663 FXUS62 KCHS 310211 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 911 PM EST WED JAN 30 2013 .SYNOPSIS... BREEZY CONDITIONS WILL REMAIN OVER THE AREA BEFORE A COLD FRONT PUSHES THROUGH THE REGION TONIGHT. HIGH PRESSURE WILL BRIEFLY BUILD INTO THE REGION THURSDAY BEFORE A DRY COLD FRONT CROSSES ON FRIDAY. MORE HIGH PRESSURE WILL MOVE IN FOR THE WEEKEND AND WILL LINGER INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A STRONG SOUTHERLY FLOW PERSISTS WITHIN THE WARM SECTOR AHEAD OF A COLD FRONT APPROACHING FROM THE WEST. VERY IMPRESSIVE WIND FIELDS ALOFT WILL CONTINUE TO MIX TO THE SURFACE THROUGH MUCH OF THIS EVENING...WITH GUSTS UPWARDS OF 30-40 MPH EXPECTED TO PERSIST. ALTHOUGH WINDS WILL LIKELY REMAIN JUST SHY OF WIND ADVISORY CRITERIA IN MOST PLACES...WILL LEAVE THE ADVISORY IN EFFECT UNTIL THE FRONT PASSES GIVEN THE POTENTIAL FOR HIGHER GUSTS TO REDEVELOP AS MIXING DEEPENS AHEAD OF THE FRONT. A LINE OF CONVECTION WILL CONTINUE TO TRACK TOWARD THE COAST THROUGH THE REST OF THE EVENING BEFORE PUSHING OFFSHORE DURING THE EARLY OVERNIGHT HOURS. POPS WILL REMAIN 90-100 PERCENT. STRONG DYNAMICAL FORCING WILL ACCOMPANY THE FRONT AS CROSSES THE AREA. 0-6 KM SHEAR BETWEEN 60-80 KNOTS ALONG WITH FAVORABLE UPPER LVL DIVERGENCE FROM A 150 KT JET AND LIFT FROM A 70-90 KT LOW LVL JET OVER THE SOUTHEAST...SUGGESTS THE POSSIBILITY OF STRONG WINDS WITH ANY CONVECTIVE ACTIVITY ALONG OR NEAR THE ADVANCING COLD FRONT THROUGH MIDNIGHT. MID LEVEL LAPSE RATES REMAIN POOR FOR STRONG CONVECTION...THUS CHANCES OF SEVERE WEATHER WILL BE LARGELY DEPENDENT ON LOW LEVEL INSTABILITY. THERE WILL BE A THREAT OF THUNDERSTORMS CAPABLE OF PRODUCING DAMAGING WIND GUSTS AND POSSIBLY AN ISOLATED TORNADO OVER THE AREA THROUGH ABOUT 1 AM...AND A TORNADO WATCH IS IN EFFECT FOR ALL AREAS. HOWEVER...GIVEN THE TIMING OF THE FRONT...THE GENERAL CONSENSUS IS THAT LOW LEVEL INSTABILITY WILL DECREASE FURTHER WITH DIURNAL HEAT LOSS THIS EVENING WELL BEFORE THE FRONT REACHES THE COAST. ONCE THE COLD FRONT SWEEPS THROUGH THE AREA AROUND OR SHORTLY AFTER MIDNIGHT...THE THREAT OF ANY SEVERE WEATHER WILL END. MOST AREAS SHOULD SEE PRECIP FOR ROUGHLY A 1-2 HOUR PERIOD AS THE FRONT ADVANCES QUICKLY EAST. TEMPERATURES COULD RISE A FEW DEGREES JUST AHEAD OF THE FRONT WITH THE STRONG WARM AIR ADVECTION. THEN...COOL AND DRY HIGH PRESSURE WILL FOLLOW BEHIND THE FRONT AFTER MIDNIGHT THROUGH THURSDAY MORNING. OVERNIGHT LOWS WILL RANGE IN THE MID 40S INLAND TO LOW 50S ALONG THE COAST. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/... THURSDAY AND THURSDAY NIGHT...THE EASTERN CONUS WILL REMAIN UNDER THE INFLUENCE OF THE LONGWAVE TROUGH ALOFT AS THE COLD FRONT PUSHES WELL OFFSHORE. HIGH PRESSURE OVER THE NORTHERN GULF OF MEXICO WILL ATTEMPT TO NOSE IN FROM THE SOUTHWEST DURING THE DAY BUT WILL EVENTUALLY BE THWARTED BY A FAST MOVING COLD FRONT APPROACHING FROM THE NORTHWEST. DEEP DRY AIR WILL MOVE IN THROUGH THE DAY LEAVING SKIES SUNNY. GOOD COLD ADVECTION AND ELEVATED LOW LEVEL FLOW WILL RESULT IN ANOTHER BREEZY DAY WITH GUSTS IN THE 25 MPH RANGE LATE MORNING THROUGH THE AFTERNOON. TEMPS WILL BE MUCH COOLER WITH HIGHS STRUGGLING TO REACH THE UPPER 50S AND LOWS FALLING INTO THE LOW TO MID 30S. FRIDAY THROUGH SATURDAY...THE LARGER SCALE LONGWAVE TROUGH WILL CONTINUE OVER THE EASTERN CONUS WITH THE PRIMARY SHORTWAVE PASSING BY TO THE NORTH ON FRIDAY. A DRY COLD FRONT WILL QUICKLY MOVE ACROSS THE FORECAST AREA EARLY FRIDAY AND A LARGE AREA OF HIGH PRESSURE WILL QUICKLY BUILD IN THROUGH SATURDAY. THE FRIDAY COLD FRONT WILL BRING A REINFORCING SHOT OF COOL AIR RESULTING IN TEMPS IN THE UPPER 50S TO NEAR 60 EACH DAY. FRIDAY NIGHT WILL BE COLD AS GOOD RADIATIONAL COOLING CONDITIONS SET UP...RESULTING IN LOWS IN THE MID TO UPPER 20S AWAY FROM THE BEACHES. WITH THE PASSAGE OF THE FRONT ON FRIDAY ANOTHER BREEZY LATE MORNING/AFTERNOON PERIOD IS EXPECTED. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE WILL QUICKLY REBUILD BEHIND A DEPARTING SHORTWAVE AND WEAK FRONT LATE SATURDAY INTO SUNDAY...THEN STEADILY SHIFT INTO THE ATLANTIC BY MONDAY. YET ANOTHER SHORTWAVE WILL SLIP EASTWARD WITHIN RATHER PROGRESSIVE FLOW ALOFT LATE MONDAY INTO TUESDAY. THE ASSOCIATED WAVE OF LOW PRESSURE AND FRONT WILL LACK A TAP INTO DEEP MOISTURE...THUS RAIN CHANCES WILL REMAIN BELOW 15 PERCENT. SINCE HIGH PRESSURE IS EXPECTED TO FOLLOW BEHIND THESE FEATURES FOR MID WEEK...DRY WEATHER APPEARS LIKELY THROUGH THE EXTENDED PERIOD. HIGH TEMPERATURES WILL REACH THE LOWER 60S EACH AFTERNOON...WITH LOWS FALLING INTO THE UPPER 30S TO AROUND 40 DEGREES. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... A BAND OF SHOWERS WILL PASS THROUGH THE TERMINALS LATE THIS EVENING AHEAD OF A WELL DEFINED FRONTAL PASSAGE WHICH SHOULD OCCUR BETWEEN 05Z-07Z. THERE MAY BE A BRIEF PERIOD OF MVFR CONDITIONS WITH THE PRE-FRONTAL SHOWERS BUT WE THINK THE MAIN STORY TONIGHT WILL CONTINUE TO BE THE STRENGTH OF THE SURFACE WINDS. VERY STRONG LOW LEVEL WIND FIELDS WILL MAINTAIN GUSTS OF 30-35 KT AT KCHS AND 25-30 KT AT KSAV THROUGH THIS EVENING. ONCE THE FRONT MOVES THROUGH...WINDS ALOFT WILL DIMINISH BUT STRONG COLD AIR ADVECTION WILL KEEP GUSTS AS HIGH AS 25-30 KT AT TIMES THROUGH MUCH OF THURSDAY. DESPITE THE STRONG GUSTS AT THE SURFACE...A BRIEF PERIOD OF LOW LEVEL WIND SHEAR HAS BEEN ADDED TO THE KCHS TAF FROM 03-07Z WITH WINDS AT 2K FT OVER SOUTHEAST SOUTH CAROLINA EXPECTED TO INCREASE TO AROUND 60 KT. EXTENDED AVIATION OUTLOOK...VFR. && .MARINE... CONDITIONS WILL DETERIORATE THIS EVENING AS A COLD FRONT DRAWS CLOSER TO THE AREA AND THE PRESSURE GRADIENT STRENGTHENS OVER ALL COASTAL WATERS. A COMPLEX MARINE FORECAST SCENARIO REMAINS THROUGH TONIGHT WITH A COOL SHELF WATERS ALONG THE SOUTHEAST COAST. WINDS WILL HAVE A TOUGH TIME MIXING DOWN WHERE SEA SURFACE TEMPS ARE IN THE MID 50S BUT WILL HAVE AN EASIER TIME MIXING CLOSER TO THE GULF STREAM WELL OFF THE GEORGIA COAST. WITH THIS IN MIND...A SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT FOR NEARSHORE WATERS SOUTH OF CHARLESTON AND INTO SOUTHEAST GEORGIA. THERE IS CONCERN ALONG THE LAND/SEA INTERFACE AND THE INTRACOASTAL WATERS IN SOUTH CAROLINA THIS EVENING...THUS HAVE MAINTAINED GALE WARNINGS FOR THE HARBOR AND THE CHARLESTON COUNTY WATERS. A GALE WARNING WILL ALSO REMAIN IN EFFECT FOR WATERS BEYOND 20 NM IN GEORGIA. WINDS WILL CONTINUE TO INCREASE THROUGH THIS EVENING AS 1000 MB GEOSTROPHIC FLOW IS MAXIMIZED IN THE 50-55 KT RANGE. PERIODS OF 35 KT WINDS ARE ANTICIPATED WHERE THE GALE WARNING IS IN EFFECT TONIGHT. SEAS SHOULD BUILD TO 7-10 FT THROUGH TONIGHT...HIGHEST BEYOND 20 NM OFF THE GEORGIA COAST. A PERIOD OF SHOWERS AND/OR THUNDERSTORMS ARE POSSIBLE WITH A COLD FRONT PUSHING OVER THE WATERS LATE TONIGHT. SOUTHERLY WINDS WILL THEN VEER AND BECOME WESTERLY AS A COLD FRONT MOVES WELL INTO THE WESTERN ATLANTIC. THURSDAY THROUGH MONDAY...MARINE CONDITIONS WILL REMAIN QUITE NASTY IN THE WAKE OF THE DEPARTING COLD FRONT THROUGH MUCH OF THE DAY ON THURSDAY. ALTHOUGH GUSTS TO GALE FORCE WILL LIKELY BE OVER...SOLID SMALL CRAFT ADVISORY CRITERIA WILL CONTINUE FOR ALL WATERS. CONDITIONS WILL REMAIN ELEVATED NEAR SMALL CRAFT ADVISORY CRITERIA THROUGH THURSDAY NIGHT BEFORE ANOTHER SURGE LATE THURSDAY NIGHT/FRIDAY MORNING ASSOCIATED WITH A PASSING COLD FRONT. HIGH PRESSURE WILL THEN BUILD DURING THE EARLY WEEKEND AND ALLOW CONDITIONS TO FALL BELOW CRITERIA SATURDAY. YET ANOTHER DRY FRONT COULD SUPPORT A BRIEF SURGE IN OFFSHORE FLOW SUNDAY. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...WIND ADVISORY UNTIL 1 AM EST THURSDAY FOR GAZ087-088-099>101- 114>119-137>141. SC...WIND ADVISORY UNTIL 1 AM EST THURSDAY FOR SCZ040-042>045- 047>052. MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EST THURSDAY FOR AMZ352-354. GALE WARNING UNTIL 4 AM EST THURSDAY FOR AMZ330-350. GALE WARNING UNTIL 7 AM EST THURSDAY FOR AMZ374. && $$ SYNOPSIS... NEAR TERM...DPB/JAQ SHORT TERM...BSH LONG TERM...79 AVIATION...JAQ/BSH MARINE...JAQ/DPB/BSH