Severe Thunderstorm Warning 303, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
223 PM EDT MON AUG 12 2013

.SYNOPSIS...
A COLD FRONT IS EXPECTED TO CROSS THE WESTERN CAROLINAS AND
NORTHEAST GEORGIA TUESDAY NIGHT. A WEDGE OF COOL AND WET HIGH
PRESSURE WILL GRADUALLY BECOME ESTABLISHED LATE IN THE WEEK...AND
REMAIN THROUGH THE WEEKEND. DAYTIME HIGH TEMPERATURES WILL BE
AROUND 10 DEGREES BELOW NORMAL.

&&

.NEAR TERM /THROUGH TUESDAY/...
AT 230 PM EDT MONDAY...AN UPPER TROUGH WILL AMPLIFY OVER THE
SOUTHEAST TONIGHT AND TUESDAY. A SHORTWAVE MOVING INTO THE BASE OF
THIS TROUGH THIS EVENING WILL SUPPORT LINGERING CONVECTION.
INSTABILITY AND SHEAR WILL SUPPORT SOME ORGANIZATION OF
THUNDERSTORMS...AND WITH RELATIVELY DRY SUB CLOUD...DOWNBURSTS COULD
PRODUCE DAMAGING WIND. RELATIVELY HIGH FREEZING LEVELS WOULD NOT BE
OVERLY SUPPORTIVE OF LARGE HAIL. STEERING FLOW WILL INITIALLY BE
RATHER LIGHT...BUT PICKS UP THIS AFTERNOON. THIS WILL LIMIT
QPF...ALTHOUGH BRIEF HEAVY DOWNPOURS COULD STILL PRODUCE RUNOFF
PROBLEMS WHERE RECENT HEAVY RAINS HAVE OCCURRED. MINIMUM
TEMPERATURES WILL SLIGHTLY ABOVE NORMAL DUE TO CLOUDS COVER AND
MOISTURE.

ACTIVITY WILL DIMINISH LATE THIS EVENING...THEN BEGIN RAMPING UP
AGAIN TOWARD DAWN AS A COLD FRONT APPROACHES FROM THE NW.
INSTABILITY WILL BE SOMEWHAT LIMITED BY GREATER CLOUD COVER
TUESDAY...BUT SHEAR WILL BE BETTER...AND SOME STORM ORGANIZATION
WILL BE POSSIBLE. FORECAST SOUNDINGS ARE NEARLY SATURATED ABOVE 3000
FT...AND POTENTIAL FOR HEAVY RAINFALL EXISTS WITH BETTER UPDRAFTS.
STEERING FLOW WILL KEEP STORMS MOVING...BUT AGAIN ANY VULNERABLE
SITES THAT GET HEAVY RAIN MY HAVE RUNOFF PROBLEMS. HIGH TEMPERATURES
WILL BE NEAR NORMAL.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 1245 PM MONDAY...HIGH PRESSURE WILL BE IN THE PROCESS OF
BUILDING INTO THE FORECAST AREA TUESDAY NIGHT. BY WEDNESDAY THE GFS
HAS THE SFC COLD FRONT DOWN ACROSS COASTAL SC...EXTENDING WESTWARD
ACROSS SRN GA AND AL. THERE WILL STILL BE UPSLOPE POOLING OF
MOISTURE ACROSS THE SW NC MTNS AS WELL AS ALONG THE BLUE RIDGE OF SC
AND GA. I STILL HAVE A PERIOD OF LIKELY POPS ACROSS THESE ZONES LATE
WED AND WED EVENING. HOWEVER...I HAVE LOWERED POPS ACROSS THE REST
OF THE FA AS THE LACK OF SFC CONVERGENCE AS WELL AS DRIER AIR MOVING
IN FROM THE NORTHEAST SHOULD GREATLY LIMIT CONVECTIVE CHANCES.

EVEN DRIER AIR MOVES IN LATE WEDNESDAY NIGHT AND THURSDAY AS THE NAM
AND GFS DEVELOP COLD AIR DAMMING OVER THE REGION. THE RAW GFS SFC
DEWPOINTS FALL INTO THE 50S OVER A GOOD BIT OF THE FORECAST AREA
DURING THE DAY ON THU...LASTING INTO THU NIGHT. THERE/S NOT MUCH YOU
CAN DO WITH THOSE DEWPOINTS WHEN IT COMES TO CHURNING OUT PCPN AND
I/VE LOWERED POPS WED NIGHT THROUGH THU NIGHT. IN FACT...I/VE
REMOVED POPS FROM THE NC FOOTHILLS AND PIEDMONT THU AND THU NIGHT.
SKIES MAY EVEN CLEAR DURING THE DAY ON THU OVER THE NC FOOTHILLS AND
PIEDMONT BEFORE UPGLIDE STARTS TO BRING THE CLOUDS BACK INTO THE
EXTENDED RANGE. WE COULD STILL SEE SOME PCPN OVER THE SRN UPSTATE
AND BACK ACROSS THE SRN SAVANNAH RIVER VALLEY DURING THIS PERIOD
WHERE UPSLOPE AND/OR THE ELEVATED FRONTAL BNDRY MAY SERVE TO
GENERATE PCPN.

WITH THE COLD AIR DAMMING...IT APPEARS THAT TEMPERATURES MAY NOT GET
OUT OF THE 70S DURING THE DAY ON THURSDAY.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 1230 PM MONDAY...PRIMARILY USED THIS MORNING/S WPC GUIDANCE
GRIDS FOR THE EXTENDED TODAY...THOUGH I DID SHADE DOWN POPS TO KEEP
PCPN CHANCES IN THE HIGH CHANCE RANGE MOST OF THE EXTENDED
RANGE.

THE MODELS AVAILABLE FOR THIS PACKAGE WERE THE 00 UTC ECMWF AND THE
06 UTC GFS. THE GFS DEVELOPS A TROPICAL LOW IN THE GOM WHICH IT
LIFTS ACROSS THE REGION BY THIS COMING SUNDAY. THIS SOLUTION APPEARS
TO BE AN OUTLIER AND THE GFS WAS LARGELY IGNORED FOR THIS PACKAGE.
INSTEAD...THE 00 UTC ECMWF WAS FAVORED FOR THE EXTENDED. IF FEATURES
A PERIOD OF COLD AIR DAMMING FOR FRIDAY AND SATURDAY WITH CLOUDY
SKIES AND WELL BELOW NORMAL MAX TEMPERATURES. THE CAD WEAKENS ON
SUNDAY AND MONDAY...THOUGH THERE IS STILL A WEAK SFC RIDGE OVER TH
FA.

ALOFT AN UPPER LOW IS PROJECTED TO CLOSE OFF OVER THE MIDDLE
MISSISSIPPI RIVER VALLEY AND DRIFT VERY SLOWLY NORTHEAST WARD
THROUGH THE EXTENDED RANGE...EVENTUALLY ENDING UP OVER THE OHIO
VALLEY BY DAY 7. THIS KEEPS THE REGION UNDER A MOIST SOUTHERLY FLOW
THROUGH THE PERIOD. AS THE ENTIRE FA LOOKS TO BE JUST ON THE COOL
SIDE OF THE BNDRY...THE QUESTION BECOMES WILL THE BULK OF THE HEAVY
RAIN AND TSTM ACTIVITY DEVELOP ALONG AND TO THE WARM SIDE OF THE
BNDRY...SPARING US WIDESPREAD HEAVY RAIN FOR THE MOST PART...OR WILL
THE LIGHT E TO SE UPSLOPE FLOW EVIDENT AT H8 ON THE ECMWF RESULT IN
HEAVIER UPSLOPE PCPN AND/OR PCPN DEVELOPING ALONG THE ELEVATED H8
FRONTAL BOUNDARY? THE ELEVATED ASCENT LOOKS PARTICULARLY GOOD FRIDAY
INTO SATURDAY AS A SFC WAVE MOVES UP THE BNDRY.

ATTM IT/S A TOUGH CALL. I PLAN TO CARRY HIGH CHANCE POPS THURSDAY
NIGHT THROUGH SUNDAY. I WILL KEEP THE MENTION OF POTENTIAL HEAVY
RAIN IN THE HWO AS WELL...THOUGH WE WILL NEED TO SEE A LITTLE MORE
MODEL CONSISTENCY BEFORE GOING WITH HIGHER PROBABILITIES IN THE
ZONES. IN OTHER WORDS...CONFIDENCE ISN/T HIGH AT THIS POINT THOUGH
THERE CERTAINLY MAY BE A HEAVY RAIN THREAT LATER IN THE WEEK.
BETTING AGAINST HEAVY RAIN THIS YEAR HAS NOT WORKED OUT VERY WELL.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
AT KCLT...MOST GUIDANCE APPEARED TOO OPTIMISTIC WITH CIGS...AND
MODEL TIME HEIGHTS WOULD SUGGEST LOW VFR CIGS FOR MUCH OF THE
FORECAST PERIOD...ONCE HEATING AND LIFT LEVERAGE LOW LEVEL MOISTURE.
THUNDERSTORM CHANCES ARE HIGH ENOUGH TO CARRY IN THE FORECAST THIS
AFTERNOON...WITH MVFR VSBY POSSIBLE. AT THIS TIME A BLEND OF MODEL
DATA WOULD FAVOR LOW VFR VSBY AT DAYBREAK TUESDAY...BUT A DIRECT HIT
BY A THUNDERSTORM THIS AFTERNOON OR EVENING COULD MOISTEN THE GROUND
ENOUGH TO SUPPORT LOWER VSBY AT DAWN. LIGHT SW WINDS WILL PERSIST.

ELSEWHERE...CONVECTION IS ALREADY DEVELOPING IN THE MOUNTAINS...AND
IS EXPECTED TO MOVE OFF THE BLUE RIDGE LATER THIS AFTERNOON. ALL
SITES WILL HAVE A MENTION OF THUNDER...WITH MVFR VSBY. MODEL TIME
HEIGHTS SUGGEST THAT LOW VFR CIGS SHOULD PREVAIL...EXCEPT AT
DAYBREAK TUESDAY WHEN KAVL IS EXPECTED TO BE MVFR. GUIDANCE FAVORS
IFR FOG AT DAYBREAK IN KAVL...AND MVFR AT KAND AND KHKY...WITH LOW
VFR AT GAP AND VFR AT KGMU. LIGHT NW WINDS WILL BACK TO SW THIS
AFTERNOON.

OUTLOOK...A COLD FRONT IS EXPECTED TO CROSS THE WESTERN CAROLINAS
AND NORTHEAST GEORGIA TUESDAY...ACCOMPANIED BY THUNDERSTORMS AND
ASSOCIATED RESTRICTIONS. RESTRICTIVE CEILINGS AND VISIBILITY MAY
BECOME A COMMON OCCURRENCE EACH NIGHT FROM WEDNESDAY THROUGH THE
WEEKEND AS A FRONT STALL NEAR THE AREA AND INTERACTS WITH GULF OR
ATLANTIC MOISTURE.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       LOW   58%     HIGH  82%     HIGH  84%     MED   73%
KHKY       HIGH 100%     HIGH 100%     HIGH  94%     MED   75%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     MED   79%

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...DEO
NEAR TERM...JAT
SHORT TERM...MCAVOY
LONG TERM...MCAVOY
AVIATION...JAT

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1028 AM EDT MON AUG 12 2013

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-131430-
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-
1028 AM EDT MON AUG 12 2013

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

.DAY ONE...TODAY AND TONIGHT.

SCATTERED TO NUMEROUS THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER
THE AREA AGAIN THIS AFTERNOON. THE MAIN HAZARDS WILL BE DAMAGING
WIND GUSTS...LOCALLY HEAVY RAINFALL AND PERHAPS FLASH FLOODING...
AND FREQUENT CLOUD TO GROUND LIGHTNING.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

NUMEROUS TO WIDESPREAD THUNDERSTORMS ARE FORECAST TO DEVELOP ACROSS
THE REGION ON TUESDAY AHEAD OF A COLD FRONT. SEVERAL OF THESE
STORMS MAY PRODUCE DAMAGING WIND GUSTS AND EXCESSIVE
RAINFALL...ESPECIALLY ACROSS THE PIEDMONT DURING THE AFTERNOON.

THE COLD FRONT IS EXPECTED TO BECOME STATIONARY OVER OR NEAR THE
PIEDMONT LATER IN THE WEEK. SEVERAL WAVES OF LOW PRESSURE
DEVELOPING OVER THE TENNESSEE VALLEY AND GULF COAST REGION MAY
INTERACT WITH TROPICAL MOISTURE TO PRODUCE SEVERAL PERIODS OF
HEAVY RAINFALL LATE THIS WEEK. THERE IS STILL CONSIDERABLE
UNCERTAINTY AS TO THE EVOLUTION OF THE WEATHER PATTERN LATE THIS
WEEK. STAY TUNED TO NOAA ALL HAZARDS WEATHER RADIO OR LOCAL NEW
MEDIA FOR THE LATEST INFORMATION.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE REQUESTED TO FORWARD ANY REPORTS OF LARGE
HAIL...DAMAGING WINDS...TORNADOES OR FLASH FLOODING TO OUR OFFICE.

07

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
416 PM EDT MON AUG 12 2013

SCZ002-005-006-010-122100-
ANDERSON-GREATER GREENVILLE-GREATER PICKENS-PICKENS MOUNTAINS-
416 PM EDT MON AUG 12 2013

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL GREENVILLE...EASTERN
PICKENS AND NORTHEASTERN ANDERSON COUNTIES THROUGH 500 PM EDT...

AT 415 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR PICKENS...MOVING EAST AT 10 MPH.

PEOPLE IN CENTRAL GREENVILLE...EASTERN PICKENS AND NORTHEASTERN
ANDERSON COUNTIES...INCLUDING THE FOLLOWING LOCATIONS...

PICKENS AND EASLEY...

SHOULD MONITOR THE WEATHER SITUATION CLOSELY. LISTEN FOR POSSIBLE
WARNINGS AND BE PREPARED TO TAKE APPROPRIATE ACTION SHOULD SEVERE
WEATHER THREATEN.

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

THE COMBINATION OF GUSTY WINDS AND WET SOIL CONDITIONS WILL CAUSE
SCATTERED TREES AND POWER LINES TO FALL. SEEK SHELTER INSIDER AN
INTERIOR ROOM.

LAT...LON 3485 8279 3500 8276 3500 8254 3499 8254
      3497 8254 3500 8247 3500 8244 3473 8246
      3472 8253

MOORE