Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 311128
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
728 AM EDT THU JUL 31 2014

.SYNOPSIS...
A COASTAL TROUGH WILL SETTLE OVER THE AREA THROUGH FRIDAY AND THEN
PERSIST THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE MID TO UPPER LEVEL FLOW IS FORECAST TO GRADUALLY BACK THROUGH
TONIGHT AS A GENERAL TROUGH PATTERN ALOFT CONTINUES TO EVOLVE OVER
THE EASTERN HALF OF THE U.S. INTO LATE WEEK AND BEYOND. TODAY THE
MAIN FORECAST ISSUES ARE RAIN CHANCES...COVERAGE...AND INTENSITIES.

THE APPROACHING MID LEVEL SHORT WAVE IS FORECAST TO SHIFT INTO
NORTH GA BY MID MORNING AND THE INLAND CAROLINAS THIS AFTERNOON.
MODELS SHOW INCREASING SURFACE WEDGING ACROSS THE CSRA AND THE
SOUTH CAROLINA MIDLANDS TODAY AS SHALLOW CONVECTIVE RAINS DEVELOP
UPSTREAM IN BROAD ISENTROPIC UPGLIDE. THIS SHOULD SHARPEN THE
SURFACE COASTAL TROUGH WITH TIME...ACTING TO ENHANCE LOW LEVEL
MOISTURE CONVERGENCE ACROSS THE FORECAST AREA. THROUGH TONIGHT...
THE MOISTURE LOOKS TO BE CHANNELED WITH COUNTIES BORDERING THE
SAVANNAH RIVER A REGION TO WATCH FOR BETTER COVERAGE OF SHOWERS
AND ISOLATED TSTMS. WE INCREASED FORECAST POPS ALONG AND WEST OF
I-95 INTO CHANCE RANGES TODAY. THERE COULD BE LOCALIZED DOWNPOURS
WITH THE CONVECTIVE RAINS TODAY AS WITNESSED LAST NIGHT IN
LOCALIZED AREAS OF BEAUFORT AND JASPER COUNTIES. DEEP LAYERED
INSTABILITY IS TEMPERED BY A LAYER OF WARM ALOFT ALOFT AND
UPDRAFTS SHOULD NOT FLOURISH WELL IN POOR LAPSE RATES AND POSITIVE
SHOWALTER INDICES. THERE LOOKS LIKE A DECENT DIFFERENTIAL HEATING
SETUP ACROSS OUR REGION WITH PLENTY OF MESOSCALE BOUNDARIES...BY
LATE MORNING AND AFTERNOON SCATTERED CONVECTION SHOULD BE THE
NORM. WARMEST TEMPS SHOULD OCCUR SOUTH OF I-16 WHERE MORE SUNSHINE
IS POSSIBLE TODAY. MANY AREAS WILL SEE MOSTLY CLOUDY SKIES THIS
AFTERNOON AND EVENING.

SHOWERS AND ISOLATED STORMS WILL PROBABLY INCREASE ALONG COASTAL
AREAS AFTER MIDNIGHT TONIGHT WITH SOME LOCALIZED DOWNPOURS AGAIN
A GOOD BET. AN ADDITIONAL SHORT WAVE IS NOTED AND CONVERGENCE PROGS
ARE GRADUALLY IMPROVING WITH THE COASTAL SURFACE TROUGH NEARING. A
SOLID TREND INTO A WETTER WEATHER PATTERN. LOW TEMPS IN THE LOWER
TO MID 70S...SLIGHTLY COOLER WELL INLAND.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY/...
FRIDAY AND FRIDAY NIGHT...THIS WILL BE THE BEGINNING OF WHAT LOOKS
LIKE QUITE AN ACTIVE PERIOD FOR THE FORECAST AREA. THE REGION WILL
BE WITHIN THE DEEP AND MOIST SOUTHWEST FLOW ALOFT ASSOCIATED WITH
THE DEEP EASTERN CONUS TROUGH. PWATS WILL STEADILY RISE AND WILL
REACH UP TO AROUND 1.9 INCHES BY LATE FRIDAY NIGHT. AT THE
SURFACE...A WELL DEFINED COASTAL TROUGH WILL BE ALIGNED ALONG THE
SOUTHEAST COAST AND IS EXPECTED TO PROVIDE ENOUGH LOW LEVEL
CONVERGENCE TO KICK OFF SHOWERS AND THUNDERSTORMS. THE MODELS SEEM
TO AGREE THAT THE BEST COVERAGE AND MOISTURE FEED WILL BE JUST TO
THE EAST EXTENDING NORTHWARD INTO EASTERN NORTH CAROLINA. AS
SUCH...WE HAVE KEPT POPS IN THE UPPER CHANCE RANGE EXCEPT FOR AN
AREA OF LIKELY POPS THAT JUST BRUSHES FAR EASTERN REACHES OF THE
FORECAST AREA. THERE IS THEN ENOUGH MOISTURE AND FORCING OVERNIGHT
TO CARRY POPS THROUGH THE NIGHT...WITH THE HIGHEST VALUES FAVORING
THE COASTAL WATERS. ONE OF MORE DAY OF UPPER 80S SEEMS LIKELY WITH
TEMPERATURES BEING HELD DOWN BY WIDESPREAD CLOUD COVER.

SATURDAY THROUGH SUNDAY...THE WEEKEND LOOKS VERY ACTIVE AND APPEARS
TO BE THE HEART OF THIS PERIOD OF UNSETTLED WEATHER. THE DEEP TROUGH
ALOFT WILL SHARPEN AS A SIGNIFICANT SHORTWAVE MOVES INTO THE OHIO
VALLEY. THE MODELS DEPICT SHORTWAVE ENERGY EMBEDDED WITHIN THE
SOUTHWEST FLOW ACROSS THE FORECAST AREA MOVING THROUGH. PWATS
INCREASE FURTHER AND SURGE TO IN EXCESS OF 2 INCHES. GIVEN THE MODEL
AGREEMENT ON THE ACTIVE PERIOD...LIKELY POPS HAVE BEEN ADDED TO THE
FORECAST. AT THIS POINT IT IS HARD TO SAY WHAT PRECISE TIME PERIODS
WILL BE MORE ACTIVE THAN OTHERS...BUT NEEDLESS TO SAY IT LOOKS WET.
GIVEN THE HIGH PWATS...ABUNDANT FORCING...AND DEEP LAYER FLOW AROUND
10 KNOTS...LOCALLY HEAVY RAINFALL WILL BE A CONCERN. IN FACT...WPC
QPF FORECASTS ADVERTISE SEVERAL INCHES OF RAIN. TEMPERATURES WILL BE
MUTED THANKS TO THE WIDESPREAD CLOUD COVER AND PERIODS OF
PRECIPITATION. LOOK FOR HIGHS IN THE MID 80S AND LOWS IN THE LOW/MID
70S.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
THANKS TO THE PRESENCE OF THE LINGERING DEEP TROUGH ALOFT AND DEEP
MOISTURE ACROSS THE AREA...THE ACTIVE PERIOD OF WEATHER WILL
CONTINUE INTO EARLY NEXT WEEK. THE SURFACE TROUGH IN THE AREA
FINALLY BEGINS TO WEAKEN TUESDAY INTO WEDNESDAY WHILE ATLANTIC
RIDGING BEGINS TO PUSH BACK IN FROM THE EAST. BY THE MIDDLE OF THE
WEEK IT APPEARS THAT WE WILL RETURN TO A MUCH MORE TYPICAL DIURNAL
PATTERN OF SHOWERS AND THUNDERSTORMS. ALSO...TEMPERATURES WILL WARM
BACK TO NEAR NORMAL VALUES LATE IN THE PERIOD.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
DEEPER MOISTURE AND PLENTY OF LOW LEVEL BOUNDARIES AROUND TODAY
SUGGEST A RISK OF SHOWERS WITH ISOLATED TSTMS ALONG THE COASTAL
CORRIDOR. 06Z MODELS SUGGEST CONVECTION SHOULD BE IN RIBBONS OF
CONVERGENCE ALONG BOUNDARIES. A BAND OF SHOWERS WITH SOME HEAVY
DOWNPOURS DRIFTING NORTH THROUGH CHATHAM COUNTY PRIOR TO 12Z THIS
MORNING COULD IMPACT THE KSAV TERMINAL THROUGH MID-LATE MORNING.
OTHERWISE...WE WILL CONTINUE TO HIGHLIGHT VCSH TODAY WITH SCT TO
BKN CUMULUS AND ALTOCU ALONG WITH AN ONSHORE NEAR 10 KT TODAY. FOR
THE MOST PART...CONDITIONS WILL BE VFR WITH ANY MVFR CIGS ONLY
BRIEFLY UNDER CONVECTIVE CELLS. SHOWER CHANCE MAY INCREASE YET
AGAIN LATER TONIGHT...TYPICAL FOR THIS TIME OF YEAR AND SYNOPTIC
PATTERN.

EXTENDED AVIATION...A SURFACE TROUGH WILL DRIFT INTO THE AREA AND
LINGER THROUGH EARLY NEXT WEEK. AN ACTIVE PERIOD IS EXPECTED AND
THERE ARE INCREASING CHANCES FOR PERIODIC FLIGHT RESTRICTIONS DUE
TO SHOWERS AND THUNDERSTORMS DURING THIS TIME.

&&

.MARINE...
ONSHORE FLOW AND WAVE HEIGHTS WERE ELEVATED FROM 24 HOURS AGO PRE-DAWN
BUT COASTAL CONDITIONS STILL WELL BELOW ANY ADVISORY CRITERIA. EAST
FLOW AROUND 15 KT AT TIMES THROUGH THIS EVENING...ON AVERAGE
ABOUT 10-15 KT THROUGH TONIGHT. SEAS 2 TO 3 FT WITH A POTENTIAL
FOR SEAS NEARING 4 FT WELL OFFSHORE. WINDS AND SEAS EXPECTED DIMINISH
LATER TONIGHT AS THE SURFACE TROUGH NEARS THE COAST.

FRIDAY THROUGH MONDAY...A COASTAL TROUGH WILL DRIFT OVER THE WATERS
AND EVENTUALLY INLAND BY EARLY NEXT WEEK. EAST TO SOUTHEAST WINDS
WILL PREVAIL FRIDAY AND SATURDAY...SWINGING AROUND TO SOUTHERLY
SATURDAY NIGHT ONCE THE TROUGH SHIFTS INLAND. THE GRADIENT MAY
TIGHTEN AT TIMES AND ALLOW FOR MODEST WIND INCREASES...BUT OVERALL
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW ADVISORY THRESHOLDS.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...
MARINE...BSH






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