974 FXUS62 KCHS 031422 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 1022 AM EDT THU OCT 3 2013 .SYNOPSIS... HIGH PRESSURE WILL PREVAIL INTO THE WEEKEND. TROPICAL STORM KAREN OVER THE GULF OF MEXICO WILL THEN COMBINE WITH AN APPROACHING COLD FRONT AS IT PROGRESSES TOWARD THE EAST COAST EARLY NEXT WEEK. HIGH PRESSURE WILL THEN RETURN TO THE REGION BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... WEAK HIGH PRESSURE WILL LINGER AT THE SFC TODAY WHILE A MID LVL RIDGE OF HIGH PRESSURE GRADUALLY FLATTENS AND SLIDES OFF THE SOUTHEAST COAST. AS THE RIDGE SHIFTS OFFSHORE...A SERIES OF WEAK H5 SHORTWAVES WILL SHIFT OVER THE AREA THIS AFTERNOON/EVENING...AND SUPPORT A FEW SHOWERS JUST OFFSHORE WHERE A WEAK COASTAL TROUGH PERSISTS THROUGHOUT THE DAY. A FEW OF THESE SHOWERS MAY APPROACH THE BEACHES NORTH OF EDISTO SC AS A LIGHT NORTHEAST/EAST FLOW OCCURS...BUT ANY MEASURABLE PRECIP OVER LAND IS NOT LIKELY AS ACTIVITY ENCOUNTERS SOME MID LVL DRY AIR. FORECAST SOUNDINGS ACROSS THE AREA DO INDICATE A POTENTIAL FOR SCATTERED TO LOCALLY BROKEN CUMULUS/STRATOCU WITH SOME LOW LVL MOISTURE PRESENT WHILE BROAD DIFLUENCE FROM A 60 KT UPPER LVL JET SUPPORTS CIRRUS CLOUDS OVER MUCH OF THE AREA. THESE CLOUDS MAY LIMIT OVERALL HIGH TEMPS TODAY...ESPECIALLY OVER NORTHERN CHARLESTON AND BERKELEY COUNTIES WHERE MOSTLY CLOUDY SKIES ARE PRESENT. FURTHER SOUTH...TEMPS WILL REMAIN SOMEWHAT LESS EFFECTED WITH MAINLY CIRRUS OVER THE AREA. EXPECT OVERALL HIGH TEMPS TO THE MID TO UPPER 80S OVER MOST LOCATIONS...HIGHEST OVER INLAND AREAS IN SOUTHEAST GEORGIA. CLEAR TO PARTLY CLOUDY SKIES TONIGHT WITH DEW POINTS INCREASING ALONG WITH POTENTIAL FOR AREAS OF FOG LATE. WE TRENDED TOWARD SOME FOG AROUND FRIDAY MORNING WITH MENTIONS OF PATCHY FOG IN THE FORECAST TO TREND. LOWS 60-65 WITH NEAR CALM WINDS. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... THE MAJORITY OF NUMERICAL MODEL SOLUTIONS INDICATE A TROPICAL WAVE IN THE GULF OF MEXICO BY FRIDAY MORNING...DRIFTING NORTHWARD BENEATH AN AMPLIFYING UPPER RIDGE ALONG THE SOUTHEAST COASTLINE. THE EVOLUTION OF THIS WAVE THEN BECOMES A MAJOR FORECAST CONCERN...WITH MODEL REPRESENTATIONS OF ITS STRENGTH AND TRACK IN NOTABLE DISAGREEMENT. THE GFS SOLUTION REMAINS THE MOST AGGRESSIVE...INTENSIFYING THE WAVE INTO A DISCRETE TROPICAL SYSTEM MAKING LANDFALL MIDDAY SATURDAY ALONG THE FLORIDA PANHANDLE...WELL AHEAD OF AN APPROACHING COLD FRONT FROM THE WEST. THE ECMWF SOLUTION HAS BEEN CONSISTENTLY WEAKER WITH THE LOW DEVELOPMENT...KEEPING THE FEATURE AS MORE OF AN OPEN WAVE THROUGH SATURDAY...BEFORE MERGING IT WITH THE SOUTHERN EXTENT OF THE FRONT ALONG THE CENTRAL GULF COAST STATES. VARIOUS OTHER MODEL SOLUTIONS AND AVAILABLE GUIDANCE SHOW THE SYSTEM TRACKING MORE WEST AND REMAINING RELATIVELY WEAKER THAN THE ROBUST GFS SCENARIO. THE LOCAL FORECAST WILL THUS LEAN TOWARD A MORE CONSERVATIVE EVOLUTION OF THIS SYSTEM PER THE ECMWF AND GIVEN WPC GUIDANCE. WILL KEEP RAIN CHANCES BELOW 15 PERCENT ACROSS LAND AREAS FRIDAY AND SATURDAY...AS ATLANTIC SURFACE HIGH PRESSURE AND UPPER LEVEL RIDGING MAINTAIN LARGE SCALE SUBSIDENCE ACROSS THE REGION. THERE IS SOME EVIDENCE THAT A COASTAL TROUGH COULD DEVELOP ALONG THE PERIPHERY OF THE ATLANTIC HIGH...AND HAVE THUS MENTIONED A SLIGHT CHANCE FOR SHOWERS OVER THE MARINE ZONES THROUGH SATURDAY. AN ISOLATED SHOWER COULD PUSH LOCALLY ONSHORE WITHIN SOLID EASTERLY FLOW...HOWEVER TIMING AND COVERAGE ARE TOO UNCERTAIN TO EXPLICITLY MENTION AT THIS POINT. WITH THE AXIS OF THE UPPER TROUGH STRENGTHENING ALONG THE EAST COAST...EVEN AS THE SYSTEM IN THE GULF TAKES SHAPE...TEMPERATURES WILL BE FAIRLY WARM FOR THIS TIME OF YEAR. AFTERNOON HIGHS WILL REACH THE MID TO UPPER 80S WITHIN RISING HEIGHTS ALOFT...WHILE DECENT LOW LEVEL MOISTURE SUPPORTS MILD NIGHTTIME LOWS IN THE LOW/MID 60S FRIDAY NIGHT AND MID/UPPER 60S SATURDAY NIGHT. A DEEP UPPER TROUGH IN THE MISSISSIPPI VALLEY REGION WILL BREAK DOWN RIDGING ALONG THE EAST COAST BY SUNDAY. THE ASSOCIATED COLD FRONT WILL STEADILY PROGRESS INTO THE OHIO/TENNESSEE VALLEY...WHILE THE GULF WAVE BECOMES SWEPT UP ALONG ITS SOUTHERN PERIPHERY. VEERING WINDS TO THE SOUTHEAST WILL TAP INTO TROPICAL MOISTURE...AT THE SAME TIME THAT CONVERGENCE ALONG AND AHEAD OF THE COLD FRONT SUPPORTS MORE WIDESPREAD CONVECTION JUST UPSTREAM. HAVE RAISED POPS INTO THE 30 PERCENT RANGE FOR SUNDAY. WILL INDICATE A SLIGHT COOLING TREND AS HEIGHTS ALOFT FALL AND CLOUD COVER INCREASES...WITH HIGHS RANGING IN THE MID 80S SUNDAY AFTERNOON. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... THE CUTOFF LOW EMBEDDED WITHIN THE LARGE UPPER TROUGH WILL LIFT INTO THE GREAT LAKES REGION MONDAY...WHILE THE COLD FRONT SHIFTS THROUGH THE FORECAST AREA AS THE DAY PROGRESSES. HAVE ADVERTISED THE BEST POTENTIAL FOR SHOWERS/THUNDERSTORMS ON MONDAY AS A RESULT OF THE FRONTAL PROGRESSION. AN EXPANSIVE SURFACE HIGH WILL THEN QUICKLY BUILD EASTWARD IN THE WAKE OF THE FRONT EARLY NEXT WEEK...EVENTUALLY INTRODUCING A DRIER AIR MASS INTO THE REGION. HAVE KEPT LOW TO SLIGHT RAIN CHANCES THROUGH MID WEEK TO ACCOUNT FOR DELAYS IN THE FRONT...HOWEVER MODELS ARE TRENDING WITH A MORE RAPID PROGRESSION. SUBSEQUENT FORECASTS WILL LIKELY BE ABLE TO DECREASE PRECIPITATION POTENTIAL FOR TUESDAY THROUGH THURSDAY IF GUIDANCE CONTINUES WITH THIS TREND. THE BUILDING SURFACE HIGH WILL HAVE TAKEN A MORE SOUTHERN ROUTE FROM THE SOUTHERN PLAINS TOWARD THE FORECAST AREA...AND WITH UPPER RIDGING REBUILDING OVER THE EASTERN HALF OF THE UNITED STATES BY MID WEEK...DO NOT EXPECT A SIGNIFICANT COOLING TREND BEHIND THE DEPARTING FRONT. HAVE INDICATED HIGH TEMPERATURES RETURNING BACK TOWARD SEASONAL NORMALS IN THE LOWER 80S TUESDAY THROUGH THE END OF THE PERIOD. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 06Z FRIDAY. IN THE LAST 6 HOURS OF THE 12Z TAF CYCLE THERE IS A POTENTIAL FOR MVFR VSBYS AT THE TERMINALS. LATER TAF RELEASES TODAY MAY NEED TO CONSIDER ADDITIONS OF REDUCED VSBYS BUT AT THIS TIME CONFIDENCE IS LOWER END. EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL. && .MARINE... TODAY AND TONIGHT...WINDS/SEAS WILL REMAIN WELL BELOW SMALL CRAFT ADVISORY LEVELS AS A WEAK COASTAL TROUGH PERSISTS ALONG HIGH PRESSURE OVER THE WATERS. THE PATTERN WILL RESULT IN NORTHEAST WINDS AT OR BELOW 15 KTS THROUGHOUT THE DAY...WITH SUBTLE DIURNAL OSCILLATIONS ALONG LAND/SEA BREEZE CYCLES. SEAS WILL RANGE BETWEEN 1-3 FT...HIGHEST IN OUTER GEORGIA WATERS. FRIDAY THROUGH MONDAY...RELATIVELY QUIET MARINE CONDITIONS ARE EXPECTED THROUGH SATURDAY. HIGH PRESSURE WILL BE IN CONTROL OF THE PATTERN ACROSS THE LOCAL WATERS...RESULTING IN A PREDOMINANTLY EAST FLOW. WIND SPEEDS WILL BE LESS THAN 15 KT AND SEAS 1-3 FT...HIGHEST OVER THE OUTER WATERS. SINCE THE FORECAST FAVORS MODEL SOLUTIONS THAT INDICATE A WAVE OF LOW PRESSURE BECOMING ABSORBED WITHIN AN APPROACHING FRONT ON SUNDAY...WILL INDICATE A SLIGHT SURGE IN SOUTHEAST FLOW INTO EARLY NEXT WEEK...YET KEEP WIND SPEEDS BELOW SMALL CRAFT ADVISORY CONDITIONS. SEAS WILL BUILD TO 3 TO 5 FT SUNDAY NIGHT INTO MONDAY AFTERNOON. THE COLD FRONT IS EXPECTED TO SHIFT OFF THE COAST LATE MONDAY. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ SYNOPSIS... NEAR TERM...DPB SHORT TERM...WMS LONG TERM...WMS AVIATION...DPB MARINE...DPB/WMS