FXUS62 KCHS 121812 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 112 PM EST FRI MAR 12 2010 .SYNOPSIS... A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND PUSH OFFSHORE TONIGHT. LOW PRESSURE WILL RESIDE NORTH OF THE AREA THIS WEEKEND BEFORE MOVING INTO THE NW ATLANTIC EARLY NEXT WEEK. RAIN CHANCES COULD RETURN BY THE MIDDLE OF NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... VERY DIFFICULT FORECAST THIS AFTERNOON AS A HIGHLY AMPLIFIED UPPER AIR PATTERN REMAINS ACROSS THE REGION. WATER VAPOR IMAGERY CONTINUES TO SHOW A SHORTWAVE ACROSS TENNESSEE AND ALABAMA AND ITS ASSOCIATED COLD FRONT WHICH WILL CONTINUE TO APPROACH FROM THE WEST. THE SHORTWAVE WILL CONTINUE TO SUPPORT SHOWER AND THUNDERSTORM DEVELOPMENT TODAY AS IT PROPAGATES TOWARD THE CWA. HAVE POPS INCREASING FROM SOUTHWEST TO NORTHEAST THROUGH TODAY AND THIS EVENING. EXPECT CHANCE TO LIKELY POPS AS EARLY AS THIS AFTERNOON FOR PORTIONS OF SOUTHEAST GEORGIA. THIS IS 3 TO 6 HOURS EARLIER THAN WHAT THE NAM AND GFS SHOWED. NEITHER MODEL APPEARED TO BE INITIALIZING WELL WITH CURRENT CONDITIONS...THUS WENT MORE IN LINE WITH THE RUC MODEL WHICH SEEMS TO HAVE A BETTER GRASP ON CURRENT TRENDS. HAVE MAINTAINED MENTION OF THUNDER THIS AFTERNOON AS MODEL INDICES SHOW DECENT POTENTIAL FOR THUNDERSTORM DEVELOPMENT. CAN/T RULE OUT AN ISOLATED STRONG TO SEVERE THUNDERSTORM LATER THIS AFTERNOON...ESPECIALLY ACROSS GEORGIA AREAS. AFTER ANALYZING A MODIFIED MODEL SOUNDING WITH WORST CASE PARAMETERS...TT COULD REACH THE MID TO UPPER 50S AND LI COULD BE NEAR -5. HOWEVER...EXPECT OVERCAST SKIES TO CONTINUE TO DOMINATE WHICH WILL KEEP OUR MAX TEMPERATURE WELL BELOW OUR CONVECTIVE TEMPERATURE THIS AFTERNOON. SLIGHTLY LOWERED HIGH TEMPERATURES THIS AFTERNOON WITH HIGHS IN THE MID TO UPPER 60S. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... SHOWERS AND TSTMS WILL BE ONGOING EARLY THIS EVENING AS A COLD FRONT PUSHES THROUGH. ACTIVITY WILL QUICKLY END FROM SOUTHWEST TO NORTHEAST AS THE EVENING PROGRESSES...CLEARING THE CHARLESTON TRI- COUNTY AREA LAST. WILL CARRY POPS UP TO 60-70 PERCENT ACROSS MOST OF THE SOUTH CAROLINA ZONES WITH CHANCE POPS FOR SOUTHEAST GEORGIA...TAPERING OFF THE NO POPS AFTER MIDNIGHT. THE RISK FOR A STRONG TO SEVERE TSTMS WILL LINGER ACROSS INTERIOR SOUTHEAST SOUTH CAROLINA UNTIL THE COLD FRONT CLEARS THE COAST. DRIER AIR AND DECREASING CLOUDS ARE EXPECTED OVERNIGHT WITH LOWS RANGING FROM THE UPPER 40S TO LOWER 50S...WARMEST AT THE COAST. && .LONG TERM /SATURDAY THROUGH THURSDAY/... THE COLD FRONT WILL SHIFT WELL OFFSHORE BY SATURDAY MORNING... HAVING BEEN PULLED EAST-NORTHEAST BY THE SURFACE LOW MOVING TOWARD COASTAL VIRGINIA. ALL MODELS SUGGEST THAT SOME WRAP AROUND PRECIPITATION COULD AFFECT AT LEAST THE WESTERN COUNTIES DURING THE DAY. A BROAD UPPER LOW WILL STILL BE CENTERED OVER THE OHIO AND TENNESSEE VALLEYS...WITH PLENTY OF ENERGY ALOFT TO SUPPORT DEEP MOISTURE JUST TO THE WEST OF THE FORECAST AREA. 00Z NAM INDICATES MORE SOLID PRECIPITATION CHANCES THAN OTHER MODELS...DUE TO A BETTER SOUTHWEST FLOW COMPONENT IN THE MID LEVELS TAPPING INTO GULF MOISTURE. WILL NOT INDICATE RAIN CHANCES AS HIGH AS THE MET GUIDANCE...BUT HAVE ADDED JUST A SLIGHT CHANCE BELOW 20 PERCENT FOR SATURDAY AFTERNOON DUE TO SOME CONSISTENCY BETWEEN THE MODELS. LOW PRESSURE AT THE SURFACE AND ALOFT WILL CONTINUE TO SLIP INTO THE NORTHWEST ATLANTIC SATURDAY NIGHT INTO EARLY NEXT WEEK. EXPECT A SLIGHT COOL DOWN IN TEMPERATURES SUNDAY AND MONDAY BEHIND THE COLD FRONT AND LOW SYSTEM...WITH HIGH TEMPERATURES IN THE MID 60S. OTHERWISE...HIGH TEMPERATURES WILL RANGE FROM THE MID TO UPPER 60S...WHILE CONDITIONS REMAIN DRY UNTIL MID WEEK. 00Z ECMWF HAS COME A BIT MORE IN LINE WITH THE 00Z GFS REGARDING THE BROAD PATTERN EVOLUTION FOR MID WEEK. HOWEVER...ENOUGH DIFFERENCE BETWEEN THE SOLUTIONS REMAINS TO ADD UNCERTAINTY TO THE PRECIPITATION FORECAST WEDNESDAY AND THURSDAY. SHORTWAVE ACTIVITY WILL ROTATE ALONG THE SOUTHERN PERIPHERY OF AN UPPER TROUGH WEDNESDAY...POSSIBLY SPINNING UP A SURFACE LOW OFF THE COAST ON THURSDAY. NEITHER GFS NOR ECMWF DEPICT A LOT OF RAIN WITH THIS SYSTEM...DUE TO LIGHT WIND FIELDS AND A MORE PERSISTENT OFFSHORE FLOW. HAVE MAINTAINED JUST A GENERIC 20 PERCENT CHANCE OF RAIN WEDNESDAY AND THURSDAY TO HINT AT THE POTENTIAL FOR SOME WETTER WEATHER. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... MVFR CIGS WILL CONTINUE AT BOTH CHS AND SAV TERMINALS THIS AFTERNOON WHILE WINDS REMAIN LIGHT AND AMPLE LOW LVL MOISTURE PERSISTS. CIGS WILL GRADUALLY IMPROVE THIS EVENING BUT REMAIN MVFR AS UPPER LVL FORCING STRENGTHENS OVER THE SOUTHEAST. A LOW CONFIDENCE FORECAST REMAINS THIS EVENING THROUGH EARLY TONIGHT AT BOTH TERMINALS. THERE WILL BE A CHANCE OF THUNDERSTORMS AT BOTH TERMINALS...BUT CONFIDENCE IN TIMING AND DURATION REMAIN TOO LOW TO INCLUDE IN TAF AT THIS TIME. HAVE MAINTAINED MENTION OF CB AT BOTH TERMINALS FROM 22Z TO 02Z WHEN ENHANCED RISK OF THUNDERSTORM ACTIVITY IS POSSIBLE. SFC WINDS WILL BEGIN TO SHIFT FROM SOUTH TO WEST OVERNIGHT AS A COLD FRONT PUSHES THROUGH THE AREA. ONCE FROPA OCCURS...CIGS WILL BEGIN TO IMPROVE. EXPECT VFR CIGS BY 09Z AT BOTH TERMINALS AS DRYER AIR FILTERS INTO THE REGION. WEST SOUTHWEST WINDS GUSTS BETWEEN 15 TO 25 KTS ARE LIKELY SATURDAY AFTERNOON AS SKIES CONTINUE TO CLEAR AND AMPLE SFC HEATING OCCURS. EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO RETURN OVER THE WEEKEND AND LINGER THROUGH EARLY NEXT WEEK. && .MARINE... HAVE EXTENDED THE SCA HEADLINE FOR THE NEAR SHORE WATERS FROM EDISTO BEACH UP TO SOUTH SANTEE RIVER AS THE CHARLESTON PILOT BOAT REPORTED 5 FOOT SEAS JUST OFFSHORE AND 41004 CONTINUES TO SHOW ELEVATED SEAS JUST SHY OF 10 FEET TODAY. EXPECT SEAS CONTINUE TO DIMINISH...BUT EXPECT A FEW 6 FT SEAS AROUND 20 NM OUT TO LINGER THROUGH THE AFTERNOON. HAVE MAINTAINED PATCHY SEA FOG THROUGH THE TONIGHT AS CONDITIONS WILL FAVOR FOG DEVELOPMENT ACROSS THE INNER COASTAL WATERS. PILOT BOAT OFFICE IN CHARLESTON HAS REPORTED VISIBILITIES AS LOW AS A MILE THIS MORNING WHICH CONDITIONS SLIGHTLY IMPROVING TO 2 TO 3 MILES RECENTLY. INCOMING SHOWERS AND TSTMS LATE THIS AFTERNOON AND EARLY THIS EVENING SHOULD HELP SCOUR ANY FOG THAT DEVELOPS OUT. THE COLD FRONT IS ON TARGET TO PUSH OFF THE COAST LATE THIS EVENING WITH WEAK COLD AIR ADVECTION DEVELOPING WITH THIS PASSAGE. WINDS WILL SURGE UP TO 15-20 KT OVER THE NEARSHORE WATERS AND 20-25 KT OVER BEYOND 20 NM. SEAS WILL RANGE FROM 2-4 FT NEARSHORE...5-7 FT OFFSHORE. SURFACE LOW PRESSURE WILL LINGER TO THE NORTH OF THE AREA THIS WEEKEND. WINDS OVER THE COASTAL WATERS WILL REMAIN ENHANCED SATURDAY AND SUNDAY WITHIN LIGHT TO MODERATE COLD ADVECTION AND A PERSISTENT TIGHT PRESSURE GRADIENT. A SMALL CRAFT ADVISORY WILL THUS CONTINUE THROUGH SUNDAY FOR THE OFFSHORE GEORGIA ZONES...WHILE NEARSHORE WATERS WILL LIKELY FALL WITHIN THE 15 TO 20 KT RANGE. A NORTHERLY FLOW COMPONENT WILL CONTINUE INTO EARLY NEXT WEEK AS THE LOW CONTINUES TO PULL FURTHER INTO THE NORTHWEST ATLANTIC AND WEAK HIGH PRESSURE BUILDS IN FROM THE WEST. THE PRESSURE GRADIENT WILL RELAX...ALLOWING MARINE CONDITIONS TO SUBSIDE BELOW ADVISORY LEVELS. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EDT MONDAY FOR AMZ374. SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ350. && $$