Severe Thunderstorm Warning 192, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
230 PM EDT WED JUL 10 2013

.SYNOPSIS...
A COLD FRONT WILL APPROACH TONIGHT...CROSSING THE REGION THURSDAY.
THE COLD FRONT WILL CROSS THE MOUNTAINS THURSDAY NIGHT...PUSHING EAST
ACROSS THE FOOTHILLS AND PIEDMONT ON FRIDAY...AND STALLING TO THE
EAST. THE REMNANTS OF TROPICAL STORM CHANTAL ARE EXPECTED TO BE NEAR
FLORIDA LATE IN THE WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 225 PM EDT WEDNESDAY...SHOWERS AND THUNDERSTORMS HAVE
DEVELOPED OVER THE NC MTNS AND OVER THE SRN PART OF THE UPSTATE AND
PARTS OF NE GA. IN BETWEEN WIDESPREAD LOW CLOUDS HAVE ONLY RECENTLY
MIXED OUT...DELAYING THE WARM-UP OVER MUCH OF THE FOOTHILLS AND
PIEDMONT. DESPITE THE DELAY...IT/S A NEAR CERTAINTY THAT CONVECTION
WILL GRADUALLY FILL IN FROM THE EDGES. THE PATTERN IS SIMILAR TO
THAT OF THE PAST FEW DAYS WITH WEAKLY DIFFLUENT UPPER
THICKNESSES...VERY HIGH BNDRY LAYER DEWPOINTS...AND A LLVL WIND
FIELD THAT WILL INCREASE TO AROUND 15 KTS BY SUNSET. THIS LOW LEVEL
JET...THOUGH JET IS A PRETTY BOLD TERM...WILL HELP CONVECTION TO
BACK BUILD AND FORM LARGE COMPLEXES JUST LIKE WE SAW MON AND TUE.
GIVEN THIS SET-UP...THE BEST CONVERGE AND GREATEST POTENTIAL FOR
FLOODING AND/OR SEVERE STORMS WILL BE FROM 6 TO 8 PM UNTIL AROUND
MIDNIGHT.

THERE WAS SOME TALK WITH NEIGHBORING OFFICES OF EXPANDING THE FLASH
FLOOD WATCH...BUT IN THE END WE DECIDED TO KEEP IT UP WHERE THE
ANTECEDENT CONDITIONS WERE THE MOST FAVORABLE FOR FLOODING WHICH
INCLUDES THE WRN UPSTATE AND NE GA.

ON THURSDAY A COLD FRONT WILL APPROACH FROM THE NW. LAYER RH/S
INCREASE DRAMATICALLY AND THERE IS MORE SUBSTANTIVE UPPER DIVERGENCE
AND DPVA. THEREFORE WE SHOULD SEE MORE WIDESPREAD CONVECTION AND I
HAVE CATEGORICAL POPS ACROSS THE FA DURING THE AFTN AND EARLY
EVENING HOURS. A FLASH FLOOD WATCH MAY BE NEEDED FOR TOMORROW FOR
PART OR ALL OF THE FA. HOWEVER...THE AGREEMENT WITH THE NEIGHBORING
OFFICES WAS THAT WE WOULD HOLD OFF ON A WATCH UNTIL AT LEAST
TONIGHT. IF WE HAVE WIDESPREAD HEAVY PCPN THIS EVENING THAT WOULD
CERTAINLY INCREASE THE NEED FOR HAVING A WATCH FOR THURSDAY.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AT 230 PM EDT WEDNESDAY...AN UPPER TROUGH WILL AMPLIFY ALONG THE
EAST COAST THURSDAY NIGHT...REACHING N FL BY FRIDAY MORNING....WHILE
AN EASTERLY WAVE MOVES ALONG THE GULF COAST. BY SATURDAY MORNING THE
MODELS CUT OF A LOW IN THIS TROUGH OVER THE NORTHEAST...AND THE GFS
CLOSES OFF ANOTHER LOW ALONG THE CENTRAL GULF COAST. AS THESE TWO
LOWS MOVE IN OPPOSITE DIRECTIONS...AN UPPER RIDGE WILL BUILD ACROSS
THE SOUTHERN APPALACHIANS ON SATURDAY NIGHT.

A COLD FRONT WILL MOVE SOUTHEAST ACROSS OUR AREA ON THURSDAY
NIGHT...MOVING SLOWLY EAST OF THE AREA ON FRIDAY. THE NAM IS MORE
AGGRESSIVE THAN THE GFS ON BRINGING DRY AIR IN BEHIND THE FRONT ON
FRIDAY THROUGH SATURDAY. THE GFS DEVELOPS ISENTROPIC UPGLIDE OVER
BOUNDARY ON FRIDAY NIGHT...LASTING THROUGH SATURDAY NIGHT. EVEN THE
NAM SHOWS LOW LEVEL MOISTURE LINGERING...WITH A POST FRONTAL
EASTERLY LOW LEVEL UPSLOPE FLOW INTO THE BLUE RIDGE.

FORECAST POPS WIL BE HIGHEST WITH THE FRONT ON THURSDAY NIGHT. SMALL
POPS WILL BE CARRIED BEHIND THE FRONT...MAINLY FAVORING THE BLUE
RIDGE FOR UPSLOPE FLOW...AND THE PIEDMONT FOR PROXIMITY TO THE
STALLED FRONT.

MINIMUM TEMPERATURES WILL RUN NEAR NORMAL IN LINGERING LOW LEVEL
MOISTURE. MAXIMUM TEMPERATURES WILL START OUT AROUND 10 DEGREES
BELOW NORMAL ON FRIDAY...THEN WILL FALL A FEW MORE DEGREES FURTHER
ON SATURDAY AS HEIGHTS FALL ALOFT AND COOLER NORTHEASTERLY FLOW SETS
UP BEHIND THE FRONT.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 200 PM EST WEDNESDAY...THE PATTERN LOOKS TO REMAIN UNSETTLED
THROUGH THE MEDIUM RANGE. BOTH GFS AND EC DEVELOP AN UPPER LEVEL LOW
OVER THE NE CONUS THIS WEEKEND...AND RECENT RUNS HAVE COME INTO
BETTER AGREEMENT ON INTENSITY AND TIMING. THE LOW DIPS SOUTH AND
RETROGRADES EARLY NEXT WEEK...AND LOOKS TO CROSS THE CWA BY THE
MIDDLE OF NEXT WEEK. A FRONTAL BOUNDARY WILL REMAIN DRAPED ACROSS
THE SC COAST OVER THE WEEKEND AND THROUGH MONDAY...PROVIDING A
TRIGGER FOR AFTERNOON SHOWERS AND STORMS. A SURFACE HIGH OVER MUCH
OF THE EASTERN US WILL MAINTAIN WEAK SOUTHEASTERLY FLOW AND DEEP
TROPICAL MOISTURE OFF THE ATLANTIC...SUGGESTING THE POSSIBILITY OF
SOME TRAINING STORMS EACH AFTERNOON. KEPT POPS ABOVE CLIMO IN THE
ENTIRE EXTENDED...MAINLY FAVORING A DIURNAL TREND.

THE OTHER MAJOR FACTOR IN THE EXTENDED IS OF
COURSE TROPICAL STORM CHANTAL. CURRENT NHC FORECAST HAS CHANTAL
STEADILY WEAKENING AND DISSIPATING JUST TO THE EAST OF JACKSONVILLE
ON SATURDAY...BUT IT STILL APPEARS LIKELY THAT THE FORECAST AREA
WILL SEE AT LEAST SOME OF THE TROPICAL MOISTURE ACCOMPANYING THE
REMNANTS BY LATE WEEKEND. IF THE CURRENT NHC FORECAST PATH
HOLDS...CHANTAL'S EFFECTS MAY NOT BE AS SIGNIFICANT AS PREVIOUSLY
THOUGHT...BUT THERE IS STILL SOME UNCERTAINTY WITH THE PATH OF THE
REMNANT LOW AFTER DISSIPATION. REGARDLESS OF CHANTAL'S TACK...THE
OVERALL PATTERN WILL BE DOMINATED BY DEEP TROPICAL MOISTURE AND WEAK
FLOW AND THE POSSIBILITY OF SOME LOCALLY HEAVY RAINFALL. HIGHS WILL
REMAIN ABOUT 5 DEGREES BELOW AVERAGE...WITH LOWS HOVERING RIGHT
AROUND SEASONAL NORMALS.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
AT KCLT...EXPECTING MVFR CIGS TO FINALLY LIFT TO LOW END VFR BETWEEN
19-20 UTC. THE UPSHOT OF THIS IS THAT THE CLOUD COVER SHOULD DELAY
THE INITIATION OF THUNDERSTORM ACTIVITY AT THE AIRFIELD FOR SEVERAL
HOURS. I/VE GONE WITH A TEMPO FOR THUNDER FROM 22-02 UTC THIS
EVENING...AND EVEN THAT MAY BE TOO EARLY. SOMEHOW THE AIRFIELD
MISSED OUT ON THE LOWEST CLOUD COVER THIS MORNING...BUT THEIR LUCK
MAY RUN OUT TONIGHT AS WIDESPREAD STRATUS IS AGAIN EXPECTED. I
BROUGHT IN A BKN012 CIG AT 0900 UTC...THOUGH A PERIOD OF IFR IS
POSSIBLE. EXPECTING QUITE A BIT OF CONVECTIVE COVERAGE DURING THE
AFTERNOON HOURS TOMORROW AS A COLD FRONT APPROACHES.

ELSEWHERE...STRATUS HAS BEEN VERY SLOW TO LIFT...BUT IT IS FINALLY
MIXING INTO A CU FIELD OVER THE UPSTATE AND SRN NC FOOTHILLS. THIS
SHOULD DELAY THE ONSET OF THUNDERSTORMS OVER MOST OF THE
UPSTATE...THOUGH THERE IS A VERY GOOD CHANCE THEY WILL EVENTUALLY
DEVELOP. THEREFORE I HAVE GONE WITH A TEMPO GROUP FROM 22-02 UTC
AND EVEN THAT MIGHT BE A LITTLE EARLY. STORMS ARE ALREADY DEVELOPING
AROUND KAVL AND THEY WILL PERSIST AROUND THE AIRFIELD FOR SEVERAL
MORE HOURS. I SEE NO REASON TO BELIEVE THAT WE WON/T SEE STRATUS
BLOSSOM OVER THE REGION AGAIN LATE TONIGHT AND I HAVE A PERIOD OF
IFR CIGS EVERYWHERE BEING AROUND 0900 UTC. THUNDERSTORMS MAY DEVELOP
EARLIER TOMORROW AS THE ATMOSPHERE WILL BE MORE MOIST AND A COLD
FRONT APPROACHES.

OUTLOOK...CHANCES FOR DIURNAL SHOWERS/STORMS AND MORNING FOG/STRATUS
WILL REMAIN HIGH THROUGH THURSDAY NIGHT. A COLD FRONT WILL STALL
NEAR THE REGION EARLY FRIDAY AND SLOWLY DISSIPATE THROUGH THE
WEEKEND...CONTINUING THE CHANCES FOR DIURNAL THUNDERSTORMS AND
MORNING FOG/LOW CLOUDS.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH  88%     HIGH  89%     MED   77%     MED   76%
KGSP       HIGH  95%     HIGH  97%     HIGH  80%     MED   69%
KAVL       HIGH  99%     HIGH  99%     MED   76%     MED   75%
KHKY       HIGH  92%     HIGH  96%     MED   75%     MED   70%
KGMU       HIGH  87%     HIGH  97%     HIGH  88%     MED   75%
KAND       HIGH  93%     HIGH 100%     HIGH  84%     HIGH  84%

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...FLASH FLOOD WATCH UNTIL 2 AM EDT THURSDAY FOR GAZ018-026-028-
     029.
NC...NONE.
SC...FLASH FLOOD WATCH UNTIL 2 AM EDT THURSDAY FOR SCZ004>006-
     010>012-019.

&&

SYNOPSIS...JAT
NEAR TERM...MCAVOY
SHORT TERM...JAT
LONG TERM...VISIN
AVIATION...MCAVOY

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
254 PM EDT WED JUL 10 2013

GAZ010-018-SCZ001-004-101930-
GREATER OCONEE-OCONEE MOUNTAINS-RABUN-STEPHENS-
254 PM EDT WED JUL 10 2013

...A STRONG THUNDERSTORM WILL AFFECT NORTHERN STEPHENS...SOUTHERN
RABUN AND WESTERN OCONEE COUNTIES THROUGH 330 PM EDT...

AT 252 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR LONG CREEK...OR 11 MILES SOUTHEAST OF
CLAYTON...MOVING EAST AT 10 MPH.

THIS STORM WILL IMPACT LOCATIONS NEAR...
  LONG CREEK...

SMALL HAIL...WIND GUSTS OF 40 TO 50 MPH AND TORRENTIAL RAIN ARE
EXPECTED WITH THIS STORM.

LAT...LON 3482 8341 3490 8317 3457 8303 3455 8338
      3464 8339 3467 8337 3469 8334 3473 8337
      3473 8340