Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 301134 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 734 AM EDT WED JUL 30 2014 .SYNOPSIS... A STATIONARY FRONT WILL REMAIN OFFSHORE THROUGH THURSDAY. THE FRONT WILL THEN WEAKEN AND MOVE BACK TOWARD THE COAST AS A SURFACE TROUGH FRIDAY THROUGH EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... A SUBTLE WEDGE PATTERN WILL DEVELOP THROUGH TONIGHT IN THE WAKE OF THE WEAK SHORT WAVE PASSING OFFSHORE AND HIGH PRES BUILDING OVER THE COASTAL MID ATLC REGION. THE SURFACE FLOW WILL TURN ONSHORE THIS AFTERNOON ALONG COASTAL AREAS. WEAK DEEP LAYERED INSTABILITY AND SEASONABLY LOW PWATS SUGGEST A MAINLY DRY DAY MOST AREAS BUT THE MODELS ALL PRODUCE SPOTTY FIELDS OF LIGHT CONVECTIVE QPF ALONG AND E OF I-95 THIS AFTERNOON AND EARLY EVENING WHICH GENERALLY SEEMS OVERDONE. FORECAST SOUNDINGS INDICATE A STRONG SUBSIDENCE CAP BETWEEN 600 AND 700 MB WHICH WOULD MAKE FOR A VERY SLIM DEEP CONVECTION POTENTIAL. A FEW SHOWERS COULD CROP UP WHERE MOISTURE CONVENES IN THE LOWER LEVELS WITH THE SEA BREEZE. WE SHOW A SLIGHT CHANCE OF A SHOWER BUT CHANCES NOT REACHING 20 PERCENT IN ANY GIVEN LOCATION AT THIS POINT. LOW LEVEL THICKNESS PROGS INDICATE LOWER 90S MAX TEMPS BUT A FEW OF THE MODELS ACTUALLY SPREAD CLOUD COVERAGE A GOOD BIT THIS AFTERNOON UNDER THE MID LEVEL CAP WHICH COULD RESTRICT READINGS TO THE UPPER 80S IN SOME AREAS. WE MADE VERY FEW CHANGES TO THE ONGOING FORECAST TRENDS OVERALL. MOISTURE TENDS TO INCREASE SOMEWHAT OVERNIGHT ALONG COASTAL AREAS AND WITH WEAK SPEED CONVERGENCE DEVELOPING AFTER MIDNIGHT...THERE WILL PROBABLY BE A FEW SHOWERS DEVELOPING NEAR THE COAST AT SOME POINT LATE...PERHAPS ALONG THE SAVANNAH RIVER ENTRANCE. WE HAVE SMALL COASTAL RAIN CHANCES...BEST POTENTIAL SEEMS TO BE AT THE BEACHES AND BARRIER ISLANDS. INLAND AREAS WILL BE DRY WITH SOME LOW TEMPS AGAIN DIPPING INTO THE UPPER 60S. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... THURSDAY AND THURSDAY NIGHT...THE DEEP AND BROAD TROUGH WILL REMAIN ACROSS THE EASTERN CONUS AS THE OFFSHORE STATIONARY FRONT BEGINS TO DRIFT BACK TOWARDS SHORE THURSDAY NIGHT. THURSDAY WILL BE A DAY WHERE DEEP MOISTURE BEGINS TO INCREASE ACROSS THE AREA WITH PWATS STARTING THE DAY AROUND 1.5 INCHES AND INCREASING TO AROUND 1.8 INCHES BY THE OVERNIGHT. LOW LEVEL FLOW WILL BE NORTHEAST TO EASTERLY THROUGH THE DAY AND MODEL SOUNDINGS SHOW A CAPPED ATMOSPHERE EVENTUALLY YIELDING WEAK INSTABILITY LATE IN THE DAY. WE WILL LIKELY SEE A SLIGHT INCREASE IN SHOWER/THUNDERSTORM ACTIVITY COMPARED TO WEDNESDAY AND SLIGHT CHANCE POPS SEEM REASONABLE. CLOUD COVER WILL BE ON THE INCREASE AS WELL WHICH WILL KEEP TEMPERATURES DOWN A BIT. LOOK FOR HIGHS IN THE UPPER 80S TO AROUND 90 WHICH IS A COUPLE OF DEGREES BELOW NORMAL. OVERNIGHT...THE OFFSHORE STATIONARY FRONT WILL WEAKEN AND BECOME AN OPEN TROUGH AS IT BEGINS TO MOVE BACK CLOSER TO SHORE. RAIN CHANCES WILL BE CONFINED TO THE ADJACENT COASTAL WATERS WHICH WILL BE CLOSER TO THE TROUGH AXIS AND ANY CONVERGENCE WITHIN IT. FRIDAY THROUGH SATURDAY...THE END OF THE WEEK AND START OF THE WEEKEND WILL FEATURE INCREASING DEEP MOISTURE AND INCREASING RAIN CHANCES ESPECIALLY BY SATURDAY. THE SURFACE TROUGH WILL BE ALIGNED RIGHT ALONG THE SOUTHEAST COAST...COINCIDENT WITH THE SOUTHWEST FLOW ALOFT ON THE EAST SIDE OF THE MID/UPPER LEVEL TROUGH AXIS. THERE WILL EVEN BE A BIT OF INCREASING UPPER DIVERGENCE IN THE ENTRANCE REGION OF A SUBTLE JET CENTERED WELL TO THE NORTHEAST. POPS FOR THIS PERIOD HAVE BEEN HELD TO BE NO HIGHER THAN HIGH CHANCE. CONFIDENCE IS INCREASING THAT LIKELY POPS...OR EVEN HIGHER WILL BE NEEDED AT SOME POINT BUT THESE ROUNDS OF HIGHER RAIN CHANCES WILL BE TIED TO SUBTLE EMBEDDED SHORTWAVE ENERGY THAT IS DIFFICULT TO PEG DOWN AT THIS TIME. BY SATURDAY...PWATS SURGE TO AROUND 2.1 INCHES AND THE POTENTIAL FOR LOCALLY HEAVY RAINFALL INCREASES. IN FACT...QPF PROGS FROM WPC ARE QUITE WET FOR THIS PERIOD AND FEATURE THE POTENTIAL FOR WIDESPREAD AMOUNTS IN EXCESS OF 1 INCH. WIDESPREAD CLOUD COVER AND ROUND OF PRECIPITATION WILL KEEP HIGHS IN THE UPPER 80S WITH LOWS IN THE LOW 70S. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... THE UNSETTLED PATTERN WILL CONTINUE FOR THE LATTER HALF OF THE WEEKEND AND AT LEAST INTO EARLY NEXT WEEK. THE TROUGH WILL REMAIN IN THE VICINITY OF THE FORECAST AREA WITH A TROUGH ALOFT AND PWATS IN EXCESS OF 2 INCHES. ALL THESE FACTORS ADD UP TO AN ACTIVE PERIOD WITH RELATIVELY HIGH RAIN CHANCES. GIVEN THE TIME RANGE POPS HAVE BEEN KEPT IN THE HIGH CHANCE RANGE...BUT IF THE MODELS CONTINUE THEIR CURRENT TRENDS IT IS LIKELY THAT HIGHER POPS WILL EVENTUALLY BE WARRANTED. LOCALLY HEAVY RAINFALL WILL REMAIN A CONCERN THROUGH EARLY NEXT WEEK WITH ROUNDS OF CONVECTION ANTICIPATED. TEMPERATURES WILL BE BELOW NORMAL...RUNNING ABOUT 3-5 DEGREES BELOW NORMAL FOR HIGHS INTO THE MID WEEK TIME PERIOD. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... VFR THROUGH THE 12Z TAF PERIOD AT BOTH KCHS/KSAV. ISOLATED CONVECTION MAINLY IN THE FORM OF SPOTTY SHOWERS POSSIBLE THIS AFTERNOON OR EARLY EVENING BUT POTENTIAL FOR ANY ONE AREA GETTING RAIN OR ISOLATED BRIEF THUNDERSTORMS IS QUITE LOW. THERE COULD BE ISOLATED SHOWERS AND TSTMS ALONG THE IMMEDIATE COAST AFTER MIDNIGHT TONIGHT BUT CONFIDENCE IS LOW WHETHER ANY RAINS CAN SPREAD INLAND AS FAR AS THE TERMINALS. EXTENDED AVIATION... A SURFACE TROUGH WILL DRIFT INTO THE AREA LATE THIS WEEK AND THROUGH THE WEEKEND. AN ACTIVE PERIOD IS EXPECTED AND OCCASIONAL FLIGHT RESTRICTIONS ARE POSSIBLE DURING THIS TIME. && .MARINE... ATMOSPHERE FAIRLY FAVORABLE FOR WATERSPOUT DEVELOPMENT THIS MORNING ALTHOUGH SOME OF THE MOISTURE PROFILES WERE LACKING. RADAR AT DAWN INDICATING SHOWERS/TSTMS OFF OF BEAUFORT COUNTY...WILL MONITOR 12Z CHARLESTON SOUNDING DATA FOR POSSIBLE MENTIONS OF WATERSPOUTS IN A MARINE WEATHER STATEMENT IF NEEDED. WEAK MOISTURE AND PRES GRADIENTS PERSIST THROUGH TONIGHT BUT A WEAK SURFACE LOW DEVELOPING OVER FLORIDA MAY ALLOW FOR A BIT MORE OF A PRONOUNCED GRADIENT TONIGHT. FLOW MAINLY ONSHORE THE NEXT 24 HOURS WITH SEAS 2 FT OR LESS TODAY INCREASING A BIT TO 2-3 FT TONIGHT. THURSDAY THROUGH SUNDAY...THE OFFSHORE STATIONARY FRONT WILL DISSIPATE INTO A SURFACE TROUGH AND DRIFT BACK TOWARD THE SOUTHEAST COAST. AS THE TROUGH MOVES INTO THE COASTAL WATERS...WINDS WILL VARY AT TIMES BUT WILL MAINLY BE EAST TO SOUTHEASTERLY. THE GRADIENT MAY TIGHTEN UP AT TIMES AND SUPPORT SOME MODESTLY STRONGER WINDS...BUT OVERALL WINDS WILL BE 15 KT OR LESS WITH SEAS GENERALLY 2-4 FT. SMALL CRAFT ADVISORIES ARE NOT ANTICIPATED AT THIS TIME. && .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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