000 FXUS62 KCHS 100327 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 1027 PM EST THU FEB 9 2012 .SYNOPSIS... HIGH PRESSURE WILL EXTEND ACROSS THE SOUTHEAST STATES THROUGH FRIDAY WHILE A TROUGH OF LOW PRESSURE DEVELOPS OVER THE NEARBY COASTAL WATERS. A COLD FRONT WILL THEN PUSH THROUGH FRIDAY NIGHT INTO SATURDAY BEHIND DEPARTING LOW PRESSURE WITH A REINFORCING COLD FRONT SATURDAY NIGHT. COLD HIGH PRESSURE WILL THEN BUILD BACK INTO THE REGION AND PERSIST THROUGH EARLY NEXT WEEK. ANOTHER STORM SYSTEM MAY AFFECT THE AREA BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... MID/HIGH LEVEL CLOUDS OF VARYING THICKNESS WILL CONTINUE TO STREAM ACROSS THE REGION OVERNIGHT. MEANWHILE...00Z NAM GUIDANCE CONTINUES TO DEPICT INCREASING LOW LEVEL MOISTURE TRANSPORT/ SHALLOW ISENTROPIC ASCENT SPREADING INTO SOUTHERN/COASTAL COUNTIES OVERNIGHT. HOWEVER...THE NAM HAS BACKED OFF ON TIMING OF SPOTTY/LIGHT SHOWERS ACROSS SOUTHERN COASTAL WATERS/FAR SOUTHERN COASTAL COUNTIES UNTIL 09Z-12Z...AND THE LATEST RUC SUGGESTS PRECIPITATION WILL DEVELOP EVEN A FEW HOURS LATER. THUS...DELAYED ONSET OF SLIGHT CHANCE/CHANCE POPS ACROSS SOUTHERN COASTAL COUNTIES/ADJACENT COASTAL WATERS UNTIL LATE TONIGHT. LOW CLOUDS COULD PRODUCE A WIDE TEMPERATURE RANGE ACROSS THE REGION OVERNIGHT. WHERE LOW CLOUDS BECOME WIDESPREAD...MOST LIKELY ACROSS COASTAL AND SOUTHERN COUNTIES...TEMPERATURES COULD BEGIN TO RISE LATE TONIGHT AND WIDESPREAD 40S/LOWER 50S COULD BE COMMON BY DAYBREAK. WELL INLAND...WHERE LOW CLOUDS WILL LIKELY NOT ARRIVE UNTIL AFTER DAYBREAK...A FEW LOCATIONS WILL BOTTOM OUT CLOSE TO FREEZING. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... MODEL SOLUTIONS ARE IN RELATIVELY GOOD AGREEMENT THROUGH THE SHORT TERM PERIODS...RESULTING IN NEAR TO SLIGHTLY ABOVE NORMAL FORECAST CONFIDENCE. THE BIGGEST FORECAST CHALLENGE IS THE RAIN POTENTIAL FRIDAY AND FRIDAY NIGHT AS A TROUGH OF LOW PRESSURE DEVELOPS OVER THE NEARBY ATLANTIC WATERS AND PUSHES TOWARD THE COAST WHILE LOW PRESSURE DEVELOPS TO THE SOUTH AND MOVES NORTHEAST BY THE AREA. THERE SHOULD BE SUFFICIENT MOISTURE AND LIFT TO PRODUCE SOME LIGHT SHOWERS...MAINLY NEAR THE COAST AND THIS IS WHERE WE WILL HIGHLIGHT THE BEST RAIN CHANCES FOR LAND AREAS. RAINFALL SHOULD END BY DAYBREAK SATURDAY WITH COLD ADVECTION TO ENSUE DURING THE DAY WHICH WILL AT FIRST BE OFFSET TO SOME EXTENT BY THE BREEZY WEST/NORTHWEST DOWNSLOPE FLOW. A REINFORCING COLD FRONT WILL THEN PUSH THROUGH SATURDAY NIGHT AS A 150+ KT UPPER JET PUSHES OFFSHORE ALLOWING ARCTIC HIGH PRESSURE TO MOVE IN FROM THE WEST WHICH WILL PERSIST THROUGH SUNDAY. TEMPERATURES WILL DROP DRAMATICALLY SATURDAY NIGHT AND STRONG COLD ADVECTION WILL PUSH TEMPERATURES INTO THE MID TO UPPER 20S MOST AREAS...LIKELY EVEN REACHING BELOW FREEZING AT THE IMMEDIATE COAST. THUS...THOSE WITH SENSITIVE VEGETATION OUTDOORS WILL WANT TO TAKE THE PROPER PRECAUTION TO PROTECT THEM. SINCE OUR FROST/FREEZE PROGRAM HAS YET TO OFFICIALLY BEGIN...WE DO NOT PLAN TO ISSUE ANY FROST ADVISORIES OR FREEZE WATCHES/WARNINGS. WILL CONTINUE TO HIGHLIGHT THE COLD WEATHER IN THE HAZARDOUS WEATHER OUTLOOK AND CONSIDER ISSUING SPECIAL WEATHER STATEMENTS AS WE GET CLOSER TO THE EVENT. SINCE WINDS WILL REMAIN IN THE 10-20 MPH RANGE THROUGH THE NIGHT...WIND CHILLS WILL MAKE IT FEEL EVEN COLDER...IN THE MID TO UPPER TEENS. HIGHS ON SUNDAY WILL STRUGGLE TO REACH 50 DEGREES AFTER A VERY COLD START. LAKE WINDS...STRONG WINDS ARE EXPECTED TO DEVELOP ON LAKE MOULTRIE FOLLOWING THE PASSAGE OF A COLD FRONT SATURDAY AND THEN MORESO BEHIND A REINFORCING COLD FRONT SATURDAY NIGHT. A LAKE WIND ADVISORY WILL LIKELY BE NEEDED SATURDAY AFTERNOON THROUGH SUNDAY MORNING. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AFTER A BRIEF BREAK FROM THE MODEL DISCONTINUITY...OPERATIONAL SOLUTIONS ARE ONCE AGAIN DISPLAYING POOR AGREEMENT FOR THE MIDDLE AND LATTER PORTIONS OF THE LONG TERM PERIOD. GUIDANCE IS IN GOOD AGREEMENT EARLY IN THE PERIOD...SHOWING HIGH PRESSURE BUILDING OVER THE REGION SUNDAY NIGHT AND MONDAY BEFORE BUILDING EASTWARD AND INTO THE WESTERN ATLANTIC MONDAY NIGHT. SOLUTIONS THEN DEVIATE ON THE POSITIONING AND PROGRESSION OF SYNOPTIC DETAILS TUESDAY THROUGH THURSDAY...LEADING TO LOWER THAN NORMAL FORECAST CONFIDENCE. GIVEN THE UNCERTAINTY IN THE TUESDAY THROUGH THURSDAY TIME FRAME...WILL TRY TO CAPITALIZE ON PERIODS WHERE THE MODELS ARE MORE CLOSELY ALIGNED WHILE TRYING TO MINIMIZE POTENTIAL FORECAST ERROR WHERE THE MODEL SOLUTIONS DIVERGE MORE SIGNIFICANTLY. AS FOR FORECAST DETAILS...WILL KEEP THE FORECAST RAIN FREE SUNDAY NIGHT THROUGH MONDAY NIGHT WITH HIGH PRESSURE REMAINING THE DOMINANT WEATHER FEATURE. DESPITE THE MODEL DIFFERENCES IN POSITIONING AND PROGRESSION OF SYNOPTIC DETAILS BEGINNING ON TUESDAY...THEY DO AGREE ON BRINGING DEEPER MOISTURE ALONG WITH A SURFACE FRONTAL BOUNDARY INTO THE REGION...SO WILL CARRY SLIGHT CHANCE POPS TUESDAY AND TUESDAY NIGHT. THE OPERATIONAL SOLUTIONS THEN DEVIATE MORE NOTICEABLY WEDNESDAY THROUGH THURSDAY. FOR NOW...WILL ADVERTISE RAIN FREE CONDITIONS WEDNESDAY THROUGH THURSDAY AS THE MODEL SOLUTIONS GENERALLY SHOW THE DEEPEST MOISTURE SHIFTING OUT OF THE REGION AND HOLDING OFF ON A RETURN OF ANY SIGNIFICANT MOISTURE RETURN THROUGH THURSDAY NIGHT. OBVIOUSLY...THIS PORTION OF THE FORECAST IS QUITE UNCERTAIN...SO CHANGES IN FORECAST THINKING ARE VERY POSSIBLE OVER THE NEXT SEVERAL DAYS. TEMPERATURES IN THE BEGINNING OF THE LONG TERM PERIODS WILL START OUT WELL BELOW CLIMATOLOGY SUNDAY NIGHT AND MONDAY...WITH LOWS IN THE 20S MOST LOCALES AND HIGHS IN THE MID TO UPPER 50S. TEMPERATURES WILL MODERATE ON TUESDAY...WITH HIGHS CLOSE TO SEASONAL LEVELS IN THE LOW TO MID 60S. TEMPERATURES WILL CONTINUE TO WARM DURING THE MID TO LATE WEEK TIME FRAME TO ABOVE NORMAL LEVELS...WITH HIGHS GENERALLY IN THE UPPER 60S TO LOWER 70S. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... VFR THIS EVENING. OVERNIGHT...MODELS CONTINUE TO PUSH LOW LEVEL MOISTURE ONSHORE...INITIALLY INTO SOUTHERN COUNTIES THEN SPREADING NORTH...AND LOW CLOUD CEILINGS SHOULD DEVELOP OVERNIGHT. SREF GUIDANCE SUGGESTS AT LEAST A 70 PERCENT CHANCE FOR MVFR CEILINGS AT KSAV BY 18Z FRIDAY...FOLLOWED BY SUBTLE LOW LEVEL DRYING/IMPROVEMENT TO VFR LEVEL CEILINGS PRIOR TO 00Z. AT KCHS...SREF GUIDANCE ALSO INDICATES A HIGH PROBABILITY FOR MVFR CEILINGS BY 21Z FRIDAY. SINCE MODEL SOUNDINGS SUPPORT THIS SCENARIO...INTRODUCED A PERIOD OF MVFR CEILINGS AT BOTH TERMINALS FRIDAY AFTERNOON. GIVEN 00Z NAM TRENDS...MVFR CEILINGS COULD DEVELOP EARLIER...AND A PERIOD OF IFR CEILINGS CANNOT BE RULED OUT. MEANWHILE...ISENTROPIC ASCENT AND UPPER LEVEL DIVERGENCE SUPPORTED BY AN INTENSIFYING JET AXIS SHOULD SUPPORT AT LEAST SOME LIGHT PRECIPITATION...THUS INTRODUCED A MENTION OF SHOWERS WITH VFR VISIBILITY. 00Z NAM GUIDANCE CONTINUES TO INDICATE HIGH POPS AND MVFR VISIBILITY IN SHOWERS...WILL CONTINUE TO ASSESS THIS SCENARIO. EXTENDED AVIATION OUTLOOK...MVFR CIGS AND/OR VSBYS COULD AFFECT THE TERMINALS THROUGH FRIDAY NIGHT AS A WAVE OF LOW PRESSURE LIFTS BY WELL OFF THE COAST OF THE SOUTHEAST UNITED STATES. MVFR CONDITIONS COULD IMPACT THE TERMINALS ONCE AGAIN ON TUESDAY AS ANOTHER STORM SYSTEM MOVES THROUGH THE AREA. IN ADDITION...GUSTY WINDS WILL IMPACT THE TERMS SATURDAY WITH LLWS POSSIBLE SATURDAY NIGHT. && .MARINE... OVERNIGHT...WEAK SURFACE TROUGHING SHOULD MAINTAIN E/NE WINDS... WITH LITTLE EVIDENCE TO SUPPORT THE 00Z NAM FORECAST OF SE WINDS. WINDS WILL REMAIN 15 KT OR LESS. SEAS WILL RANGE FROM 2-3 FT WITHIN NEARSHORE WATERS TO 3-4 FT BEYOND 20 NM. FRIDAY THROUGH TUESDAY...A WAVE OF LOW PRESSURE WILL DEVELOP OFF THE SOUTHEAST COAST ON FRIDAY AND PUSH NORTHEASTWARD AND AWAY FROM THE AREA FRIDAY NIGHT AS A COLD FRONT PUSHES THROUGH THE MARINE AREA. A REINFORCING COLD FRONT WILL THEN MOVE THROUGH THE WATERS ON SATURDAY...FOLLOWED BY HIGH PRESSURE THROUGH EARLY NEXT WEEK. ANOTHER STORM SYSTEM MAY AFFECT THE AREA BY NEXT TUESDAY. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS FRIDAY BUT WINDS COULD REACH ADVISORY RANGE FRIDAY NIGHT AS THE PRESSURE GRADIENT TIGHTENS AND LOW-LEVEL WINDS/COLD ADVECTION STRENGTHEN BEHIND THE DEPARTING AREA OF LOW PRESSURE. ALL WATERS ARE EXPECTED TO SEE ADVISORY CONDITIONS BY SATURDAY NIGHT AS A REINFORCING COLD FRONT MOVES THROUGH. GALE FORCE GUSTS ARE ALSO POSSIBLE...MAINLY BEYOND 20 NM. SLOWLY IMPROVING CONDITIONS ARE EXPECTED ON SUNDAY AS THE COLD AIR ADVECTION/TIGHT PRESSURE GRADIENT REGIME BEGINS TO WEAKEN. AT THIS TIME...IT APPEARS THAT CONDITIONS WILL DROP BELOW ADVISORY LEVELS ACROSS THE NEARSHORE WATERS BY NOON ON SUNDAY...WITH SEAS MOST LIKELY REMAINING AT OR ABOVE SMALL CRAFT THRESHOLDS ACROSS THE OUTER GEORGIA WATERS THROUGH LATE SUNDAY AFTERNOON OR EARLY SUNDAY EVENING. CONDITIONS WILL CONTINUE TO IMPROVE SUNDAY NIGHT THROUGH MONDAY NIGHT...THEN POSSIBLY GO DOWNHILL AGAIN TUESDAY AS A LOW PRESSURE SYSTEM POSSIBLY TRACKS THROUGH THE AREA. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$