Issued by NWS Charleston, SC
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS62 KCHS 111740 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 140 PM EDT WED MAR 11 2009 .SYNOPSIS... ATLANTIC HIGH PRESSURE WILL EXTEND ACROSS THE REGION TODAY. A COLD FRONT WILL APPROACH FROM THE NORTHWEST THIS EVENING AND WILL PUSH SOUTH OF THE AREA BY SUNRISE THURSDAY. THE FRONT WILL STALL SOUTH OF THE AREA THURSDAY NIGHT THROUGH THE WEEKEND WHILE A HIGH PRESSURE WEDGE BUILDS IN FROM THE NORTH. SEVERAL WAVES OF LOW PRESSURE WILL DEVELOP ALONG THE FRONT...RESULTING IN COOLER AND UNSETTLED CONDITIONS THROUGH THE WEEKEND INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... FOG HAS QUICKLY ERODED THIS MORNING ACROSS LAND AREAS AS SW FLOW INCREASES AND TEMPERATURES WARM. THE EXCEPTION IS THE SEA FOG THAT DEVELOPED YESTERDAY AFTERNOON. THERE WAS A LULL IN COVERAGE AROUND DAYBREAK...BUT ANOTHER SURGE IN LOW-LEVEL MOISTURE ACROSS THE COOL SHELF WATERS HAS CAUSED A THIN BAND OF SEA FOG TO DEVELOP ALONG THE CHARLESTON COUNTY COAST. WEB CAMS FROM ISLE OF PALMS AND FOLLY BEACH INDICATE THIS FOG HAS PUSHED RIGHT TO THE COAST AND IS QUITE DENSE. THE PREVAILING FLOW WILL BE SW TODAY AHEAD OF AN APPROACHING COLD FRONT...THUS WITH ONLY A LATE AFTERNOON SEABREEZE...THE FOG SHOULD REMAIN RIGHT ALONG THE COAST AND NOT ADVECT INTO THE CHARLESTON HARBOR. PLAN TO EXTEND THE DENSE FOG ADVISORY FOR THE ATLANTIC WATERS ADJACENT TO CHARLESTON COUNTY THROUGH THE AFTERNOON. ANOTHER WARM DAY IS IN STORE DESPITE A SLIGHTLY COOLER START AND SOME CLOUDS AND FOG IN THE TRI-COUNTY REGION. THICKNESSES FROM THE CHS AND JAX SOUNDING INDICATE POTENTIAL FOR HIGHS OF 86-87. THESE TEMPS WILL BE QUITE POSSIBLE ACROSS INLAND AREAS...ALTHOUGH COASTAL SECTIONS WILL BE A FEW DEGREES COOLER...EITHER DUE TO A MID-LATE AFTERNOON SEABREEZE OF HAVING LOST TWO HOURS OF SUN DUE TO CLOUDS/FOG THIS MORNING. TWEAKED HIGH TEMP FORECAST UPWARD BY ABOUT TWO DEGREES ON AVERAGE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... A COLD FRONT WILL APPROACH FROM THE NORTHWEST THIS EVENING...THEN SHIFT ACROSS THE AREA DURING THE OVERNIGHT HOURS. A LACK OF ANY SIGNIFICANT MOISTURE IN THE LOW OR MID LEVELS OF THE ATMOSPHERE WILL MAKE IT A DRY FRONTAL PASSAGE. THERE IS THE POTENTIAL FOR SOME PATCHY FOG JUST AHEAD OF THE COLD FRONT...BUT VERY LOW VISIBILITIES DO NOT APPEAR LIKELY. LOW TEMPERATURES ARE EXPECTED TO BE IN THE LOWER TO MID 50S ACROSS THE AREA. SURFACE HIGH PRESSURE WILL BEGIN TO WEDGE SOUTH ACROSS THE AREA ON THURSDAY FOLLOWING THE PASSAGE OF THE COLD FRONT. DEEPER MOISTURE WILL ADVECT INTO THE AREA ON A NORTHEAST FLOW AS THE DAY PROGRESSES. WHILE CLOUD COVER WILL BE RATHER SIGNIFICANT BY LATE IN THE DAY...ANY SHOWERS SHOULD REMAIN ISOLATED...MAINLY ALONG THE COAST WHERE LOW LEVEL CONVERGENCE WILL BE GREATEST. THE DEVELOPING WEDGE WILL ALSO MARK THE END OF THE UNSEASONABLY WARM WEATHER...WITH HIGHS EXPECTED TO RANGE FROM THE MID 60S NEAR THE SOUTH SANTEE RIVER TO THE LOWER/MID 70S NEAR THE ALTAMAHA RIVER. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... BACKDOOR FRONT WILL SETTLE S OF THE AREA THU NIGHT WHILE A HIGH PRES WEDGE DEVELOPS FROM THE N...WITH EACH FEATURE EXPECTED TO GENERALLY HOLD ITS POSITION THROUGH MONDAY...RESULTING IN COOLER NE FLOW AND INCREASING CHCS FOR RAIN EACH PERIOD. WHILE THE FRONT STALLS THU NIGHT INTO FRIDAY...A COASTAL TROUGH WILL GRADUALLY FORM OFF THE GA/SC COAST...HELPING ENHANCE SFC CONVERGENCE CLOSEST TO THE SHORES AND OVER NRN PORTIONS OF THE AREA SO HAVE HIGHLIGHTED HIGHEST POPS FOR ERN AND NRN SECTIONS DURING THIS TIME. ISENTROPIC LIFT INCREASES OVER THESE PORTIONS IN RESPONSE TO THE HIGH PRES WEDGE STRENGTHENING AND SEVERAL WEAK MID-LEVEL SHORTWAVES LOOK TO PUSH THROUGH THE AREA...THUS HAVE NUDGED POPS INTO THE HIGH CHC/LOW-END LIKELY CATEGORIES BY LATE FRI INTO FRI NIGHT. WITH THE INLAND WEDGE/COASTAL TROUGH/SRN FRONT REGIME REMAINING IN PLACE SAT THROUGH MON...ALONG WITH SEVERAL WAVES OF LOW PRES RIDING NE ALONG THE STALLED FRONT AND SEVERAL MORE SHORTWAVES EXPECTED TO MOVE OVER THE AREA...CLOUDY CONDITIONS WITH CHANCES FOR PRECIP WILL REMAIN IN THE FORECAST THROUGH THE WEEKEND INTO EARLY NEXT WEEK AS ISENTROPIC LIFT REMAINS HIGHLIGHTED OVER THE AREA AND DEEPER MOISTURE REMAINS IN PLACE. THE REGIME BREAKS DOWN MON NIGHT INTO TUE AS A POTENT UPPER LEVEL TROUGH DIGS OVER THE LOWER-MID MISS RIVER VALLEY MON AND SHIFTS E OVER THE LOWER APPALACHIANS TUE. THE HIGH PRES WEDGE WILL GIVE WAY TO A STRONGER SFC LOW PRES CENTER THAT WILL DEVELOP OVER THE ERN GOMEX AND SHIFT INTO THE WRN ATLC TUE. CONFIDENCE IS NOT TOO GREAT FOR THE WEDGE BREAKDOWN...SO HAVE ONLY KEPT SLGT CHC POPS ATTM. AS IS TYPICAL WITH A WEDGE PATTERN...SUSTAINED NE WINDS WILL BRING IN NOTICEABLY COOLER TEMPS FOR THE END OF THE WEEK THROUGH EARLY NEXT WEEK. FRI TEMPS WILL RANGE FROM THE MID 50S N TO MID 60S S... THEN WILL RISE SOMEWHAT FOR SAT-TUE...WITH MAX TEMPS FROM THE MID 60S TO AROUND 70. DIURNALS WILL BE RELATIVELY SMALL WITH THE PERSISTENT CLOUD COVER AND NE WINDS. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...-- Changed Discussion --A LATE AFTERNOON SEABREEZE WILL CAUSE WINDS TO BECOME SLIGHTLY MORE SOUTHERLY AND PERHAPS A FEW CUMULUS WILL DEVELOP. TONIGHT WINDS SHOULD GO LIGHT AND VARIABLE UNTIL AFTER A BACKDOOR COLD FRONT DROPS THROUGH THE AREA. BY LATE TONIGHT WINDS WILL PICK UP FROM THE NORTHEAST BEHIND THE FRONT AS HIGH PRESSURE WEDGES IN FROM THE NORTH. A COASTAL TROUGH SHOULD START TO DEVELOP THU MORNING AND SOME VFR CEILINGS WILL DEVELOP. BY EARLY THU AFTERNOON...ENOUGH LOW-LEVEL MOISTURE AND POSSIBLY SOME LIGHT SHOWERS MAY BRING CEILINGS DOWN TO MVFR. MODELS MAY BE MOISTENING THE PROFILE TOO QUICKLY...THUS HELD OFF ON INCLUDING ANY CIG RESTRICTIONS DURING THIS 18Z TAF SET. EXTENDED AVIATION OUTLOOK...MVFR/IFR CONDITIONS POSSIBLE THU AFTERNOON THROUGH SUNDAY AS THE FRONT SETTLES S OF THE AREA AND LOW CLOUDS WITH OCCASIONAL SHOWERS PERSIST THROUGH THE PERIOD.-- End Changed Discussion --&& .MARINE...-- Changed Discussion --SINCE THE SEA FOG HAS DISSIPATED...WE HAVE CANCELLED THE DENSE FOG ADVISORY FOR THE NEARSHORE ATLANTIC WATERS. ATLANTIC HIGH PRESSURE WILL RESULT IN SOUTHERLY WINDS ACROSS THE WATERS INTO THIS EVENING...WITH LOCAL ENHANCEMENTS LIKELY ALONG THE LAND/SEA INTERFACE AS A SEA BREEZE DEVELOPS THIS AFTERNOON. WINDS WILL SHIFT SOUTHWEST IN ADVANCE OF AN APPROACHING COLD FRONT THIS EVENING...WITH THE FLOW VEERING OFFSHORE AS THE FRONT MOVES OFF THE COAST TOWARD SUNRISE THURSDAY. WINDS THROUGHOUT THE COASTAL WATERS WILL GENERALLY BE LESS THAN 15 KT THROUGH TONIGHT. SEAS SHOULD BE NO GREATER THAN 3 FT WITHIN 20 NM OF THE COAST AND 3 OR 4 FT WITHIN 60 NM OF THE NORTHERN GEORGIA COAST. A NORTHEAST WIND SURGE WILL DEVELOP FOLLOWING THE PASSAGE OF THE COLD FRONT THURSDAY AS HIGH PRESSURE WEDGES SOUTH ACROSS INLAND AREAS...TIGHTENING THE SURFACE PRESSURE GRADIENT OVER THE COASTAL WATERS. WINDS AND SEAS COULD REACH SMALL CRAFT ADVISORY CRITERIA THURSDAY AFTERNOON OVER THE SOUTH CAROLINA COASTAL WATERS NORTH OF EDISTO BEACH...BUT GIVEN THE WORST CONDITIONS ARE EXPECTED TO OCCUR LATE IN THE THIRD PERIOD...WILL REFRAIN FROM ISSUING THE ADVISORY AT THIS TIME. A FRONT WILL SETTLE JUST S OF THE CHS MARINE AREA THU NIGHT...THEN WOBBLING NEAR OR JUST S OF THE ALTAMAHA RIVER THROUGH THE WEEKEND WHILE HIGH PRES DEVELOPS INLAND AND A COASTAL TROUGH FORMS OVER THE WATERS. THIS WILL MAKE FOR PERSISTENT NE WINDS FROM THE END OF THIS WEEK THROUGH THE START OF NEXT WEEK. A TIGHTENING PRESSURE GRADIENT BETWEEN THE INLAND HIGH PRESSURE AND THE COASTAL TROUGH WILL LIKELY INCREASE WIND SPEEDS THU NIGHT INTO FRI WITH THE INITIAL SURGE OF HIGH PRES...AND THE FAVORABLE NE FETCH WILL ALLOW SEAS TO REACH 6 FT FOR ALL BUT POSSIBLY THE NEARSHORE GA WATERS. SOME UNCERTAINTY REMAINS AS TO HOW STRONG THE NE SURGE WILL BE THU NIGHT INTO FRI... BUT IT WOULD NOT BE UNREASONABLE IF WIND SPEEDS REACH SCA LEVELS. CONDITIONS SETTLE DOWN A BIT SAT INTO SUN AS THE PRESSURE GRADIENT RELAXES DUE TO A WEAKENING COASTAL TROUGH...BUT THE NE FETCH WILL REMAIN THROUGH THE WEEKEND.-- End Changed Discussion --&& .CHS WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --GA...NONE. SC...NONE. MARINE...NONE.-- End Changed Discussion --&& $$ JRL
