444 FXUS62 KCHS 150756 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 356 AM EDT THU AUG 15 2013 .SYNOPSIS... A STATIONARY FRONT WILL WAVER OVER THE AREA THROUGH THE WEEKEND. AN ACTIVE PATTERN WILL PERSIST WITH SEVERAL ROUNDS OF HEAVY RAIN POSSIBLE. THE FRONT WILL EVENTUALLY DISSIPATE EARLY NEXT WEEK...WITH HIGH PRESSURE BUILDING INTO THE REGION THEREAFTER. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A STATIONARY FRONT SHOULD REMAIN SOUTH OF THE REGION TONIGHT... AND HIGH PRESSURE CENTERED NORTH OF THE AREA WILL MAINTAIN A WEDGE OF MUCH COOLER AIR ACROSS THE REGION. HIGH TEMPERATURES WILL RANGE FROM THE MID/UPPER 70S ACROSS NORTHERN/INLAND COUNTIES TO THE LOWER TO MID 80S ALONG/SOUTH OF I-16. FORECAST ATTENTION FOCUSES ON POPS AND THE POTENTIAL FOR ADDITIONAL HEAVY RAIN TODAY. S/SW WINDS ALOFT WILL CONTINUE TO TRANSPORT DEEP LAYER MOISTURE OVER THE LOW-LEVEL WEDGE...THUS THE DAY WILL START WITH NUMEROUS TO WIDESPREAD SHOWERS ACROSS NORTHERN/INLAND COUNTIES...TAPERED TO ISOLATED/SCATTERED SHOWERS SOUTH OF I-16. AS THE BOUNDARY LAYER WARMS THUNDERSTORMS WILL DEVELOP AND WILL BECOME MORE COMMON. FURTHER...THE OVERRUNNING REGIME AND UPPER DIVERGENCE/WEAK QG FORCING PROVIDED BY SERIES OF SHORTWAVES ROTATING THROUGH A LONGWAVE UPPER TROUGH WILL SUPPORT ABOVE AVERAGE PRECIPITATION COVERAGE...WITH AT LEAST LIKELY POPS JUSTIFIED JUST ABOUT EVERYWHERE AT SOME POINT DURING THE DAY...MAINLY THIS AFTERNOON ALONG/SOUTH OF I-16. ALSO OF CONCERN... PWATS EXCEEDING 2 INCHES WILL AGAIN SUPPORT LOCALLY HEAVY RAINFALL AND LOCALIZED FLASH FLOODING. WHILE MOST CONVECTION WILL ADVANCE STEADILY TOWARD THE E/NE...CONDITIONS WILL REMAIN FAVORABLE FOR STATIONARY BANDS OF HEAVIER RAIN TO OCCASIONALLY DEVELOP ALONG MESOSCALE BOUNDARIES...DEPOSITING LOCALLY HEAVY/EXCESSIVE RAINFALL. AS THE FLASH FLOOD THREAT WILL REMAIN LOCALIZED AND THE LOCATIONS FOR POTENTIAL FLASH FLOODING REMAIN UNCERTAIN...OPTED NOT TO RAISE A FLASH FLOOD WATCH FOR THE ENTIRE FORECAST AREA. HOWEVER...FORECASTS AND THE HAZARDOUS WEATHER OUTLOOK WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR HEAVY RAIN/FLASH FLOODING. ALSO OF NOTE...INSTABILITY COULD SUPPORT ISOLATED/BRIEF EPISODES OF SEVERE WEATHER THIS AFTERNOON...ESPECIALLY WHERE BOUNDARY INTERACTIONS OCCUR ALONG/SOUTH OF I-16. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... TONIGHT...THE THREAT FOR THUNDERSTORMS WITH LOCALLY HEAVY RAIN GUIDANCE SUGGESTS THAT DEEPEST MOISTURE/FORCING COULD GRADUALLY SHIFT NORTH OF THE REGION. WHILE CONFIDENCE IN THIS SCENARIO IS NOT HIGH...NUDGED FORECASTS IN THIS DIRECTION WITH POPS GRADUALLY TAPERING TO CHANCE OVERNIGHT. FRIDAY THROUGH SUNDAY...THE OVERALL PATTERN CONTINUES TO LOOK QUITE ACTIVE AND WET. ALOFT...THE SYNOPTIC SETUP WILL BECOME QUITE AMPLIFIED AS THE LONGWAVE TROUGH DIGS INTO THE MID MS VALLEY AND A RIDGE DEEPENS OVER THE ATLANTIC. THIS WILL CREATE A WELL DEFINED SOUTHWEST TO NORTHEAST FLOW OF DEEP GULF MOISTURE ACROSS THE SOUTHEAST. THE FORECAST AREA WILL BE RIGHT IN THE MIDDLE OF THIS TROPICAL MOISTURE FLOW AS IT IS SANDWICHED BETWEEN THE TWO LARGE SCALE FEATURES. THE FRONT WE HAVE DISCUSSED FOR THE PAST FEW DAYS WILL START OFF THE PERIOD FRIDAY MORNING LIFTING BACK NORTHWARD AND INTO THE CENTRAL CAROLINAS WHERE IT WILL REMAIN AND EVENTUALLY DISSIPATE THROUGH THE WEEKEND. THE MOST SIGNIFICANT SURFACE FEATURES TO AFFECT THE AREA APPEAR TO BE A SERIES OF WAVES OF LOW PRESSURE THAT DEVELOP ALONG THE PERIPHERY OF THE WEDGE AND COLD FRONT AND LIFT NORTHEASTWARD ACROSS SOUTHEAST GEORGIA AND SOUTHEAST SOUTH CAROLINA. THE MODELS GENERALLY PRODUCE THE MOST PRECIP WITH SURGES IN MOISTURE AND FORCING ASSOCIATED WITH THESE SURFACE WAVES WHICH MOVE THROUGH FRIDAY NIGHT AND INTO SATURDAY. I HAVE ONCE AGAIN KEPT POPS THROUGH THE PERIOD IN THE HIGH END LIKELY RANGE...MAINLY DUE TO THE FACT THAT THERE WILL BE PERIODS OF HIGHER POPS AND CORRESPONDING PERIODS OF LOWER POPS NEEDED. THE PRIMARY THREAT CONTINUES TO BE HEAVY RAINFALL. PWATS WILL SURGE AT TIMES TO AROUND 2.3 INCHES WHICH APPROACHES 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF YEAR. THE SEVERE THREAT CONTINUES TO BE LOW...THOUGH A FEW WET MICROBURSTS CANNOT BE RULED OUT IN THE STRONGER THUNDERSTORMS THAT DEVELOP DURING THE TIME OF PEAK HEATING...ESPECIALLY IF THERE IS ANY ORGANIZATION THAT OCCURS. TEMPS WILL BE HELD BELOW NORMAL THANKS TO THE PLENTIFUL CLOUD COVER AND RAINFALL...WITH HIGHS IN THE MID/UPPER 80S EACH DAY. WILL CONTINUE TO HIGHLIGHT THE HEAVY RAINFALL THREAT IN THE HWO. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... THE HIGHLY AMPLIFIED PATTERN WILL PERSIST INTO THE BEGINNING OF THE LONG TERM PERIOD. THE TROUGH TO THE WEST WILL BEGIN TO LIFT OUT EARLY NEXT WEEK AS THE ATLANTIC RIDGE ATTEMPTS TO BUILD IN FROM THE EAST. THE MODELS CONTINUE TO DIFFER A BIT THROUGH MID WEEK AS TO WHETHER OR NOT THE RIDGE BUILDS IN AND ENCOMPASSES MUCH OF THE EASTERN CONUS OR IF WE CONTINUE TO HANG ON TO AT LEAST SOME DEGREE OF A TROUGH TO THE NORTHWEST. REGARDLESS...THE PREFERRED SURFACE PATTERN CONTINUES TO FEATURE A LARGE AND DIFFUSE AREA OF HIGH PRESSURE ACROSS THE SOUTHEAST AND MID ATLANTIC. THIS WILL LEAD TO A RETURN TO MORE CLIMATOLOGICALLY NORMAL CONDITIONS WITH MAINLY DIURNALLY FOCUSED RAIN CHANCES AND HIGHS AROUND 90/LOWS IN THE LOW TO MID 70S. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... AS A STATIONARY FRONT REMAINS SOUTH OF THE ALTAMAHA RIVER...TERMINALS WILL REMAIN WITHIN AN UNSEASONABLE WEDGE REGIME. LOWER CEILINGS ARE EXPECTED TO DEVELOP OVERNIGHT AT KSAV...AND FLIGHT RESTRICTIONS SHOULD PREVAIL MUCH OF THE TIME THROUGH AT LEAST MIDDAY THURSDAY...MAINLY MVFR CEILINGS BUT OCCASIONALLY DETERIORATING TO IFR/LIFR ESPECIALLY AS SHOWERS WITH BRIEF HEAVY RAIN IMPACT THE TERMINALS. GUIDANCE DEPICTS SOME IMPROVEMENT TO VFR CEILINGS OUTSIDE SHOWERS/THUNDERSTORMS BY 16-18Z THURSDAY...THUS INDICATED SOME IMPROVEMENT WITHIN 06Z TAFS BUT CONFIDENCE IN THIS SCENARIO REMAINS LOW. THUNDERSTORMS SHOULD AGAIN BECOME COMMON THURSDAY...ESPECIALLY IN THE AFTERNOON. SPECIFIC TIMING OF THUNDERSTORMS/ASSOCIATED IMPACTS REMAINS ELUSIVE WITHIN THE 06Z TAFS...BUT THE POTENTIAL REMAINS HIGH FOR PRECIPITATION AT ANY TIME THROUGH THE 00Z TAF PERIOD. EXPECT FREQUENT AMENDMENTS ESPECIALLY TO ADDRESS NEAR TERM CONVECTIVE TRENDS. EXTENDED AVIATION OUTLOOK...THERE CONTINUES TO BE HIGH CHANCE FOR AT LEAST PERIODIC WIDESPREAD FLIGHT RESTRICTIONS AS A COLD FRONT BECOMES STATIONARY NEAR THE REGION. OCCASIONAL SHOWERS AND THUNDERSTORMS WILL ALSO OCCUR...WITH HEAVY RAIN AND GUSTY WINDS COMMON. CONDITIONS WILL BEGIN TO IMPROVE EARLY NEXT WEEK AS THE FRONT DISSIPATES. && .MARINE... OUTSIDE CONVECTION...WINDS AND SEAS SHOULD REMAIN BELOW SMALL CRAFT ADVISORY LEVELS THROUGH TONIGHT. EVEN OUTSIDE THUNDERSTORMS...TODAY AND TONIGHT OFFER A COMPLEX FORECAST REGIME ACROSS COASTAL WATERS. THIS MORNING...A MODEST SURGE OF E/NE WINDS WILL SPREAD ACROSS SC WATERS...WHILE A WEAKER GRADIENT WILL CLOSER TO THE STATIONARY FRONT ACROSS THE SOUTH. THIS AFTERNOON...THE GRADIENT SHOULD WEAKEN ACROSS SC WATERS WHILE THE SEA BREEZE CIRCULATION DEVELOPS...PRODUCING MORE WIND DIRECTION/SPEED VARIABILITY. TONIGHT...THE STATIONARY FRONT COULD PUSH BACK INTO THE WATERS AS A WARM FRONT...ALTHOUGH THE N/NW PROGRESS SHOULD REMAIN LIMITED. THUS...WIND FORECASTS REMAIN UNCERTAIN. SEAS WILL AVERAGE 2-3 FT WITHIN NEARSHORE WATERS AND AS HIGH AS 3-5 FT BEYOND 20 NM. MEANWHILE...THUNDERSTORMS WILL GREATLY ALTER LOCAL WINDS AT ANY TIME THROUGH TONIGHT. FRIDAY THROUGH MONDAY...THE COLD FRONT WILL NORTHWARD AND FURTHER INLAND ON FRIDAY LEAVING THE LOCAL WATERS IN A GENERAL SOUTHERLY FLOW AT 10 KTS OR LESS. A COUPLE OF WAVES OF LOW PRESSURE WILL MOVE THROUGH THIS WEEKEND WHICH WILL RESULT IN PERIODS OF SHIFTING WIND DIRECTIONS...THOUGH SPEEDS WILL NOT SEE MUCH CHANGE. SEAS WILL RANGE FROM 2-3 FT THROUGH THE PERIOD AND WE WILL STAY WELL BELOW SMALL CRAFT ADVISORY CRITERIA INTO EARLY NEXT WEEK. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...SPR SHORT TERM...BSH/SPR LONG TERM...BSH AVIATION...SPR MARINE...BSH/SPR TIDES/COASTAL FLOODING...