AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 128 AM EDT MON APR 18 2011 .SYNOPSIS... HIGH PRESSURE WILL PREVAIL THROUGH WEDNESDAY. A BACKDOOR COLD FRONT AND WEDGE OF HIGH PRESSURE WILL AFFECT THE AREA THURSDAY AND FRIDAY. HIGH PRESSURE WILL THEN BUILD IN FROM THE WESTERN ATLANTIC NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... HIGH PRESSURE AND LIGHT WINDS WILL PROVIDE EXCELLENT RADIATIONAL COOLING CONDITIONS INLAND...WITH LITTLE IMPACT FROM THIN HIGH CLOUDS STREAMING INTO THE REGION FROM THE WEST. THUS...LOWS IN THE 40S WILL BE COMMON AWAY FROM THE IMMEDIATE COAST. ON SEA ISLANDS/BEACHES...SOME DEGREE OF PARALLEL SHORE/ONSHORE FLOW WILL HOLD TEMPERATURES WITHIN A FEW DEGREES OF 60F. NO MAJOR CHANGES NEEDED WITH THE 130 AM UPDATE. PATCHY GROUND FOG CANNOT BE RULED OUT TOWARD DAYBREAK...BUT MOST FOG SHOULD REMAIN QUITE SHALLOW AND PRODUCE LITTLE/NO IMPACTS. && .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/... HIGH PRESSURE WILL REMAIN IN FIRM CONTROL OF THE AREAS WEATHER THROUGH THE SHORT TERM PERIODS. MODEL SOUNDINGS INDICATE A STRONG CAPPING INVERSION ACROSS THE AREA THROUGH THE PERIOD...AND WITH NO SIGNIFICANT LIFTING MECHANISM ASIDE FROM THE SEA BREEZE TO BREAK THE CAP...WE ARE NOT ANTICIPATING ANY AFTERNOON SHOWER/THUNDERSTORM DEVELOPMENT. THEREFORE...WILL KEEP THE FORECAST RAIN FREE MONDAY THROUGH WEDNESDAY. COULD SEE SOME PATCHY FOG DEVELOPMENT MONDAY NIGHT AND TUESDAY NIGHT WITH GENERALLY CLEAR SKIES IN PLACE...BUT VISIBILITIES DON/T APPEAR THAT THEY WILL DROP TO LEVELS THAT WARRANT A MENTION IN THE FORECAST AT THIS TIME. TEMPERATURES ARE EXPECTED TO RUN CLOSE TO NORMAL ON MONDAY...BEFORE WARMING TO WELL ABOVE NORMAL LEVELS TUESDAY AND WEDNESDAY. IN FACT...COULD SEE HIGHS TOP 90 DEGREES AWAY FROM THE COAST ON WEDNESDAY. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... MEDIUM RANGE GUIDANCE IS IN GENERAL AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN IN THE LONG TERM PERIOD...BUT DIFFER WITH REGARDS TO THE DETAILS. A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH ON THURSDAY...BUT AS IT BECOMES NEARLY PARALLEL TO THE FLOW ALOFT IT SHOULD BEGIN TO SLOW ITS PROGRESSION TOWARD THE AREA. IT APPEARS THAT THE FRONT COULD STALL SOMEWHERE ACROSS THE AREA THURSDAY NIGHT INTO FRIDAY...IF NOT PUSH JUST SOUTH OF THE AREA. A WEDGE OF HIGH PRESSURE WILL THEN BUILD FROM THE NORTH AND PERSIST INTO SATURDAY. IT THEN APPEARS THAT THE WEDGE SHOULD ERODE EARLY IN THE WEEKEND AS THE PARENT HIGH SHIFTS OFFSHORE TO THE NORTH...WITH A SOUTHERLY RETURN FLOW RETURNING BY LATE IN THE WEEKEND. THIS PATTERN WOULD SUPPORT AT LEAST A SLIGHT CHANCE OR LOW CHANCE OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS THURSDAY AND FRIDAY...WITH A RETURN TO RAIN FREE CONDITIONS OVER THE WEEKEND. HIGH TEMPERATURES WILL REMAIN ABOVE NORMAL AHEAD OF THE FRONT ON THURSDAY...BUT THEN COOL AS THE WEDGE BUILDS ON FRIDAY WITH A LARGE GRADIENT POSSIBLE FROM NORTH TO SOUTH ACROSS THE AREA. WARMER CONDITIONS WILL THEN RETURN FOR THE WEEKEND. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... VFR. ONSHORE WINDS WILL PICK UP WITH THE SEA BREEZE THIS AFTERNOON...AVERAGING AROUND 10 KT. EXTENDED AVIATION OUTLOOK...PATCHY GROUND FOG COULD RESULT IN MVFR OR LOWER VISIBILITIES AROUND DAYBREAK TUESDAY THROUGH THURSDAY. && .MARINE... THERE ARE NO MARINE CONCERNS THROUGH DAYBREAK WITH HIGH PRES OVER THE AREA. WINDS WILL REMAIN 10 KT OR LESS WITH SEAS 1-3 FT...DOMINATED BY A 7-10 SECOND PERIOD SWELL. MONDAY THROUGH FRIDAY...ATLANTIC HIGH PRESSURE WILL DOMINATE THROUGH THURSDAY...THEN A BACKDOOR COLD FRONT COULD AFFECT THE AREA LATE IN THE WEEK. OVERALL...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH THE FORECAST PERIOD. THE ONE EXCEPTION MAY BE IN CHARLESTON HARBOR WHERE THE SEA BREEZE MAY ALLOW WINDS TO REACH 20 KNOTS DURING THE MID TO LATE AFTERNOON HOURS TUESDAY AND WEDNESDAY. SEA FOG...SREF GUIDANCE ALONG WITH THE NAM12 CONTINUE TO INDICATE THE POTENTIAL FOR SEA FOG DEVELOPMENT BEGINNING AS EARLY AS MONDAY NIGHT AND CONTINUING THROUGH WEDNESDAY. THIS APPEARS LARGELY OVERDONE...GIVEN THE SMALL WINDOW OF RETURN FLOW PRIOR THE MODELS DEVELOPING THE SEA FOG. THE MOST PROBABLE TIME FOR ANY SEA FOG DEVELOPMENT IF AT MANAGES TO FORM APPEARS TO BE TUESDAY NIGHT INTO WEDNESDAY MORNING WHEN SURFACE DEWPOINTS ARE EXPECTED TO RISE INTO THE UPPER 60S TO AROUND 70 DEGREES. IT CERTAINLY ISN/T A SLAM DUNK GIVEN NEARSHORE WATER TEMPERATURES IN THE UPPER 60S TO LOWER 70S...ALONG WITH INCREASING BOUNDARY LAYER WINDS AS THE GRADIENT TIGHTENS OVER THE REGION. NEVERTHELESS...IT WILL BE SOMETHING TO WATCH FOR OVER THE NEXT SEVERAL DAYS. && .TIDES/COASTAL FLOODING... PREDICTED TIDE LEVELS REMAIN CLOSE TO SHALLOW COASTAL FLOODING LEVELS EACH EVENING THROUGH WEDNESDAY. COASTAL FLOOD ADVISORIES MAY EVENTUALLY BE NEEDED FOR PORTIONS OF THE SOUTH CAROLINA AND GEORGIA COASTS. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$