AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 730 PM EDT MON APR 18 2011 .SYNOPSIS... HIGH PRESSURE WILL PREVAIL THROUGH WEDNESDAY. A COLD FRONT WILL STALL OVER OR JUST NORTH OF THE REGION THURSDAY AND FRIDAY...BEFORE HIGH PRESSURE BUILDS INTO THE AREA OVER THE WEEKEND AND INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... ATLANTIC HIGH PRESSURE WILL EXTEND WEST ACROSS THE REGION TONIGHT. CLEAR SKIES AND LIGHT WINDS WILL PROMOTE ANOTHER SOLID RADIATIONAL COOLING SETUP...ALTHOUGH A DEEPENING ONSHORE FLOW WILL TEMPER THERMAL DECLINES SOMEWHAT ESPECIALLY CLOSE TO THE COAST. GENERALLY CUT THE COOLEST MODEL GUIDANCE BY 2-3 DEGREES BASED ON MODEL PERFORMANCE LAST NIGHT. LOWS WILL RANGE FROM THE LOWER 50S INLAND TO AROUND 60F BEACHES. INCREASING DEWPOINTS AND A LIGHT/CALM WIND REGIME COULD SUPPORT PATCHY GROUND FOG OVERNIGHT...BUT POTENTIAL IMPACT REMAINS INSUFFICIENT TO JUSTIFY A MENTION WITHIN PUBLIC FORECASTS. THE ONLY EXCEPTION COULD BE NEAR RIVERS...HARBORS AND OTHER WATERWAYS WHERE SIGNIFICANT STEAM FOG COULD FORM PRIOR TO SUNRISE. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... MODEL SOLUTIONS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM PERIODS THIS AFTERNOON. HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL BE THE DOMINANT WEATHER INFLUENCE OVER THE SOUTHEAST STATES TUESDAY THROUGH WEDNESDAY NIGHT. A COUPLE MODEL SOLUTIONS TRY TO DEVELOP SOME CONVECTION ALONG THE SEA BREEZE...BUT WITH A STRONG CAPPING INVERSION IN PLACE ALONG WITH SEA SURFACE TEMPERATURES STILL WELL SHY OF 80 DEGREES FAHRENHEIT...PROBABILITIES OF ANY SHOWERS/THUNDERSTORMS ARE TOO LOW TO MENTION IN THE FORECAST AT THIS TIME. THEREFORE...WILL KEEP THE FORECAST RAIN FREE TUESDAY THROUGH WEDNESDAY NIGHT. HIGH PRESSURE BUILDING WELL NORTH OF THE REGION ON THURSDAY WILL ALLOW FOR A SURFACE COLD FRONT TO PUSH SOUTHWARD TOWARD OR INTO THE FORECAST AREA. THERE IS STILL SOME UNCERTAINTY WITH RESPECT TO HOW FAR SOUTH THIS FRONT WILL MAKE IT BEFORE IT STALLS OUT...BUT REGARDLESS...IT APPEARS THAT DEEP MOISTURE WILL BE ON THE INCREASE. AS A RESULT...WILL CARRY CHANCE POPS FOR SHOWERS/THUNDERSTORMS ACROSS THE FORECAST AREA...HIGHEST ACROSS NORTHERN ZONES IN CLOSEST PROXIMITY TO THE FRONT. EXPECT UNSEASONABLY WARM TEMPERATURES THROUGH THE SHORT TERM PERIODS...WITH HIGHS IN THE MID 80S TO LOWER 90S AWAY FROM THE COAST AND LOWS IN THE 60S. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 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 /00Z TUESDAY THROUGH SATURDAY/... LOW PROBABILITY THAT SHALLOW GROUND FOG COULD BRIEFLY DEEPEN TO PRODUCE MVFR OR LOWER VISIBILITIES AT BOTH TERMINALS LATE TONIGHT/ AROUND DAYBREAK TUESDAY...NOT MENTIONED WITHIN 00Z TAFS. OTHERWISE...VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH TUESDAY. EXTENDED AVIATION OUTLOOK...THERE IS A CHANCE FOR MVFR OR LOWER CIGS AND/OR VSBYS AROUND DAYBREAK WEDNESDAY THROUGH FRIDAY. THUNDERSTORMS MAY ALSO IMPACT THE TERMINALS THURSDAY AFTERNOON AND FRIDAY AFTERNOON WITH MVFR/IFR VSBYS AND/OR CIGS. && .MARINE... THERE ARE NO MARINE CONCERNS THROUGH TONIGHT AS HIGH PRES SLOWLY SHIFTS FARTHER E INTO THE ATLANTIC. WINDS WILL REMAIN 10 KT OR LESS WITH SEAS 3 FT OR LESS...DOMINATED BY AN 8-10 SECOND PERIOD SWELL. TUESDAY THROUGH SATURDAY...ATLANTIC HIGH PRESSURE WILL DOMINATE THROUGH WEDNESDAY NIGHT...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 THERE IS A CHANCE THAT SMALL CRAFT ADVISORIES MAY BE NEEDED...PARTICULARLY ON WEDNESDAY AFTERNOON. OVER THE NEARSHORE COASTAL WATERS A NOCTURNAL LOW LEVEL JET WILL ENHANCE WINDS TO AROUND 15 KNOTS...POSSIBLY BRIEFLY AS HIGH AS 20 KNOTS BOTH TUESDAY NIGHT AND WEDNESDAY NIGHT. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH THE FORECAST PERIOD. SEA FOG...SREF GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SEA FOG DEVELOPMENT BEGINNING AS EARLY AS TUESDAY AND CONTINUING THROUGH WEDNESDAY. THE LATEST NAM12 HAS TRENDED STRONGLY AWAY FROM ANY SIGNIFICANT AREAS OF SEA FOG DEVELOPMENT...WHICH IS MORE IN LINE WITH FORECAST THINKING. THE SREF GUIDANCE CONTINUES TO APPEAR LARGELY OVERDONE IN IT/S FOG/VSBY DEPICTION. THE MOST PROBABLE TIME FOR ANY SEA FOG DEVELOPMENT IF ANY MANAGES TO FORM APPEARS TO BE TUESDAY NIGHT INTO EARLY WEDNESDAY MORNING WHEN SURFACE DEWPOINTS ARE EXPECTED TO RISE INTO THE UPPER 60S TO AROUND 70 DEGREES. IT CERTAINLY IS NOT A SLAM DUNK GIVEN NEARSHORE WATER TEMPERATURES NOW AROUND 70 TO THE 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 COUPLE DAYS. RIP CURRENTS...WILL EXTEND THE MODERATE RIP CURRENT RISK INTO THE TUESDAY EVENING WHERE LINGERING LUNAR INFLUENCES AND A SMALL 2 FT 9 SECOND SWELL WILL HELP ENHANCED THE RISK FOR RIP CURRENTS. && .TIDES/COASTAL FLOODING... ON CHARLESTON HARBOR...EARLY EVENING TIDE LEVELS REMAIN JUST A SHADE BELOW PREDICTED LEVELS...SUFFICIENT TO HOLD THE 916 PM HIGH TIDE BELOW 7.0 FT MEAN LOWER LOW WATER/SHORT OF COASTAL FLOOD ADVISORY THRESHOLDS. EVEN ON TYBEE ISLAND...THE EVENING TIDE WAS RUNNING SLIGHTLY ABOVE PREDICTED LEVELS BUT WILL FALL SHORT OF THE 9.2 FT MLLW REQUIRED TO PRODUCE SHALLOW SALT WATER FLOODING. PREDICTED TIDE LEVELS REMAIN CLOSE TO SHALLOW COASTAL FLOODING LEVELS TUESDAY EVENING. 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. && $$