Special Weather Statement, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
756 PM EDT TUE AUG 6 2013

.SYNOPSIS...
GENERAL HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH SATURDAY
WITH A WEAK WARM FRONT AFFECTING THE REGION ON WEDNESDAY. A COLD
FRONT WILL PUSH IN FROM THE NORTH SUNDAY AND BECOME STATIONARY
THROUGH MONDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 750 PM...SOLID SCATTERED TO NUMEROUS COVERAGE OF CONVECTION
HAS BEEN REALIZED ACROSS MUCH OF THE UPPER SAVANNAH RIVER VALLEY AND
PORTIONS OF THE SOUTHERN NC MTNS. ALTHOUGH CELLS HAVE NOT BEEN
ESPECIALLY DEEP...SLOW MOVEMENT IS RESULTING IN SOME HEAVY RAINFALL
RATES. AS THE DIURNAL COOLING CYCLE COMMENCES...COVERAGE IS
GENERALLY EXPECTED TO GRADUALLY WANE IN THE PIEDMONT...BUT AT LEAST
SCATTERED SHOWERS WILL LIKELY CONTINUE FOR MUCH OF THE OVERNIGHT
NEAR THE BLUE RIDGE. A THREAT FOR LOCALIZED FLASH FLOODING WILL
GRADUALLY INCREASE NEAR THE SOUTHERN ESCARPMENT LATER THIS EVENING
AND INTO THE OVERNIGHT. IN FACT...WE ARE MONITORING CONVECTIVE
TRENDS FOR A POTENTIAL SHORT FUSE FFA FOR THESE AREAS FOR THE NEXT
FORECAST UPDATE.

AS OF 420 PM...CONVECTION IS GRADUALLY INCREASING IN COVERAGE AND
INTENSITY THIS AFTERNOON IN AREAS THAT HAVE SEEN SOME PEAKS OF SUN/
APPRECIABLE DESTABILIZATION...NAMELY THE SOUTHWEST QUADRANT OF THE
CWA. NEVERTHELESS...THE VERY NEAR TERM FORECAST IS A BIT MORE
PESSIMISTIC THAN RADAR/OBSERVATIONAL TRENDS SUPPORT...SO POPS HAVE
BEEN SCALED BACK 10-15 PERCENT OVER THE NEXT 2-3 HOURS...REACHING A
NADIR AT AROUND 00Z. IT APPEARS THE MAIN THREAT WILL CONTINUE TO BE
HEAVY RAIN ASSOCIATED WITH SLOW MOVING CELLS.

CONVECTION DEVELOPING ALONG THE UPPER SAV RIVER VALLEY AND SRN NC
MTNS WHERE WARMING HAS OCCURRED AND MODERATE INSTABILITY HAS
DEVELOPED. CONVECTION ALLOWING MDLS SHOW ADDITIONAL DEVELOPMENT
ALONG THE BLUE RIDGE THRU THE AFTERNOON. THIS CONVECTION SLIDES SE
INTO THE NC FOOTHILLS AND THE WRN UPSTATE/NE GA. WITH CONVECTION
ALREADY ONGOING...HAVE PLACED THE HIGHEST POP OVER THESE AREAS WITH
LOWER...BUT STILL SCT POP...OVER THE TN BORDER COUNTIES AND THE NC
PIEDMONT WHERE INSTABILITY IS LOWER. DCAPE IS INCREASING OVER THE
UPPER SAV RIVER VALLEY AND THERE IS WEAK WIND SHEAR OVER MUCH OF THE
WRN CWFA. THEREFORE...CANNOT RULE OUT AN ISOLATED SVR STORM OVER THE
UPPER SAV RIVER VALLEY. SLOW MOVING STORMS WILL ALSO CONTINUE THE
ISOLATED FLASH FLOOD THREAT. THE CONVECTION SHUD DIMINISH THIS
EVENING WITH THE LOSS OF HEATING. HOWEVER...EXPECT AN INCREASE IN
SHRA ACTIVITY AFTER MIDNIGHT AS DEEP MOISTURE...STRENGTHENING LOW
LEVEL FLOW AND UPPER DIVERGENCE RETURN FROM THE WEST. CANNOT SAY
THAT WE WILL SEE A REPEAT OF TUE MORN. HOWEVER...IT IS POSSIBLE THAT
SHRA ACTIVITY COULD PRODUCE HEAVY RAINFALL AND TRAINING ECHOES
SOMEWHERE OVER THE WRN CWFA.

GUIDANCE SHOWS WEAK INSTABILITY DEVELOPING WED AS A WEAK SHORT WAVE
MOVES OVER THE AREA. DEEP MOISTURE WILL ALREADY BE IN PLACE WITH
GOOD SLY LOW LEVEL FLOW. EXPECT CONVECTION TO DEVELOP AGAIN OVER THE
MTNS AND SPREAD EASTWARD ACROSS THE AREA DURING THE AFTERNOON. WILL
AGAIN HAVE THE HIGHEST POP OVER THE WRN CWFA DECREASING TO CHC POP
OVER THE EAST. HIGHS WILL AGAIN BE WELL BELOW NORMAL ACROSS MUCH OF
THE AREA.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF MIDDAY TUESDAY...SFC RIDGE INITIALLY CENTERED OFF THE NEW
ENGLAND COAST WILL SHIFT SOUTHWARD TO A CLASSIC BERMUDA HIGH POSITION
BY THE END OF THE FORECAST PERIOD. WITH THE CWFA REMAINING ON THE WRN
FRINGE OF THE HIGH...AS ONE MIGHT EXPECT SOME DEGREE OF MOIST
SOUTHERLY FLOW WILL CONTINUE DURING THIS TIME. THE NORTHERN POSITION
OF THE HIGH EARLIER IN THE PERIOD ALSO WILL ALLOW FOR SOME ISENTROPIC
UPGLIDE WED NIGHT AND THU...BUT IT DIMINISHES BY FRIDAY. QUASI-ZONAL
FLOW SEEN AT 500MB THRU THE PERIOD WITH A COUPLE OF DISTURBANCES
PASSING FROM THE OHIO VALLEY INTO THE MID-ATLANTIC...REMAINING TO OUR
NORTH.

MOISTURE REMAINS ABUNDANT THROUGH THE PERIOD...WITH ABOVE-NORMAL
PWATS OF AROUND 2 INCHES OVER MUCH OF THE AREA. GIVEN THE LACK OF
STRONG FORCING AND SLOW MEAN LAYER FLOW...MULTICELL TSTMS PRODUCING
HEAVY RAIN WILL LIKELY OCCUR EACH AFTERNOON. HAVE FAVORED QPF BLENDS
WEIGHTED TOWARD WETTER GUIDANCE...THOUGH ISOLATED HEAVIER ACCUMS
CAUSING SOME FLASH FLOODING ARE POSSIBLE. NAM SHOWS LOWER CAPE VALUES
AND DRIER AIR IN THE UPPER LEVELS ON FRI...AND IT PRODUCES LOWER QPF
AS A RESULT. GFS ACTUALLY DEVELOPS BETTER CAPE FRI AND
CORRESPONDINGLY HIGHER QPF. REGARDLESS...TRENDS WILL STILL REFLECT A
DIURNAL PEAK IN CONVECTION THOUGH SOME CHANCE IS MAINTAINED OVERNIGHT
DUE TO THE LLVL FORCING MECHANISMS DESCRIBED ABOVE.

MOIST AND MOSTLY CLOUDY CONDITIONS WILL CONTINUE THRU THE
PERIOD...LIMITING DIURNAL TEMP RANGE. LOWS WILL BE SLIGHTLY ABOVE
NORMAL AND HIGHS BELOW NORMAL.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF MIDDAY TUESDAY...THE MEDIUM RANGE PERIOD IS CHARACTERIZED BY
THE GRADUAL PROGRESSION OF A FRONTAL BOUNDARY SOUTHWARD ACROSS THE
ERN CONUS WHICH LEADS TO A WEAKENING OF THE BERMUDA HIGH. 06Z GFS AND
00Z EC INITIALLY AGREE FAIRLY WELL. THE EC IS HOWEVER SOMEWHAT SLOWER
IN AMPLIFYING THE ERN TROUGH...BUT EVENTUALLY ITS DEPICTION OF THE
TROUGH IS MUCH STRONGER THAN THAT ON THE GFS. IT WOULD FAVOR A DRIER
FCST OVER THE WEEKEND AND MORE ACTIVE WX TO START THE WORK WEEK. WPC
FCST FOLLOWS A MORE GFS LIKE SOLUTION. WHILE THE FRONT DOES NOT HAVE
MUCH OF AN IMPACT ON LLVL TEMPS IN OUR AREA...IT WILL PROVIDE SOME
LLVL CONVERGENCE AND ENCOUNTERS ENOUGH DEEP MOISTURE TO EXPECT POPS
ABOVE CLIMO THRU THE PERIOD...WITH A DIURNAL EMPHASIS AND TSTM
MENTIONS DUE TO TYPICAL SUMMERTIME INSTABILITY. GFS SHEAR IS
INSUFFICIENT TO EXPECT STORMS TO BECOME WELL ORGANIZED DESPITE THE
FRONT. HOWEVER THE AMPLIFYING EC TROUGH LEADS IT TO PRODUCE IMPROVING
DEEP SHEAR LATE IN THE PERIOD SUGGESTING A GREATER SEVERE THREAT WITH
TSTMS AT THAT TIME...IF THAT SOLUTION VERIFIES. TEMPS WILL INITIALLY
BE SLIGHTLY ABOVE NORMAL...MODERATING SOMEWHAT BY MONDAY FOLLOWING
THE FRONTAL PASSAGE.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT AND KHKY...QUITE A BIT OF UNCERTAINTY AS TO HOW CIG TRENDS
ARE GOING TO EVOLVE OVER THE NEXT 3 OR 4 HOURS...AS JUST ABOUT
ANYTHING IS POSSIBLE. AS SUCH...HAVE OPTED TO GO WITH STEADY CIGS IN
THE LOW MVFR RANGE THROUGH 04Z...THEN INTRODUCE TEMPOS FOR IFR BTW
04 AND 06Z. WITH CONTINUED SOUTHERLY FLOW AND COPIOUS MOISTURE...
EXPECT CIGS WILL EVENTUALLY SETTLE INTO IFR/LIFR TONIGHT...THE ONLY
QUESTION BEING A MATTER OF TIMING. PERSISTENT LOW CLOUD COVER HAS
LIMITED THE INSTABILITY AND THEREFORE INHIBITED NEW CONVECTION FROM
INITIATING ACROSS THE PIEDMONT...OR UPSTREAM ACROSS THE NORTHERN NC
MTNS. THEREFORE...HAVE OPTED TO OMIT ANY SHOWER MENTION...ALTHOUGH
CHANCES MAY BEGIN TO GRADUALLY INCREASE LATER THIS EVENING AND INTO
THE EARLY MORNING HOURS. CIGS SHOULD ONCE AGAIN BE SLOW TO LIFT ON
WED...BUT VFR SHOULD BE REALIZED AT SOME POINT DURING THE
AFTERNOON...WITH SCATTERED CONVECTION EXPECTED.

ELSEWHERE...SCATTERED/NUMEROUS SLOW-MOVING SHOWERS PERSISTED AT
MID-EVENING ALONG A NARROW AXIS FROM WEST OF KAVL AND KGMU TO AROUND
KAND. ACTIVITY HAS GRADUALLY BEEN DEVELOPING TO THE EAST WITH
TIME...SO TEMPOS FOR SHRA/MVFR VISBY (IFR AT KAND) HAVE BEEN
INTRODUCED THIS EVENING. CONVECTIVE COVERAGE IS EXPECTED TO BECOME
MORE CONCENTRATED ALONG THE BLUE RIDGE BY LATE EVENING...BUT SHOWERS
CANNOT BE RULED OUT ANYWHERE AT ANYTIME DURING THE OVERNIGHT.
OTHERWISE...CIGS ARE EXPECTED TO REMAIN/LOWER TO MVFR BY 06Z AT MOST
TERMINALS...WITH IFR CONDITIONS EXPECTED LATE TONIGHT. CIGS SHOULD
ONCE AGAIN BE SLOW TO LIFT ON WED...BUT VFR SHOULD BE REALIZED AT
SOME POINT DURING THE AFTERNOON...WITH SCATTERED CONVECTION
EXPECTED.

OUTLOOK...MOISTURE AND INSTABILITY CONTINUE THROUGH THE WEEKEND...
LEADING TO CONTINUED CHANCES FOR MAINLY DIURNAL CONVECTION. EARLY
MORNING PATCHY FOG AND LOW CLOUDS MAY OCCUR OVER AREAS OF RECENT
RAINFALL AND IN MTN VALLEYS.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       MED   73%     LOW   59%     MED   63%     HIGH 100%
KGSP       MED   79%     LOW   49%     HIGH  80%     HIGH  88%
KAVL       MED   76%     HIGH  92%     HIGH  88%     HIGH  88%
KHKY       MED   70%     MED   69%     HIGH  84%     HIGH  93%
KGMU       HIGH  89%     MED   68%     HIGH  89%     HIGH  95%
KAND       HIGH 100%     HIGH  83%     MED   65%     HIGH  98%

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...JDL/RWH
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
249 PM EDT TUE AUG 6 2013

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-071900-
RABUN-HABERSHAM-STEPHENS-FRANKLIN-HART-ELBERT-AVERY-ALEXANDER-
IREDELL-DAVIE-MADISON-YANCEY-MITCHELL-SWAIN-HAYWOOD-BUNCOMBE-CATAWBA-
ROWAN-GRAHAM-NORTHERN JACKSON-MACON-SOUTHERN JACKSON-TRANSYLVANIA-
HENDERSON-CLEVELAND-LINCOLN-GASTON-MECKLENBURG-CABARRUS-UNION NC-
CALDWELL MOUNTAINS-GREATER CALDWELL-BURKE MOUNTAINS-GREATER BURKE-
MCDOWELL MOUNTAINS-EASTERN MCDOWELL-RUTHERFORD MOUNTAINS-
GREATER RUTHERFORD-POLK MOUNTAINS-EASTERN POLK-OCONEE MOUNTAINS-
PICKENS MOUNTAINS-GREENVILLE MOUNTAINS-GREATER OCONEE-
GREATER PICKENS-GREATER GREENVILLE-SPARTANBURG-CHEROKEE-YORK-
ANDERSON-ABBEVILLE-LAURENS-UNION SC-CHESTER-GREENWOOD-
249 PM EDT TUE AUG 6 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST GEORGIA...PIEDMONT
NORTH CAROLINA...WESTERN NORTH CAROLINA AND UPSTATE SOUTH CAROLINA.

.DAY ONE...TONIGHT.

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS THE AREA
INTO THE EVENING. THE STORMS WILL BE SLOW MOVING AND SOME OF THEM
WILL DROP LOCALLY EXCESSIVE RAINFALL...RESULTING IN AN ISOLATED
FLASH FLOOD THREAT. IN ADDITION...MODERATE INSTABILITY AND WEAK
SHEAR OVER NORTHEAST GEORGIA AND THE WESTERN UPSTATE WILL LEAD TO
THE POTENTIAL FOR AN ISOLATED SEVERE THUNDERSTORM...WITH DAMAGING
WINDS THE MAIN THREAT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

NONE.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
728 PM EDT TUE AUG 6 2013

SCZ001-070000-
OCONEE MOUNTAINS-
728 PM EDT TUE AUG 6 2013

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL OCONEE COUNTY THROUGH
800 PM EDT...

AT 723 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM 5 MILES NORTHWEST OF WESTMINSTER...OR 6 MILES
SOUTHWEST OF WALHALLA...MOVING NORTH AT 5 MPH.

THIS STORM WILL IMPACT LOCATIONS NEAR...
  WALHALLA...

TORRENTIAL RAIN IS EXPECTED WITH THIS STORM.

HEAVY RAINS MAY FLOOD AREAS WITH POOR DRAINAGE...SUCH AS DITCHES AND
UNDERPASSES. AVOID THESE AREAS AND DO NOT CROSS FLOODED ROADS. WATER
LEVELS OF SMALL STREAMS AND RIVERS MAY ALSO RISE RAPIDLY. SEEK HIGHER
GROUND IF THREATENED BY FLOOD WATERS.

LAT...LON 3484 8321 3481 8300 3469 8304 3463 8312
      3463 8313 3463 8314 3466 8328

NED

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
828 PM EDT TUE AUG 6 2013

SCZ001-004-005-070100-
GREATER OCONEE-GREATER PICKENS-OCONEE MOUNTAINS-
828 PM EDT TUE AUG 6 2013

...A STRONG THUNDERSTORM WILL AFFECT EASTERN OCONEE AND SOUTHWESTERN
PICKENS COUNTIES THROUGH 900 PM EDT...

AT 823 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR SENECA...OR 7 MILES SOUTHEAST OF WALHALLA...
MOVING EAST AT 10 MPH.

THIS STORM WILL IMPACT LOCATIONS NEAR...
  SENECA...
  CLEMSON...

TORRENTIAL RAIN IS EXPECTED WITH THIS STORM.

HEAVY RAINS MAY FLOOD AREAS WITH POOR DRAINAGE...SUCH AS DITCHES AND
UNDERPASSES. AVOID THESE AREAS AND DO NOT CROSS FLOODED ROADS. WATER
LEVELS OF SMALL STREAMS AND RIVERS MAY ALSO RISE RAPIDLY. SEEK HIGHER
GROUND IF THREATENED BY FLOOD WATERS.

LAKE KEOWEE IS IN THE PATH OF THIS STORM. CLOUD TO GROUND LIGHTNING
AND GUSTY WINDS WILL CREATE DANGEROUS BOATING CONDITIONS. MOVE TO
SHORE IMMEDIATELY.

LAT...LON 3456 8301 3484 8308 3485 8290 3484 8289
      3482 8290 3481 8288 3486 8280 3486 8275
      3471 8271 3466 8280

NED