-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 182348
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
748 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/...
-- Changed Discussion --
AS OF 745 PM EDT SATURDAY...NOT MUCH CHANGE THE PAST COUPLE HOURS AS
SCT SHOWERS CONTINUE TO DEVELOP HERE AND THERE ACROSS THE FA. ONE
RATHER PERSISTENT AREA HAS BEEN AFFECTING NRN GREENVILLE COUNTY.
HOPEFULLY THE CELLS WILL START TO MOVE SOON. WITH THE SFC WINDS
BACKED OUT OF THE SE AND 925MB WINDS EXPECTED TO INCREASE TO AROUND
20-25 KTS FROM THE SOUTH AFTER SUNSET...A LITTLE STATIONARY AREA OF
SHOWERS LIKE THAT COULD SHOW A TENDENCY TO INTENSIFY AND DROP
LOCALLY HEAVY RAIN. WE/LL KEEP AN EYE ON IT.

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.
-- End Changed Discussion --

&&

.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 /00Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
AT KCLT/KHKY...A WEAK UPPER WAVE WILL CROSS THE REGION LATER IN THE
NIGHT. THERE CONTINUE TO BE SCATTERED SHOWERS DEVELOPING WELL TO THE
WEST OF OF KCLT...ALONG THE BLUE RIDGE AND INTO UPSTATE SC. THESE
ARE LIKELY TO PERSIST FOR SEVERAL MORE HOURS AND MAY AFFECT THE
AIRFIELD INTO THE EARLY MORNING HOURS. I KEPT A BROAD PERIOD OF VCSH
AS CONVECTIVE CELLS COULD REALLY DEVELOP AT ANY TIME. A THUNDERSTORM
IS POSSIBLE...BUT WITH THE AIRMASS SATURATED THE UPDRAFTS WILL BE
WEAK...FAVORING SHOWERS. THE WINDS HAVE BACKED TO THE SE AND EVEN E
AT TIMES AS A WEAK BACK DOOR COLD FRONT HAS SETTLED INTO THE
REGION. FOR THE MOST PART THE WINDS SHOULD REMAIN OUT OF THE SE
OVERNIGHT. CIGS ARE EXPECTED TO DROP THROUGH THE NIGHT AND AT SOME
POINT AN EXTENSIVE IFR TO LIFR STRATUS DECK WILL DEVELOP OVERNIGHT.
THUNDER CHANCES LOOK MUCH BETTER SUNDAY AFTERNOON.

ELSEWHERE...A WEAK UPPER LOW WILL CROSS THE REGION LATER TONIGHT.
WITH A MOIST AIRMASS AND WEAK INSTABILITY...SCATTERED SHOWERS MAY
LAST MUCH OF THE NIGHT. A FEW TSTMS WILL ALSO BE POSSIBLE...BUT
COVERAGE IS NOT EXPECTED TO BE GREAT ENOUGH TO INCLUDE IN THE TAF.
WINDS WILL GENERALLY BE OUT OF THE SE THE REST OF THE NIGHT AT LIGHT
SPEEDS. WITH SUCH A SATURATED AIRMASS AND THE DEVELOPMENT OF A WEAK
20-25 KT LLVL JET...WIDESPREAD IFR TO LIFR STRATUS IS EXPECTED TO
DEVELOP LATE TONIGHT AND ONLY SLOWLY MIX OUT SUNDAY MORNING. THUNDER
CHANCES LOOK MUCH BETTER SUNDAY AFTERNOON.

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

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-23Z
KCLT       HIGH 100%     HIGH  91%     HIGH  87%     HIGH  92%
KGSP       HIGH  88%     HIGH  91%     HIGH  83%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  98%     HIGH  97%
KHKY       HIGH  90%     HIGH  98%     HIGH  97%     HIGH 100%
KGMU       HIGH  84%     HIGH  91%     HIGH  84%     HIGH  95%
KAND       HIGH  83%     HIGH  80%     MED   78%     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
-- End Changed Discussion --

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...MCAVOY
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...MCAVOY