Severe Thunderstorm Warning 333, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
550 PM EDT SUN SEP 1 2013

.SYNOPSIS...
MOIST SOUTHERLY FLOW WILL REMAIN ACROSS THE AREA AS WEAK HIGH
PRESSURE SLOWLY SLIDES OFFSHORE THIS EVENING. THIS MOIST FLOW WILL HELP TO
KICK OFF SHOWERS AND THUNDERSTORMS THROUGH LABOR DAY. A COLD FRONT
WILL CROSS THE CAROLINAS ON TUESDAY WITH DRY HIGH PRESSURE RETURNING
ON WEDNESDAY. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
RETURN BY NEXT WEEKEND.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 545 PM EDT SUNDAY...INCREASED POPS INTO THE CATEGORICAL RANGE
OVER THE NC PIEDMONT AND SRN FOOTHILLS WHERE A SLOW MOVING MCS WILL
CONTINUE TO PRODUCE AREAS OF HEAVY RAIN FOR ANOTHER COUPLE HOURS. WE
HAVE HAD A FEW REPORTS OF FLOODING. THE LLVL FLOW IS CROSSING THE
E-W ORIENTED OUTFLOW BNDRY AT ABOUT A 60 DEGREE ANGLE...AND THIS
SHOULD CONTINUE TO SUPPORT TRAINING CELLS ALONG THE NC/SC BOARDER
FOR A WHILE LONGER. ADDITIONAL FLASH FLOODING IS POSSIBLE IN THIS
AREA. THE CELLS TODAY HAVE ALSO PUT OUT HEALTHIER OUTFLOW THAN WOULD
BE EXPECTED WITH RATHER WEAK D-CAPE VALUES...AND WE CONTINUE TO SEE
A DAMAGING WIND THREAT.

AS OF 245 PM...REGIONAL RADAR INDICATED A OUTFLOW SUPPORTED LINE OF
STORMS ACROSS THE UPPER SAVANNAH RIVER VALLEY WITH CLUSTERS OF
STORMS ACROSS THE NC MTNS AND NRN FOOTHILLS. THE CONVECTION APPEARS
TO BE SUPPORTED BY THE APPROACH OF A S/W RIPPLING ACROSS EASTERN
KY/TN. LATEST MESOSCALE ANALYSIS SHOWS THAT CAPES ACROSS THE CWA
RANGE FROM 2000 J/KG ACROSS THE MTNS TO 3500 J/KG ACROSS THE
PIEDMONT. SIMILAR TO SATURDAY...THE FORECAST AREA WILL LIKELY SEE
AFTERNOON DEWPOINTS IN THE LOW TO MID 70S WITH HIGHS IN THE U80S.
DCAPE VALUES MAY CONTINUE TO RANGE BELOW 1000 J/KG. KFFC AND KGSO
FZL ABOVE 14 KFT/WBZ ABOVE 12 KFT AND WEAK SHEAR WILL NOT FAVOR
LARGE HAIL. I ANTICIPATE THAT STORM COVERAGE WILL CONTINUE TO
INCREASE THROUGH THE REST OF THE AFTERNOON. HOWEVER...THE MODERATELY
UNSTABLE ENVIRONMENT COUPLED WITH INCREASING UPPER SUPPORT WILL
LIKELY RESULT IN A BROAD BAND OF TSRA FORMING OVER THE MTNS LATE
THIS AFTERNOON...TRACKING EAST DURING THE EVENING. STORM COVERAGE
SHOULD BE THE GREATEST DURING THE LATE AFTERNOON TO EARLY EVENING
HOURS. STORMS THROUGH THIS EVENING COULD PRODUCE SEVERAL DAMAGING
WIND EVENTS AND TORRENTIAL RAINFALL...HIGHLIGHTED WELL IN THE HWO.

TONIGHT...MODERATE AFTERNOON CAPE VALUES WILL SLOWLY ERODE THROUGH
THE LATE NIGHT HOURS. THE LINGERING INSTABILITY AND EXPECTED PASSAGE
OF WEAK VORTS MAY SUPPORT COVERAGE THROUGH MOST OF TONIGHT.
CONVECTION ALLOWING MODELS INDICATE THAT SHRA/TSRA MAY LINGER UNTIL
9Z. HOWEVER...THE GFS CONTINUES QPF ACROSS THE MTNS...POSSIBLY
ASSOCIATED WITH THE ARRIVAL OF CONVECTION FROM THE WEST. I WILL KEEP
POPS OVER THE MTNS WITHIN CHC RANGE...EAST OF THE MTNS WILL REMAIN
SCHC. LOW TEMPERATURES SHOULD ARE FORECAST TO RANGE FROM MID 60S
ACROSS THE MTNS TO AROUND 70 EAST.

LABOR DAY...THE GFS INDICATES THAT H85 TEMPS WILL WARM 2 TO 3
DEGREES FROM THIS AFTERNOON. MOS GUIDANCE INDICATE THAT HIGHS ARE
FORECAST TO WARM ABOVE TODAYS VALUES BY A FEW DEGREES. WARMER
TEMPERATURES AND DEWPOINTS IN THE L70S SHOULD ONCE AGAIN RESULT IN
CAPES AROUND 3000 J/KG. THE PASSAGE OF THE MID LEVEL TROUGH...WITH
MODERATE INSTABILITY WILL RESULT MID DAY MTN THUNDERSTORMS. SIMILAR
TO TODAY...STEERING FLOW SHOULD PUSH COVERAGE EAST DURING THE HEAT
OF THE AFTERNOON. AFTERNOON AND EVENING STORMS MAY RESULT IN SEVERAL
DAMAGING WIND EVENTS AND TORRENTIAL RAINFALL.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 140 PM SUNDAY...UPPER LEVEL L/WV TROUGH AXIS IS SLATED FOR
PASSAGE SOME TIME TUESDAY MORNING WITH THE BETTER LARGE SCALE FORCING
DEVELOPING TOWARD THE COAST TUESDAY AFTERNOON. AT THE SFC...WEAK
COLD FRONT NW OF THE MTNS MONDAY NIGHT REMAINS PROGGED TO JUMP INTO
EXISTING LEE TROUGH POSITION ON TUESDAY. WITHIN THE BROAD UVV/S ALONG
FRONT SIDE OF UPPER TROUGH...AT LEAST SMALL POP WILL NEED TO BE IN
THE FCST ALL NIGHT INTO TUESDAY MORNING. AS TUESDAY WEARS ON...THE
INFLUX OF DRIER LLVL AIR WOULD SEEM TO INCREASINGLY LIMIT DIURNAL
DEEP CONVECTIVE CHANCES TO AREAS E/SE OF THE BLUE RIDGE...ROUGHLY
COINCIDENT WITH THE EASTWARD PROGRESSION OF THE FRONTAL BOUNDARY.

DEEP LAYERED DRY AIR AND WEAK RIDGING ARE STILL EXPECTED TO SPREAD
INTO THE REGION THROUGH WEDNESDAY RESULTING IN QUIET WX CONDS AND
MAX TEMPERATURES A COUPLE OF DEG F BELOW THE EARLY SEPT CLIMO.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 1 PM SUNDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
THURSDAY WITH THE STEEP UPPER RIDGE PERSISTING OVER THE WESTERN
CONUS AND BROAD UPPER TROFFING OVER THE EAST. THIS PATTERN WILL
LARGELY MAINTAIN ITSELF UNTIL A CLOSED H5 LOW SPINS UP OVER THE
PACIFIC NW ON FRI AND THEN GRADUALLY SLIDES EASTWARD AND UP OVER THE
RIDGE. THE LONG RANGE MODELS SUGGEST THAT THIS LOW WILL ACT TO
FLATTEN THE UPPER RIDGE TOWARDS THE END OF THE PERIOD ON
SUN...LEAVING A MORE ZONAL SYNOPTIC PATTERN OVER MOST OF THE CONUS.
AT THE SFC...DRY CANADIAN HIGH PRESSURE WILL BE SLIDING OVER THE
REGION WITH WEAK FLOW AT THE SFC AND ALOFT. AS WE MOVE INTO FRI AND
THE WEEKEND...THE BERMUDA HIGH WILL GRADUALLY SPREAD MOIST SLY FLOW
OVER THE FCST AREA WITH INCREASING CHANCES FOR SCT SH AND TS EACH
DAY/EVENING. TEMPS SHOULD START THE PERIOD NEAR CLIMO AND DROP A
DEGREE OR 2 BY DAYS 6 AND 7.

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
AT KCLT...LATEST VISIBLE SATELLITE IMAGES AND WEB CAMS INDICATE
WEAKLY DEVELOPED CU ACROSS THE TERMINAL AT TAF ISSUANCE TIME.
REGIONAL RADARS INDICATE A FEW TSRA BANDS EXITING THE
FOOTHILLS...ON A TRACK TO MOVE NORTH AND SOUTH OF THE TERMINAL.
HOWEVER...THE SPC SSEO INDICATES THAT CONVECTION WILL RAPIDLY
DEVELOP OVER THE MTNS LATER THIS AFTERNOON AS A MODERATE S/W MOVES
TOWARD THE SOUTHERN APPALACHIANS. STEERING FLOW SHOULD BRING THE
CONVECTION ACROSS THE TERMINAL BETWEEN 22Z TO 2Z. SFC WINDS AHEAD OF
THE CONVECTION SHOULD REMAIN SW AROUND 10 KTS. FOLLOWING THE PASSAGE
OF THE STORMS...THICK DEBRIS CLOUDS SHOULD REMAIN OVER THE REGION
FOR MOST OF THE NIGHT. VFR FOG MAY DEVELOP OVER RAIN SOAKED AREAS
AROUND DAWN. ONE OR TWO HOURS AFTER SUNRISE MONDAY...WITH SHOULD
INCREASE TO AROUND 5 KTS FROM THE WSW WITH SCT CU BASES AROUND 030.

ELSEWHERE...KAND/KGSP/KGMU/KAVL WILL HAVE A GOOD CHANCE FOR
OBSERVING A SHRA OR TSRA DURING THE BEGINNING HOURS OF THE 18Z TAF.
I WILL INCLUDE A MENTION OF TEMPO FOR TS OR VCTS FOR EACH SITE. KHKY
SHOULD SEE VCTS BY 21Z. THE SPC SSEO INDICATES THAT CONVECTION WILL
RAPIDLY DEVELOP OVER THE MTNS LATER THIS AFTERNOON AS A MODERATE S/W
MOVES TOWARD THE SOUTHERN APPALACHIANS. STEERING FLOW SHOULD BRING
THE CONVECTION ACROSS THE TERMINALS THROUGH EARLY EVENING. SFC WINDS AHEAD
OF THE CONVECTION SHOULD REMAIN SW AROUND 10 KTS. FOLLOWING THE
PASSAGE OF THE STORMS...THICK DEBRIS CLOUDS SHOULD REMAIN OVER THE
REGION FOR MOST OF THE NIGHT. MVFR FOG MAY DEVELOP OVER RAIN SOAKED
AREAS AROUND DAWN. FORECAST SOUNDINGS INDICATE THAT KAVL WILL LIKELY
SEE ANOTHER PERIOD AROUND DAWN OF LIFR FOG AND CEILINGS. ONE OR TWO
HOURS AFTER SUNRISE MONDAY...WITH SHOULD INCREASE TO AROUND 5 KTS
FROM THE WSW WITH SCT CU WITH VFR BASES.

OUTLOOK...DIURNALLY DRIVEN ISOLD TO SCT CONVECTION EXPECTED AGAIN
MONDAY. DAYBREAK FOG WILL BE MOST LIKELY IN MOUNTAIN VALLEYS AND
WHERE RAIN FELL THE DAY BEFORE. A COLD FRONT WILL CROSS THE AREA ON
TUESDAY...BUT CONVECTIVE CHANCES ARE UNCERTAIN AT THIS TIME. DRIER
AIR WILL FOLLOW THE FRONT.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH  87%     HIGH  95%     HIGH 100%
KAVL       HIGH 100%     HIGH  83%     MED   71%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH  87%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH  95%     HIGH 100%
KAND       HIGH 100%     HIGH  98%     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...MCAVOY/NED
SHORT TERM...CSH
LONG TERM...JPT
AVIATION...NED