AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 423 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 INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... SURFACE HIGH PRESSURE WILL CONTINUE TO SLIDE OFFSHORE AND INTO THE ATLANTIC. SHOULD SEE A GOOD BIT OF SUN TODAY AS MOST OF THE HIGH CLOUDS ASSOCIATED WITH SOME WEAK SHORTWAVE/JET ENERGY REMAIN NORTH OF THE AREA. INCREASING LOW-LEVEL THICKNESSES SUPPORT WARMER TEMPERATURES COMPARED TO YESTERDAY...GENERALLY AROUND 80 OR LOWER 80S AWAY FROM THE LOCALLY COOLER COASTAL AREAS. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... TONIGHT...MORE ESTABLISHED RETURN FLOW WILL YIELD HIGHER DEWPOINTS AND WITH MAINLY CLEAR SKIES THERE WILL BE THE RISK FOR SOME FOG AFTER MIDNIGHT. THIS WILL ALSO KEEP TEMPERATURES UP A BIT...GENERALLY BOTTOMING OUT IN THE MID TO UPPER 50S AWAY FROM THE MILDER COASTAL AREAS. TUESDAY THROUGH THURSDAY... UPPER LEVEL RIDGING WILL BUILD OVER THE SOUTHEASTERN STATES TUESDAY AND WEDNESDAY...THEN FLATTEN ON THURSDAY AS A TROUGH PASSES TO THE NORTH. AT THE SURFACE...ATLANTIC HIGH PRESSURE WILL PREVAIL THROUGH WEDNESDAY NIGHT. A BACKDOOR COLD FRONT WILL THEN LIKELY DROP INTO THE AREA ON THURSDAY AND STALL AS IT BECOMES NEARLY PARALLEL TO THE UPPER LEVEL FLOW. STRONG SUBSIDENCE...VERY LIMITED MOISTURE AND A LACK OF A FORCING MECHANISM OTHER THAN THE DAILY SEA BREEZE WILL RESULT IN RAIN-FREE CONDITIONS THROUGH WEDNESDAY NIGHT. DEEPENING MOISTURE PROFILES AND WEAK LOW LEVEL CONVERGENCE/LIFT ALONG THE BACKDOOR COLD FRONT WILL SUPPORT EITHER A SLIGHT CHANCE OR LOW CHANCE OF SHOWERS AND PERHAPS A FEW THUNDERSTORMS ON THURSDAY. PATCHY FOG AND/OR LOW STRATUS IS ALSO POSSIBLE TUESDAY NIGHT...WITH ATLANTIC MOISTURE ADVECTING ONSHORE AND BECOMING TRAPPED BENEATH A NOCTURNAL INVERSION. SINCE IT IS STILL UNCERTAIN IF WINDS WILL BE LIGHT ENOUGH TO SUPPORT FOG OR A BIT STRONGER RESULTING IN A STRATUS DECK...WILL KEEP MENTION OUT OF THE FORECAST AT THIS TIME. BUILDING HEIGHTS ALOFT AND A SOLID SOUTHERLY RETURN FLOW WILL SUPPORT RISING AND WELL ABOVE NORMAL TEMPERATURES THROUGH WEDNESDAY. IT IS VERY POSSIBLE THAT HIGHS BY WEDNESDAY COULD REACH THE UPPER 80S TO AROUND 90 AWAY FROM THE COAST. TEMPERATURES ON THURSDAY WILL BE HIGHLY DEPENDENT ON THE TIMING OF THE BACKDOOR COLD FRONT...BUT WITH INCREASING MOISTURE AND CLOUD COVER THINK TEMPERATURES WILL COOL FROM WEDNESDAY WITH A DECENT NORTH TO SOUTH GRADIENT. && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN IN THE LONG TERM PERIOD. A DIFFUSE BACKDOOR COLD FRONT WILL LINGER NEAR OR OVER THE AREA INTO FRIDAY...AS A COOL/MOIST WEDGE OF HIGH PRESSURE BUILDS FROM THE NORTH. THE WEDGE WILL BEGIN TO ERODE FRIDAY NIGHT INTO SATURDAY AS THE PARENT HIGH SHIFTS OFFSHORE NORTH OF THE AREA. THE HIGH WILL THEN PREVAIL OVER THE ATLANTIC INTO EARLY NEXT WEEK...ESTABLISHING A SOUTHERLY RETURN FLOW OVER THE REGION. THERE WILL BE A SLIGHT/LOW CHANCE OF SHOWERS AND A FEW THUNDERSTORMS THURSDAY NIGHT INTO FRIDAY NIGHT WITH THE LINGERING BOUNDARY AND WEDGING IN PLACE. RAIN FREE CONDITIONS ARE THEN EXPECTED THROUGH THE REMAINDER OF THE LONG TERM PERIOD. AS FOR TEMPERATURES...A LARGE GRADIENT IS EXPECTED FROM NORTH TO SOUTH ON FRIDAY...WHICH SHOULD BE THE COOLEST DAY OF THE WEEK...THEN TEMPERATURES SHOULD GRADUALLY WARM ABOVE NORMAL OVER THE WEEKEND INTO EARLY NEXT WEEK. && .AVIATION /08Z 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 TONIGHT AS HIGH PRES SLOWLY SHIFTS FARTHER E INTO THE ATLC. WINDS WILL MAINLY BE 10 KT OR LESS WITH SEAS 3 FT OR LESS...DOMINATED BY ABOUT A 9 SECOND PERIOD SWELL. RIP CURRENTS...MODERATE RISK OF RIPS TODAY MAINLY DUE TO THE ENHANCED ASTRONOMICAL EFFECTS AND AROUND 9 SECOND E SWELL. TUESDAY THROUGH SATURDAY...ATLANTIC HIGH PRESSURE WILL DOMINATE THROUGH THURSDAY...THEN A BACKDOOR COLD FRONT COULD AFFECT THE AREA LATE IN THE WEEK. ATLANTIC HIGH PRESSURE WILL THEN RETURN ON SATURDAY. WINDS COULD SURGE UPWARDS OF 15-20 KT IN CHARLESTON HARBOR DURING THE MID TO LATE AFTERNOON HOURS TUESDAY AND WEDNESDAY WITH THE SEA BREEZE...AND OVER THE COASTAL WATERS TUESDAY NIGHT AND WEDNESDAY NIGHT WITH THE DEVELOPMENT OF A NOCTURNAL LOW LEVEL JET. OTHERWISE...WINDS/SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH THE FORECAST PERIOD. SEA FOG...SREF GUIDANCE ALONG WITH THE NAM12 CONTINUE TO INDICATE THE POTENTIAL FOR SEA FOG DEVELOPMENT BEGINNING AS EARLY AS TUESDAY 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 ANY 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 AT LEAST TUESDAY. 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. && $$