000 FXUS62 KCHS 242114 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 414 PM EST TUE NOV 24 2009 .SYNOPSIS... A WEDGE OF HIGH PRES OVER THE INLAND CAROLINAS WILL SLOWLY WEAKEN THROUGH TONIGHT. AN AREA OF LOW PRES WILL LIFT NE...WELL OFF THE COAST OF THE SOUTHEAST UNITED STATES WED AND WED NIGHT. A DRY COLD FRONT WILL MOVE THROUGH THE AREA THU...WITH HIGH PRES THEN BUILDING INTO THE REGION. ANOTHER STORM SYSTEM MAY APPROACH THE REGION EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A DEVELOPING SOUTHERN STREAM SYSTEM WILL EJECT ENE FROM THE NE GULF OF MEXICO TONIGHT...REACHING THE FL PENINSULA BY SUNRISE WED MORNING. MEANWHILE...THE HIGH PRES WEDGE ENTRENCHED OVER THE INLAND CAROLINAS WILL SLOWLY ERODE OVERNIGHT. ALTHOUGH DEEPER MOISTURE IS STREAMING IN FROM THE SW AHEAD OF THE STORM SYSTEM...LOW LEVEL MOISTURE TRAPPED UNDER THE WEDGE IS KEEPING LOW CLOUDS IN PLACE. THE LOW STRATUS MAY LOWER AT TIMES TO A FOG LAYER...BUT THE PRESENCE OF ANY SIGNIFICANT FOG BEYOND PATCHY COVERAGE IS NOT EXPECTED AS THE WEDGE ERODES. WITH THE EXTENSIVE CLOUD COVER IN PLACE OVERNIGHT...LOWS WILL ONLY DROP TO THE UPR 40S WELL INLAND TO THE MID 50S ALONG THE SHORES. MODEL AGREEMENT HAS IMPROVED FOR THE TIMING OF THE PRECIP INTO THE CHS CWFA...LOOKING LIKE IT WILL START NEAR THE ALTAMAHA RIVER ARND 06Z THEN SLOWLY SPREAD N THROUGH THE REST OF THE OVERNIGHT HOURS. WITH THE LOW PRES AREA KEEPING A SRN TRACK...COASTAL PORTIONS OF SE GA WILL HAVE THE BEST SHOT AT SEEING PRECIP SO HAVE INCLUDED A SMALL AREA OF LIKELY POPS...THEN TRENDING DOWNWARD GOING N AND W. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... THE AREA OF LOW PRESSURE CENTERED OVER THE FL PENINSULA ARND DAYBREAK WILL SHIFT INTO THE ATLC...OFF THE GA/SC BY LATE DAY. ASIDE FROM THE NOGAPS...WHICH KEEPS THE PRECIP OFFSHORE...THE WRF/GFS/GEM ALL AGREE THAT THE RAIN SHIELD WILL SPREAD N AND W AHEAD OF THE LOW. ISENTROPIC LIFT ON THE NW AND N SIDES OF THIS SYSTEM ARE QUITE ENHANCED AND WILL MAKE EFFICIENT USE OF THE DEEP MOISTURE BEING WRAPPED AROUND THIS SYSTEM FROM THE ATLC. PWATS INCREASE TO AROUND 1.50 INCHES...ESP NEAR THE COAST...THUS HAVING ISOLD QPF/S UPWARDS OF 0.50 INCHES IS NOT UNREASONABLE. HAVE INCREASED POPS TO THE LIKELY RANGE FOR THE IMMEDIATE COAST... TRENDING DOWNWARD GOING INLAND TMRW. WITH THE QUICK NNE SPEED THAT THIS SYSTEM WILL SHIFT OFF TO THE OUTER BANKS TMRW AND TMRW NIGHT...THE RAIN SHOULD ALSO GO WITH IT RATHER QUICKLY. THUS... HAVE DROPPED OFF POPS STEADILY THROUGH THE AFTN AND EVE HOURS... RESULTING IN A DRY FCST FOR TMRW NIGHT. MAX TEMPS WILL NOT RISE MUCH TOMORROW WITH THE EXTENSIVE CLOUD COVER AND AREAS OF RAIN. WILL ADVERTISE HIGHS IN THE LWR 60S BUT WOULD NOT BE SURPRISED IF SOME LOCATIONS...ESP IN NRN PORTIONS... REMAIN IN THE UPR 50S. MIN TEMPS WILL BE A BIT COOLER AS THE OFFSHORE LOW DEPARTS AND SOME CLEARING OCCURS BEHIND IT. EXCEPT FOR LOWS ARND 50 NEAR THE SHORES...LOWS WILL BE IN THE 40S. && .LONG TERM /THURSDAY THROUGH TUESDAY/... MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH SUNDAY BEFORE MODEL DIFFERENCES LEAD TO LESS FORECAST CONFIDENCE SUNDAY NIGHT THROUGH TUESDAY. HIGH PRESSURE WILL SHIFT INTO THE AREA FROM THE WEST THURSDAY BEHIND A DEPARTING AREA OF LOW PRESSURE MOVING NORTHEAST OFF THE NORTH CAROLINA COAST. THE HIGH WILL REMAIN OVER THE AREA THROUGH THE WEEKEND PROVIDING DRY BUT UNSEASONABLY COOL CONDITIONS. IN FACT...WE COULD BE SEEING FROST INLAND FRIDAY MORNING WITH FREEZING TEMPERATURES INLAND SATURDAY MORNING. HIGH PRESSURE WILL SLIDE EASTWARD INTO THE ATLANTIC SUNDAY...ALLOWING RETURN FLOW TO SET UP ACROSS THE FORECAST AREA. MODEL DIFFERENCES BEGIN SUNDAY NIGHT INTO MONDAY REGARDING A DEVELOPING AREA OF LOW PRESSURE MOVING FROM THE LOWER MISSISSIPPI VALLEY NORTHEAST INTO THE GREAT LAKES/MID-ATLANTIC REGION. FOR NOW HAVE DECIDED TO FOLLOW THE SLOWER GUIDANCE AS FAVORED BY HPC... WHICH KEEPS OUR FORECAST AREA IN THE WARM SECTOR THROUGH TUESDAY. THE FORECAST WILL REMAIN DRY THROUGH SUNDAY NIGHT BEFORE RAIN CHANCES INCREASE MONDAY. WE MAY EVEN BE DEALING WITH SOME THUNDERSTORMS IF ENOUGH INSTABILITY CAN DEVELOP. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... HIGH PRES WEDGE STILL HOLDING FORT OVER THE INLAND CAROLINAS THE REST OF TDA BUT WILL GRADUALLY ERODE TO THE NE TONIGHT IN ADVANCE OF A STORM SYSTEM MOVING FROM THE GULF OF MEXICO ACROSS FL TOMORROW. LOW CIGS...LIKELY IFR...WILL PERSIST AT BOTH SITES THROUGH TONIGHT ALTHOUGH THERE ARE SOME INDICATIONS THAT AS THE HIGH PRES WEDGE ERODES...SOME IFR CIGS MAY LIFT TO MVFR CIGS FOR A BRIEF PERIOD LATE THIS AFTN. SOME UPSTREAM OBS OVER SRN GA INDICATE THIS THINKING SO HAVE INCLUDED IT AT BOTH TERMINALS. UPON NIGHTFALL...CIGS WILL FALL BACK TO IFR LEVELS AND REMAIN THERE. THE NEXT PROBLEM IS PRECIP TIMING. PER WRF/GFS/SREF BLEND...RAIN LOOKS TO START NEAR KSAV A FEW HOURS BEFORE SUNRISE FOLLOWED BY KCHS AROUND SUNRISE. WILL MAINTAIN IFR CIGS THROUGH TMRW MRNG ALONG WITH MVFR VSBYS...ALTHOUGH POCKETS OF MOD/HVY RAIN COULD PRODUCE IFR VSBYS AT TIMES. THE RAINFALL LOOKS TO SHIFT AWAY BY MIDDAY...SO HAVE INDICATED AN END OF THE RAINFALL BY LATE MORNING AT KSAV BUT IT LOOKS TO BE AFTER 18Z TMRW AT KCHS. MODEL SOUNDINGS QUICKLY IMPROVE CONDITIONS ARND 18Z AT BOTH SITES BUT DO NOT BELIEVE IMPROVEMENT WILL BE SO RAPID...ESP WITH SOME UNCERTAINTY AS TO TIMING ISSUES WITH THE RAINFALL. EXTENDED AVIATION OUTLOOK...MVFR/IFR CIGS WITH OCCASIONAL MVFR/IFR VSBYS EXPECTED WED EVENING AS A STORM SYSTEM EXITS THE AREA. VFR CONDITIONS ARE EXPECTED LATE WED NIGHT THROUGH SAT. && .MARINE... COOL WATERS WITH AN ERODING HIGH PRES WEDGE WILL RESULT IN A RELATIVELY LIGHT NE FLOW WITH SPEEDS AOB 10 KT TONIGHT. SEAS ARE CONTINUING THEIR GRADUAL DOWNWARD TREND WITH WAVES NO HIGHER THAN 3 FT. AN AREA OF LOW PRESSURE DEVELOPING IN THE NE GULF OF MEXICO WILL DEEPEN FURTHER AS IT CROSSES THE FL PENINSULA EARLY WED AND SHIFTS NE ALONG THE CAROLINA COAST WED INTO WED NIGHT. WITH HIGH PRES STILL RESIDING INLAND...THE GRADIENT BETWEEN BOTH SYSTEMS WILL BECOME NOTICEABLY TIGHTER. WINDS WITHIN 20 NM OF SHORE WILL INCREASE TO NEAR 15 KT WHILE THE OUTER GA WATERS WILL SEE WINDS INCREASE TO THE 15-20 KT RANGE MIDDAY TMRW. THE SYSTEM WILL QUICKLY EJECT TO THE NE...ALLOWING THE PRESSURE GRADIENT TO SLACKEN OFF A BIT WED NIGHT WHICH WILL ALLOW WIND SPEEDS TO DROP ABOUT 5 KT ACROSS ALL MARINE ZONES. SEAS WILL CREEP UP A LITTLE...BUT STILL REMAIN CAPPED AT 5 KT THUS SMALL CRAFT ADVISORY CONDITIONS ARE NOT EXPECTED THRU WED NIGHT. THURSDAY THROUGH SUNDAY...A COLD FRONT WILL MOVE THROUGH THE WATERS THURSDAY AFTERNOON...WITH HIGH PRESSURE THEN BUILDING BACK INTO THE REGION THROUGH THE WEEKEND. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT LEVELS THROUGH THURSDAY. EXPECT A PRETTY DECENT SURGE IN STRONG COLD AIR ADVECTION THURSDAY NIGHT...AND SMALL CRAFT ADVISORIES APPEAR LIKELY FOR ALL WATERS INCLUDING CHARLESTON HARBOR. SMALL CRAFT CONDITIONS LOOK TO LINGER INTO FRIDAY...WITH WINDS AND SEAS THEN SUBSIDING BELOW SMALL CRAFT THRESHOLDS AS HIGH PRESSURE BUILDS IN FOR THE WEEKEND. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ JPC/RJB