Special Weather Statement, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
738 PM EDT FRI AUG 19 2011

.SYNOPSIS...
ATLANTIC HIGH PRESSURE WILL PREVAIL OVER THE REGION THROUGH THIS
WEEKEND. A COLD FRONT WILL APPROACH FROM THE NORTHWEST MONDAY...
THEN WILL STALL AND EVENTUALLY DISSIPATE OVER OR NEAR THE AREA
THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
SCATTERED THUNDERSTORMS SUPPORTED BY PERSISTENT OUTFLOW BOUNDARIES
WILL CONTINUE TO PUSH TOWARD THE COAST THIS EVENING. AFTER SUNSET...
DIURNAL STABILIZATION SHOULD PROMOTE A GRADUAL DISSIPATION TREND.
UNTIL THEN...BOUNDARY INTERACTIONS/CELL MERGERS WILL SUPPORT A
LOW-END THREAT FOR ISOLATED DAMAGING WIND GUSTS.

TONIGHT...THE CWA WILL REMAIN UNDER A RATHER BAGGY AND LOW
AMPLITUDE TROF ALOFT. GUIDANCE CONTINUES TO SUGGEST THAT SOME
UPSTREAM CONVECTION...SUPPORTED BY VORTICITY MAXIMA EMBEDDED
WITHIN THE PARENT TROUGH...COULD DEVELOP AND PUSH INTO
INLAND/NORTHERN COUNTIES OVERNIGHT. FOR THAT REASON..MAINTAINED
SLIGHT CHANCE POPS IN THESE AREAS FOR A FEW HOURS AFTER
MIDNIGHT.

ALSO...GIVEN RAINFALL THAT OCCURRED INLAND ADDED A MENTION OF
PATCHY FOG THERE OVERNIGHT.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY...NOT YET SURE HOW THE EARLY MORNING SHORT WAVE MOVING
THROUGH THE NW FLOW WILL RELATE TO CONDITIONS AT THE SURFACE AT THE
START OF THE DAY. BUT FOR NOW HAVE KEPT A RAINFREE FORECAST IN THE
MORNING...ALTHOUGH THERE CERTAINLY COULD BE SOME ISOLATED ACTIVITY
IS AN ORGANIZED AREA OF CONVECTION IS ABLE TO FORM TO OUR NW
OVERNIGHT TONIGHT. OTHERWISE...THE MAIN TRIGGER FOR CONVECTION IN
THE AFTERNOON/EVENING WILL BE THE SEA BREEZE AND OUTFLOW BOUNDARIES
COMING IN FROM THE NW. THE RIGHT REAR QUAD OF THE UPPER LEVEL JET
AND ITS ASSOCIATED UPPER LEVEL DIVERGENCE WILL IMPACT THE AREA
DURING THE PEAK HEATING HOURS. THAT ALONG WITH DECENT SBCAPES AND
INSTABILITY AND DECENT LOW LEVEL LAPSE RATES WILL SUPPORT 20-30
POPS. HIGHEST COVERAGE WILL BE FROM BERKELEY TO JENKINS COUNTY WHERE
THE BEST BOUNDARY INTERACTION WILL OCCUR. A DEEP OFFSHORE FLOW WILL
PREVENT THE SEA BREEZE FROM MAKING HEADWAY TO FAR INLAND...AND THAT
ALONG WITH 850 MB TEMPS NEAR 19-20C WILL SUPPORT MAX TEMPS IN THE
LOWER AND MIDDLE 90S AWAY FROM THE BEACHES. THICKNESS SUPPORT HIGHER
TEMPS...BUT MOS GUIDANCE SHOWS LOWER VALUES SO WILL SPLIT THE
DIFFERENCE.

SUNDAY...THE MID AND UPPER RIDGE FROM TEXAS WILL BUILD EAST...WITH
ITS ASSOCIATED RIDGE AXIS ACROSS THE CENTRAL AND SOUTHERN PORTIONS
OF THE CWFA. WITH A LITTLE MORE LARGE SCALE SUBSIDENCE AND THE MAIN
TRIGGERS THE SEA BREEZE AND THE PROXIMITY OF THE LEE SIDE
TROUGH...WE HAVE OPTED TO CARRY NO MORE THAN 20 POPS.
HOWEVER...SHOULD BOUNDARY INTERACTIONS OCCUR WITH THE WEST AND NW
FLOW ALOFT...THERE HIGHER POPS WOULD BE IN ORDER ESPECIALLY INLAND
BY LATE IN THE DAY. THERE ARE EVEN SOME INDICATIONS THAT AN
ORGANIZED MCS COULD FORM AND IMPACT THE AREA LATE SUNDAY OR SUNDAY
NIGHT. WE/LL SEE IF THIS COMES TO FRUITION IN LATER FORECAST
CYCLES...BUT FOR NOW HAVE GONE WITH A CONSERVATIVE APPROACH. SIMILAR
850 MB TEMPS AND LOW LEVEL THICKNESS SUPPORTS TEMPS AGAIN IN THE
LOWER AND MIDDLE 90S AWAY FROM THE BEACHES.

MONDAY...THE MID AND UPPER RIDGE SLIDES SOUTH AHEAD OF THE NEXT
TROUGH THAT MOVES INTO THE EAST ALOFT. WITH A NEARBY COLD FRONT TO
THE NW...AN INCREASE IN MOISTURE AND MODEST INSTABILITY...WE WILL
BUMP POPS UP INTO THE CHANCE RANGE FOR ALL AREAS. DEPENDENT UPON
CLOUD COVER IS OUR TEMP FORECAST...BUT GIVEN SOME COMPRESSIONAL
HEATING AHEAD OF THE FRONT AND 850 MB TEMPS NEAR 18-20C...TEMPS WILL
AGAIN BE ABOVE SEASONAL NORMS.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
DETAILS OF THE EXTENDED FORECAST WILL BE HIGHLY DEPENDENT ON THE
POTENTIALLY STALLED FRONT ACROSS THE AREA THROUGH AT LEAST THE
MID WEEK PERIOD. WITH THE FRONT LIKELY LINGERING IN THE
VICINITY BEFORE DISSIPATING...WHILE UPPER RIDGING RETREATS
SLIGHTLY TO THE WEST...A MORE UNSETTLED PATTERN COULD PREVAIL.
WILL THUS MAINTAIN RAIN CHANCES GENERALLY IN THE 20 TO 30 PERCENT
RANGE TUESDAY THROUGH THURSDAY...HIGHEST DURING THE CLIMATOLOGICALLY
FAVORED AFTERNOON/EVENING PERIODS. TEMPERATURES ARE EXPECTED TO
RUN NEAR TO SLIGHTLY ABOVE NORMAL DURING THIS TIME.

ANY TROPICAL SYSTEM FROM THE ATLANTIC IS FORECAST TO BE FAR TO THE
SOUTH OF THE LOCAL AREA BY LATE IN THE WEEK.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
THUNDERSTORMS WILL IMPACT KSAV BY 02Z AND THUNDERSTORM OUTFLOW
WILL IMPACT KCHS BY THAT TIME. OVERNIGHT...LOW LEVEL MOISTURE
COULD SUPPORT A PERIOD OF MVFR OR LOWER VISIBILITY AT BOTH SITES.
CBS SHOULD REDEVELOP SATURDAY AFTERNOON.

EXTENDED AVIATION OUTLOOK...SCATTERED AFTERNOON/EVENING SHOWERS AND
THUNDERSTORMS MAY BRIEFLY REDUCE VSBYS AND/OR CIGS THROUGH THE
PERIOD.

&&

.MARINE...
THUNDERSTORM OUTFLOW WILL PRODUCE SHIFTING WINDS AND WILL ALTER
THE PRESSURE PATTERN ACROSS NEARSHORE WATERS THIS EVENING. THEN...
EXPECT SOUTH TO SOUTHWEST WINDS LESS THAN 15 KT OVERNIGHT AS WEAK
HIGH PRESSURE IN THE WESTERN ATLANTIC MOVES LITTLE. 2-3 FT
SEAS WILL PREVAIL...DOMINATED BY A 7-9 SECOND SE SWELL.

SATURDAY THROUGH WEDNESDAY...THE COASTAL WATERS WILL REMAIN ON
THE WEST AND NW PERIPHERY OF THE SUB TROPICAL ATLANTIC RIDGE
THROUGH THE WEEKEND...RESULTING IN SOUTH TO SW WINDS AT NO MORE
THAN 10 OR 15 KT. EVEN WITH A LITTLE SE SWELL...COMBINED SEAS WILL
HOLD AT 3 FT OR LESS.

A COLD FRONT WILL THEN APPROACH FROM THE NW EARLY NEXT WEEK...AND
LATEST INDICATIONS ARE THAT IT WILL STALL OUT IN OR NEAR THE COASTAL
WATERS. WE/LL STAY MORE WITH CLIMATOLOGY WHICH SUGGESTS THAT THE
FRONT DOESN/T GET THIS FAR SOUTH AND MAKE ADJUSTMENTS IF NECESSARY
IN LATER FORECASTS. EITHER WAY...CONDITIONS LOOK TO REMAIN BELOW AND
SCA CONDITIONS THROUGH MID WEEK.

&&

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

&&