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000
FXUS62 KGSP 080739
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
239 AM EST SUN DEC 8 2013

.SYNOPSIS...
CANADIAN HIGH PRESSURE WILL BUILD IN FROM THE NORTHEAST SUNDAY WITH
MOIST SOUTHWESTERLY FLOW ALOFT MAINTAINED INTO MONDAY. ANOTHER COLD
FRONT IS EXPECTED TO CROSS THE AREA EARLY TUESDAY WITH RELATIVELY
COLD HIGH PRESSURE BUILDING BACK IN ON WEDNESDAY AND REMAINING OVER
THE REGION THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 AM EST SUNDAY...POSITIVELY TILTED LONGWAVE UPPER TROF
CONTINUES TO DIG ACROSS THE FOUR CORNERS AS DEEP MOISTURE ADVECTION
REGIME STRENGTHENS ACROSS THE SOUTH DUE TO FLOW AROUND WESTERN
PERIPHERY OF GULF RIDGE.  1038MB SURFACE RIDGE ACROSS THE GREAT
LAKES REGION CONTINUES TO SHIFT EASTWARD AS NORTHEASTERLY COLD
ADVECTION WRAPS AROUND THE SOUTHERN APPALACHIANS.

LATEST GUIDANCE REMAINS IN GOOD AGREEMENT WITH REGARDS TO ISENTROPIC
ASCENT REGIME RAMPING UP ACROSS NORTHEAST GA AND THE WESTERN
CAROLINAS THROUGH THE DAY.  AS A CONSEQUENCE...SHOWERS WILL INCREASE
IN COVERAGE OVER THE NEXT FEW HOURS AND WILL PERSIST THROUGH MUCH OF
THE NEAR TERM PERIOD.  THUS...POPS WILL INCREASE FROM CURRENT SOLID
CHANCE TO HIGH END CATEGORICAL LEVELS BY LATE MORNING.  THE MAIN
CONCERN TODAY REMAINS ICE ACCUMULATION POTENTIAL AS HIGH PRESSURE
CAD WEDGE EXTENDS SOUTHWARD THROUGH THE NORTHERN
MOUNTAINS/FOOTHILLS.  CURRENT OBS AROUND THIS REGION ARE ALREADY
INDICATIVE OF FREEZING TEMPERATURES WITH LIGHT SNOW SHOWERS AT SOME
LOCATIONS.  WITH THAT SAID...ANY SNOW SHOWERS WILL BE BRIEF AS WARM
NOSE ALOFT STRENGTHENS.  SURFACE TEMPERATURES WILL SLOWLY FALL
ACROSS THE ENTIRE REGION TODAY WITH TEMPERATURES IN THE MID 30S TO
LOWER 40S SOUTH OF THE I40 CORRIDOR AND UPPER 20S TO LOWER 30S
FURTHER NORTH.  AN ICE STORM WARNING REMAINS IN EFFECT FOR THE
HIGHER ELEVATIONS WHERE TEMPERATURES WILL BE THE COLDEST.
SIGNIFICANT ICE ACCUMULATIONS ON THE ORDER OF A QUARTER TO THREE
TENTHS OF AN INCH ARE POSSIBLE IN THESE REGIONS.  EXTENDING FURTHER
SOUTH...AND EAST...FROM THE WARNED AREA REMAINS A FREEZING RAIN
ADVISORY WHERE ICE ACCUMULATIONS WILL RANGE FROM A TRACE TO A TENTH
OF AN INCH.  THEREFORE...NOT PLANNING ON MAKING ANY CHANGES TO THE
CURRENT ACTIVE WSW PRODUCT.

ELSEWHERE...LIGHT TO MODERATE RAIN WILL PERSIST THROUGH THE DAY WITH
POPS DECREASING ACROSS THE EASTERN MOST ZONES AS LOW LEVEL FLOW
VEERS THEREBY WEAKENING ISENTROPIC UPGLIDE COMPONENT OF FORCING.
POPS WILL REMAIN ELEVATED ACROSS THE WEST DUE TO PROXIMITY OF DEEPER
MOISTURE PLUME ADVECTING IN FROM THE SOUTHWEST ALONG WITH UPSLOPE
FLOW FORCING COMPONENT ALONG THE HIGH TERRAIN.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 230 AM EST SUNDAY...STRONG SHORTWAVES WILL ROTATE AROUND THE
DEEP CENTRAL CANADIAN LOW PRESSURE SYSTEM IN THE ACTIVE NRN STREAM
ON MONDAY...WHILE A POSITIVE TILT TROUGH STRETCHES ACROSS THE FOUR
CORNERS REGION IN THE SRN STREAM. DEEP LAYER SW FLOW EAST OF THESE
FEATURES WILL CONTINUE ACROSS THE SOUTHEAST REGION THROUGH MUCH OF
THE PERIOD. AN ASSOCIATED PLUME OF DEEP MOISTURE WILL LINGER ALONG
THE SRN APPALACHIANS THROUGH MONDAY...WITH THE RESIDUAL COLD AIR
DAMMING SLOWLY DISSIPATING. THE LOW LEVEL SW FLOW WILL CREATE
UPSLOPE FORCING IN THE EXTREME SOUTHERN APPALACHIANS...AND
PRECIPITATION RATES MAY BE FURTHER ENHANCED BY SFC LOW PRES MOVING
UP THE STALLED FRONTAL ZONE FROM THE GULF OF MEXICO MONDAY. GIVEN
THE CLOUDS AND PRECIPITATION...WILL KEEP MAX TEMPS ON THE COOL SIDE
OF GUIDANCE DESPITE THE WEAKENING WEDGE. STEEPER LAPSE RATES ALOFT
AND SLIGHTLY BETTER SFC BASED INSTABILITY ARE INDICATED IN THE LOWER
PIEDMONT MON AFTN AS THE CAD LAYER ERODES AND RETREATS NWD.
HOWEVER...INSTABILITY REMAINS TOO WEAK FOR A TSTM MENTION.

A VERY BRIEF BREAK IN THE DEEP MOISTURE IS INDICATED MON EVENING
BEFORE THE MOISTURE SURGES IN AGAIN AHEAD OF THE SRN STREAM WAVE
SHEARING EASTWARD THROUGH TUE MORNING. WILL THUS KEEP CONTINUED
LIKELY POPS GOING....ESPECIALLY IN SW SECTIONS...THROUGH TUE
MORNING. UPPER FLOW BECOMING INCREASINGLY ZONAL TUE AFTN THROUGH TUE
NIGHT WILL ALLOW THE SFC FRONT TO PASS THROUGH THE REGION WITH
THICKNESSES FALLING FROM THE W. EXPECT SOME HIGH MTN SNOW TO MIX IN
THROUGH LATE TUE...AND A BRIEF WINDOW OF ISOLD THUNDER COULD OCCUR
JUST PRIOR TO FROPA IN FAR SE PIEDMONT SECTIONS. THIS WILL NEED TO
BE WATCHED GIVEN THE ANTICIPATED 40 TO 50 KT LOW LEVEL JET.
HOWEVER...IT STILL APPEARS THAT THE BEST INSTABILITY WILL LINE UP
WELL SE OF OUR FORECAST AREA ON TUE. WILL FAVOR THE STRONGER TUE
NIGHT DRYING OF THE NAM/ECMWF OVER THE SLIGHTLY WETTER GFS GIVEN THE
ZONAL FLOW ALOFT AND THE BUILDING SFC HIGH POST FROPA.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 2 AM EST SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 12Z ON
WEDNESDAY WITH A RELATIVELY FLAT UPPER PATTERN OVER THE REGION AND
BROAD UPPER TROFFING WELL TO OUR NORTH. OVER THE NEXT 24 HRS OR
SO...THE AXIS OF THE UPPER TROF IS EXPECTED TO SLIDE EASTWARD AND
SHOULD BE TO OUR NORTH. AS WE MOVE INTO FRIDAY...HEIGHTS WILL LIKELY
RISE A BIT AS THE UPPER TROF TRANSLATES OFF THE NEW ENGLAND COAST.
AS WE MOVE INTO THE WEEKEND...THE MODELS DEEPEN AN UPPER SHORTWAVE
OVER THE SOUTHERN PLAINS AND APPEAR TO NEARLY CLOSE IT OFF BY EARLY
SUNDAY AS IT MOVES TOWARDS THE NORTHERN GULF OF MEXICO.

AT THE SFC...THE EVOLUTION OF THE SYNOPTIC PATTERN APPEARS LESS
CONSISTENT OVERALL BETWEEN THE OPERATIONAL MODELS COMPARED TO THE
UPPER LVLS. ON WED...HIGH PRESSURE WILL SLIDE OVER THE REGION FROM
THE WEST...ALTHOUGH SOME LINGERING MOISTURE FROM THE EARLIER CAD
COULD REMAIN OVER THE REGION THRU MOST OF THE DAY/EVENING. ON
THURS...THE HIGH REINFORCES ITSELF AND STRENGTHENS OVER THE
CAROLINAS AS THE MODELS DEVELOP ANOTHER LOW OFFSHORE AND QUICKLY
MOVE IT OUT OVER THE CENTRAL ATLANTIC. THE REINFORCING HIGH WILL
SLIDE NE OF THE FCST AREA BY EARLY SAT...HOWEVER BEYOND THIS POINT
MODEL SOLUTIONS DIVERGE QUITE A BIT. THE NEWER 00Z RUN OF THE GFS
MOVES A COLD FRONT OVER THE CWFA SAT NIGHT AND TRIES TO SPIN UP A
SERIES OF LOWS ALONG THE FRONTAL BNDY BY THE END OF THE PERIOD EARLY
SUN...WHILE THE OLDER 12Z RUN OF THE ECMWF DEVELOPS A LOW OVER THE
FAR SE AND MOVES IT NE AND OFF THE NC COAST BY LATE SAT. BOTH
SCENARIOS WOULD LIKELY BRING WIDESPREAD PRECIP TO THE AREA ON SAT
WITH MIXED FROZEN PRECIP POSSIBLE. FOR THE TIME BEING...I BRING POPS
UP TO SLIGHT CHANCE ON FRI AND HIGH END CHANCE BY MIDDAY SAT AND SAT
NIGHT. TEMPS WERE NOT CHANGED SIGNIFICANTLY WITH VALUES STARTING OUT
WELL BELOW NORMAL AND WARMING TOWARDS THE END OF THE PERIOD.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KCLT...INITIAL VFR CONDITIONS WILL DETERIORATE SHORTLY AFTER TAF
ISSUANCE THUS PREVAILED VFR THROUGH 07Z WITH MVFR RESTRICTIONS
THEREAFTER.  ISENTROPIC UPGLIDE WILL CONTINUE TO INCREASE ACROSS THE
REGION OVERNIGHT AS HIGH PRESSURE WEDGE BUILDS.  THUS...ADDED 09Z
GROUP TO INTRODUCE -RA WITH MVFR CIGS CONTINUING.  VISB WILL LIKELY
DETERIORATE TO MVFR LEVELS BY MORNING AS SHOWER ACTIVITY SPREADS
ACROSS THE REGION AND THE BOUNDARY LAYER BECOMES MORE SATURATED.
WITH THAT...WENT WITH 4SM RA AT 16Z ALONG WITH IFR CIGS WHICH WILL
PREVAIL THROUGH THE MAJORITY OF THE DAY SUNDAY PER LATEST GUIDANCE.
BAND OF HEAVIEST SHOWERS WILL SLOWLY SHIFT WESTWARD LATE IN THE
PERIOD...THUS DECIDED TO LOWER TO -RA WITH FINAL 01Z FM GROUP
KEEPING IFR RESTRICTIONS THROUGH THE REMAINDER OF THE TAF CYCLE.
WINDS THROUGH THE PERIOD WILL REMAIN NORTHEASTERLY WITH GUSTS
SUBSIDING WITHIN THE NEXT FEW HOURS YIELDING SUSTAINED FLOW IN THE
8-12KTS RANGE.

ELSEWHERE...PRECIPITATION WILL SLOWLY RAMP UP THROUGH THE EVENING AS
ABOVE MENTIONED ISENTROPIC UPGLIDE STRENGTHENS ACROSS THE REGION.
WITH THAT...RESTRICTIONS DUE TO ONSET OF RA WILL OCCUR BY EARLY
MORNING AS MVFR CIGS GIVE WAY TO IFR CONDITIONS.  THESE IFR
RESTRICTIONS SHOULD LAST THROUGH THE REMAINDER OF THE DAY AT ALL
SITES.  KAVL WILL EXPERIENCE THE MOST ACTIVE WX DURING THIS TAF
CYCLE AS COLD AIR DAMMING EFFECTS ALLOW FOR SUBFREEZING SURFACE
TEMPS BY MORNING.  THUS KEPT FZRA FROM PREVIOUS TAF ISSUANCE WITH
SLIGHT ADJUSTMENTS TO TIMING.  FINALLY..ADDED FM GROUP LATE IN THE
PERIOD AS STRONG SOUTHWESTERLY LLJ RAMPS UP WARRANTING MENTION OF
POSSIBLE LLWS ON THE ORDER OF 30-40KTS ACROSS THE MOUNTAINS.
OTHERWISE...WINDS WILL REMAIN NORTHEASTERLY AT ALL SITES THROUGH THE
PERIOD WITH THE EXCEPTION OF KAVL WHERE FLOW AT THE SFC SHOULD
REMAIN SOUTHERLY DUE TO CHANNELING IN THE FRENCH BROAD RIVER
VALLEY.

OUTLOOK...RESTRICTIVE CIGS AND VSBY CAN BE EXPECTED IN PRECIPITATION
THROUGH TUESDAY...ESPECIALLY EARLY EACH MORNING. DRIER AIR AND
FLIGHT CONDITIONS SHOULD RETURN MID-WEEK.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-07Z
KCLT       HIGH  84%     MED   78%     HIGH  85%     HIGH  88%
KGSP       HIGH  95%     MED   79%     HIGH  85%     HIGH  91%
KAVL       HIGH  89%     HIGH  84%     HIGH  92%     HIGH  98%
KHKY       HIGH  98%     HIGH  93%     HIGH  98%     HIGH  91%
KGMU       HIGH  95%     MED   79%     HIGH  85%     HIGH  91%
KAND       HIGH  95%     MED   71%     HIGH  85%     HIGH  91%

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...ICE STORM WARNING UNTIL 8 PM EST THIS EVENING FOR NCZ033-050-
     501-503-505.
     FREEZING RAIN ADVISORY UNTIL 8 PM EST THIS EVENING FOR
     NCZ035>037-049-052-053-056-064-065-502-504-506-507-509.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...CDG
SHORT TERM...HG
LONG TERM...JPT
AVIATION...CDG