Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201430
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
930 AM EST SAT DEC 20 2014

.SYNOPSIS...
A WAVE OF LOW PRESSURE ALONG WITH BRIEF DEEPER MOISTURE WILL MOVE
QUICKLY ACROSS THE REGION EARLY TODAY...BEFORE MOVING OFFSHORE BY
TONIGHT. LOW LEVEL MOISTURE WILL GRADUALLY RETURN BEHIND THE WAVE
FROM THE SOUTH SUNDAY THROUGH MONDAY...WITH DEEPER MOISTURE ARRIVING
ON TUESDAY AHEAD OF A SHARP COLD FRONT. THE COLD FRONT WILL CROSS
THE AREA FROM THE WEST ON WEDNESDAY. COLD AND WINDY CONDITIONS WILL
SET UP IN THE MOUNTAINS THROUGH THURSDAY...BUT WITH DRIER LATE WEEK
CONDITIONS EAST OF THE MOUNTAINS.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 0930 AM...BASED ON SOCIAL MEDIA REPORTS HAVE REDONE THE WEATHER
GRIDS ACROSS THE NORTHERN NC PIEDMONT/FOOTHILLS TO INCLUDE A
RAIN/SNOW MIXTURE FOR A COUPLE HOURS. PRECIP WILL BE LIGHT WITH NO
ACCUMS EXPECTED. OTHERWISE...LOOKS LIKE FORECAST IS ON TRACK.

AT 0800...WILL DO A QUICK UPDATE MAINLY FOR POP TRENDS BASED ON
LATEST RADAR. WILL INITIALIZE WITH CATEGORICAL POPS ACROSS NE
GA/UPSTATE SC AND THE CLT METRO AREA PER LATEST METARS/RADAR. WILL
TAPER POPS DOWNWARD TO THE NORTH...BUT THEN UPWARD AGAIN AT HIGH
ELEVATIONS PER WEBCAMS/OBSERVATIONS. TEMPS WELL ABOVE FREEZING
EXCEPT FOR ELEVATIONS GENERALLY ABOVE 4000FT. HENCE...PRECIP IS
MAINLY RAIN...BUT SOME LIGHT SNOW AT HIGH ELEVATIONS. COULD ALSO BE
SOME PATCHY FREEZING RAIN AT HIGH ELEVATIONS. BASED ON RADAR LOOP
AND MESO-MODELS...BULK OF PRECIP SHOULD MOVE EAST OF THE AREA BY
ABOUT 18Z AND WILL DEPICT THAT TREND IN THE GRIDS.  ENOUGH WINTRY
PRECIPITATION REMAINS AT HIGH ELEVATIONS TO CONTINUE THE SPS THOUGH
SNOW ACCUMS WILL BE <1 INCH.

UPPER SHORT WAVE MOVES WELL EAST OF THE AREA BY EVENING ALLOWING FOR
SOME PARTIAL CLEARING...BUT THIS MAY ONLY RESULT IN BREAKS IN THE
OVERCAST AS NO DOWNSLOPE SCOURING WILL OCCUR. AREAS OF DENSE FOG
MAY DEVELOP OVERNIGHT AS THE BOUNDARY LAYER REMAINS MOIST AND DRYING
ALOFT OCCURS. MIN TEMPS WILL BE ABOUT A CATEGORY ABOVE CLIMO.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
AS OF 230 AM EST SAT...A WEAK SHORTWAVE WILL MOVE EAST FROM THE SRN
PLAINS TO THE LOWER MS RIVER VALLEY SUNDAY AND SUNDAY NIGHT. AHEAD
OF THIS FEATURE...A 130 KT JET STREAK LINGERING OVER THE FORECAST
AREA WILL GRADUALLY PULL INCREASING UPPER DIVERGENCE INTO THE REGION
FROM THE SE. ALTHOUGH THE DEEPER MOISTURE MAY STAY CONFINED TO AREAS
SE OF THE FORECAST AREA...LOW LEVEL MOISTURE WILL STEADILY RETURN AS
ISENTROPIC LIFT DEVELOPS IN RESPONSE TO THE WEAK UPPER FORCING. WILL
KEEP MAX TEMPS BELOW GUIDANCE SUN AFTN AND REINTRODUCE SCHC TO CHC
POPS FOR LIGHT RAIN FROM THE S BY LATE DAY.

1026 MB SFC HIGH PRESSURE WILL SETTLE OVER TO THE N SUN NIGHT
THROUGH MONDAY. ISENTROPIC LIFT WILL GRADUALLY IMPROVE OVER THE
DEVELOPING HYBRID SFC CAD LAYER...WITH WIDESPREAD CLOUDS AND MUCH
MORE LIKELY CHANCES OF LIGHT RAIN AND DRIZZLE. TEMPERATURE PROFILES
ALONG THE NRN BLUE RIDGE EARLY MONDAY MAY BRIEFLY BE JUST COLD
ENOUGH FOR WINTRY MIXED PTYPES...BUT THIS WOULD BE MAINLY SPOTTY
LIGHT FREEZING RAIN OR FREEZING DRIZZLE GIVEN THE SHALLOW NATURE OF
THE MOISTURE. WILL KEEP TEMPS WELL BELOW GUIDANCE AGAIN MON AFTN
GIVEN THE ANTICIPATED CAD...ALBEIT WITH FAIRLY LIGHT PRECIPITATION
INTO THE WEDGE.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 230 PM SAT...A FULL LATITUDE TROUGH WILL DEVELOP FROM THE
PLAINS TO THE MS RIVER VALLEY MON NIGHT TO TUE NIGHT. MOISTURE WILL
STEADILY INCREASE AHEAD OF THIS SYSTEM ACROSS THE SOUTHEAST
TUESDAY...WITH THE DEEPEST LAYER FORCING LIKELY CROSSING THE
FORECAST AREA TUE NIGHT INTO WED MORNING JUST AHEAD OF THE
ASSOCIATED SHARP COLD FRONT. THE RESIDUAL CAD LAYER OVER THE REGION
WILL STEADILY ERODE TUE THROUGH TUE NIGHT...WITH NON DIURNAL WARMING
TEMPS IN THE PIEDMONT LIKELY LATE TUE NIGHT. A 40+ KT SRLY LOW LEVEL
JET IS EXPECTED JUST AHEAD OF THE COLD FRONT...BUT SFC BASED
INSTABILITY AND MARGINAL LAPSE RATES ALOFT SHOULD BE STRONG LIMITING
FACTORS FOR SEVERE CONVECTION WED MORNING. A LOWER PIEDMONT ISOLD
THUNDER MENTION COULD BE WARRANTED. ANTICIPATE COLD FROPA FROM THE
WEST 12Z TO 18Z WED...WITH A DRY SLOT ARRIVING QUICKLY WED AFTN.

FAIRLY DEEP MOISTURE IN THE COLD ADVECTION NW FLOW IS EXPECTED WED
NIGHT. THE SFC TO 850 FLOW MAY BE SUFFICIENTLY BACKED THAT THE
UPSLOPE COMPONENT IS NOT TREMENDOUS...BUT MOISTURE WILL BE DEEP AND
850 MB TEMPS MAY FALL TO NEAR MINUS 8 C OVER THE WRN MTNS BY
DAYBREAK. LIGHT SNOW ACCUMULATIONS LOOK QUITE POSSIBLE IN THE WRN NC
MOUNTAINS EARLY CHRISTMAS MORNING. ANTICIPATE A STRONG PRES GRADIENT
BEHIND THE TROUGH THU...WITH WINDY CONDITIONS POSSIBLE. THE UPPER
FLOW SHOULD BECOME MORE ZONAL THU NIGHT INTO FRIDAY...WITH A WEAK
FRONT APPROACHING FROM THE WEST IN RELATIVELY DRY PROFILES.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...GUIDANCE SUPPORTS PROLONGED LOW CLOUDS OVER THE
AREA...AND LOWERS THE CIG FROM LOW VFR TO MVFR BY MIDDAY. THE CIG
BRIEFLY RISES TO LOW VFR LATE IN THE DAY...BEFORE DROPPING BACK TO
MVFR THIS EVENING...WHERE IT REMAINS TIL DAWN SUNDAY. PRECIPITATION
ASSOCIATED WITH A MID LEVEL SYSTEM IS EXPECTED TO TAPER OFF THIS
AFTERNOON. GUIDANCE IS IN GOOD AGREEMENT OF FOG OVERNIGHT...WITH IFR
VSBY BEFORE DAWN. WINDS WILL FAVOR THE NE.

ELSEWHERE...LOW VFR CIGS ARE EXPECTED TO LOWER TO MVFR IN SC THIS
MORNING...THEN RETURN TO LOW VFR THIS AFTERNOON. GUIDANCE THEN TAKES
SC CIGS BACK TO MVFR THIS EVENING...WHERE THEY REMAIN TIL DAWN.
GUIDANCE KEEPS NC CIGS LOW VFR DURING THIS TIME...BUT WITH GUIDANCE
HITTING FOG VERY HARD TOWARD DAYBREAK SUNDAY...WITH IFR OR LOWER
VSBY EXPECTED...CONFIDENCE IS LOW THAT CIGS WILL STAY UP OVERNIGHT.
LIGHT PRECIPITATION WILL TAPER OFF LATE TODAY. WINDS WILL FAVOR THE
NE...EXCEPT AT KAVL WHERE THEY WILL CHANNEL DOWNVALLEY FORM THE SE.

OUTLOOK...LINGERING LOW LVL MOISTURE MAY KEEP LOW STRATUS AND NIGHT
FOG AROUND THRU SUNDAY NIGHT. A WETTER SYSTEM WILL THEN TRACK INTO
THE AREA FOR MONDAY LIKELY BRINGING WIDESPREAD CLOUDS AND PRECIP
RESTRICTIONS. YET ANOTHER STORM SYSTEM IS EXPECTED TO CROSS THE AREA
LATE TUESDAY OR EARLY WEDNESDAY...WITH ANOTHER ROUND OF PRECIP.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       MED   70%     HIGH  85%     MED   60%     MED   65%
KGSP       HIGH  91%     MED   70%     MED   68%     MED   76%
KAVL       MED   70%     MED   72%     LOW   56%     MED   69%
KHKY       HIGH 100%     HIGH 100%     MED   73%     MED   63%
KGMU       HIGH  93%     MED   68%     MED   68%     HIGH  85%
KAND       HIGH  93%     MED   66%     MED   78%     MED   79%

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...HG
NEAR TERM...LG
SHORT TERM...HG
LONG TERM...HG
AVIATION...JAT



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