Severe Thunderstorm Warning 166, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
128 PM EDT SAT MAY 20 2006

.SHORT TERM /REST OF TODAY/...
UPDATING FORECAST TO INCLUDE DAMAGING WIND AND LARGE HAIL MENTION
WITHIN THE NEWLY ISSUED WATCH AREA. WILL ALSO PUSH POPS UP ABOUT
10 PERCENT IN THE SW MTNS WITH CONVECTION EXTENDING FROM CSV TO
CHA AT PRESENT.

&&

.PREV DISCUSSION...
 /ISSUED 1108 AM EDT SAT MAY 20 2006/

SHORT TERM /REST OF TODAY/...
MESOSCALE CONVECTIVE COMPLEX CROSSED THE FORECAST AREA OVERNIGHT
AND THAT FEATURE HAS MOVED TO THE COASTAL AREAS. ATMOSPHERE
REMAINS CONDUCIVE TO CONVECTIVE REDEVELOPMENT AND THIS AFTERNOON
COULD BE AN INTERESTING ONE OVER THE SOUTHERN HALF OF THE CWFA.

12Z SURFACE ANALYSIS SHOWS LOW PRESSURE IN WEST TENNESSEE...AND
ANOTHER CIRCULATION...A STRONGER ONE...IN NORTHWEST
ARKANSAS/SOUTHEAST MISSOURI. THESE ARE EXPECTED TO TREK STEADILY TO
THE SOUTHWEST TODAY...WITH CWFA REMAINING IN A STRONG NORTHWEST
FLOW ALOFT. AS THE SURFACE LOWS APPROACH...FRONTAL ZONE JUST NORTH
OF OUR CWFA SHOULD GET PUSHED SOUTHWARD. 12KM NAM DEVELOPS A
VORTICITY MAXIMUM OVER SOUTHERN TENNESSEE THIS AFTERNOON AND TAKES
THAT FEATURE OVER OUR WESTERN MOST AREAS THROUGH EARLY EVENING.
THE UPPER AIR ANALYSIS SHOWS A STRONGER SHORTWAVE TROF EMBEDDED IN
THE NORTHWEST FLOW...AND THAT FEATURE SHOULD KEEP SCATTERED
CONVECTION IN THE WESTERN CWFA THIS EVENING AND OVERNIGHT. UPPER
JET IS PROTRUDING INTO THE NORTH CAROLINA PORTION OF THE FORECAST
AREA ON THE 12Z UPPER AIR ANALYSIS...WITH MID LEVEL TEMPERATURES
PROJECTED TO RISE SOME ALSO.

CONVECTIVE PARAMETERS QUITE INTERESTING TODAY. BUFKIT SOUNDINGS
FOR THE SOUTHERN CWFA SHOW FAT...JUICY CAPES WITH NICE TURNING
PROJECTED ON THE SOUNDINGS AND ON HODOGRAPHS. WE ARE A BIT
CONCERNED THAT OUR SURFACE WIND AT PRESENT IS MUCH MORE
SOUTHWESTERLY THAN PROJECTED BY THE MODEL SOUNDINGS FOR THIS TIME
EARLIER CELLS THAT DEVELOPED SHOWED SOME WEAK ROTATION AND WITH
WIND FIELDS STRENGTHENING TODAY...WE THINK THERE MAY BE A BIT MORE
TURNING OF THE WIND THAN PROJECTED BY THE MODELS AS IT IS...STORM
TYPE COMING VERY CLOSE TO SUPERCELLULAR FOR THE UPSTATE AND THE
SOUTHERN PIEDMONT OF NORTH CAROLINA. IN ADDITION...A NUMBER OF WEAK
BOUNDARIES ARE NO DOUBT LURKING IN THE WAKE OF THE OVERNIGHT
MESOSCALE CONVECTIVE COMPLEX. SURFACE DEWPOINTS REMAIN IN THE 60S
ACROSS THE SOUTH...AND THE ONLY REAL SIGNIFICANT DRYING SHOULD
OCCUR IN THE NORTH LATER.

ACROSS THE SOUTHERN CWFA...DEBRIS CLOUDINESS REMAINS FROM THE
CENTRAL UPSTATE TO OUR SOUTHEAST CORNER...AND IS RIDING ALONG A
NORTHWEST-SOUTHEAST ORIENTED BOUNDARY IN PLACE WITHIN THE
NORTHWEST FLOW. SKIES HAVE CLEARED OUT NICELY ACROSS WEST
GEORGIA...THE WESTERN UPSTATE AND MOST OF THE SOUTHERN FOOTHILLS
AND PIEDMONT OF NORTH CAROLINA. BROAD MID LEVEL CLOUDS COVER THE
MOUNTAINS AND SOME OF THAT IS SHIFTING EAST INTO THE NORTHERN
FOOTHILLS AND NORTHWEST PIEDMONT. WITH TIME...WE EXPECT A GOOD
DOSE OF DAYTIME HEATING ACROSS THE SOUTHERN CWFA...WITH
TEMPERATURES ALREADY OFF TO A RATHER WARM START. LOW LEVEL
THICKNESS SCHEME SUGGESTS UPPER 80S POSSIBLE FOR THE SOUTHWEST
UPSTATE AND NORTHEAST GEORGIA THIS AFTERNOON...WITH WRF FIELDS
PROJECTING SOME LOWER 90S. IF THAT VERIFIES...WE COULD SEE CAPES
APPROACH 2500 TO 3000 J/KG...AS SHOWN ON SOME NAM PLAN VIEW
SOUNDINGS. WITH STRONG HEATING...LOW LEVEL LAPSE RATES WILL GET
QUITE STEEP...AND MID LEVEL LAPSE RATES STEEP ENOUGH FOR LARGE
HAIL. WITH FFC SOUNDING LOOKING QUITE DRY IN THE MID
LEVELS...DEWPOINTS WILL NEED TO BE WATCHED CAREFULLY AS DEEP
MIXING COULD ENSUE AND COUNTERACT THE STRONGER UPGLIDE SHAPING UP
FOR THE SOUTHERN-MOST AREAS OF THE CWFA...WHERE SOME MID 60S ARE
SHOWN IN THE GUIDANCE BY LATE DAY.

FOR THE UPDATE...WE WILL EXPAND CHANCE OF RAIN NORHTWARD TO THE
SOUTHERN PART OF THE INTERSTATE 40 CORRIDOR WITH SURFACE BOUNDARY
DROPPING SOUTH...THERE MAY BE STILL BE ENOUGH LOW LEVEL MOISTURE
TO GET SOME SHOWERS GOING THERE. COVERAGE WAS INCREASED ALL OTHER
LOCATIONS..WITH 50% CHANCE NOW FOR THE SOUTHWEST CWFA...40% FOR
THE CENTRAL AND EASTERN UPSTATE TO THE SOUTHERN FOOTHILLS AND
PIEDMONT OF NORTH CAROLINA. WE DID RAISE AFTERNOON MAXES A DEGREE
JUST ABOUT EVERYWHERE. THE STORM PREDICITON CENTER MADE NO CHANGES
TO THE SLIGHT RISK AREA ON THEIR LATEST UPDATE...WHICH STILL
INCLUDES EVERYONE IN THE FORECAST AREA SOUTH OF INTERSTATE 40.

PRESSURE GRADIENT SHOULD STRENGTHEN THROUGH THE AFTERNOON. WE WILL
FEATURE BREEZY CONDITIONS IN THE SOUTHERN CWFA AND HOLD OFF ON ANY
LAKE WIND ADVISORY FOR NOW. AS MIXING INCREASES IN THE SOUTH THIS
AFTERNOON...WIND GUSTS COULD APPROACH 30 MPH AGAIN IN SOME
LOCATIONS.

PREV DISCUSSION...
 /ISSUED 223 AM EDT SAT MAY 20 2006/

SHORT TERM /TODAY THROUGH SUNDAY/...
NAM AND WRF WERE RIGHT ON TARGET DEVELOPING WIDESPREAD CONVECTION
OVER EASTERN TN AND WRN NC EARLY THIS MORNING. AS THE LLVL FLOW
VEERS MORE OUT OF THE WEST AND INCREASES...CONVECTION SHOULD BE
FAIRLY PROGRESSIVE...THOUGH THERE IS NO SAYING JUST HOW LONG STORMS
WILL CONTINUE TO DEVELOP UPSTREAM. THE GENERAL MODEL CONSENSUS IS
THAT CONVECTION WL TAPER OFF AND MOVE EAST OF THE CWFA BETWEEN 12-15
UTC...AND HIGHS POPS WILL PROBABLY BE NEEDED OVER THE NC FOOTHILLS
AND PIEDMONT EARLY INTO THE FIRST PERIOD TODAY (THAT IS...AFTER 6
AM EDT).

RECENTLY THERE HAS BEEN A TREND FOR CLOUD TOPS TO COOL OVER ERN TN
WHILE THE REFLECTIVITY IN THE CONVECTIVE CORES HAS BEEN
DECREASING. THIS APPEARS TO BE A SIGN THAT THE ATMOSPHERE IS
BECOMING MORE MOIST IN THE VICINITY OF THE TRAINING CELLS. THIS
WILL TEMPER THE SEVERE THREAT BUT WILL RESULT IN HEAVIER
RAIN...AND AN ISOLATED FLASH FLOODING THREAT COULD DEVELOP OVER
THE NEXT FEW HOURS.

DURING THE AFTERNOON HOURS SURFACE BASED CAPE ON THE NAM AND WRF
RISES TO AROUND 2500 J/KG OVER THE UPSTATE AND NE GA...WITH
DOWNSLOPE RESULTING IN LOWER DEWPOINTS INTO THE NORTH CAROLINA
FOOTHILLS AND PIEDMONT. WITH MODERATE TO STRONG SPEED SHEAR...EXPECT
THAT STORMS WILL DEVELOP ALONG THE HIGH TERRAIN OVER THE SRN NC MTNS
AND THE HIGHER ELEVATIONS OF SC AND GA. CONVECTION SHOULD STRENGTHEN
AS IT QUICKLY MOVES SOUTHEAST...WITH A FEW SEVERE STORMS A GOOD BET
OVER THE SOUTHEAST PARTS OF THE CWFA BY MID TO LATE AFTERNOON. THERE
SHOULD ALSO BE SEVERAL OUTFLOW BOUNDARIES RESULTING FROM THIS
MORNING/S CONVECTION...AND STORMS THIS AFTERNOON MAY ALSO INITIATE
AND TRACK ALONG THESE BOUNDARIES...THOUGH THE EXACT LOCATION OF THIS
KIND OF MESOSCALE FORCING WON/T BE KNOWN UNTIL LATER IN THE DAY.
WITH HIGH CLOUD BASES AND COOL MID LEVEL TEMPS...THERE SHOULD BE
BOTH A HAIL AND WIND THREAT.

TONIGHT AND SUNDAY THE GFS KEEPS AN AXIS OF INSTABILITY OVER THE SRN
PART OF THE FORECAST AREA...ESPECIALLY THE SOUTHWEST MOUNTAINS. THE
NAM AND WRF ARE A LITTLE DRIER WITH STRONGER NORTHWESTERLY FLOW
ACROSS THE MOUNTAINS. WILL COMPROMISE AND KEEP LOW CHANCE POPS OVER
THE SOUTHWEST.

DUE TO ONGOING CONVECTION...DID NOT MAKE ANY CHANGES TO THE ZONES
BEYOND SUNDAY.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
ANOTHER DAY...ANOTHER LOW CONFIDENCE MEDIUM RANGE FORECAST. GENERAL
PATTERN REMAINS THE SAME...TROFINESS IN THE EAST AND RIDGE IN THE
WEST. THIS CREATES NORTHWESTERLY FLOW ACROSS OUR AREA WITH DIFFICULT
TO TIME SHORT WAVES MOVING THRU THE FLOW. THERE COULD BE A PATTERN
CHANGE BY THE END OF THE PERIOD WITH THE TROF AND RIDGE MOVING EAST.
AT THE SURFACE A STATIONARY FRONT REMAINS NEAR OR OVER THE AREA
UNTIL THURSDAY WHEN IT MOVES BACK NORTH AS A WARM FRONT THEN EAST OF
THE AREA THURSDAY. THAT SAID...EACH MODEL DIFFERS WITH THE POSITION
AND TIMING OF THE FEATURES WITH EACH NEW RUN. THEREFORE...HAVE GONE
VERY CLOSE TO HPC NATIONAL GUIDANCE. POP DISTRIBUTION GENERALLY
SLIGHT CHC WEST/NOTHING EAST EARLY...THEN SLIGHT CHC MOST AREAS
MIDDLE PERIOD...AND CHC WEST/SLIGHT CHC EAST BY THE END. TEMPS NEAR
NORMAL EARLY RISING TO ABOVE NORMAL MIDDLE PERIODS AND REMAINING THRU
THE END OF THE FORECAST.

AVIATION...
VSBY/CIG RESTRICTIONS DURING THE PRE-DAWN HOURS HIGHLY DEPENDENT ON
TRACKS OF INDIVIDUAL DEEP CONVECTIVE CELLS AND BASED ON 88D
DEPICTION...CERTAINLY KAVL STANDS THE BEST CHANCE OF THIS HAPPENING.
BASED ON ORIENTATION OF COLDEST CLOUD TOPS AND THE EVOLUTION OF LLVL
WAA MAX...HIGHEST CHANCES FOR DEEP CONVECTION THROUGH ABOUT 12 UTC
WILL BE ACRS KAVL/KGSP AND THEN MOVING ON TOWARD KCLT. POTENTIAL TSTM
CLUSTER SHOULD BE DOWNSTREAM OF KCLT BY A FEW HOURS AFTER SUNRISE
WITH A DIURNAL LULL IN PCPN CHANCES. DEEP MIXED LAYER AGAIN THIS
AFTERNOON...SO GUSTY WESTERLY WINDS EXPECTED FOR KGSP/KAND/KCLT. WRF
DEPICTION OF AFTERNOON DEVELOPMENT AS GOOD AS A GUESS AS ANYTHING...
SPREADING CONVECTIVE PCPN BACK INTO THE MTNS AND UPSTATE INTO EARLY
EVENING.

&&

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

SHORT TERM...HG

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
600 AM EDT SAT MAY 20 2006

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-211000-
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-
600 AM EDT SAT MAY 20 2006

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

.DAY ONE...TODAY AND TONIGHT

SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING OVER
MUCH OF THE WESTERN CAROLINAS AND NORTHEAST GEORGIA...WITH THE
BEST CHANCE ALONG AND SOUTH OF A LINE FROM ASHEVILLE TO GREENVILLE
AND ROCK HILL.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORMS WILL AGAIN BE POSSIBLE OVER THE WESTERN CAROLINAS
AND NORTHEAST GEORGIA WEDNESDAY AND THURSDAY. A FEW OF THESE COULD
PRODUCE DAMAGING WINDS AND LARGE HAIL.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

MCAVOY

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1137 AM EDT SAT MAY 20 2006

GAZ010-017-018-026-028-029-NCZ048-051>053-058-059-062>065-068>072-
082-507>510-SCZ001>014-019-202115-
RABUN-HABERSHAM-STEPHENS-FRANKLIN-HART-ELBERT-MADISON-SWAIN-
HAYWOOD-BUNCOMBE-GRAHAM-NORTHERN JACKSON-MACON-SOUTHERN JACKSON-
TRANSYLVANIA-HENDERSON-CLEVELAND-LINCOLN-GASTON-MECKLENBURG-
CABARRUS-UNION NC-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-
INCLUDING THE CITIES OF...CLAYTON...CLARKESVILLE...TOCCOA...
HARTWELL...ELBERTON...CHEROKEE...WAYNESVILLE...ASHEVILLE...
SYLVA...FRANKLIN...BREVARD...HENDERSONVILLE...SHELBY...
LINCOLNTON...GASTONIA...CHARLOTTE...CONCORD...MONROE...
LAKE LURE...RUTHERFORD...COLUMBUS...GREENVILLE...SPARTANBURG...
GAFFNEY...ROCK HILL...ANDERSON...ABBEVILLE...LAURENS...UNION...
CHESTER...GREENWOOD
1137 AM EDT SAT MAY 20 2006

...SEVERE WEATHER OUTLOOK...

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR LOCATIONS
SOUTH OF INTERSTATE 40 THIS AFTERNOON. A COLD FRONT DROPPING SOUTH
OUT OF NORTHERN NORTH CAROLINA AND EAST TENNESSEE...AND
PERTURBATIONS IN THE MIDDLE LEVELS OF THE ATMOSPHERE WITH STRONG
WIND FIELDS ALOFT...WILL CREATE INGREDIENTS FAVORABLE FOR SEVERE
WEATHER PRODUCTION. THE MOST FAVORED LOCATIONS ARE THE SOUTHWEST
MOUNTAINS OF NORTH CAROLINA...ALL OF EXTREME NORTHEAST GEORGIA AND
UPSTATE SOUTH CAROLINA.

THE MOST LIKELY FORM OF SEVERE WEATHER THIS AFTERNOON WOULD BE
LARGE HAIL AND DAMAGING STRAIGHT LINE WINDS. IN ADDITION...THUNDERSTORMS
TODAY WILL LIKELY EXHIBIT ROTATION AND AN ISOLATED TORNADO COULD
NOT BE RULED OUT ACROSS THE UPSTATE OR NORTHEAST GEORGIA SOUTH AND
WEST OF A LINE FROM GAFFNEY TO CHESTER. THE GREATEST COVERAGE OF
THUNDERSTORMS SHOULD EXIST FROM 3 PM THROUGH SUNSET.

STAY TUNED TO NOAA WEATHER RADIO...LOCAL RADIO AND TELEVISION OR
CABLE TELEVISION FOR THE LATEST WEATHER INFORMATION.

44

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
157 PM EDT SAT MAY 20 2006

GAZ018-026-028-SCZ004-010-201900-
ANDERSON-FRANKLIN-GREATER OCONEE-HART-STEPHENS-
157 PM EDT SAT MAY 20 2006

...STRONG THUNDERSTORMS WERE AFFECTING ANDERSON...FRANKLIN...
HART...OCONEE AND STEPHENS COUNTIES...

AT 157 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR TOCCOA...MOVING SOUTHEAST AT 30 MPH.
ANOTHER STRONG THUNDERSTORM WAS LOCATED NEAR WESTMINSTER...ALSO
MOVING SOUTHEAST AT 30 MPH.

THESE THUNDERSTORMS ARE CAPABLE OF PRODUCING PEA SIZE HAIL...AND
WIND GUSTS OF 40 TO 50 MPH. THE THUNDERSTORMS WILL MOST LIKELY
AFFECT THE AREA FROM LAVONIA TO TOWNVILLE THROUGH 230 PM...AND THEN
FROM HARTWELL TO ANDERSON BY 300 PM.

HG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
225 PM EDT SAT MAY 20 2006

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0205 PM     HAIL             EASTANOLEE              34.52N 83.26W
05/20/2006  E0.75 INCH       STEPHENS           GA   TRAINED SPOTTER

0220 PM     HAIL             CLEMSON                 34.68N 82.81W
05/20/2006  E0.75 INCH       PICKENS            SC   TRAINED SPOTTER

0221 PM     HAIL             TOWNVILLE               34.56N 82.90W
05/20/2006  E0.88 INCH       OCONEE             SC   TRAINED SPOTTER

&&

HGERAPET

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
235 PM EDT SAT MAY 20 2006

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0225 PM     HAIL             PENDLETON               34.65N 82.78W
05/20/2006  E0.75 INCH       ANDERSON           SC   COUNTY OFFICIAL

&&

HG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
236 PM EDT SAT MAY 20 2006

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     HAIL             CLEMSON                 34.68N 82.81W
05/20/2006  E1.00 INCH       PICKENS            SC   TRAINED SPOTTER

            SPOTTER REPORTS NICKEL TO QUARTER SIZE HAIL

&&

HG