907 FXUS62 KCHS 180532 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 132 AM EDT TUE JUN 18 2013 .SYNOPSIS... HIGH PRESSURE WILL CONTINUE TO RETREAT FARTHER INTO THE ATLANTIC EARLY THIS WEEK. A COLD FRONT WILL APPROACH FROM THE NORTHWEST TUESDAY...THEN SLOWLY PROGRESS THROUGH THE AREA WEDNESDAY AND THURSDAY. HIGH PRESSURE WILL THEN BUILD FROM THE NORTH INTO THE WEEKEND. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... CLUSTERS OF SHOWERS/TSTMS ARE APPROACHING THE CHARLESTON TRI- COUNTY AREA FROM THE SW AND WILL IMPACT MUCH OF THE METRO AREA THROUGH 3 AM. LOCALLY HEAVY RAINFALL...GUSTY WINDS AND CLOUD TO GROUND LIGHTNING WILL ACCOMPANY THESE STORM. MODIFIED POPS TO MATCH GOING TRENDS. THE BULK OF THE RAINFALL SHOULD MOVE OUT OF THE LOCAL FORECAST AREA BY 5 AM OR SO...BUT A RISK FOR MEASURABLE RAINFALL WILL LINGER THROUGH SUNRISE. && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/... TUESDAY...SFC HIGH PRESSURE WILL GRADUALLY BREAK DOWN EARLY AS A SFC LOW TRACKS OVER THE TENNESSEE VALLEY AND TO THE MID ATLANTIC STATES. SOUTHWEST FLOW AHEAD OF THE SFC LOW WILL LIKELY CONTRIBUTE TO INCREASING LOW LVL MOISTURE OVER THE SOUTHEAST WHILE A SERIES OF H5 SHORTWAVES BEGIN TO SWING AROUND THE SOUTHERN PERIPHERY OF A BROAD MID LVL TROUGH CENTERED NORTHEAST OF THE GREAT LAKES. CHANCES OF SHOWERS/THUNDERSTORMS SHOULD INCREASE IN COVERAGE DURING THE AFTERNOON AS TEMPS WARM INTO THE MID/UPPER 80S...ESPECIALLY FOR INLAND LOCATIONS. GIVEN SFC DEWPTS IN THE LOW 70S...PWATS NEAR 2.0 INCHES...AND WEAK MID/UPPER LVL FLOW...EXPECT PULSE TYPE THUNDERSTORMS CAPABLE OF PRODUCING BRIEF WIND GUSTS AND HEAVY RAINFALL. SHOWER/THUNDERSTORM ACTIVITY SHOULD CONTINUE THROUGH THE OVERNIGHT PERIOD AS A SFC COLD FRONT APPROACHES FROM THE WEST/NORTHWEST LATE. OVERNIGHT LOWS ARE EXPECTED TO BE IN THE LOW/MID 70S. WEDNESDAY AND THURSDAY...A SFC COLD FRONT WILL SLOWLY SHIFT OVER SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA WEDNESDAY MORNING BEFORE GRADUALLY STALLING OVER OR JUST SOUTH OF THE REGION ON THURSDAY. AS THIS OCCURS...PWATS NEAR 2.0 INCHES ALONG WITH MID LVL FORCING SHOULD FAVOR A PERIOD OF SHOWERS/THUNDERSTORMS EARLY WEDNESDAY WITH COLD FROPA BEFORE ACTIVITY SHIFTS SOUTH OVER GEORGIA ZONES ON THURSDAY. SHOWERS/THUNDERSTORMS MAY PRODUCE HEAVY RAINFALL GIVEN THE AMOUNT OF MOISTURE AND WEAK WINDS IN PLACE. GREATEST COVERAGE OF ACTIVITY WILL LIKELY BE ALONG OR NEAR THE FRONT WEDNESDAY MORNING...WITH A 40-60 PERCENT CHANCE OF PRECIPITATION. BY THURSDAY...CHANCES OF PRECIP SHOULD BEGIN TO DECLINE OVER SC ZONES WHILE THE FRONT STALLS AND WEAKENS SOUTH OF INTERSTATE 16 IN GEORGIA. HAVE MAINTAINED 30-40 POPS OVER THE REGION THURSDAY WITH HIGHEST CHANCES FOR SOUTHERN GA ZONES. OVERALL HIGH TEMPS ARE EXPECTED TO PEAK IN THE MID/UPPER 80S OVER MOST LOCATIONS WEDNESDAY...WITH SLIGHTLY COOLER TEMPS IN THE MID 80S OVER SOUTH CAROLINA ON THURSDAY BEHIND THE FRONT. WEDNESDAY NIGHT LOWS ARE EXPECTED TO BE IN THE UPPER 60S TO LOWER 70S. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... THE CENTER OF UPPER LEVEL RIDGING WILL REMAIN WEST OF THE REGION...ALLOWING THE PATTERN ALOFT FOR THE SOUTHEAST STATES TO BE SOMEWHAT WEAK AND PROGRESSIVE THROUGH MUCH OF THE EXTENDED PERIOD. THE LINGERING FRONT NEAR THE SOUTHERN PERIPHERY OF THE FORECAST AREA LOOKS TO REMAIN GENERALLY IN PLACE...EVENTUALLY TRANSITIONING INTO A COASTAL FRONT/COASTAL TROUGH FEATURE AS HIGH PRESSURE BUILDS FROM THE NORTH. MEDIUM RANGE MODEL SOLUTIONS STILL DIVERGE ON DETAILS FOR THE LATE WEEK AND WEEKEND PERIOD...AND HAVE DECIDED TO MAINTAIN A RATHER GENERIC 30 PERCENT POP DURING THE DAYTIME HOURS FRIDAY THROUGH AT LEAST SUNDAY. IF THE COASTAL TROUGH PATTERN DOES INDEED TAKE SHAPE...THEN EXPECT BEST CONVECTIVE COVERAGE TO TRANSITION OFFSHORE EACH NIGHT. HIGH TEMPERATURES WILL VARY LITTLE EACH AFTERNOON...REACHING THE UPPER 80S TO AROUND 90 DEGREES AWAY FROM THE LOCALLY COOLER COASTLINE. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... TSTMS WILL MOVE ACROSS THE KCHS TERMINAL 06-08Z BRINGING GUSTY WINDS AND LOCALIZED IFR VSBYS. THE NEAR TERM RISK FOR TSTMS SHOULD END BY 08Z WITH A RETURN TO VFR CONDITIONS. VFR WILL DOMINATE AT KSAV THROUGH SUNRISE WITH THE BULK OF THE TSTMS ACTIVITY PASSING TO THE NORTH OF THAT TERMINAL. HIGH RESOLUTION MODELS SHOW ANOTHER BATCH OF SHOWERS/TSTMS MOVING ACROSS THE COASTAL CORRIDOR BY LATE MORNING AFTERNOON AS A POTENT SHORTWAVE PUSHES THROUGH. WILL CARRY TEMPO GROUPS FOR 4SM TSRA BR BKN040CB FROM 18-21Z AT KCHS AND 16-19Z AT KSAV TO COVER. ADJUSTMENTS WILL MOST CERTAINLY BE NEEDED AS THE MORNING PROGRESSES. EXTENDED AVIATION...PERIODIC FLIGHT RESTRICTIONS TUESDAY THROUGH THURSDAY IN ASSOCIATION WITH SCATTERED TO NUMEROUS SHRA/TSRA...MAINLY DURING AFTERNOON HOURS. && .MARINE... TONIGHT...SOUTHERLY WINDS WILL INCREASE SLIGHTLY AHEAD OF AN APPROACHING COLD FRONT FAR UPSTREAM. SPEEDS COULD REACH AS HIGH AS 15 TO 20 KT AT TIMES WITH SEAS BUILDING TO 2 TO 4 FT...HIGHEST BEYOND 20 NM. TUESDAY THROUGH FRIDAY...WINDS/SEAS WILL LIKELY REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS FOR MUCH OF THE DAY TUESDAY BEFORE INCREASING TUESDAY NIGHT AS THE PRESSURE GRADIENT TIGHTENS BETWEEN HIGH PRESSURE OVER THE WESTERN ATLANTIC AND A SFC COLD FRONT APPROACHING THE WATERS FROM THE WEST/NORTHWEST LATE. AS A RESULT...SOUTH/SOUTHWEST FLOW IS ANTICIPATED TO SURGE TUESDAY NIGHT WITH 20-25 KT WINDS AND SEAS UP TO 5 FT BEYOND 20 NM. EXPECT WIND DIRECTIONS TO VEER WEST/NORTHWEST AS THE FRONT STEADILY SLIPS OVER THE WATERS WEDNESDAY INTO THURSDAY...WITH WIND SPEEDS DIMINISHING AS THE FRONT WEAKENS/STALLS. NUMERICAL MODEL SOLUTIONS DIFFER REGARDING THE PRECISE LOCATION OF THE STALLING FRONT...BUT WILL LEAN TOWARD PERSISTENCE IN INDICATING A GENERAL EAST/NORTHEAST FLOW FOR THURSDAY AND FRIDAY. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW ADVISORY CONDITIONS THROUGH THE PERIOD. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ ST