AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
921 PM EDT THU JUL 7 2011

.SYNOPSIS...
LOW PRESSURE STRETCHING FROM THE EASTERN GULF OF MEXICO NORTHEAST
OFF THE SOUTHEAST US COAST WILL PERSIST THROUGH FRIDAY...WHILE A
COLD FRONT APPROACHES FROM THE NORTHWEST DURING THE WEEKEND. THE
FRONT WILL DISSIPATE OVER THE AREA SUNDAY AND MONDAY...BEFORE
ANOTHER FRONT APPROACHES FROM THE NORTH BY THE MIDDLE OF NEXT
WEEK.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
SUBSIDENCE ALONG THE NORTHERN PERIPHERY OF THE BROAD AREA OF
DISTURBED WEATHER STRETCHING FROM THE EASTERN GULF INTO THE
ATLANTIC WATERS OFF THE SOUTH CAROLINA COAST HELPED LIMIT
CONVECTIVE COVERAGE ACROSS SOUTHEAST SOUTH CAROLINA AND SOUTHEAST
GEORGIA TODAY.

SATELLITE AND BUOY OBSERVATION SHOW A SLUG OF DEEP TROPICAL
MOISTURE IS POISED TO MOVE ONSHORE OVERNIGHT AS WEAK LOW PRESSURE
ORGANIZES OVER THE EASTERN GULF OF MEXICO. INCREASING LOW-LEVEL
CONVERGENCE ALONG THE COAST AND THE ADJACENT COASTAL WATERS
COUPLED WITH A MOIST ATMOSPHERE /NOTED PWATS OF 1.88 INCHES OF THE
00Z CHS RAOB/ WILL SUPPORT ISOLATED TO SCATTERED SHOWERS THROUGH
SUNRISE. LOW-LEVEL TRAJECTORY FORECASTS TEND TO FAVOR THE
CHARLESTON COUNTY COAST FOR ANY SHOWERS THAT FORM...BUT WE CAN
NOT RULE OUT SHOWER ACTIVITY AFFECTING ANYWHERE ALONG AND EAST OF
THE I-95 CORRIDOR. WILL FORECAST 20 PERCENT POPS ALONG I-95 WITH
POPS UP TO 40 PERCENT ACROSS MUCH OF CHARLESTON COUNTY TONIGHT.

INCREASING CLOUD COVER AND A MODEST 20 KT 925 MB LOW-LEVEL JET
SUGGESTS FULL DECOUPLING IS UNLIKELY. THIS WILL HELP KEEP
TEMPERATURES UP. WILL INCREASE LOWS BY 1-2 DEGREES FOR MOST
LOCATIONS. LOWS WILL RANGE FROM THE LOWER-MID 70S INLAND WITH
MID-UPPER 70S COAST.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
THE FORECAST FOR THE SHORT TERM PERIOD CONTINUES TO LOOK
DIFFICULT...AS MUCH OF THE SENSIBLE WEATHER IMPACTS WILL BE HIGHLY
DEPENDENT ON A LOW SYSTEM OVER THE EASTERN GULF OF MEXICO AND A
COLD FRONT APPROACHING FROM THE NORTHWEST. MOST NUMERICAL MODEL
SOLUTIONS INDICATE THE MAIN SURFACE LOW REMAINING OVER THE
GULF...WHILE A SUBTLE WAVE OF LOW PRESSURE TRACKS NORTHWARD ALONG
THE EAST COAST. PLENTIFUL DEEP MOISTURE WILL SHIFT UP THE COAST
WITHIN SOUTHERLY FLOW BETWEEN THE ATLANTIC RIDGE AND A BROAD UPPER
TROUGH OVER THE GULF. THE NAM AND GFS DISAGREE ON THE AMOUNT OF
DEEP MOISTURE PUSHING ONSHORE BY FRIDAY AFTERNOON...WITH THE NAM
SOLUTION SUGGESTING THE FORECAST AREA COULD BE CAUGHT IN THE DRY
SLOT ALONG THE WESTERN PERIPHERY OF THE SURFACE WAVE. THUS THERE
IS SOME RATHER SIGNIFICANT MODEL DISAGREEMENT REGARDING RAIN
COVERAGE FOR FRIDAY. SREF AND ECMWF RUNS LEAN TOWARD A WETTER
SOLUTION SIMILAR TO THE GFS...AND WILL INDICATE A SOLID CHANCE FOR
SHOWERS/THUNDERSTORMS IN THE 40 TO 50 PERCENT RANGE FRIDAY
AFTERNOON. HESITANT TO INDICATE ANY HIGHER PROBABILITIES UNTIL THE
NAM SOLUTION COMES INTO BETTER AGREEMENT WITH OTHER MODELS.

THE WAVE OF LOW PRESSURE WILL DISSIPATE NORTH OF THE AREA BY
SATURDAY...WITH THE REGION BECOMING LOCATED BETWEEN ATLANTIC HIGH
PRESSURE AND THE FRONTAL TROUGH TO THE WEST/NORTHWEST. ABUNDANT
DEEP MOISTURE AND PWAT VALUES ABOVE 2 INCHES LEND CONFIDENCE
TOWARD 50 PERCENT SHOWER/THUNDERSTORM CHANCES ON SATURDAY.
ALTHOUGH THE FRONT WILL REMAIN NORTH OF THE AREA ON
SATURDAY...THE SURFACE TROUGH WILL LIKELY SAG INTO THE AREA AND
PROVIDE ADDITIONAL SYNOPTIC SUPPORT FOR THUNDERSTORM FORMATION.

THE WEAKENING FRONT WILL DESCEND INTO THE FORECAST AREA ON
SUNDAY...AS SURFACE HIGH PRESSURE ATTEMPTS TO BUILD FROM THE
NORTH. THE BEST MOISTURE AND CONVERGENCE WILL BE ACROSS SOUTHERN
SECTIONS OF THE AREA BY SUNDAY AFTERNOON...AND WILL CONTINUE TO
INDICATE HIGHEST RAIN PROBABILITIES SOUTH OF THE CHARLESTON TRI
COUNTY AREA. MOISTURE PROFILE WILL STILL REMAIN FAVORABLE FOR
SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE ENTIRE FORECAST AREA ON
SUNDAY...AND WILL THEREFORE INDICATE POPS FROM THE 30 PERCENT
RANGE NORTH TO THE 40 PERCENT RANGE SOUTH.

HIGH TEMPERATURES WILL GENERALLY REACH THE LOW TO MID 90S AWAY
FROM THE LOCALLY COOLER COASTLINE EACH AFTERNOON. SATURDAY WILL
LIKELY BE THE COOLEST DAY DUE TO THICKER CLOUD COVER...WHILE
TEMPERATURES ON SUNDAY COULD BE THE WARMEST WITHIN A BUILDING
UPPER RIDGE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
THE ATMOSPHERE WILL DRY OUT SOME ON MONDAY AND TUESDAY AS UPPER
RIDGING BUILDS BACK IN AND PWATS DROP TO BELOW NORMAL LEVELS.
HOWEVER...DUE TO FEWER CLOUDS...TEMPS WILL BE A COUPLE OF DEGREES
HIGHER AWAY FROM THE COAST...MEANING THAT WE ARE STILL LIKELY TO AT
LEAST REACH THE CONVECTIVE TEMP EACH AFTERNOON. SLIGHT CHANCE OF
CONVECTION SHOULD COVER IT FOR NOW. THE NEXT FRONT STARTS TO
APPROACH FROM THE NORTH FOR WEDNESDAY AND THURSDAY...BUT IT IS VERY
HARD TO TELL THIS FOR OUT IN TIME IF THE FRONT WILL HAVE ENOUGH PUSH
TO MAKE IT INTO THE AREA...OR IF THE MID LEVEL RIDGE WILL HOLD ON
STRONG ENOUGH TO KEEP THE FRONT AT BAY TO OUR NORTH. I HAVE GONE
WITH CLIMO POPS AND TEMPS.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
SATELLITE AND BUOY OBSERVATIONS INDICATE A SLUG OF DEEP TROPICAL
MOISTURE IS POISED TO MOVE ONSHORE OVERNIGHT. THIS WILL RESULT IN
AN INCREASE IN CLOUD COVER...ESPECIALLY AT KCHS. CURRENT
INDICATIONS ARE THAT CONDITIONS WILL GENERALLY REMAIN VFR...EXCEPT
AT KCHS WHERE A PERIOD OF MVFR AND IFR CIGS COULD DEVELOP LATER
TONIGHT. THE MOST LIKELY TIME FOR THIS TO OCCUR IS BETWEEN
06-09Z SO WILL SHOW A TEMPO GROUP OF BKN018 DURING THIS TIME.
ADJUSTMENTS WILL MOST LIKELY BE NEEDED AS THE NIGHT PROGRESSES.

ISOLATED-SCATTERED SHOWER ACTIVITY WILL OCCUR OVER THE COASTAL
WATERS TONIGHT SOME OF WHICH WILL MAKE A RUN FOR THE COASTAL
TERMINALS. AGAIN...LOW-LEVEL TRAJECTORIES WOULD FAVOR KCHS FOR
ANY SHOWER IMPACTS. WILL MAINTAIN A MENTION OF CB/S OVERNIGHT BUT
KEEP SHOWER ACTIVITY OUT OF BOTH TERMINALS UNTIL TRENDS BECOME MORE
APPARENT. SCATTERED SHOWER/TSTM ACTIVITY WILL LIKELY IMPACT THE
REGION AGAIN FRIDAY AFTERNOON. BEST COVERAGE LOOKS TO REMAIN
INLAND FROM KCHS/KSAV SO WILL CONTINUE TO HIGHLIGHT CB/S FOR NOW.

EXTENDED AVIATION OUTLOOK...VISIBILITIES AND CEILINGS COULD
BECOME BRIEFLY LOWER WITHIN ANY SHOWERS AND THUNDERSTORMS THROUGH
THE PERIOD. DIFFICULT TO KNOW WHETHER THERE WILL STILL BE SMOKE
AROUND AS IT DEPENDS ON THE STATE OF THE WILDFIRES AT THAT TIME.

&&

.MARINE...
TONIGHT...WINDS TO INCREASE TONIGHT AS A WEAK WAVE OF LOW PRES
APPROACHES FROM THE S CAUSING AN INCREASE IN THE PRES GRADIENT.
WINDS MAY DIMINISH TOWARD DAYBREAK...ESPECIALLY ACROSS THE GA
WATERS...AS THE LOW/WAVE PUSHES INTO THE SC WATERS. SEAS LOOK TO
BUILD AS WELL...MOSTLY DUE TO INCREASING SE SWELL. WILL KEEP CONDS
BELOW ADVISORY LEVELS FOR NOW BUT IT WILL BE CLOSE FOR THE WATERS
BEYOND 20 NM.

FRIDAY THROUGH TUESDAY...SOUTHERLY WINDS WILL SURGE FRIDAY NIGHT
INTO SATURDAY AS THE PRESSURE GRADIENT TIGHTENS BETWEEN ATLANTIC
HIGH PRESSURE AND A COLD FRONT APPROACHING FROM THE NORTHWEST.
LATEST THINKING IS THAT WIND SPEEDS WILL REMAIN JUST BELOW SMALL
CRAFT ADVISORY CRITERIA DURING THIS TIME...HOWEVER OCCASIONAL
GUSTS ABOVE 20 KT COULD OCCUR FOR PORTION OF THE WATERS. WINDS
WILL WEAKEN AND BECOME A BIT MORE VARIABLE IN DIRECTION AS THE
WEAKENING FRONT SLIPS SOUTHWARD INTO THE WATERS ON SUNDAY. THE
WINDS WILL COME DOWN A BIT ON MONDAY AND TUESDAY WITH WEAK HIGH
PRESSURE BUILDING INTO THE AREA. WINDS AND SEAS SHOULD STAY BELOW
ADVISORY CRITERIA THROUGH THE PERIOD.

RIP CURRENTS...SE SWELLS WILL INCREASE THROUGH MOST OF FRIDAY AND
THIS WILL CONTRIBUTE TO AN ENHANCED RISK FOR RIP CURRENTS THROUGH
THEN.

&&

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

&&

$$