000
FXUS62 KGSP 182142
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
542 PM EDT SAT MAY 18 2013

.SYNOPSIS...
A WEAK UPPER LEVEL TROUGH WILL LINGER OVER THE REGION THROUGH
MONDAY...THEN LIFT NORTHEAST. THE FORECAST AREA WILL REMAIN IN A
MOIST AND RATHER UNSTABLE AIRMASS...BEFORE A COLD FRONT CROSSES EAST
LATE NEXT WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 515 PM EDT SATURDAY...ISOLATED TO SCT SHOWERS HAVE BEGUN TO
DEVELOP OVER OVER THE UPSTATE...NE GA AND THE NC MTNS. THE PCPN
ISN/T WIDESPREAD...AND SO FAR IT HAS NOT HAD A TENDENCY TO BE VERY
DEEP. A FEW TSTMS ARE CERTAINLY POSSIBLE THIS EVENING AS THE UPPER
SHORT WAVE DRIFTS EASTWARD ACROSS THE REGION...BUT PER THE LATEST SB
CAPE ANALYSIS...WE APPEAR TO BE TOO STABLE ACROSS THE SRN
APPALACHIAN REGION FOR MORE THAN ISOLATED TSTMS INTO THIS EVENING.
THEREFORE I/VE CUT BACK ON THUNDER POTENTIAL AND CUT BACK POPS A
LITTLE AS WELL. MORE WIDESPREAD LIGHT RAIN AND SHOWERS WILL CONTINUE
TO SLOWLY TRAVERS THE WRN NC PIEDMONT.

PREVIOUS DISCUSSION...
REMNANT AREA OF SHOWERS MAY BE TRYING TO MAKE A COMEBACK OVER THE
EASTERN HALF OF THE AREA...WHERE THE AIR MASS HAS BECOME WEAKLY
UNSTABLE. NEVERTHELESS...IT APPEARS THAT THE ATM HAS BECOME TOO
STABLE FOR STRONG CONVECTION (AT LEAST FOR NEXT FEW HOURS)...AND
INDEED THE MORE ROBUST ACTIVITY IS DEVELOPING AHEAD OF THE SHOWER
BAND (EAST OF THE AREA). ADDITIONAL ACTIVITY WAS DEVELOPING OVER THE
TENN VALLEY AT MID-AFTERNOON. WITH SOME BREAKS IN THE OVERCAST
OBSERVED ACROSS THE WESTERN CAROLINAS AND NORTH GEORGIA...EXPECT
SCATTERED TO NUMEROUS SHOWERS/SCATTERED TS TO DEVELOP WEST OF THE
ONGOING SHOWER BAND THROUGHOUT THE AFTERNOON AND INTO THE EVENING.
THIS WILL WARRANT LIKELY POPS ACROSS MUCH OF THE AREA DURING THE
EARLY HALF OF THE FIRST PERIOD...ESP AS VORT MAX ASSOCIATED WITH
FILLING UPPER LOW DRIFTING ACROSS THE TENN VALLEY. CONVECTION WILL
CONTINUE TO MOVE SLOWLY...THUS HEAVY RAIN WILL REMAIN THE PRIMARY
CONCERN.

TONIGHT SHOULD SEE GRADUAL DIMINISHMENT OF CONVECTION...ALTHOUGH IN
THE MOST ENVIRONMENT SUPPORTED BY THE UPPER VORT MAX...AT LEAST
SCATTERED SHOWERS/STORMS SHOULD PERSIST THROUGH THE OVERNIGHT. THERE
WILL BE A SLIGHTLY ENHANCED THREAT FOR ORGANIZED PRECIP/HEAVY
RAINFALL LATE TONIGHT ACROSS THE NC PIEDMONT...AS THE MODELS SUGGEST
A 20-25 KT RELATIVE LLJ WILL DEVELOP. ASSOCIATED SPEED CONVERGENCE
COULD SUPPORT TRAINING CELLS IN THIS AREA.

SUNDAY...CONVECTION WILL REINVIGORATE NO LATER THAN EARLY
AFTERNOON...AS SECONDARY VORT MAX DRIFTS ACROSS THE AREA...AND
PROFILES REMAIN VERY MOIST. THIS WILL SUPPORT HIGH LIKELY POPS
ACROSS MUCH OF THE CWFA DURING THE AFTERNOON...WITH A CONTINUED
THREAT FOR LOCALIZED HEAVY RAINFALL.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
DEEP RIDGING WILL BE IN PLACE OVER THE REGION FOR THE SHORT TERM...
THOUGH EMBEDDED SHORTWAVE WILL SLIDE ACROSS THE CWFA SUN NIGHT INTO
THE EARLY DAY MONDAY. WEAK DPVA WILL PROVIDE SOME FORCING DURING THIS
TIME THOUGH Q-VECTOR RESPONSE IS UNIMPRESSIVE. NONETHELESS IT COULD
BE ENOUGH TO DRIVE SOME ELEVATED CONVECTION SUN NIGHT OVER THE ERN
HALF OF THE CWFA...BUT SOUNDINGS SUGGEST THAT WITH CONTINUING
MIDLEVEL WAA CIN MAY BE DIFFICULT TO OVERCOME. WEAK WAA CONTINUES
THROUGH THE DAY MONDAY AS RIDGE DEEPENS TO OUR WEST...WITH
SIGNIFICANT INSTABILITY DEVELOPING BY AFTERNOON. BY PEAK HEATING THE
SYNOPTIC FORCING HAS DIMINISHED. SHEAR IS GENERALLY QUITE WEAK AND AS
LOW-TO-MID LEVEL TEMPS REMAIN WARM THERE STILL MAY BE SOME
CAPPING...SO KEPT POPS IN CHANCE RANGE BUT WITH BASICALLY EQUAL
THUNDER CHANCES. NAM AND GFS DIFFER WIDELY ON TEMPS...WITH THE GFS
BEING MUCH WARMER ESPECIALLY OVER THE WEST WHERE SKIES SHOULD BE A
BIT CLEARER. MODEL BLEND IS NEAR SREF MEAN AND DO THINK ENOUGH
MID-HIGH CLOUD COVER WILL BE PRESENT TO KEEP TEMPS BELOW THE GFS
VALUES...WITH HIGHS BEING JUST SLIGHTLY ABOVE NORMAL.

POPS DIMINISH TO UNMENTIONABLY LOW VALUES MON NIGHT WITHOUT
SUFFICIENT MOISTURE TO EXPECT PRECIP FROM WAA AND WITH ENOUGH CIN TO
PRECLUDE CONVECTION. SKIES EXPECTED TO CLEAR OVERNIGHT WHICH WILL
PROMOTE BETTER HEATING EARLY ON TUESDAY...SO TEMPS WILL RISE INTO THE
MID-UPPER 80S ACROSS MUCH OF THE AREA. THE WARMER TEMPS WILL ALLOW
CONVECTION TO FIRE MORE EASILY ON TUE THOUGH WITH THE RIDGE CENTERED
OVERHEAD SYNOPTIC FORCING IS PRACTICALLY NIL. POPS WILL BE SIMILAR
THOUGH A TAD LOWER ON TUE AND MORE REFLECTIVE OF A DIURNAL CYCLE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
SFC AND UPPER RIDGE PROGGED MIDWEEK BY THE LONG TERM MODELS OVER THE
SE CONUS WITH DEVELOPING LOW PRESSURE OVER THE CENTRAL STATES. 06Z
GFS SOLUTION IS TO KEEP CLOSED UPPER LOW SOMEWHAT STATIONARY OVER THE
UPPER MIDWEST THU-FRI...WITH 00Z EC FEATURING A STRONGER TROUGH
DIGGING INTO ERN CANADA WHICH SWALLOWS UP THAT FEATURE AND DEVELOPS A
STRONGER NE CONUS CYCLONE. IN EITHER SCENARIO A COLD FRONT WOULD DRAG
THROUGH THE OH/TN VALLEYS AND THERE IS REASON TO EXPECT INCREASING
PRECIP CHANCES WED NIGHT THRU THU BEFORE FROPA. DIURNAL CONVECTION
SUGGESTED BY MODEL CAPE AND GFS SOUNDINGS...BUT ESPECIALLY THU AND
FRI AS COOLER MIDLEVEL AIR ARRIVES WITH TROUGHING ALOFT. DRIER HIGH
PRESSURE BUILDS BACK IN FOR THE WEEKEND AS TROUGH DIGS OVER ERN
SEABOARD...THOUGH SOUNDINGS CONTINUE TO SUGGEST DIURNALLY DRIVEN
SHOWERS/TSTMS. HIGH SUMMERLIKE LLVL THICKNESS VALUES SUGGEST
POTENTIAL FOR TEMPS TO RISE WELL ABOVE NORMAL BEFORE THE COOLER AIR
ARRIVES BEHIND THE FRONT...THOUGH CLOUDS AND PRECIP ARE LIKELY TO
OFFSET THE WARM COLUMN. TEMPS THUS EXPECTED CLOSE TO NORMAL THU AND
FRI BEFORE TEMPS DROP SLIGHTLY BELOW NORMAL SAT.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
AT KCLT/KHKY...THE BAND OF SHOWERS HAS BECOME MORE RAGGED/LESS
CONCENTRATED AS IT MOVES ACROSS THE NC FOOTHILLS AND PIEDMONT. WILL
CONTINUE TO INCLUDE A TEMPO FOR SHRA/MVFR CONDITIONS AT KCLT FOR THE
FIRST COUPLE OF HOURS OF THE PERIOD. IT IS SOMEWHAT UNCLEAR AS TO
HOW CONVECTIVE TRENDS WILL EVOLVE THIS AFTERNOON...AS THE SHOWERS
HAVE STABILIZED THE ATM ACROSS MUCH OF THE REGION. HOWEVER...SOME
CLEARING IS OCCURRING ACROSS NW SOUTH CAROLINA AND PORTIONS OF THE
NC MTNS. CONVECTION WILL LIKELY REIGNITE IN THESE AREAS DURING THE
AFTERNOON...AND POSSIBLY APPROACH KCLT BY EARLY EVENING. TEMPOS HAVE
THEREFORE BEEN INCLUDED FOR TSRA. OCCASIONAL SHOWERS AND POSSIBLE TS
WILL CONTINUE OFF AND ON THROUGH THE END OF THE PERIOD. WITH THE
VERY MOIST AIR MASS IN PLACE...DETERIORATING FLT CONDITIONS ARE
EXPECTED OVERNIGHT...WITH IFR CIGS EVENTUALLY BECMG LIKELY. GRADUAL
IMPROVEMENT IS EXPECTED BY THE END OF THE PERIOD.

ELSEWHERE...SHOWERS HAVE CLEARED THE TERMINALS LEAVING MVFR/VFR
CONDITIONS IN THEIR WAKE. (THE SMALL AREA OF IFR CIGS AT KGSP SHOULD
LIFT NO LATER THAN 19Z). CONVECTION IS EXPECTED TO REDEVELOP OVER
THE TENN VALLEY/SOUTHERN APPALACHIANS/UPPER SAVANNAH RIVER VALLEY
THIS AFTERNOON...AND VCTS/SHRA WILL BE CARRIED FROM LATE AFTERNOON
ON. OCCASIONAL SHOWERS AND POSSIBLE TS WILL CONTINUE OFF AND ON
THROUGH THE END OF THE PERIOD. WITH THE VERY MOIST AIR MASS IN
PLACE...DETERIORATING FLT CONDITIONS ARE EXPECTED OVERNIGHT...WITH
IFR CIGS EVENTUALLY BECMG LIKELY. GRADUAL IMPROVEMENT IS EXPECTED BY
THE END OF THE PERIOD.

OUTLOOK...SHOWERS AND THUNDERSTORMS...AND ASSOCIATED RESTRICTIONS...
WILL PERSIST THROUGH MONDAY. FAIR WEATHER MAY RETURN BY TUESDAY.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       HIGH 100%     HIGH  95%     HIGH  92%     HIGH  94%
KGSP       HIGH  90%     HIGH  89%     HIGH  96%     HIGH  83%
KAVL       HIGH  82%     HIGH  90%     HIGH  97%     HIGH  97%
KHKY       HIGH  81%     HIGH  94%     HIGH 100%     HIGH 100%
KGMU       HIGH  91%     HIGH  91%     HIGH  92%     HIGH  80%
KAND       HIGH  94%     HIGH  80%     HIGH  88%     HIGH  80%

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...SBK
NEAR TERM...MCAVOY
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL