Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 301746 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 146 PM EDT THU JUL 30 2015 .SYNOPSIS... A WEAK PRESSURE PATTERN WILL PERSIST TODAY. A WEAK COLD FRONT WILL STALL OVER THE REGION FRIDAY INTO EARLY NEXT WEEK. ATLANTIC HIGH PRESSURE WILL GRADUALLY BUILD INTO THE REGION BY THE MIDDLE OF NEXT WEEK. AN INLAND TROUGH WILL THEN DEVELOP BY LATE WEEK. && .NEAR TERM /THROUGH TONIGHT/... EARLY THIS AFTERNOON...THE CUMULUS FIELD IS MORE DEVELOPED ACROSS THE FORECAST AREA THAN IT WAS 24 HOURS AGO. SHOWERS AND THUNDERSTORMS ARE DEVELOPING UPSTREAM ACROSS THE MIDLANDS...AND THESE WILL MOVE SOUTHWARD WITHIN THE PREVAILING DEEP LAYER NORTHERLY FLOW. INSTABILITY IS STILL NOT IMPRESSIVE WITH WEAK MID LEVEL LAPSE RATES. THE SEVERE THREAT IS STILL QUITE LOW...THOUGH WE WILL LIKELY SEE MORE COVERAGE THAN WE DID WEDNESDAY AFTERNOON. NO CHANGES WERE MADE TO THE GOING FORECAST AS IT IS STILL ON TRACK. TONIGHT...A WEAK SW SYNOPTIC FLOW WILL ENSUE IN THE WAKE OF THE GULF STREAM LOW AND THE APPROACH OF A WEAK COLD FRONT. MODELS DEEPEN MOISTURE PROFILES OVERNIGHT AND SUGGEST A FEW SHOWERS AND TSTMS COULD LINGER OVERNIGHT ACROSS THE AREA. WE HELD ONTO SLIGHT CHANCE POPS ALL ZONES AFTER THE MID EVENING HOURS. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... FRIDAY...A WEAK COLD FRONT WILL PUSH INTO THE REGION FROM THE NORTHWEST. THIS FEATURE WILL HELP FOCUS A BAND OF MOISTURE FEATURING PWATS EXCEEDING 2 INCHES...1-3 STANDARD DEVIATIONS ABOVE NORMAL... WITHIN THE WEAK UPPER TROUGH/WEAKNESS BETWEEN ATLANTIC AND INLAND RIDGES. THIS SCENARIO IS STILL EXPECTED TO SUPPORT AN ACTIVE CONVECTIVE REGIME ESPECIALLY FRIDAY AFTERNOON...WHEN THE LATEST FORECAST INCLUDES LIKELY POPS AT MANY LOCATIONS...AND SCATTERED SHOWERS/THUNDERSTORMS SHOULD LINGER THROUGH FRIDAY NIGHT. A COMPLEX CONVECTIVE OUTFLOW ENVIRONMENT SHOULD DEVELOP...AND THIS WILL IN TURN MODULATE PROPAGATION THROUGH THE PERIOD. THUS...THE LATEST GENERALIZED PRECIPITATION FORECAST WILL REQUIRE SIGNIFICANT SHORT/NEAR TERM ADJUSTMENTS TO ADDRESS AS YET UNKNOWN DETAILS. OVERALL...A FEW PULSE SEVERE THUNDERSTORMS WITH DAMAGING WET MICROBURSTS WILL BE POSSIBLE...AND WEAK STEERING WINDS/HIGH PRECIPITATION EFFICIENCY COULD SUPPORT LOCALLY HEAVY RAINFALL. TEMPERATURES COULD TOP OUT IN THE LOWER 90S AWAY FROM THE COAST PRIOR TO THUNDERSTORM DEVELOPMENT...THEN HOURLY TEMPERATURES COULD TURN OUT MUCH COOLER WHERE THUNDERSTORMS DEVELOP. SATURDAY AND SUNDAY...MODEL DISAGREEMENT REGARDING THE PROGRESS OF DRIER AIR FROM THE NORTH/NORTHWEST TRANSLATES TO FORECAST UNCERTAINTY REGARDING POPS AND TEMPERATURES. THE 30/00Z NAM APPEARS TOO DRY AND WAS NOT EXPLICITLY INCORPORATED INTO THE LATEST FORECAST. THE 30/00 GFS DEPICTS A FAIR DEGREE OF DRYING ACROSS NORTHERN/INLAND COUNTIES...RESULTING IN SOMEWHAT REDUCED COVERAGE OF DIURNAL CONVECTION AND ALLOWING INLAND TEMPERATURES TO RECOVER INTO THE LOWER/MID 90S. ON THE OTHER HAND...THE 30/00Z EUROPEAN SOLUTION DEPICTS SUFFICIENT MOISTURE TO SUPPORT ABOVE NORMAL POPS ESPECIALLY EACH AFTERNOON/EVENING...WITH THE RESULTING PRECIPITATION/CLOUD COVER HOLDING DOWN TEMPERATURES. AS A COMPROMISE...GRADUATED SATURDAY PM POPS FROM CHANCE NORTH/INLAND TO LIKELY SOUTH...AND SUNDAY AFTERNOON POPS ARE TAPERED FROM 30-40 PERCENT NORTH/INLAND TO AROUND 50 PERCENT SOUTH. DUE TO UNEVEN MODEL TRENDS/RUN TO RUN CONSISTENCY...FORECAST CONFIDENCE REMAINS LESS THAN IDEAL THIS WEEKEND...AND ADDITIONAL ADJUSTMENTS CAN BE EXPECTED WITHIN SUBSEQUENT FORECASTS. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... THE REMNANTS OF THE STATIONARY FRONT WILL GRADUALLY DISSIPATE EARLY NEXT WEEK...AND THE BAND OF DEEPEST MOISTURE SHOULD PUSH JUST OFF THE COAST. THEN...ATLANTIC HIGH PRESSURE IS EXPECTED TO EXPAND INTO THE REGION THROUGH MIDWEEK. THUS...AFTERNOON/EVENING POPS REMAIN SLIGHTLY ABOVE NORMAL MONDAY...THEN DIURNAL POPS DIMINISH TUESDAY THROUGH THURSDAY. BY LATE WEEK...A TROUGH OF LOW PRESSURE COULD DEVELOP INLAND...AND DEPENDING ON THE POSITION OF THE TROUGH A SOMEWHAT MORE ACTIVE CONVECTIVE REGIME COULD DEVELOP. OTHERWISE... THIS PATTERN SHOULD SUPPORT NORMAL TO ABOVE NORMAL TEMPERATURES. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 18Z FRIDAY. THE BEST COVERAGE OF SHOWERS AND STORMS THIS AFTERNOON WILL REMAIN INLAND AND AWAY FROM THE TERMINALS. THEN OVERNIGHT...THE POTENTIAL FOR FOG/STRATUS DEVELOPMENT IS QUITE LOW. EXTENDED AVIATION OUTLOOK...THUNDERSTORMS COULD PRODUCE FLIGHT RESTRICTIONS AT TERMINALS ANYTIME FRIDAY AFTERNOON THROUGH MONDAY...ESPECIALLY DURING THE AFTERNOON/EVENING HOURS. OUTSIDE THUNDERSTORMS...MAINLY VFR. && .MARINE... A WEAK PRES PATTERN REMAINS TODAY AS AN OFFSHORE LOW MOVES TO THE NE OF THE WATERS BY THIS EVENING. LIGHT AND VARIABLE FLOW TODAY WITH A BIT OF NW COMPONENT AREA AND ONSHORE COMPONENT LATE. FLOW WILL BECOME SW TONIGHT WITH A SURGE TO AROUND 15 KT OFFSHORE AND PERHAPS ALONG THE CHARLESTON COUNTY COAST. SEAS 1 TO 2 FT THIS MORNING WILL BE MORE IN THE 2 TO 3 FT RANGE TONIGHT. FRIDAY THROUGH TUESDAY...AS A COLD FRONT APPROACHES THEN STALLS OVER THE REGION...S/SW WINDS WILL PREVAIL MUCH OF THE TIME. THE SEA BREEZE CIRCULATION WILL CAUSE WINDS TO BACK TO THE S/SE AND INCREASE IN SPEED EACH AFTERNOON...AND NOCTURNAL SURGES OF SOUTH/SOUTHWEST WINDS COULD OCCUR EACH NIGHT. THIS REGIME WILL BE DISRUPTED BY THE LATE NIGHT/EARLY MORNING LAND BREEZE...WHEN LIGHTEST WINDS/ BOUNDARIES COULD SUPPORT WATERSPOUTS...AND BY THUNDERSTORMS WHICH WILL PERIODICALLY CROSS THE WATERS. OUTSIDE THESE EXCEPTIONS... HIGHEST WINDS SHOULD REMAIN CAPPED AT 15-20 KNOTS...ALTHOUGH THE PROBABILITY FOR SMALL CRAFT ADVISORY GUSTS TO 25 KT WILL INCREASE DURING THE NIGHTTIME EARLY NEXT WEEK. SEAS WILL REMAIN 2-4 FT MUCH OF THE TIME...ALTHOUGH PERIODS OF 4-5 FT SEAS ARE POSSIBLE AT NIGHT ESPECIALLY LATE WEEKEND INTO EARLY NEXT WEEK. && .TIDES/COASTAL FLOODING... COASTAL FLOOD ADVISORIES ARE LIKELY ALONG THE SOUTH CAROLINA COAST AROUND THE TIME OF HIGH TIDE THIS EVENING. AN ADVISORY IS ALSO POSSIBLE AT FORT PULASKI AS HIGH TIDE EXCEEDS 9 FT MLLW. ELEVATED HIGH TIDE LEVELS WILL CONTINUE FRIDAY THROUGH THE UPCOMING WEEKEND THANKS TO THE UPCOMING PERIGEAN SPRING TIDE. SHALLOW COASTAL FLOODING IS LIKELY INTO EARLY NEXT WEEK ESPECIALLY DURING EACH EVENING HIGH TIDE. WILL CONTINUE TO HIGHLIGHT THE SHALLOW COASTAL FLOOD THREAT WITHIN THE HAZARDOUS WEATHER OUTLOOK. ALSO OF NOTE...THERE IS A CHANCE THAT HEAVY RAIN COULD COINCIDE WITH THE ELEVATED HIGH TIDES. IF THIS OCCURS...MORE SERIOUS LOCALIZED FLOODING COULD OCCUR...PARTICULARLY IN DOWNTOWN CHARLESTON. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ NEAR TERM...BSH SHORT TERM...SPR LONG TERM...SPR AVIATION...BSH MARINE...SPR TIDES/COASTAL FLOODING...

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