Severe Thunderstorm Warning 77, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
240 PM EDT TUE MAY 5 2009

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN OVER THE AREA INTO EARLY
WEDNESDAY...EXTENDING FROM THE CENTRAL GULF STATES TO THE MID
ATLANTIC COAST. WEAK DISTURBANCES WILL PROPAGATE ALONG THE BOUNDARY
FROM WEST TO EAST...BEFORE THE BOUNDARY LIFTS NORTH OF THE AREA
WEDNESDAY EVENING. A COLD FRONT WILL PUSH INTO THE AREA
THURSDAY...AND STALL OVER THE SOUTHEAST STATES THROUGH SATURDAY.
HIGH PRESSURE WILL THEN BUILD INTO THE AREA FROM THE WEST FOR SUNDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
THE BACKDOOR SURFACE BOUNDARY STRETCHES ROUGHLY FROM CHARLOTTE TO
RUTHERFORDTON TO THE NRN NC MTNS THIS AFTERNOON. UPPER DIVERGENCE IS
STILL EXPECTED TO INCREASE AND HELP FOCUS CONVECTION ALONG AND SOUTH
OF THE BOUNDARY ACROSS THE PIEDMONT...WHILE THE POTENT H5 VORT
BRUSHING THE NW PART OF THE CWFA CONTINUES TO TRIGGER MOUNTAIN AND
FOOTHILL CONVECTION THROUGH THE LATE AFTERNOON. COVERAGE FROM THE
UPPER FORCING MAY BE A LITTLE HIGHER THROUGH THE EVENING ACROSS THE
NRN TIER...BUT SCATTERED TO NUMEROUS TSTMS WILL LIKELY BE STRONGER
SOUTHEAST OF INTERSTATE 85 WHERE LAPS CAPES ARE SHOWING VALUES OF
2000 TO 3000 J/KG. THE MORE SIGNIFICANT TRAINING CONVECTION WITH THE
MCS OVER GA/SRN SC WILL REMAIN SOUTHEAST OF THE FORECAST AREA.
LIKELY POPS WILL BE CARRIED INTO THE EARLY EVENING HOURS...EXCEPT
HIGH END CHC IN SW SECTIONS WHERE THERE IS LESS TRIGGERING. ISOLATED
SEVERE REMAINS POSSIBLE GIVEN THE RELATIVELY LOW FREEZING LEVELS AND
30 KT OF SFC TO 3 KM SHEAR.

A BRIEFLY ZONAL FLOW WILL DEVELOP BEHIND THE PASSING UPPER DYNAMICS
OVERNIGHT. THE SURFACE BOUNDARY SHOULD SAG SLIGHTLY FARTHER SOUTH TO
BISECT THE FORECAST AREA BY MORNING. SLIGHT COOLING IS POSSIBLE
ALONG THE NRN TIER...BUT MOST LOCATIONS WILL SEE ANOTHER WARM NIGHT.
ISOLATED TO SCATTERED SHOWERS COULD PERSIST OVERNIGHT IN THE MOIST
AIRMASS NEAR THE LURKING BOUNDARY. THE UPSTREAM TROUGH WILL THEN
SHARPEN UP QUICKLY THROUGH THE DAY ON WED. UPPER SUPPORT WILL
INCREASE FROM THE W THROUGH THE AFTN HOURS AND THE BOUNDARY SHOULD
LIFT BACK NORTH AS A WARM FRONT AS LOW PRESSURE MOVES THROUGH SE KY.
850 MB FLOW WILL BACK TO SOUTHERLY THROUGH THE AFTERNOON AND
INCREASE IN MAGNITUDE. THE COMBINATION OF GOOD UPPER DYNAMICS...DEEP
LAYER SHEAR...AND MODERATE INSTABILITY WILL HEIGHTEN THE SEVERE TSTM
THREAT. WILL CONTINUE TO ADVERTISE THIS POTENTIAL IN THE HWO.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 200 PM TUESDAY...UNSETTLED WEATHER PATTERN WILL CONTINUE IN
THE SHORT TERM AS QUASI-STATIONARY BOUNDARY REMAINS IN THE VICINITY
ALONG WITH ZONAL FLOW ALOFT WITH EMBEDDED WAVES. A DISTINCT SHORT
WAVE WILL CROSS THE REGION WED NIGHT. WIDESPREAD SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO ACCOMPANY THIS FEATURE...WITH MODERATE
TO EVEN HEAVY RAINFALLY. HOWEVER...IT LOOKS LIKE ANY EXCESSIVE
RAINFALL WILL BE LOCALIZED IN AREAS OF UPSLOPE ENHANCEMENT.
AS WAVE MOVES TO THE EAST LATE WED NIGHT...PRECIP SHOULD END FROM W
TO E WITH A WEAK FRONT SETTLING S TO A POSITION SOMEWHERE ACROSS THE
SOUTHERN PIEDMONT. BOTH GFS/NAM ARE SIGNALING THAT CONVECTION ON THU
SHOULD BE SUPPRESSED AS A MESO HIGH DEVELOPS IN THE WAKE OF
AFOREMENTIONED WAVE. HENCE...WILL LIMIT SCATTERED TYPE POPS TO OVER
THE SOUTHERN PIEDMONT IN THE VICINITY OF SURFACE BOUNDARY. MODELS
ALSO INDICATE THAT IT SHOULD REMAIN QUIET THU NIGHT AS SURFACE
BOUNDARY DISSIPATES AND WINDS TURN SW. ANOTHER WAVE IS FORECAST TO
MOVE ACROSS THE AREA ON FRI WHICH SHOULD PRODUCE AT LEAST SCATTERED
CONVECTION. SURFACE BOUNDARY BECOMES STATIONARY AGAIN ACROSS THE
AREA FRI NIGHT WHICH WILL SERVE AS A FOCUS FOR MORE CONVECTION
POSSIBLY LATE FRI NIGHT AS ANOTHER UPPER WAVE APPROACHES FROM THE W.
WILL HAVE SOLID CHANCE POPS OVER THE W FOR FRI NIGHT.

TEMPERATURES WILL REMAIN WARM WITH MAX TEMPS A CATEGORY OR SO  ABOVE
AVERAGE. USED A MOS BLEND FOR MAX/MIN TEMPS...EXCEPT GMOS FOR
FRI.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 220 PM TUESDAY...THE EXTENDED RANGE EXHIBITS FAIRLY GOOD
CONFIDENCE AS FAR AS THE TIMING AND PLACEMENT OF THE SAT/SUN COLD
FRONT. THE ECMWF IS ACTUALLY THE OUTLIER AND QUICKER THAN THE OTHER
OP MODELS...HOWEVER THERE IS GOOD AGREEMENT BTW THE 12Z GFS MEAN H5
AND IT/S ENS MEMBERS AND WITH THE 00Z GGEM. THE ECMWF IS LOOKING
RATHER BULLISH WITH THE RETURN OF AN ACTIVE WARM FRONT TO THE CWFA
BY 12Z MON AND THIS SOLN HAS BEEN THROWN OUT ALL TOGETHER. DO EXPECT
SOME TYPE OF RETURN FLOW...BUT FOR NOW WILL GO WITH THE STRONGER LOW
TO MID LEVEL RIDGE ADVERTISED BY THE GFS.

THE TIMING OF THE THE FROPA WILL BE THE KEY SAT AS A HIGHLY UNSTABLE
AIRMASS WILL DEVELOP BY MID AFTERNOON. THE BEST DEEP LAYERED SHEAR
WILL BE NORTH OF THE REGION...HOWEVER SBCAPES WILL RISE TO AROUND
1200 J/KG WHILE H7-H5 LAPSE RATES WILL BE NEAR 8 C. THE FRONT ITSELF
WILL BE RATHER WEAK...HOWEVER THE LLVL CONVERGENCE PRODUCED SHOULD
BE MORE THAN ENOUGH TO HELP GENERATE A QLCS SITUATION WITH PROBABLE
ISOLATED AREAS OF SEVERE WX...MAINLY DAMAGING WINDS DUE TO THE DRY
AIR ALOFT AND THE HIGH FREEZING LEVELS PREVENTING MUCH OF A
SIGNIFICANT HAIL THREAT.

WILL EXPECT A MODERATE AIRMASS CHANGE BY 12Z SUN AND WILL COUNT ON
HIGH PRESSURE BUILDING IN FROM THE NORTH...SLOWLY MODIFYING THROUGH
MON. THE LVLV WIND FIELD WILL BE RELATIVELY WEAK...YET A WARMING
DOWNSLOPE COMPONENT SHOULD ADD A COUPLE DEGREES TO THE MAX AND ALLOW
HIGHS TO REACH A FEW DEGREES ABOVE NORMAL SUN AND MON. WILL REMAIN
ON THE 12Z GFS BANDWAGON FOR THE PATTERN TRANSITION MON. THE IDEA OF
BRINGING A DRY WARM FRONT...MAINLY MID/UPPER LEVEL CLOUDS...TO THE
REGION IS PLAUSIBLE AND WILL ANTICIPATE LLVL MOISTURE TRANSPORT
VECTORS TO REMAIN NON/SOUTHERLY UNTIL 03Z TUE. THIS COULD BE SETTING
UP ANOTHER STRONG TO SEVERE EVENT FOR TUE AS THE THERMAL GRADIENT
TIGHTENS ACROSS THE EASTERN PART OF THE CWFA AND GOM MOISTURE FLOW
INCREASES INTO THE CONVERGENT ZONE. ALL IN ALL...A NORMAL SPRING
TIME PATTERN IS EXPECTED TO CONTINUE THROUGH THE EXTENDED AND
BEYOND.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
IFR TO MVFR CONDITIONS CONTINUE ALONG AND NORTH OF THE FRONTAL
BOUNDARY FROM KCLT TO KHKY. SKIES HAVE SCATTERED A BIT MORE FARTHER
TO THE SOUTH...BUT SHOULD FILL BACK IN WITH CONVECTIVE CUMULUS AS
UPPER FORCING INCREASES LATER THIS AFTERNOON AND OUTFLOWS DEVELOP.
WINDS SHOULD REMAIN SOUTHERLY FROM KAND TO KGSP TO KGMU THROUGH THE
PERIOD...ALTHOUGH THE BACKDOOR FRONT COULD FLIRT WITH KGSP LATE
TONIGHT. N TO NE WINDS ARE EXPECTED FROM KHKY TO KCLT...WITH
VARIABLE FLOW IN THE FRENCH BROAD VALLEY NEAR KAVL. CEILINGS WILL
LIKELY FALL BACK THROUGH THE MVFR RANGE TO IFR THROUGHOUT BY LATE
TONIGHT. ANY TSTMS REMAIN VERY DIFFICULT TO TIME...AS JUST ABOUT ANY
LOCATION COULD EXPERIENCE A SHOWER AT JUST ABOUT ANY TIME THE NEXT
24 HOURS...AND ANY SHOWER COULD BECOME A THUNDERSTORM.

AT KCLT...TCLT RADAR SHOWS BOUNDARY OVERHEAD AT 18Z. HAVE ADJUSTED
WIND DIRECTIONS TO NORTHERLY THIS AFTN...WITH A NE COMPONENT JUST
BEHIND THE FRONT OVERNIGHT...ALBEIT LIGHT. THE NE FLOW WILL LIKELY
KEEP MVFR CIGS IN PLACE AND A RETURN TO IFR CONDITIONS IS EXPECTED
BY 08Z. THE BEST CHANCE OF STRONGER THUNDERSTORMS IN THE VICINITY
WILL BE FROM BETWEEN 21Z AND 03Z. WINDS WILL RETURN TO LIGHT S OR SE
AS THE BOUNDARY LIFTS BACK NORTH AS A WARM FRONT WED.

OUTLOOK...STRONG THUNDERSTORMS MAY DEVELOP THROUGH WEDNESDAY NIGHT
ACROSS THE REGION AS THE FRONT REMAINS IN THE VICINITY WITH LOW PRES
MOVING EAST ALONG IT. THE FRONT WILL PUSH SE OF THE AREA THURSDAY TO
PROVIDE SOME DRYING. ANOTHER FRONT WILL PUSH SE INTO THE AREA FRIDAY
AND REMAIN THROUGH THE WEEKEND. ANOTHER ROUND OF SHOWERS AND MVFR TO
IFR CONDITIONS CAN BE EXPECTED FRI TO SUN.

&&

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

&&

SYNOPSIS...SBK
NEAR TERM...HG
SHORT TERM...LG
LONG TERM...SBK
AVIATION...HG

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
336 PM EDT TUE MAY 5 2009

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-061945-
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-
336 PM EDT TUE MAY 5 2009

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 TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL DEVELOP
ACROSS THE WESTERN CAROLINAS AND NORTHEAST GEORGIA THIS AFTERNOON
AND EVENING. ISOLATED SEVERE STORMS ARE POSSIBLE.THE MAIN THREAT
WILL BE LARGE HAIL AND DAMAGING WIND GUSTS.

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

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
DEVELOP ACROSS THE WESTERN CAROLINAS AND NORTHEAST GEORGIA ON
WEDNESDAY...ESPECIALLY IN THE AFTERNOON AND EVENING. THERE IS A
SLIGHT RISK FOR SEVERE THUNDERSTORMS...WITH THE MAIN THREAT BEING
LARGE HAIL AND DAMAGING WINDS. ISOLATED TORNADOES WILL BE POSSIBLE
AS WELL. LOCALLY HEAVY RAIN IS ALSO POSSIBLE WEDNESDAY EVENING
WHICH COULD CREATE SOME LOCALIZED FLOODING.

.SPOTTER INFORMATION STATEMENT...

NONE.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
456 PM EDT TUE MAY 5 2009

NCZ070-052130-
GASTON-
456 PM EDT TUE MAY 5 2009

...A STRONG THUNDERSTORM WILL AFFECT GASTON COUNTY THROUGH 530 PM
EDT...

AT 456 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR CROWDERS...OR 6 MILES SOUTHWEST OF
GASTONIA...MOVING NORTHEAST AT 20 MPH.

PEOPLE IN GASTON COUNTY...INCLUDING THE FOLLOWING LOCATIONS...

GASTONIA...CRAMERTON...LOWELL...BELMONT AND MOUNT HOLLY...

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

WIND GUSTS OF 30 TO 40 MPH ARE EXPECTED WITH THIS STORM.

BSH