Severe Thunderstorm Warning 309, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
152 PM EDT THU AUG 22 2013

.SYNOPSIS...
WEAK HIGH PRESSURE WILL LINGER OVER THE AREA INTO EARLY FRIDAY WHEN
A COLD FRONT BEGINS TO MOVE INTO THE AREA. THE COLD FRONT IS
EXPECTED TO CROSS THE REGION FRIDAY NIGHT INTO SATURDAY...USHERING
IN DRIER WEATHER FOR THE WEEKEND. HIGH PRESSURE THEN BUILDS BACK IN
FOR THE FIRST PART OF THE WEEK...BEGINNING A GRADUAL WARMING TREND.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 1140 AM EDT THURSDAY...A COUPLE OF THE CONVECTION ALLOWING
MODELS DEVELOP A LINE OF THUNDERSTORMS ACROSS THE NC AND NRN SC
FOOTHILLS LATER THIS AFTN AND PUSH IT TO THE SE INTO THE EVENING
HOURS. THIS HAPPENS AS PVA INCREASES ACROSS THE FA BETWEEN 21-00
UTC. THERE IS NO INHIBITION EVIDENT ON THE MORNING SOUNDINGS WHEN
THEY ARE MODIFIED FOR CONDITIONS LATER IN THE DAY. FOR NOW I/VE
ADDRESSED THIS BY INCREASING POPS INTO THE LOW END OF THE CHANCE
RANGE OUT ACROSS THE NC FOOTHILLS AND PIEDMONT AND THE NE PIEDMONT
OF SC WHERE BEFORE WE HAD SLIGHT CHANCES. I ALSO UPPED MAX TEMPS
AROUND 3 DEGREES FOR THIS AFTN...PUSHING 90 OVER PARTS OF THE
PIEDMONT.

AS OF 910 AM EDT THURSDAY...FOG HAS LIFTED OVER THE FA FOR THE MOST
PART AND THE DENSE FOG ADVISORY WAS ALLOWED TO EXPIRE. THERE IS
STILL QUITE A BIT OF LOW STRATUS OVER THE NC PIEDMONT AND
FOOTHILLS...THOUGH DOWNSLOPE FLOW SHOULD HELP THAT TO BURN OFF
QUICKLY. SCATTERED SHRA ARE AFFECTING EXTREME NE GA ATTM. AS THESE
SHOWERS ARE ALMOST CERTAINLY ELEVATED...THEY SHOULD WEAKEN AS MIXING
DEEPENS THIS MORNING.

AS OF DAYBREAK...THE PATCHES OF DENSE FOG OVER THE NC FOOTHILLS AND
PARTS OF THE UPSTATE HAVE GRADUALLY MORPHED INTO MORE OF A VERY LOW
STRATUS DECK. SOME LOCATIONS IN AND AROUND THE ADVISORY STILL HAD
VISBY OF 1/2 MILE OR LESS...SO THE ADVISORY WILL BE ALLOWED TO RUN
ITS COURSE. MEANWHILE...SHOWERS WERE BLOSSOMING OVER THE HIGHER
TERRAIN OF N GEORGIA/SE TN/SW NC. WILL RAMP UP THE POP A BIT EARLIER
OVER THE SOUTHERN MTNS AND NE GEORGIA AS A RESULT. THIS ACTIVITY
MIGHT FIND DIFFICULTY MOVING E OF THE MTNS.

WATER VAPOR IMAGERY SHOWS THE AXIS OF AN UPPER TROF MOVING ACROSS
THE WESTERN CAROLINAS EARLY THIS MORNING. IN THE WAKE OF THIS
FEATURE...MID AND UPPER LEVELS SHOULD BECOME DECIDEDLY UNFAVORABLE
FOR DEEP CONVECTION TODAY E OF THE MTNS...WITH MID LEVEL DNVA AND
Q-DIVERGENCE. THE LOW LEVEL FLOW WILL ALSO VEER AROUND TO SOMETHING
MORE WESTERLY...THUS THE DOWNSLOPE WILL ALSO NOT PROVIDE ANY
SUPPORT. THE MOSGUIDE POP FOR TODAY WAS UNDER 15 PERCENT FOR MOST OF
THE REGION. THE NEW FCST FOLLOWS THAT TREND BUT DOES NOT GIVE UP
ENTIRELY E OF THE MTNS IN ORDER TO MAINTAIN SOME CONTINUITY. THE
MTNS STAND THE BEST CHANCE OWING TO DIFFERENTIAL HEATING...BUT THAT
WAS LIMITED TO 30-40 PCT. WHAT MANAGES TO DEVELOP WILL HAVE SOME
SEVERE POTENTIAL BECAUSE OF STEEP THETA E LAPSE RATES WITH DRY MID
LEVELS. TEMPS WILL REBOUND THIS AFTERNOON TO SOMETHING ABOUT FIVE
DEGREES WARMER THAN YESTERDAY. SHOWERS SHOULD TAPER OFF DURING THE
EARLY EVENING. BEYOND THAT...THE NAM SHOWS SOME POTENTIAL FOR AN MCS
REMNANT TO MAKE A RUN TOWARD THE NC MTNS AROUND DAYBREAK FRIDAY.
WILL HINT AT THAT WITH AN INCREASE IN POP LATE ALONG THE TN BORDER.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
AS OF 300 AM THURSDAY...A COLD FRONT WILL PUSH INTO THE AREA FROM
THE N ON FRIDAY. IT WILL HAVE PLENTY OF MOISTURE AND INSTBY TO WORK
WITH PER MODEL CONSENSUS...DESPITE A LGT NLY LLVL FLOW. IN FACT...AS
THE FRONT BECOMES MORE OF A BACKDOOR BNDRY...LLVL CONVERGENCE IS
ENHANCED ACRS THE I-85 CORRIDOR LATE IN THE DAY...WITH MUCAPE OF
2000+ J/KG. SO EXPECT DECENT COVERAGE OF SHWRS AND TSTMS...WITH A
FEW ISOLD SEVERE STORMS POSSIBLE. TEMPS WILL BE NEAR NORMAL IN THE
70S TO LWR 80S IN THE MTNS...AND GENERALLY MID-UPR 80S ACRS THE
PIEDMONT.

CONVECTION SHUD DIMINISH AND PUSH S OF THE AREA DURING THE EVENING
HOURS. TEMPS WILL BE NEAR NORMAL WITH LINGERING CLOUDINESS WITH THE
PASSAGE OF THE BACKDOOR FRONT.

ON SATURDAY...THE FRONT SHUD PUSH THRU THE AREA...BUT THE LINGERING
MOISTURE NEAR ITS VICINITY MAY BE ENUF FOR SOME INSTBY WITH DAYTIME
HEATING AND ELY UPLSOPE FLOW ACRS THE SRN BLUE RIDGE AND UPR
SAVANNAH VLY. MOST OF THE AREA WILL PROBABLY BE DRY WITH SEASONABLY
COOL AFTN TEMPS...A CATEGORY OR TWO BELOW NORMAL. CLOUDS MAY LINGER
INTO SATURDAY NIGHT WITH ELY LLVL FLOW...BUT COOL NELY BL FLOW SHUD
ALLOW TEMPS TO DROP A CATEGORY BELOW NORMAL.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 215 PM THURSDAY...A STRONG UPPER RIDGE WILL BE CENTERED OVER
THE MID MS RIVER VALLEY ON MONDAY...WITH SURFACE HIGH PRESSURE
LOCATED FROM THE SOUTHERN APPALACHIANS...EASTWARD INTO THE ATLANTIC.
THE UPPER HIGH WILL PERSIST THROUGH THE WEEK WHILE THE SURFACE HIGH
WILL BE GRADUALLY SUPPRESSED SOUTHWARD OVER TIME AS AN UPPER TROUGH
DIGS ALONG THE EAST COAST BY LATE IN THE WEEK. A BACKDOOR COLD FRONT
WILL APPROACH THE AREA FROM THE NORTH BY LATE WEEK.

PRECIPITATION WILL BE SUPPRESSED THROUGH MID WEEK AS MID LEVEL
WARMING CAPS CONVECTION. SOME ISOLATED UPDRAFTS MAY BREAK THROUGH
THE CAP OVER THE HIGH ELEVATIONS EACH AFTERNOON MON-WED...BUT POPS
WILL BE BELOW CLIMO THROUGH WED. THE APPROACHING FRONT ON THU AND
DIMINISHING MID LEVEL CAPPING INVERSION WILL ALLOW CONVECTIVE CHANCES
TO INCREASE THU AFTERNOON WITH POPS NEAR CLIMO. TEMPS WILL START OFF
THE PERIOD ABOUT A CATEGORY BELOW AVERAGE...BUT INCREASE NEAR NEAR
NORMAL BY MIDWEEK...AND THEN A LITTLE ABOVE NORMAL BY LATE WEEK.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AT KCLT...SOME MODELS SHOW THUNDERSTORMS DEVELOPING OVER THE NC
FOOTHILLS AND APPROACHING THE AIRFIELD BY LATE AFTN. A FEW SHRA ARE
DEVELOPING OVER THIS AREA NOW...AND IT/S CERTAINLY POSSIBLE THAT
CONVECTION WILL INCREASE IN COVERAGE AND INTENSITY. CONFIDENCE ISN/T
THAT HIGH HOWEVER AND I/VE STUCK WITH VCSH STARTING AT 21 UTC. NOT
EXPECTING AS MUCH FOG OR STRATUS TONIGHT...THOUGH MVFR VSBYS ARE
FAVORED BY THE GUIDANCE WHICH IS WHAT I/VE CARRIED. THERE IS A
BETTER CHANCE OF STORMS ON FRIDAY...THOUGH IT LOOKS TO BE JUST AFTER
THE VALID PERIOD OF THE TAF.

ELSEWHERE...CARRIED TEMPO GROUPS FOR THUNDER OVER THE UPSTATE AS
SHOWERS AND TSTMS ARE ORGANIZING OVER THE SC MTNS ATTM AND THEY
SHOULD GRADUALLY MOVE OUT TO THE EAST. ADDED A SHORTER DURATION
TEMPO AT KAVL. KHKY IS DRYING OUT A LITTLE AND I/M NOT EXPECTING AS
MUCH COVERAGE THERE. PATCHY STRATUS IS POSSIBLE
OVERNIGHT...ESPECIALLY WHERE HEAVIER RAIN FALLS. HOWEVER...THE MODEL
CONSENSUS LOOKS BE FOR LESS IN THE WAY OF RESTRICTIVE CIGS/VSBYS AND
I HAVE ONLY CARRIED MVFR FOG OVER THE FOOTHILLS AND PIEDMONT. KAVL
STILL LOOKS AS THOUGH THEY WILL SEE MORE WIDESPREAD VALLEY FOG AND
STRATUS...UNLESS HIGH CLOUDS SPREAD IN SHORTLY AFTER MIDNIGHT.

OUTLOOK...A DRIER PATTERN IS EXPECTED AS HIGH PRESSURE GRADUALLY
BUILDS IN FROM THE NORTH. LINGERING MOISTURE AND UPSLOPE FLOW MAY
RESULT IN MORNING RESTRICTIONS IN LOW CLOUDS AND FOG EARLY SATURDAY.
BUT CONSIDERABLY DRIER CONDITIONS ARE EXPECTED SATURDAY NIGHT INTO
NEXT WEEK.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH  97%     HIGH  97%
KGSP       HIGH 100%     HIGH 100%     HIGH  94%     HIGH 100%
KAVL       HIGH 100%     HIGH  94%     MED   74%     LOW   55%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  97%
KGMU       HIGH 100%     HIGH 100%     HIGH  97%     HIGH  97%
KAND       HIGH 100%     HIGH 100%     HIGH  97%     HIGH  94%

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...PAT
NEAR TERM...MCAVOY/PM
SHORT TERM...ARK
LONG TERM...LG
AVIATION...MCAVOY

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1146 AM EDT THU AUG 22 2013

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-231600-
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-
1146 AM EDT THU AUG 22 2013

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 SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
THE REGION THIS AFTERNOON INTO THIS EVENING. THE MAIN THREATS WILL
BE TORRENTIAL DOWNPOURS AND CLOUD TO GROUND LIGHTNING. HOWEVER...AN
ISOLATED MICROBURST THREAT CANNOT BE RULED OUT IN THE STRONGEST
STORMS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

A COLD FRONT WILL PUSH INTO THE AREA FROM THE NORTH FRIDAY
AFTERNOON INTO FRIDAY NIGHT. SCATTERED THUNDERSTORMS ARE EXPECTED
ALONG AND AHEAD OF THE FRONT...WITH A FEW POSSIBLY PRODUCING LARGE
HAIL AND DAMAGING WIND GUSTS.

.SPOTTER INFORMATION STATEMENT...

NONE.

07

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1254 PM EDT THU AUG 22 2013

SCZ001-221730-
OCONEE MOUNTAINS-
1254 PM EDT THU AUG 22 2013

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN OCONEE COUNTY
THROUGH 130 PM EDT...

AT 1249 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR LAKE JOCASSEE...OR 16 MILES NORTH OF
WALHALLA...MOVING SOUTHEAST AT 5 MPH.

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

CLOUD TO GROUND LIGHTNING AND GUSTY WINDS WILL CREATE DANGEROUS
BOATING CONDITIONS ON LAKE JOCASSEE. MOVE TO SHORE IMMEDIATELY.

LAT...LON 3503 8299 3501 8292 3499 8294 3497 8292
      3494 8290 3487 8296 3499 8304

LANE

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
214 PM EDT THU AUG 22 2013

GAZ017-018-026-221900-
FRANKLIN-HABERSHAM-STEPHENS-
214 PM EDT THU AUG 22 2013

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN HABERSHAM...
SOUTHWESTERN STEPHENS AND WESTERN FRANKLIN COUNTIES THROUGH 300 PM
EDT...

AT 211 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR MOUNT AIRY...OR 8 MILES SOUTH OF
CLARKESVILLE. THIS STORM WAS NEARLY STATIONARY.

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

LAT...LON 3458 8349 3450 8329 3437 8337 3438 8339
      3442 8339 3446 8340 3448 8347 3448 8351
      3449 8354

LG