Severe Thunderstorm Warning 163, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1050 AM EDT FRI JUN 20 2008

.SYNOPSIS...
WEAK LOW PRES WILL MEANDER OVER THE SE U.S. THROUGH THIS WEEKEND.
A SERIES OF WEAKENING COLD FRONTS WILL MOVE THROUGH THE AREA
SUNDAY THROUGH MONDAY. HIGH PRESSURE WILL THEN BUILD OVER THE AREA
DURING THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE 14Z SURFACE MAP SHOWS A WEAK AREA OF LOW PRESSURE ACROSS SE GA
WITH A TROUGH EXTENDING NWD ACROSS SE SC. ISOLATED THUNDERSTORMS
HAD ALREADY DEVELOPED ACROSS THE AREA THIS MORNING...A PRECURSOR TO
ANOTHER ACTIVE DAY.

SCENARIO TODAY APPEARS SIMILAR TO THAT OF THURSDAY...WITH AN
UPPER TROUGH PERSISTING OVER THE REGION...ACCOMPANIED BY AN INLAND
SURFACE TROUGH AND A PROGRESSIVE AFTERNOON/EVENING SEA BREEZE
BOUNDARY. BY EARLY AFTERNOON... SCATTERED THUNDERSTORMS WILL
AGAIN FIRE ALONG THE SEA BREEZE... WHICH WILL ADVANCE INLAND
WITHIN AN ENVIRONMENT FEATURING SBCAPES 1500-2500 J/KG AND LIFTED
INDICES -4 TO -6. GIVEN EXPECTED WET BULB ZERO HEIGHTS 9.5-10.5
KFT...-10C TO -30C CAPES 400-800 J/KG AND DOWNBURST CAPES AS HIGH
AS 1500 J/KG...ANY PULSE THUNDERSTORMS MAY PRODUCE LARGE HAIL AND
DAMAGING MICROBURSTS. HOWEVER...AS WAS THE CASE THURSDAY...THUNDERSTORMS
DEVELOPING ALONG THE SEA BREEZE WILL PUSH BACK TOWARD THE COAST
DUE TO THE W/NW STEERING FLOW ALOFT. THE RESULTING ENHANCED LOW
LEVEL STORM INFLOW/ HELICITY...ACCOMPANIED BY 0-6 KM BULK SHEAR
30-40 KNOTS...MAY SUPPORT ISOLATED SUPERCELLS WITH VERY LARGE
HAIL...MORE PERSISTENT DAMAGING MICROBURSTS AND EVEN A BRIEF
TORNADO.

A COUPLE OF PARAMETERS DIFFER FROM THURSDAY AND MAY RESULT IN FEWER
SEVERE THUNDERSTORMS. SPECIFICALLY...THE LATEST MODEL GUIDANCE
SUGGESTS THAT 500 MB TEMPS WILL WARM A DEGREE OR TWO THIS
AFTERNOON... POSSIBLY RESULTING IN SLIGHTLY LOWER MID-LEVEL LAPSE
RATES. ALSO...THE SIGNIFICANT DEWPOINT BOUNDARY WHICH SEPARATED
DEWPOINTS IN THE 40S/50S WEST TO THE 60S/70S EAST MAY BE LOCATED
SLIGHTLY FARTHER INLAND THIS AFTERNOON...LEAVING ONLY THE SEA
BREEZE AND CONVECTIVE OUTFLOW TO INITIATE CONVECTION.

WILL CONTINUE MENTION OF THE POTENTIAL FOR ISOLATED SEVERE
THUNDERSTORMS WITHIN THE HAZARDOUS WEATHER OUTLOOK /HWO/.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
STRONGEST CONVECTION SHOULD DIMINISH WITH DIURNAL STABILIZATION THIS
EVENING. HOWEVER...0Z GUIDANCE HINTS AT LINGERING INSTABILITY...
ISENTROPIC ASCENT AND LOW LEVEL CONVERGENCE/MOISTURE ADVECTION.
THUS...MAINTAINED SLIGHT CHANCE POPS OVERNIGHT.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
AS ONE DEEP LONGWAVE TROF MOVES OFFSHORE SAT MRNG...ANOTHER LONGWAVE
TROF WILL DEEPEN OVER THE GREAT LAKES WITH ITS AXIS SWINGING
THROUGH THE MID AND LOWER MISS RIVER VALLEYS. UNDER THE TROF NEAR
THE SFC...A DIFFUSE FRONTAL BOUNDARY NEARLY PARALLEL TO THE FL
PANHANDLE WILL DEVELOP AN AREA OF LOW PRESSURE ALONG IT OVER S GA
SAT AND SHIFT NEWD THROUGH SUN. THIS WILL THEN BRING THE FNTL BNDRY
N...SO CONVERGENCE AT THE SFC WILL INCREASE WITHIN THE DEEP MOISTURE
PROGGED TO BE IN PLACE. WHILE THE DEEP UPPER TROF WILL STILL REMAIN
W OF THE CWFA SAT...PLENTY OF SHORTWAVES WILL PUSH THROUGH THAT WILL
HELP TRIGGER SHWR/TSTM ACTIVITY WITH THE SFC FRONTAL BOUNDARY AND
THE EXPECTED DIURNAL SEABREEZE. AM NOT QUITE CONFIDENT TO GO WITH
LIKELY POPS DUE TO HIGH UNCERTAINTY WITH PRECIP COVERAGE...BUT WILL
MAINTAIN HIGH/MID CHC POPS FOR SAT. WITH THE MAIN TROF APPROACHING
AND NUMEROUS SURFACE BOUNDARIES REMAINING IN PLACE THROUGH SUN...
WILL KEEP THE MID/HIGH CHC POPS GOING THROUGH SUN. ALONG WITH THE
COVERAGE QUESTIONS...THERE IS THE QUESTION OF STORM STRENGTH AND
POTENTIAL FOR SEVERE WX. WITH THE NUMEROUS BOUNDARIES IN PLACE...THE
UPPER SHORTWAVES COMING THROUGH AND DEEP MOISTURE IN PLACE...THE
INGREDIENTS ARE THERE TO AT LEAST HAVE ISOLD SEVERE TSTMS. LOW TO
MID LEVEL LAPSE RATES LOOK TO REMAIN STEEP AND LOW LEVEL JETTING
AHEAD OF THE DEEP TROUGH MAY BE NEAR ENOUGH TO ALSO BE A PLAYER. SPC
SWODY2 CURRENTLY HAS THE AREA UNDER A SEE TEXT...BUT IS RESERVING
THE RIGHT TO UPGRADE LATER. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL
FOR SEVERE WX IN THE HWO.

ONCE THIS STRONG TROF AXIS PUSHES OFFSHORE SUN NIGHT...ANOTHER DEEP
LONGWAVE TROF AXIS WILL PUSH THROUGH THE SOUTHEAST STATES MON INTO
MON NIGHT...KEEPING AT LEAST SLGT CHC POPS GOING FOR MON INTO MON
NIGHT. THERE ARE SIGNALS OF VARYING STRENGTH OF THIS LAST TROUGH
AMONG THE LONGER RANGE MODELS...SO AM HESITANT TO RAISE POPS ATTM.

ONCE THIS TROUGH MOVES OFFSHORE...THEN SFC HIGH PRESSURE WITH WEAK
UPPER LEVEL RIDGING WILL MOVE OVER THE AREA MAKING THE ONLY FEATURE
FOR THE PROMOTION OF SHWRS/TSTMS THROUGH MIDWEEK THE DIURNAL
SEABREEZE. THUS...HAVE TUNED POPS AS SUCH BY FOCUSING POPS MAINLY
DURING THE AFTN AND EVE HOURS EACH DAY.

TEMPS WILL GENERALLY RUN WITHIN A FEW DEGREES OF NORMAL EACH DAY
THROUGH THIS WEEKEND INTO THE FIRST HALF OF NEXT WEEK.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
CANNOT RULE OUT A SHOWER/THUNDERSTORM IN THE VICINITY OF EITHER
TERMINAL THIS MORNING...DUE TO A WEAK SURFACE TROUGH AND AN
UNSTABLE AIRMASS. HOWEVER...MOST CONVECTION WILL OCCUR THIS
AFTERNOON/EARLY EVENING...AS THE SCENARIO APPEARS SIMILAR TO THAT
OF THURSDAY AFTERNOON/EVENING. THUNDERSTORMS WILL INITIATE ALONG
THE SEA BREEZE AND WILL MOVE TOWARD THE E/SE. 12Z TAFS CONTINUE TO
INDICATE VCTS AT BOTH SITES DURING THE 16-23Z TIME FRAME. EITHER
SITE COULD BE DIRECTLY IMPACTED BY THUNDERSTORMS...THUS EXPECT
AMENDMENTS TODAY AS DICTATED BY NEAR TERM CONVECTIVE TRENDS.
THEN...THE 12Z FORECAST INDICATES A TYPICAL DIURNAL DISSIPATION OF
THUNDERSTORMS THIS EVENING. HOWEVER...00Z-06Z GUIDANCE HINTS AT
CONVECTION PERSISTING INTO THE NIGHT...AND LATER FORECAST
ADJUSTMENTS MAY BE REQUIRED.

EXTENDED AVIATION OUTLOOK...OCCASIONAL MVFR OR LOWER CONDITIONS
MAY DEVELOP IN SHOWERS/THUNDERSTORMS SAT THROUGH SUN. MAINLY VFR
CONDITIONS ARE EXPECTED EARLY NEXT WEEK.

&&

.MARINE...
S/SE WINDS MAY DIMINISH SOMEWHAT FOR A TIME THIS MORNING.
THEN...SEA BREEZE ENHANCEMENT WILL INCREASE WINDS TO AROUND 15 KNOTS
THIS AFTERNOON. A DIURNAL SURGE MAY PUSH S WINDS INTO THE 15-20 KT
RANGE TONIGHT. SEAS WILL AVERAGE 2-3 FT THROUGH TONIGHT...ALTHOUGH
MAY REACH 4 FT BEYOND 20 NM OUT OVERNIGHT.

A SERIES OF WEAK LOW PRESSURE SYSTEMS AND ASSOCIATED COLD FRONTS
WILL PUSH THROUGH THE WATERS OVER THE WEEKEND THROUGH THE START OF
NEXT WEEK. NONE LOOK IMPRESSIVE ENOUGH ATTM TO BRING WINDS AND/OR
WAVES TO SCA LEVELS...BUT THERE WILL BE ENOUGH OF A SURGE LATE SAT
THROUGH SAT EVE AS A LOW PRES CENTER MOVES NE AND BRINGS A FRONT
INTO THE WATERS THAT WIND SPEEDS OVER THE OUTER GA WATERS MAY OCNLY
REACH 20 KT. HOWEVER...THE PREVAILING SPEEDS WILL BE BELOW THAT
LEVEL SO WILL CAP SPEEDS AT 15-20KT. THERE ALSO DOES NOT APPEAR TO
BE ANY PROLONGED ONSHORE FETCHES TO ALLOW SEAS TO BUILD TO ANY GREAT
DEGREE SO WILL CAP SEAS AT 5 FT.

THIS SERIES OF DISTURBANCES WILL EVENTUALLY PUSH COMPLETELY AWAY
FROM THE WATERS BY LATE MON NIGHT INTO TUE MORNING...ALLOWING HIGH
PRES TO MOVE INTO THE WATERS. BOTH WINDS AND WAVES WILL GRADUALLY
SUBSIDE BY THE MIDDLE OF NEXT WEEK IN RESPONSE TO THIS CHANGE.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHARLESTON SC
422 AM EDT FRI JUN 20 2008

AMZ330-350-352-354-374-GAZ087-088-099>101-114>119-137>141-SCZ040-
042>045-047>051-211000-
CHARLESTON HARBOR-
WATERS FROM SOUTH SANTEE RIVER TO EDISTO BEACH SC OUT 20 NM-
WATERS FROM EDISTO BEACH SC TO SAVANNAH GA OUT 20 NM-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA OUT 20 NM...INCLUDING
GRAYS REEF NATIONAL MARINE SANCTUARY-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA EXTENDING FROM 20 TO
60 NM-JENKINS-SCREVEN-CANDLER-BULLOCH-EFFINGHAM-TATTNALL-EVANS-
INLAND BRYAN-COASTAL BRYAN-INLAND CHATHAM-COASTAL CHATHAM-LONG-
INLAND LIBERTY-COASTAL LIBERTY-INLAND MCINTOSH-COASTAL MCINTOSH-
ALLENDALE-HAMPTON-INLAND COLLETON-DORCHESTER-BERKELEY-INLAND JASPER-
BEAUFORT-COASTAL COLLETON-CHARLESTON-COASTAL JASPER-
422 AM EDT FRI JUN 20 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR ATLANTIC COASTAL
WATERS...SOUTHEAST GEORGIA AND SOUTHEAST SOUTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

SEVERE THUNDERSTORMS...AS THE SEA BREEZE ADVANCES INLAND...SCATTERED
THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND EARLY THIS EVENING.
AS THESE THUNDERSTORMS MOVE TOWARD THE EAST AND SOUTHEAST...A FEW
MAY BECOME SEVERE WITH DAMAGING WIND GUSTS EXCEEDING 60 MPH AND
LARGE HAIL EXCEEDING ONE INCH IN DIAMETER...ESPECIALLY BETWEEN 2
PM AND 9 PM. ANY THUNDERSTORMS MAY ALSO PRODUCE FREQUENT AND
DANGEROUS CLOUD TO GROUND LIGHTNING AND VERY HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.

SEVERE THUNDERSTORMS...A SERIES OF SURFACE AND UPPER LEVEL
DISTURBANCES WILL AFFECT THE SOUTHEASTERN UNITED STATES SATURDAY
THROUGH SUNDAY. THESE DISTURBANCES...IN COMBINATION WITH THE DAILY
AFTERNOON SEA BREEZE AND A CONTINUED UNSTABLE AIRMASS...MAY LEAD TO
A FEW STRONG TO SEVERE THUNDERSTORMS ACROSS SOUTHERN SOUTH CAROLINA
AND SOUTHEAST GEORGIA. THE MAIN HAZARDS FROM THE STRONGEST STORMS
THAT DEVELOP WILL BE GUSTY WINDS...HAIL...FREQUENT CLOUD TO GROUND
LIGHTNING AND HEAVY RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHARLESTON SC
1220 PM EDT FRI JUN 20 2008

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

1149 AM     TSTM WND GST     EDISTO BEACH            32.49N 80.32W
06/20/2008  M45.00 MPH       COLLETON           SC   MESONET

            REPORT FROM AWS SITE.

&&

33

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHARLESTON SC
1236 PM EDT FRI JUN 20 2008

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

1152 AM     HAIL             EDISTO BEACH            32.49N 80.32W
06/20/2008  E0.50 INCH       COLLETON           SC   PUBLIC

            DIME SIZE HAIL WAS REPORTED AT BIG PLANTATION GOLF COURSE
            IN EDISTO BEACH.

1150 AM     HAIL             EDISTO ISLAND           32.56N 80.30W
06/20/2008  E0.50 INCH       CHARLESTON         SC   PUBLIC

            DIME SIZE HAIL WAS REPORTED IN EDISTO ISLAND. SMALL LIMBS
            DOWN ALSO.

&&

REB

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE CHARLESTON SC
1244 PM EDT FRI JUN 20 2008

SCZ045-201715-
BERKELEY-
1244 PM EDT FRI JUN 20 2008

...STRONG THUNDERSTORMS WILL IMPACT BERKELEY COUNTY THROUGH 115 PM
EDT...

AT 1240 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM CAPABLE OF PRODUCING SMALL HAIL...AND GUSTY WINDS
OF 30 TO 40 MPH.  THIS STORM WAS LOCATED NEAR BONNEAU BEACH...OR
ABOUT 9 MILES SOUTHWEST OF SAINT STEPHEN...MOVING NORTH AT 18 MPH.

AREAS IN AND AROUND BONNEAU...BONNEAU BEACH...CROSS AND EADYTOWN WILL
BE IMPACTED THROUGH 115 PM EDT.

FREQUENT LIGHTNING IS OCCURRING WITH THIS THUNDERSTORM. IF
OUTDOORS...STAY AWAY FROM ISOLATED HIGH OBJECTS. IF INDOORS...STAY
AWAY FROM WINDOWS AND DOORS. AVOID USING TELEPHONES UNLESS IT IS AN
EMERGENCY.

BE ALERT FOR RAPIDLY CHANGING WEATHER CONDITIONS AS STORMS APPROACH.
BE READY TO TAKE IMMEDIATE ACTION IN CASE A SEVERE THUNDERSTORM
WARNING IS ISSUED FOR YOUR LOCATION.

PLEASE CONTACT THE NATIONAL WEATHER SERVICE IN CHARLESTON TOLL FREE
AT 1-888-383-2024 IF YOU OBSERVE SEVERE WEATHER SUCH AS HAIL...DOWNED
TREES...LIMBS AND POWER LINES.