAME.
VSBY IMPROVES TO MVFR AS THE RAIN MOVES OUT DURING THE EARLY
EVENING. HOWEVER...IFR CIGS CONTINUE WITH GOOD LOW LEVEL MOISTURE
AND DELAYED SCOURING NW WINDS. WINDS WILL BE TRICKY AS SELY WINDS
DEVELOP NEAR DAYBREAK THEN GO ENE BY MID MORNING. THE WINDS THEN GO
NLY AS LOW PRESSURE MOVES NEAR THE FALL LINE. WINDS COULD THEN GO
LIGHT SWLY BY THE END OF THE PERIOD.

ELSEWHERE...SIMILAR CONDITIONS TO KCLT...XCPT FOR EARLIER ONSET OF
RAIN AND RESTRICTIONS. LLWS WILL BE EARLIER AS WELL. PRECIP ENDS
EARLIER WITH VSBY IMPROVING BUT IFR CIGS REMAINING. SWLY WINDS MORE
LIKELY BEFORE THE END OF THE PERIOD. KAVL KEEPS S TO SELY WIND THRU
THE DAY ALONG WITH A LONGER PERIOD OF LLWS. NLY WIND DEVELOPS DURING
THE EVENING.

OUTLOOK..CONDITIONS WILL DRY OUT FROM THE SW SUNDAY...WITH DRY/VFR
CONDITIONS EXPECTED TO PERSIST WELL INTO NEXT WEEK.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-05Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

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...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JDL/MCAVOY/RWH
SHORT TERM...NED
LONG TERM...JPT
AVIATION...RWH