Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 162334 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 734 PM EDT TUE SEP 16 2014 .SYNOPSIS... A COLD FRONT WILL PUSH OFFSHORE LATE TONIGHT. HIGH PRESSURE WILL EXTEND DOWN INTO THE CAROLINAS FROM THE NORTH BEHIND THIS FRONT...PROVIDING FALL-LIKE WEATHER FOR THE REMAINDER OF THE WEEK. THE NEXT COLD FRONT WILL MOVE THROUGH BY MONDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 730 PM TUESDAY...IN THE BATTLE OF MODELS...THE 18Z GFS AND 20Z HRRR APPEAR TO BE THE BEST SOLUTIONS OVERNIGHT. THE 18Z NAM IN PARTICULAR HAS PROBLEMS WITH ITS DEEPENING OF THE SURFACE LOW ACROSS THE SC COASTAL PLAIN RATHER THAN OFFSHORE AS THE BULK OF THE LATEST MODELS SHOW. THIS FEEDS BACK INTO PROBLEMS WITH THE NAM`S WIND FORECAST AND ITS CONSIDERABLE COVERAGE OF PRECIPITATION VERY LATE TONIGHT INLAND. GOING WITH THE GFS/HRRR SOLUTION MEANS THE CURRENT CONVECTIVE ACTIVITY IN THE NC FOOTHILLS/WESTERN PIEDMONT SHOULD SLIDE DOWN INTO THE BENNETTSVILLE/LUMBERTON AREA IN THE 9-11 PM TIMEFRAME. POPS HAVE BEEN INCREASED TO NEAR 50 PERCENT HERE. THE COLD FRONT CURRENTLY ACROSS THE NC MOUNTAINS AND NEAR THE NC/VA BORDER WILL BE DRAWN SOUTHWARD OVERNIGHT...PULLED INTO THE ZONE OF LOWERING PRESSURES ACROSS THE SC OFFSHORE WATERS. CONVECTIVE ACTIVITY ACROSS FROM MIDNIGHT ONWARD IS LESS CERTAIN...BUT A WIDESPREAD ZONE OF 20-30 POPS REMAINS IN THE FORECAST AS RATHER STEEP LAPSE RATES ALOFT DEVELOP WITH THE APPROACHING UPPER TROUGH AND CONSIDERABLE LOW LEVEL MOISTURE POOLS NEAR THE FRONT. A 300 MB JET STREAK MAY ALSO BECOME FAVORABLY ALIGNED AFTER MIDNIGHT...ALTHOUGH IT APPEARS THIS WILL MAINLY BE A FACTOR FOR OFFSHORE CONVECTION RATHER THAN ACTIVITY ON LAND. NO CHANGES HAVE BEEN MADE TO TEMPERATURE FORECASTS WITH LOWS FALLING IN THE UPPER 60S INLAND TO LOWER 70S ON THE COAST. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...WEAK LOW PRESSURE ALONG LINGERING FRONT WILL GET PUSHED FARTHER OFF SHORE AS HIGH PRESSURE BUILDS DOWN FROM THE NORTHWEST THROUGH MID WEEK. THE EASTERLY FLOW AROUND THE TOP OF THE LOW WILL COME UP AGAINST W-NW FLOW AS HIGH PRESSURE BUILDS IN. THIS WILL PRODUCE SOME LOW LEVEL CONVERGENCE THROUGH WED AND THE LAST BIT OF ENERGY IN THE MID LEVELS WILL ROUND THE BASE OF THE TROUGH BEFORE IT LIFTS OFF TO THE NORTHEAST. THEREFORE WILL KEEP SOME CLOUDS AND POPS IN FORECAST ON WED. THE MID TO UPPER TROUGH RUNNING DOWN THE EAST COAST WILL SHIFT SLOWLY EAST AND WILL LIFT FARTHER OFF TO THE NORTHEAST WED INTO THURS. AS TROUGH AXIS CROSSES THE COAST EARLY THURS...A DEEPER N-NW FLOW WILL ESTABLISH ITSELF OVER THE CAROLINAS WITH CONSIDERABLE DRYING AND SUBSIDENCE THROUGH THE MID LEVELS. HIGH PRESSURE WILL BUILD IN WITH LIGHT NORTHERLY WINDS VEERING AROUND TO THE NE THROUGH LATE THURS. PCP WATER VALUES DROP FROM AROUND 1.5 INCHES WED AFTN DOWN CLOSER TO AN INCH BY THURS EVE. DEWPOINT TEMPS IN THE MID TO UPPER 60S WED AFTN WILL DROP INTO THE LOWER 60S THROUGH THURS. OVERALL EXPECT CONDITIONS TO IMPROVE WITH INCREASING SUNSHINE AND MORE FALL LIKE WEATHER. AS AIR MASS TRANSITIONS TO A DRIER MORE SEASONABLE AIR MASS...SO WILL THE TEMPS. TEMPS OVERNIGHT WED WILL BE WARMER THAN THURS NIGHT BY A COUPLE OF DEGREES...MID 60S BOTH NIGHTS. TEMPS WILL REACH INTO THE 80S ON WED BUT ON THURS TEMPS WILL RUN A FEW DEGREES COOLER EVEN WITH A GREATER AMOUNT OF SUNSHINE. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 PM TUESDAY...ON FRIDAY A LARGE AREA OF COOL HIGH PRESSURE WILL BE SLIDING EAST ACROSS NEW ENGLAND. THIS ANTICYCLONE WILL HAVE A RIDGE AXIS EXTENDING ALL THE WAY DOWN INTO THE CAROLINAS. FLOW ALOFT WILL BE VERY WEAK BUT STILL HAVE SOME SENSE OF TROUGHINESS. MODELS HAVING A HARD TIME TELLING HOW MUCH THIS TROUGHINESS ERODES THE EASTERN PERIPHERY OF THE SURFACE RIDGE. THE MORE AGGRESSIVE GFS MANAGES TO FLING MOISTURE ASHORE AND HAS THE SUPPORT OF THE CMC. THE (00Z) ECMWF DOES THE SAME BUT WITH A MUCH SLOWER SENSE OF TIMING KEEPING MOST PLACES DRY TIL SUNDAY. WILL SHOW JUST SLIGHT CHANCE POPS ALONG THE COAST THROUGH THESE DAYS. THE WEDGE APPEARS TO WASH OUT BY MONDAY AT WHICH TIME RAIN CHANCES SHIFT TO BEING TIED TO A DEVELOPING PIEDMONT TROUGH AND TEMPS REBOUND TO NORMAL OR HIGHER. A COLD FRONT APPEARS SLATED FOR A MONDAY NIGHT ARRIVAL. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 00Z...RADAR IMAGERY THIS EVENING SHOWS SOME PRE-FRONTAL CONVECTION APPROACHING FROM THE NORTHWEST. HI-RES GUIDANCE INCLUDING THE HRRR HOLDS THIS ACTIVITY TOGETHER THROUGH THE EVENING HOURS...SO WILL INCLUDED VCSH/VCTS FOR KFLO/KLBT EARLY TONIGHT. TEMPO MVFR/IFR CONDITIONS COULD ACCOMPANY ONE OF THESE STORMS IF IT MOVES DIRECTLY OVER A TAF SITE...BUT COVERAGE IS LIMITED SO WILL NOT INCLUDE ANY RESTRICTIONS ATTM. A PERIOD OF CALM WINDS IS EXPECTED TONIGHT AHEAD OF THE COLD FRONT...WHICH COULD ALLOW VSBYS TO DROP TO MVFR/TEMPO IFR LEVELS IN BR. THE GFS/NAM DIFFER IN REGARDS TO THE TIMING OF THE FRONT AND ITS ASSOCIATED NORTHEASTERLY SURGE. BUT THE MORE REALISTIC GFS SOLUTION SHOWS NORTHEAST WINDS AROUND 5 KT DEVELOPING BY 09Z WED...WHICH WOULD HELP MIX THE SFC LAYER AND IMPROVE VSBYS BEFORE DAYBREAK. THUS...THE FOG POTENTIAL MAY ACTUALLY BE HIGHER EARLIER TONIGHT AS OPPOSED TO THE NORMALLY FAVORED PRE-DAWN HOURS. THIS LOWERS MY CONFIDENCE IN DENSE FOG DEVELOPING OVERNIGHT...AND THUS HAVE REMOVED MENTION OF IFR VSBYS. MVFR CONDITIONS MAY PERSIST THROUGH 12Z WED BEFORE CIGS GRADUALLY IMPROVE TO VFR BY MIDDAY. NORTHEAST WINDS LESS THAN 10 KT WILL PREVAIL DURING THE DAY WED. EXTENDED OUTLOOK...EARLY MORNING MVFR/IFR CIGS POSSIBLE ON THU. GUSTY NORTHEAST WINDS EXPECTED FRI/SAT AS THE COOL AIR WEDGE STRENGTHENS OVER THE CAROLINAS. VFR ON SUNDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 730 PM TUESDAY...LIGHT GENERALLY ONSHORE WINDS WILL BACK AROUND TO THE NORTHEAST OVERNIGHT AS PRESSURES FALL OFF THE SOUTH CAROLINA COAST IN ASSOCIATION WITH LOW PRESSURE DEVELOPING OFFSHORE. A COLD FRONT CURRENTLY ACROSS THE NC MOUNTAINS AND ALONG THE NC/VA BORDER WILL ALSO BE PULLED THROUGH THE AREA LATE...WITH THE STRONGEST WINDS (10-15 KNOTS) DEVELOPING AROUND DAYBREAK. SHOWER ACTIVITY NEAR GEORGETOWN/WINYAH BAY SHOULD DIMINISH OVER THE NEXT COUPLE HOURS BUT ADDITIONAL SCATTERED SHOWERS AND T-STORMS MAY POP UP AHEAD OF AND NEAR THE FRONT OVERNIGHT. BASED ON CURRENT BUOY OBSERVATIONS SEAS HAVE BEEN ADJUSTED DOWNWARD TO 1-2 FEET CURRENTLY. THE LOCAL SWAN WAVE MODEL IS OFTEN TOO AGGRESSIVE BUILDING SEAS WITH LONG PERIOD SWELLS...AND SEA HEIGHT FORECASTS HAVE BEEN ADJUSTED DOWNWARD TO NEAR THE NOAA WAVEWATCH GUIDANCE OVERNIGHT. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...WILL MAINTAIN E-NE WINDS THROUGH MID WEEK AS HIGH PRESSURE BUILDS DOWN FROM THE NORTH. INITIALLY WINDS WILL BE LIGHTER AND MORE EASTERLY. THE ON SHORE FLOW UP TO 10 KTS ON WED WILL COMBINE WITH THE SEA BREEZE AND A LONG PERIOD UP TO 16 SEC EASTERLY SWELL TO PUSH SEAS UP TO 2 TO 4 FT WITH SOME 5 FTERS IN OUTER WATERS WED AFTN. THE LONGER PERIOD EASTERLY SWELLS FROM EDOUARD WELL OUT IN THE ATLANTIC WATERS WILL PEAK AROUND 16 SECONDS VERY EARLY WED AND WILL DIMINISH SLOWLY THROUGH THURS. SEAS WILL ACTUALLY DROP SLIGHTLY THROUGH EARLY THURS BUT A SLIGHT INCREASE IN NE WINDS UP TO 10-15 KNOTS THROUGH THUR NIGHT SHOULD PRODUCE ANOTHER SPIKE IN SEAS BY FRI MORNING. LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 300 PM TUESDAY...A WEDGE OF HIGH PRESSURE MORE REMINISCENT OF THE COOL SEASON WILL DEVELOP ON FRIDAY. THE PINCHED NORTHEASTERLY GRADIENT COULD YIELD A FEW ADVISORY-WORTHY 6 FT SEAS INTO NRN ZONES...BUT WNA GUIDANCE HAS COME DOWN FROM PREVIOUS RUNS AND IT MAY BE QUITE MARGINAL. CURRENT FCST STILL SHOWING A RAMP UP TO 4 TO 6 THOUGH. WAVE SHADOWING WILL PRECLUDE ADVISORY OVER SOUTHERN WATERS. A MODERATE NORTHEASTERLY FLOW WILL REMAIN IN PLACE FOR THE REST OF THE PERIOD WITH A GRADUAL DECREASE IN STRENGTH. BORDERLINE SCEC/ADVISORY MAY CONTINUE OVER NRN ZONES INTO SATURDAY. FURTHER WEAKENING OF THE HIGH PRESSURE WILL BRING QUIETER CONDITIONS COME SUNDAY. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...COASTAL FLOOD ADVISORY UNTIL 6 PM EDT THIS EVENING FOR NCZ107. MARINE...NONE. && $$ NEAR TERM...TRA SHORT TERM...RGZ LONG TERM...MBB AVIATION...BJR

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