Severe Thunderstorm Warning 173, NWS Columbia, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
ISSUED BY NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1041 AM EDT TUE AUG 11 2009

.SYNOPSIS...
AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL WEAKEN AND SHIFT WEST
THIS WEEK...WHILE AN UPPER LEVEL TROUGH DEVELOPS OVER THE REGION.
THIS TROUGH...IN ADDITION TO INCREASING ATMOSPHERIC MOISTURE AND
AN APPROACHING FRONTAL BOUNDARY...WILL INCREASE OUR RAIN CHANCES
WEDNESDAY THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
SFC ANALYSIS AT 14Z INDICATES A TROF ACROSS THE NRN TIER OF THE
FORECAST AREA. MESOSCALE MODELS SLIDE THE TROF SLOWLY EAST ACROSS
THE MIDLANDS THROUGH THE AFTERNOON AND INTO THE EVENING.
ALOFT...H5 RIDGE AXIS WILL CONTINUE TO PIVOT SOUTH...LEAVING THE
CWA UNDER ZONAL FLOW BY 21Z. BASED ON OBS TRENDS AND LATEST MOS...HIGH
TEMPERATURES SHOULD EASILY REACH THE U90S...A LITTLE LOWER THAN
MONDAY. DEWPOINTS WILL LIKELY REMAIN IN THE U60S THIS
AFTERNOON...YIELDING HEAT INDEX VALUES BETWEEN 100-103 FOR 2-3
HOURS THIS AFTERNOON.

SFC CONVERGENCE WITHIN THE ADVANCING TROF AXIS MAY PROVIDE ENOUGH
LIFT TO OVERCOME WEAK LLVL CIN BY MID AFTERNOON. BASED ON THE
TIMING OF THE TROF...IT APPEAR THAT DEEP CONVECTION WILL INITIATE
ALONG AND EAST OF I-20 BETWEEN 18-21Z. CONVECTIVE CLUSTERS AND
OUTFLOW BOUNDARIES ORIGINATING OVER THE MTNS MAY ARRIVE OVER THE
CWA BETWEEN 21-0Z...RESULTING IN ANOTHER WAVE OF SCT CONVECTION. I
WILL FAVOR SCT COVERAGE OVER THE SAVANNAH RIVER VALLEY BETWEEN
18-21Z...INCREASING SCT COVERAGE ACROSS THE ENTIRE CWA BY 0Z. 12Z
OBSERVED SOUNDINGS INDICATE VERY HIGH FZLVLS NEAR 16 KFT WITH WBZ
OVER 13 KFT. MODERATE CAPE VALUES MAY SUPPORT ONE OR TWO HAIL
EVENTS...HOWEVER...ISO WET MICROBURST APPEARS THE MOSTLY LIKELY
THREAT WITH THESE TSRA.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
OPERATIONAL MODELS ARE IN FAIR AGREEMENT IN LOWERING 500MB HEIGHTS
OVER THE FORECAST AREA ON WEDNESDAY IN RESPONSE TO AN UPPER TROUGH
MOVING INTO THE SOUTHERN OHIO VALLEY AND APPALACHIAN REGION. NAM
IS A BIT MORE AGGRESSIVE AND CUTS OFF THE UPPER LOW BY WEDNESDAY
EVENING THROUGH THURSDAY. EITHER WAY...THERE SHOULD BE INCREASED
UPPER SUPPORT IN THE FORM OF SHORTWAVE ENERGY MOVING THROUGH THE
BASE OF THE TROUGH OVER THE CAROLINAS WEDNESDAY THROUGH THURSDAY.
A WEAK FRONTAL BOUNDARY WILL ALSO PUSH INTO THE PIEDMONT AND
MIDLANDS AREA WEDNESDAY AFTERNOON...WHICH WILL PROVIDE A FOCUS FOR
CONVECTIVE DEVELOPMENT.

THE DEGREE TO WHICH THE ATMOSPHERE CAN DESTABILIZE BOTH DAYS WILL
BE DEPENDENT ON THE AMOUNT OF CLOUD COVER...BUT THERE SHOULD BE
SUFFICIENT INSTABILITY TO SUPPORT SCATTERED TO LIKELY COVERAGE OF
SHOWERS AND THUNDERSTORMS. WILL INCREASE POPS TO LIKELY WEDNESDAY
AFTERNOON AND EVENING ACROSS THE FORECAST AREA...THEN SHIFT THE
LIKELY POPS TO THE EASTERN MIDLANDS ON THURSDAY AS THE DEEPER
MOISTURE SHIFTS A BIT EAST WITH THE SURFACE BOUNDARY. TEMPERATURES
SHOULD BE QUITE A BIT COOLER IN THE LOWER 90S.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
THE FRONTAL BOUNDARY APPEARS TO WASH OUT OVER THE REGION BY THE
END OF THE WEEK...BUT ABUNDANT MOISTURE REMAINS OVER THE FORECAST
AREA. WILL CONTINUE CHANCE POPS THROUGH THE EXTENDED PERIODS WITH
INSTABILITY AND MOISTURE IN PLACE...DESPITE A SOLID TRIGGER FOR
CONVECTION. THE UPPER RIDGE BUILDS BACK OVER THE AREA BY THE END
OF THE PERIOD...WHICH SHOULD LOWER RAIN CHANCES A BIT...BUT NOT
COMFORTABLE REMOVING POPS FROM THE FORECAST. TEMPERATURES WILL BE
NEAR OR SLIGHTLY BELOW NORMAL.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
AFTER BRIEF MVFR VISIBILITIES AT AGS AND OGB THIS MORNING...EXPECT
VFR CONDITIONS THROUGH THE TAF PERIOD. MOISTURE WILL BE ON THE
INCREASE ACROSS THE REGION DURING THE DAY. WEAK LEE SIDE TROUGH WILL
SETUP THIS AFTERNOON...WHICH MAY HELP TO FOCUS SCATTERED AFTERNOON
THUNDERSTORMS...MAINLY AFTER 20Z.  ACTIVITY MAY LAST INTO THE
EVENING AND SHOULD END BY 03Z.  CONFIDENCE NOT HIGH AT ANY TAF
SITE...SO HAVE ONLY GONE CB IN TAFS FOR NOW.

PERIODS OF MVFR VISIBILITIES MAY BE ENCOUNTERED IN SHOWERS AND
THUNDERSTORMS ON WEDNESDAY.  OTHERWISE...NO SIGNIFICANT IMPACTS EXPECTED
DURING THE EXTENDED PERIOD.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE COLUMBIA SC
ISSUED BY NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1053 AM EDT TUE AUG 11 2009

GAZ040-063>065-077-SCZ015-016-018-020>022-025>031-035>038-041-121500-
LINCOLN-MCDUFFIE-COLUMBIA-RICHMOND-BURKE-LANCASTER-CHESTERFIELD-
MCCORMICK-NEWBERRY-FAIRFIELD-KERSHAW-EDGEFIELD-SALUDA-LEXINGTON-
RICHLAND-LEE-AIKEN-SUMTER-BARNWELL-ORANGEBURG-CALHOUN-CLARENDON-
BAMBERG-
1053 AM EDT TUE AUG 11 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL GEORGIA AND
CENTRAL SOUTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT

ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE THIS
THIS AFTERNOON AND TONIGHT. SOME OF THESE THUNDERSTORMS COULD BECOME SEVERE
AND PRODUCE DAMAGING WINDS...LARGE HAIL...HEAVY RAINFALL...AND
DANGEROUS CLOUD TO GROUND LIGHTNING.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
DEVELOP IN A WARM AND UNSTABLE AIRMASS DURING THE AFTERNOON HOURS
ON WEDNESDAY AND THURSDAY. SOME STORMS MAY BE STRONG TO
SEVERE...WITH THE MAIN THREATS BEING DAMAGING WINDS AND HAIL.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TODAY.