Flash Flood and Hail in South Carolina, August 20, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
622 PM EDT SAT AUG 20 2011

.SYNOPSIS...
WEAK HIGH PRESSURE WILL GIVE WAY TO A COLD FRONT THAT WILL APPROACH
FROM THE NORTHWEST LATE SUNDAY. THE FRONT IS EXPECTED TO STALL JUST
SOUTH OF OUR AREA EARLY IN THE WEEK AND SLOWLY DISSIPATE. MOISTURE
WILL INCREASE LATE IN THE WEEK AS WE BECOME MORE CONCERNED OF
TROPICAL ACTIVITY.

&&

.NEAR TERM /THROUGH SUNDAY/...
2015 UTC UPDATE...POPS HAVE BEEN RAISED IN THE NC FOOTHILLS...IN THE
UPPER FRENCH BROAD RIVER VALLEY...AND NEAR LAKE HARTWELL. WINDS HAVE
BEEN UPDATED FROM A BLEND OF THE LATEST ADJUST MAV AND NAM. AREAS OF
MORNING FOG HAVE BEEN REALIGNED TO FIT THE LATEST VISIBILITY
FORECAST.

PREVIOUS DISCUSSION...BUILDING MID LEVEL HEIGHTS HAS RESULTED IN AN
AREA OF NVA ACROSS THE SOUTHERN APPALACHIAN AREA THIS AFTERNOON AND
EVENING. OBSERVED SOUNDING AT KFFC INDICATED A SIGNIFICANT INVERSION
AROUND H5. THE COMBINATION OF HIGHS IN THE MID 80S ACROSS THE MTNS
TO L90S EAST AND DWPTS IN THE MID 60S HAVE RESULTED IN AFTERNOON
CAPES BETWEEN 2000 TO 2500 J/KG. GIVEN THE WEAK FORCING AND
LINGERING CIN...POPS ACROSS THE MTNS AND FOOTHILLS WILL REMAIN CHC
THROUGH EARLY THIS EVENING...I WILL FAVOR SCHC POPS EAST THIS
AFTERNOON WITH A SLIGHT INCREASE TO LCHC EARLY THIS EVENING AS MTN
ACTIVITY MOVES SLOWLY EAST. BASED ON THE OBSERVED PROFILES AND
INSTABILITY...AN ISO SVR EVENT OR AREA OF EXCESSIVE RAINFALL IS A
POSSIBILITY.

BY MIDNIGHT...EXPECT THE ENVIRONMENT TO LARGELY STABILIZE.
HOWEVER...FORECAST SOUNDINGS SHOW ELEVATED INSTABILITY REMAINING
THROUGH THE NIGHT. BY THE PRE DAWN HOURS...EXPECTED SHRA ACTIVITY TO
END COMPLETELY...LEAVING ONLY DEBRIS CLOUDS AND LIGHT TO CALM WINDS.
HOWEVER...FOG MAY DEVELOP LATE TONIGHT NEAR AREAS OF RECENT RAIN AND
MTN VALLEYS. LOW TEMPS WILL REMAIN SLIGHTLY ABOVE NORMAL.

SUNDAY...A COLD FRONT WILL SWEEP EAST ACROSS KY/TN THROUGH THE
DAY...REACHING THE SOUTHERN APPALACHIANS DURING THE LATE AFTERNOON.
SOUTH SFC WINDS AHEAD OF THE FRONT WILL STRENGTHEN THROUGH THE
DAY...MAINTAINING DEWPOINT VALUES IN THE UPPER 60S TO AROUND 70.
HIGH TEMPS WILL WARM INTO THE MID 80S ACROSS THE MTNS TO AROUND 90
EAST. FORECAST SOUNDINGS INDICATE THAT THE MID INVERSION WILL
FLATTEN...STEEPENING LAPSE RATES BELOW H6. IN FACT...FORECAST
SOUNDINGS SUPPORT CAPES BETWEEN 2000 TO 3000 J/KG. IN ADDITION...LOW
TO MID LEVEL WINDS WILL INCREASE TO 20 TO 30 KTS...ESPECIALLY IN THE
MID LEVELS. MESOSCALE MODELS INDICATE THAT TSRA WILL DEVELOP ACROSS
THE MTNS AROUND MID DAY AND DEVELOP INTO A BAND PARALLEL TO THE
FRONT. 4 KM WRF INDICATES THAT THE LINE WILL DEVELOP A HEALTHY COLD
POOL AND ACCELERATE EAST ACROSS THE FOOTHILLS AND PIEDMONT DURING
THE AFTERNOON. GIVEN THE INSTABILITY AND WINDS...IT APPEARS THAT
MULTICELL LINES WILL HAVE THE POTENTIAL FOR SVR WIND AND POSSIBLY
SVR HAIL...ESPECIALLY ACROSS THE NC ZONES GIVEN GREATER WIND SPEEDS.
I WILL INCREASE POPS TO LIKELY ACROSS THE AREA. WE WILL HIGHLIGHT
THE SVR POTENTIAL IN THE HWO.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 230 PM SATURDAY...THE MODELS REINFORCE THE UPPER TROF ALONG
THE EAST COAST ON SUNDAY NIGHT AS A STRONG UPPER SHORT WAVE ROTATES
THROUGH THE EASTERN GREAT LAKES. THIS SHOULD HAVE NO TROUBLE PUSHING
A COLD FRONT THROUGH THE FORECAST AREA SUNDAY EVENING. EXPECT A
CONTINUATION OF THE CONVECTIVE ACTIVITY THAT WE HAVE AT SUNSET
SUNDAY EVENING...MOVING EAST ACROSS THE PIEDMONT WITH THE FRONT.
HAVE HELD ONTO A LOW CHANCE POP ON THE TN BORDER FOR LINGERING
UPSLOPE SHOWERS AS THE FRONT MOVES THROUGH. THE SHOWERS SHOULD BE TO
THE EAST OF THE FORECAST AREA BY AROUND SUNRISE ON MONDAY.
THEREAFTER...EXPECT A QUIET START TO THE WORK WEEK.

THE WESTERN CAROLINAS SHOULD BE UNDER A DEEP AND DRY NW FLOW ALOFT
BOTH MONDAY AND TUESDAY AS THE UPPER TROF AXIS HOLDS ALONG THE E
COAST. THAT WILL SUPPORT SURFACE HIGH PRESSURE SETTLING DOWN OVER
THE CENTRAL APPALACHIANS AND MID ATLANTIC THROUGH TUESDAY. FOR THE
MOST PART...THIS SHOULD DISCOURAGE DEEP CONVECTION. ON MONDAY
AFTERNOON...THOUGH...HAVE ALLOWED A SLIGHT CHANCE OVER THE HIGHER
TERRAIN OWING TO LINGERING LOW LEVEL MOISTURE. MONDAY NIGHT...
TUESDAY...AND TUESDAY NIGHT SHOULD BE PRECIP-FREE. TEMPS WERE NUDGED
TOWARD A BLEND OF GUIDANCE IN GENERAL...BUT THE LOWER MET GUIDANCE
WAS FAVORED FOR TUESDAY NIGHT.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM SATURDAY...WE WILL BEGIN WITH WHAT SEEMS REASONABLY
CERTAIN...AND THAT IS SOME MOISTURE RETURN STARTING EARLY WEDNESDAY
AND CONTINUING THROUGH THE END OF THE WEEK. ANOTHER REINFORCING
SHORT WAVE IS EXPECTED TO DROP DOWN THROUGH THE MIDWEST AND OH
VALLEY TUESDAY NIGHT AND WEDNESDAY WHICH WILL PUSH ANOTHER COLD
FRONT INTO THE REGION. WITH THE SURFACE HIGH MOVING OFF THE MID
ATLANTIC COAST TUESDAY NIGHT...EXPECT AN INFLUX OF MOISTURE FROM THE
ATLANTIC AHEAD OF THE FRONT. SO...SCATTERED THUNDERSTORMS LOOK LIKE
A SAFE BET ON WEDNESDAY AFTERNOON AND EVENING...AT LEAST OVER THE
MTNS AND FOOTHILLS. THE CONTINUATION OF THE MOIST EASTERLY FLOW
SHOWN BY THE MODELS SUGGESTS THAT WE WILL NOT SEE MUCH OF A DIURNAL
DROP OFF WEDNESDAY NIGHT...SO THE CHANCE POP WILL RUN RIGHT THROUGH
FRIDAY FOR THE MOST PART AS THE FRONT STALLS NEARBY.

WHICH BRINGS US TO THE WEEKEND...WHICH IS BY NO MEANS CERTAIN. IT
SEEMS REASONABLE TO EXPECT SOME PART OF THE SOUTHEAST TO BE IN SOME
DANGER FROM A TROPICAL CYCLONE SHOWN BY THE COLLECTION OF MODEL
GUIDANCE IN THE VICINITY OF THE FL PENINSULA ON SATURDAY. GOING WITH
THE HPC POSITION OVER THE ERN GULF SATURDAY MORNING...EXPECT EVEN
MORE ATLANTIC MOISTURE TO RUN UPSLOPE FROM THE SOUTHEAST AND HAVE
SOME FOCUS ALONG THE OLD SURFACE FRONT OVER THE CAROLINAS. SO...HAVE
LEANED TOWARD A LOWER DIURNAL RANGE OF TEMPS FOR SATURDAY AND
TRENDED TOWARD THE COOLER FIRST CUT OF HPC TEMPS. HAVE ALSO GONE
WITH A BLANKET CHANCE OF PRECIP THROUGH THE END OF THE DAY. PEOPLE
ACROSS THE CAROLINAS WILL WANT TO KEEP TRACK OF THIS ONE FOR
SATURDAY NIGHT AND SUNDAY.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
AT KCLT...STEADY SOUTHEAST WINDS WILL SLOWLY VEER SOUTH THROUGH
TONIGHT...WITH SPEEDS FAVORING 5 KTS. SCT CU SHOULD DEVELOP ACROSS
THE TERMINAL BY 19Z AND REMAIN UNTIL SUNSET. SLIGHT RISK OF
SHRA/TSRA THIS AFTERNOON AND EARLY EVENING...TOO LOW OF A CHANCE TO
MENTION IN THE TAF AT THIS TIME. LIGHT WINDS AND NARROW DEWPOINT
DEPRESSIONS MAY SUPPORT LIGHT FOG OR HAZE AROUND DAWN. BEFORE
18Z...INCREASING SOUTH WIND AND CU AFTER SUNRISE. A LINE OF
SHRA/TSRA IS EXPECTED TO SWEEP ACROSS THE TERMINAL DURING THE LATE
AFTERNOON...BUT BEYOND THE SCOPE OF THE 18Z TAF.

ELSEWHERE...SCT SHRA/TSRA WILL CONTINUE TO DEVELOP OVER THE MTNS AND
FOOTHILLS THROUGH EARLY EVENING. I WILL CARRY A CB IN THE TAFS
DURING THE LATE AFTERNOON THROUGH EARLY EVENING...EXCEPT FOR KAND.
STEADY SOUTHEAST WINDS WILL SLOWLY VEER SOUTH THROUGH TONIGHT...WITH
SPEEDS FAVORING 5 KTS POSSIBLY BECOMING CALM OVERNIGHT. MOS
CONSENSUS ONCE AGAIN INDICATING DENSE FOG FOR KAVL DURING THE PRE
DAWN HOURS. HOWEVER...CLOSE DEWPOINT DEPRESSIONS AND A FAIR CHC FOR
FRESH RA BY THE END OF THE EVENING MAY SUPPORT FOG OVERNIGHT. FOR
KAVL...I WILL VIS DOWN TO 1SM BY 8Z WITH RECOVERY AROUND 14Z. BEFORE
18Z...INCREASING SOUTH WIND AND CU AFTER SUNRISE. A LINE OF
SHRA/TSRA IS EXPECTED TO SWEEP ACROSS THE TERMINAL DURING THE LATE
AFTERNOON...BUT BEYOND THE SCOPE OF THE 18Z TAF.

OUTLOOK...THROUGH EARLY NEXT WEEK...A MORE UNSETTLED WEATHER PATTERN
SHOULD RESULT IN CONTINUED DEVELOPMENT OF ISOLATED TO WIDELY
SCATTERED DIURNAL CONVECTION EACH AFTN. MORNING FOG WILL ALSO BE
POSSIBLE...ESP IN MTN VALLEYS AND WHERE RAIN FALLS THE DAY BEFORE.

AN EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLE SHOWING THE
PERCENTAGE OF GUIDANCE MEMBERS AGREEING WITH THE SCHEDULED ISSUANCE
CATEGORY IS AVAILABLE AT FOLLOWING LINK (USE LOWER CASE)...

WWW.WEATHER.GOV/GSP/AVIATION/TABLES.HTM

&&

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

&&

SYNOPSIS...PAT
NEAR TERM...JAT/NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...NED

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
256 PM EDT SAT AUG 20 2011

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-211900-
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-
256 PM EDT SAT AUG 20 2011

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

.DAY ONE...THIS AFTERNOON AND TONIGHT.

SCATTERED THUNDERSTORMS WILL DEVELOP ACROSS THE WESTERN CAROLINAS
AND NORTHEAST GEORGIA THIS AFTERNOON AND EVENING. THE MAIN THREATS
WITH THESE THUNDERSTORMS WILL BE CLOUD TO GROUND LIGHTNING AND
BRIEFLY HEAVY RAINFALL. AN ISOLATED SEVERE THUNDERSTORM CANNOT BE
RULED OUT.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

A LINE OF THUNDERSTORMS MAY DEVELOP OVER THE MOUNTAINS AND BLUE
RIDGE SUNDAY AFTERNOON...AND THEN SHOULD MOVE EAST ACROSS THE
FOOTHILLS AND PIEDMONT IN THE AFTERNOON AND EVENING. SOME OF THESE
THUNDERSTORMS MAY CONTAIN DAMAGING WIND GUSTS AND LARGE HAIL...
ESPECIALLY ACROSS NORTH CAROLINA.

.SPOTTER INFORMATION STATEMENT...

NONE.

MOORE

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
446 PM EDT SAT AUG 20 2011

NCZ503>506-202130-
BURKE MOUNTAINS-EASTERN MCDOWELL-GREATER BURKE-MCDOWELL MOUNTAINS-
446 PM EDT SAT AUG 20 2011

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN MCDOWELL AND
WESTERN BURKE COUNTIES THROUGH 530 PM EDT...

AT 444 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM 5 MILES NORTHEAST OF LAKE JAMES...OR 11 MILES
NORTHEAST OF MARION...MOVING SOUTHEAST AT 5 MPH.

THIS STORM WILL BE NEAR...
  LAKE JAMES...

DIME SIZE HAIL...AND WIND GUSTS OF 40 TO 50 MPH ARE EXPECTED WITH
THIS STORM.

LAT...LON 3590 8173 3587 8171 3586 8167 3565 8174
      3574 8210 3587 8201 3589 8198 3591 8198

RWH

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
504 PM EDT SAT AUG 20 2011

NCZ033-501-503-202145-
AVERY-BURKE MOUNTAINS-CALDWELL MOUNTAINS-
504 PM EDT SAT AUG 20 2011

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN BURKE...
NORTHWESTERN CALDWELL AND SOUTHERN AVERY COUNTIES THROUGH 545 PM
EDT...

AT 501 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM 4 MILES EAST OF JONAS RIDGE...OR 10 MILES
SOUTHEAST OF NEWLAND...MOVING SOUTHEAST AT 10 MPH.

THIS STORM WILL BE NEAR...
  GLOBE...

DIME SIZE HAIL...AND WIND GUSTS OF 40 TO 50 MPH ARE EXPECTED WITH
THIS STORM.

LAT...LON 3615 8182 3612 8181 3610 8149 3596 8160
      3590 8173 3590 8191 3596 8194 3595 8196
      3592 8195 3592 8199 3595 8204 3598 8206

RWH

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
539 PM EDT SAT AUG 20 2011

NCZ064-202230-
TRANSYLVANIA-
539 PM EDT SAT AUG 20 2011

...A STRONG THUNDERSTORM WILL AFFECT TRANSYLVANIA COUNTY THROUGH 630
PM EDT...

AT 534 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR BREVARD...MOVING SOUTHEAST AT 10 MPH.

THIS STORM WILL BE NEAR...
  ROSMAN...

DIME SIZE HAIL...AND WIND GUSTS OF 40 TO 50 MPH ARE EXPECTED WITH
THIS STORM.

LAT...LON 3526 8260 3522 8261 3514 8258 3512 8266
      3513 8268 3510 8270 3507 8278 3508 8277
      3509 8279 3527 8292 3532 8285 3532 8283
      3540 8274

RWH