Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 012211 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 611 PM EDT WED OCT 1 2014 .SYNOPSIS... HIGH PRESSURE WILL PERSIST ACROSS THE AREA TONIGHT INTO THURSDAY. A STRONG COLD FRONT WILL THEN MOVE THROUGH THE REGION FRIDAY NIGHT...WITH HIGH PRESSURE BUILDING BACK OVER THE SOUTHEAST STATES THROUGH EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... FLAT RIDGING ALOFT AND WEAK SURFACE HIGH PRESSURE WILL GENERATE CONSIDERABLE LARGE SCALE SUBSIDENCE TONIGHT AND ALLOW FOR A RAPID DECOUPLING OF THE TROPOSPHERE. OTHER THAN SOME LINGERING STRATOCUMULUS/ALTOCUMULUS SOUTH OF I-16 THIS EVENING AND A FEW THIN CIRRUS MOVING IN OVERNIGHT...SKIES WILL BE MOSTLY CLEAR. THIS SETS THE STAGE FOR ANOTHER NIGHT WITH NEAR IDEAL RADIATIONAL COOLING. WE/RE STARTING OUT WARMER THIS EVENING...BUT THE LENGTHENING NIGHT TIME HOURS WILL STILL ALLOW FOR LOWS TO DROP INTO THE UPPER 50S AND LOWER 60S FOR MOST COMMUNITIES INLAND FROM US-17...WITH MID AND UPPER 60S NEAR/ALONG THE COAST. WE WERE A LITTLE TOO AGGRESSIVE ON FOG LAST NIGHT...AND THE SOILS ARE CONTINUING TO DRY OUT. PLUS OUR GROUND TEMPS ARE STILL QUITE WARM...IN THE LOWER 70S. SO WE/RE NOT CERTAIN ON THE EXTENT OF FOG FORMATION...MAYBE EVEN A LITTLE GUN SHY AFTER NOT SEEING TOO MUCH FOG LAST NIGHT. BUT SEVERAL FACTORS STILL POINT TO AT LEAST PATCHY FOG DEVELOPING. WE/LL PASS OUR CROSS-OVER TEMPS AFTER MIDNIGHT...FOG STABILITY INDICES ARE MAINLY IN THE TEENS AND MRI VALUES CLEARLY SHOW THE DECOUPLED BOUNDARY LAYER. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... THURSDAY...SURFACE HIGH PRESSURE AND A RIDGE ALOFT WILL LINGER ALONG THE EAST COAST. EXPECT SUFFICIENT SUBSIDENCE AND MID-LEVEL CAPPING WITHIN A RATHER DRY AIR MASS TO EFFECTIVELY SUPPRESS RAIN CHANCES ONCE AGAIN. HAVE THUS MAINTAINED A DRY FORECAST...INDICATING SLIGHTLY MORE CLOUD COVERAGE SOUTH OF THE SAVANNAH WITHIN RETURN FLOW ON THE PERIPHERY OF THE SURFACE HIGH. TEMPERATURES WILL RISE WELL ABOVE SEASONAL NORMALS...PEAKING IN THE UPPER 80S AWAY FROM THE LOCALLY COOLER COASTLINE. NIGHTTIME LOW TEMPERATURES WILL TREND SLIGHTLY WARMER...FALLING INTO THE LOW TO MID 60S INLAND. FRIDAY...RIDGING AT THE SURFACE AND ALOFT WILL STEADILY SLIP OFF THE EAST COAST EARLY IN THE DAY...AS A DIGGING UPPER TROUGH MOVES FROM THE CENTRAL UNITED STATES INTO THE OHIO AND TENNESSEE VALLEYS. NUMERICAL MODEL SOLUTIONS CONTINUE TO SUGGEST AN EVENING OR EVEN NIGHTTIME FRONTAL PASSAGE...DELAYING THE ONSET OF BEST RAIN COVERAGE UNTIL AFTER SUNSET. HAVE INDICATED SHOWER/THUNDERSTORM CHANCES INCREASING FROM SOUTHWEST TO NORTHEAST AHEAD AND ALONG THE FRONT...PEAKING IN THE 50 TO 60 PERCENT RANGE BETWEEN 00Z AND 06Z FRIDAY NIGHT. CONSIDERING THE EXPECTED INCREASE IN CLOUD COVERAGE WELL AHEAD OF THE FRONT...AS WELL AS ISOLATED PRE-FRONTAL PRECIPITATION ASSOCIATED WITH RETURN FLOW AND/OR A SUBTLE LIFTING WARM FRONT...INSTABILITY IN MODEL SOLUTIONS APPEARS RATHER MARGINAL FRIDAY AFTERNOON AND EVENING. BULK SHEAR VALUES STILL REACH 30 TO 40 KT DURING THE EVENING...YET CONSIDERING THE MARGINAL INSTABILITY AND LESS-FAVORABLE FRONTAL TIMING...SEVERE WEATHER POTENTIAL CONTINUES TO LOOK GENERALLY LOW. WILL CONTINUE TO MONITOR TRENDS...YET PREFER NOT TO MENTION ANY SEVERE STORM CONCERNS IN THE HAZARDOUS WEATHER OUTLOOK. HIGH TEMPERATURES WILL STILL BE A DEGREE OR TWO ABOVE SEASONAL NORMALS DUE TO SOME PRE-FRONTAL COMPRESSION EFFECTS AND WARM SOUTHERLY FLOW...YET BE COOLER THAN THE PREVIOUS DAY UNDER THE THICKENING CLOUD COVER. SATURDAY...THE STRONG COLD FRONT WILL MAKE RAPID PROGRESS THROUGH THE FORECAST AREA FRIDAY NIGHT...SWIFTLY MOVING OFF THE COAST AND FARTHER INTO THE ATLANTIC INTO SATURDAY MORNING. EXPECT THUNDERSTORM CHANCES TO ALSO QUICKLY DECREASE FROM WEST TO EAST AS A NOTABLY DRIER AND COOLER AIR MASS MOVES INTO THE REGION IN THE WAKE OF THE FRONT. PREFER TO ADVERTISE RAIN CHANCES BELOW 15 PERCENT BY SUNRISE SATURDAY AND FALLING TO ZERO BY THE AFTERNOON. DESPITE CLEARING SKIES AND MORE ABUNDANT SUNSHINE...AMPLE COLD ADVECTION BEHIND THE FRONT WILL SUPPRESS HIGH TEMPERATURES IN THE 70S SATURDAY AFTERNOON. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE WILL MOVE EASTWARD OVER THE AREA THROUGH EARLY NEXT WEEK WITH TEMPS SLOWLY MODERATING. THE COOLEST TEMPS WILL COME SUNDAY MORNING WHEN 40S ARE POSSIBLE INLAND. THE CHILLY START WILL YIELD A COOL AFTERNOON WITH HIGHS SUNDAY POSSIBLY NOT GETTING OUT OF THE 60S. && .AVIATION /22Z WEDNESDAY THROUGH MONDAY/... VFR WITH A SLIGHT CHANCE OF MVFR/LOWER VSBYS TOWARD DAYBREAK ON THURSDAY MORNING WITH ANOTHER BOUT OF RADIATIONAL FOG. EXTENDED AVIATION OUTLOOK...LATE NIGHT/EARLY MORNING FOG AND/OR STRATUS ARE POSSIBLE EARLY THURSDAY AND FRIDAY. FLIGHT RESTRICTIONS WILL BE LIKELY LATE FRIDAY INTO EARLY SATURDAY...AS A COLD FRONT WITH SHOWERS AND THUNDERSTORMS MOVES THROUGH THE REGION. VFR CONDITIONS WILL PREVAIL OTHERWISE. && .MARINE... TONIGHT...THE SOUTHERN EXTENSION OF A LARGE AREA OF MODIFYING CANADIAN HIGH PRESSURE WILL BE LOCATED ACROSS THE MARINE TERRITORY...WITH A RELAXED EAST AND NE FLOW TO PREVAIL. SEAS WON/T BE NO MORE THAN 2 OR 3 FT...HIGHEST AS ONE NAVIGATES ACROSS THE OUTER GA WATERS. THURSDAY THROUGH MONDAY...HIGH PRESSURE ON THURSDAY WILL DEPART FARTHER OFFSHORE AHEAD OF AN APPROACHING COLD FRONT LATE FRIDAY. SOUTHERLY WINDS WILL INCREASE ON FRIDAY AHEAD OF THE FRONT...BEFORE FLOW SHIFTS WEST EARLY SATURDAY AS THE FRONT PUSHES THROUGH THE REGION. A TIGHT PRESSURE GRADIENT AND COLD ADVECTION WILL SUPPORT ANOTHER SURGE BEHIND THE FRONT SATURDAY...WITH CONDITIONS POSSIBLY REACHING MARGINAL ADVISORY LEVELS...ESPECIALLY BEYOND 20 NM. WINDS/SEAS WILL IMPROVE RATHER QUICKLY SATURDAY NIGHT INTO SUNDAY...AS HIGH PRESSURE BUILDS IN FROM THE WEST AND TRANQUIL CONDITIONS PERSIST INTO MONDAY. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...

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