Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 171909 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 309 PM EDT WED SEP 17 2014 .SYNOPSIS... HIGH PRESSURE WILL EXTEND DOWN INTO THE CAROLINAS FROM THE NORTH PROVIDING FALL-LIKE WEATHER FOR THE REMAINDER OF THE WEEK. THE NEXT COLD FRONT WILL MOVE THROUGH ON TUESDAY FOLLOWED BY COOL AND DRY HIGH PRESSURE THROUGH THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM WEDNESDAY...A DEEP TROUGH WILL REMAIN ALOFT THROUGH TONIGHT WHILE AT THE SURFACE...HIGH PRESSURE WILL RIDGE MORE STRONGLY SOUTH ACROSS THE EASTERN CAROLINAS. WEAK DISTURBANCES EMBEDDED IN FAST PACED...UP TO 70 KT FLOW...WILL CONTINUE TO TRAVERSE THE AREA. MODELS CONTINUE TO KEY IN ON REMNANT MCV ACROSS THE MID MISSISSIPPI/TENNESSEE VALLEY WITH A PIECE OF THIS ENERGY PERHAPS BRUSHING OUR FORECAST AREA LATE AFTERNOON/THIS EVE. STILL NO ORGANIZED CONVECTION OF SIGNIFICANCE HAS DEVELOPED ON THE LEADING EDGE OF THIS FEATURE ACROSS THE SOUTHEAST STATES AS OF MID AFTERNOON. WATER VAPOR IMAGERY SHOWS PLENTY OF DRY AIR ACROSS THE BREATH OF THE CAROLINAS. A FEW SHOWERS HAVE MANAGED TO OVERCOME THIS DRY AIR... DEVELOPING ALONG A PORTION OF THE CONVERGENT SEABREEZE IN A RATHER UNSTABLE AIRMASS GIVEN MODEST COOLING CONTINUES IN THE MID LEVELS. WE DO EXPECT MORE IN THE WAY OF SHOWERS AND POSSIBLY SOME THUNDERSTORMS TO DEVELOP THROUGH LATE AFTERNOON/EARLY EVE. THE CONVECTION SHOULD SHARPLY WANE WITH LOSS OF HEATING THUS ALLOWING THE INSTABILITY TO GREATLY DIMINISH. WILL SHOW SCATTERED POPS DECREASING FROM W TO E TONIGHT...LASTLY ALONG THE COAST...AS THE AIRMASS STABILIZES AND UPPER LEVEL SUPPORT MOVES BY. WHILE CONVECTION SHOULD CONTINUE TO HAVE A DIFFICULT TIME BUILDING TO A SIGNIFICANT DEPTH...THE POTENTIAL IS THERE FOR SHOWERS/ THUNDERSTORMS TO PRODUCE STRONG/GUSTY WINDS. THIS IS REFLECTED IN THE HIGH DOWNDRAFT CAPE VALUES ACROSS THE AREA THIS AFTERNOON DUE TO DRIER AIR ABOVE AND BELOW THE NEARLY SATURATED LAYER...2-12 KFT. ALSO...LOW WET BULB ZEROS AND LOW 50 DBZ CORE THRESHOLDS SUGGEST A POTENTIAL FOR SMALL HAIL IN THUNDERSTORMS THAT ARE ABLE TO ATTAIN ADEQUATE HEIGHT. FOG/STRATUS MAY AGAIN FILL IN OVERNIGHT AND THU MORNING AS A STRENGTHENING SUBSIDENCE INVERSION TRAPS A CONTINUOUS SUPPLY OF MOISTURE BELOW 1 KFT ON LOW-LEVEL EASTERLY FLOW. MODEL SOUNDINGS SHOW THE INVERSION WILL BE MOST PRONOUNCED INLAND. LOWS TONIGHT SHOULD BE SIMILAR TO LAST NIGHT IF NOT A DEGREE OR TWO COOLER...ESPECIALLY ALONG THE COAST. WILL FORECAST LOWS IN THE MID 60S WITH SEVERAL INLAND COMMUNITIES DROPPING INTO THE LOWER 60S WHILE SEVERAL BEACH TOWNS ONLY REACH THE UPPER 60S TO NEAR 70. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...HIGH PRESSURE BUILDING DOWN INTO THE CAROLINAS FROM THE GREAT LAKES ON THURS WILL SHIFT EAST PRODUCING A VERY PRONOUNCED WEDGE PATTERN BY FRI AFTN. AT THE SAME TIME THE MID TO UPPER TROUGH OVER THE EAST COAST WILL LIFT OFF TO THE NORTHEAST. BEFORE THE TROUGH LIFTS OFF...A COUPLE OF MINOR PERTURBATIONS RIDING AROUND THE BASE MAY ENHANCE CLOUDS AND LOW END PCP ON THURS...BUT NOT COUNTING ON MUCH. AS TROUGH LIFTS OFF THROUGH FRI...IT MAY PROVIDE ENOUGH OF A WEAKNESS TO ALLOW DEVELOPING LOW PRESSURE OFF THE SOUTHEAST COAST TO RETROGRADE BACK TO THE W-NW THROUGH FRI NIGHT. OVERALL EXPECT DECENT NORTHEAST FLOW AS GRADIENT BECOMES MORE PINCHED AS TROUGH OF LOW PRESSURE SHIFTS NORTH TOWARD THE SOUTHEAST COAST THROUGH LATE FRI INTO FRI NIGHT. THE NAM HAS THE LOW MOVING FARTHER WEST WITH A GREATER ON SHORE FLOW OF MOISTURE THROUGH FRI AND A MUCH WETTER FORECAST...WHILE THE GFS/ECMWF CONFINE THE GREATEST MOISTURE OFF SHORE AND JUST ALONG THE COAST. FOR NOW WILL GO WITH BRUNT OF CLOUDS AND POPS OFF SHORE AND JUST ALONG THE COAST IN NE FLOW THROUGH FRI NIGHT. NORTHEAST FLOW WILL HELP KEEP HIGH TEMPERATURES ALONG THE COAST A LITTLE BELOW CLIMO THROUGH THE PERIOD. FARTHER INLAND HIGHS WILL BE NEAR CLIMO WITH A LITTLE MORE SUN. LOW TEMPERATURES WILL END UP A LITTLE ABOVE CLIMO DUE TO CLOUDS AND BOUNDARY LAYER MIXING. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 300 PM WEDNESDAY...POTENTIALLY UNSETTLED TO START THE PERIOD...BUT EVEN BY D4 THERE IS CONSIDERABLE MODEL SPREAD. STALLED BOUNDARY OFFSHORE WILL BE A FOCUS FOR LOW PRESSURE DEVELOPMENT...BUT THE QUESTION REMAINS HOW CLOSE TO THE COAST THIS LOW WILL FORM. THE NAM/CMC ARE IN ONE CAMP WITH DEEP EASTERLY FLOW AHEAD OF A LOW PRESSURE MOVING RIGHT ALONG THE COAST...CAUSING WIDESPREAD AND POSSIBLY HEAVY...RAINFALL. THE GFS/ECMWF ARE FURTHER OFFSHORE...WITH NE FLOW THROUGH THE WEEKEND AS THE LOW PRESSURE STAYS WELL OFF THE COAST. WPC FAVORING THE ECMWF AND ITS ENSEMBLES...WHICH HAVE FLUCTUATED LITTLE FROM LAST WEEK...AND THUS WILL CONTINUE WITH THE INHERITED FORECAST LEANING SIGNIFICANTLY ON THE ECMWF WITH SOME BLENDING WITH THE WETTER SOLUTIONS. THIS SUGGESTS AT LEAST WIDESPREAD CLOUD COVER SATURDAY AS THE LOW PRESSURE MAKES ITS CLOSEST APPROACH...WITH SHOWERS MOST LIKELY ACROSS THE EASTERN ZONES. IMPROVEMENT WILL OCCUR ON SUNDAY AS THE LOW PRESSURE PULLS OFF TO THE NORTHEAST...AND TEMPS WILL BE AROUND SEASONABLE THROUGH THE WKND...ALTHOUGH SUNDAY WILL LIKELY BE A BIT WARMER. A BRIEF PERIOD OF RETURN FLOW DEVELOPS AHEAD OF A STRONG COLD FRONT WHICH IS SLATED TO CROSS TUESDAY AFTN. THIS BRINGS A DAY OR TWO OF WARMER TEMPERATURES...BEFORE CANADIAN HIGH PRESSURE ENVELOPS THE REGION FOR MID-WEEK. CONVECTION LOOKS LIKELY ON TUESDAY WITH THE COLD FRONT...AND WILL BUMP POP TO CHC FOR TUESDAY AS SURFACE CONVERGENCE...PVA...AND SOME JET-LEVEL DIFFLUENCE COMBINE IN A RICH THETA-E AIR MASS. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 18Z...TERMINALS ARE VFR THIS AFTERNOON EXCEPT FOR MVFR CIGS AT KLBT. AN UPPER IMPULSE WILL MOVE THROUGH LATE DAY COUPLED WITH PEAK HEATING. ISOLATED/SCATTERED CONVECTION WILL DEVELOP...WITH MODERATE CONFIDENCE KILM WILL EXPERIENCE A THUNDERSTORM BY 21Z. PRECIPITATION SHOULD GRADUALLY DIMINISH THIS EVENING. BY MIDNIGHT IFR/LIFR STRATUS/VSBYS WILL BE AN INCREASING CONCERN. ALL MOS GUIDANCE INDICATES IFR/LIFR CONDITIONS. CONFIDENCE IS HIGH MVFR CONDITIONS WILL DEVELOP. CONFIDENCE MODERATE TO HIGH LIFR CONDITIONS WILL DEVELOP WITH LOWEST CONFIDENCE AT KLBT. CIGS RISE TO MVFR BY MID-MORNING. EXTENDED OUTLOOK...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 300 PM WEDNESDAY...NE WINDS WILL REMAIN THROUGH THE PERIOD AS HIGH PRESSURE RIDGES MORE STRONGLY SOUTHWARD. A SLIGHT NE SURGE TONIGHT WILL INCREASE WIND SPEEDS UP TO 10 TO 15 KT. AN EASTERLY SWELL FROM DISTANT HURRICANE EDOUARD WILL ALLOW SEAS TO BE CONSIDERABLY HIGHER THAN THE WIND SPEEDS WOULD OTHERWISE INDICATE. SEAS OF 3 TO 4 FT WILL BE COMMON WITH SOME 5 FT SEAS ACROSS THE OUTERMOST WATERS. THE SWELL PERIOD WILL BE ON THE ORDER OF 12 TO 13 SECONDS. SEAS WILL TREND ABOUT A FOOT LOWER OVERNIGHT. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...HIGH PRESSURE RIDGING DOWN FROM THE NORTH WILL PRODUCE LIGHT NORTHEAST FLOW ON THU AROUND 10 KTS OR LESS. WINDS WILL WILL INCREASE SIGNIFICANTLY THROUGH FRI AS DISTINCT HIGH PRESSURE WEDGE SETS UP AND LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST. NE WINDS WILL INCREASE UP TO 20 KT WITH HIGHER GUSTS THROUGH FRI INTO FRI NIGHT AND MAY BECOME MORE EASTERLY DEPENDING ON POSITION AND STRENGTH OF DEVELOPING LOW OFF THE SOUTHEAST COAST. SEAS 2 TO 4 FT ON THURS WILL DIMINISH SLIGHTLY THROUGH THE DAY AS LONG PERIOD SWELLS DECREASE. AS NE WINDS INCREASE THROUGH FRI...SEAS MAY REACH SCA THRESHOLDS INTO FRI EVE...ESPECIALLY NORTH OF CAPE FEAR...BUILDING TO 4 TO 5 FT WITH POTENTIAL FOR 6 FT. MAINLY IN OUTER WATERS. LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 300 PM WEDNESDAY...CONCERN THROUGH THE EXTENDED INVOLVES A LOW PRESSURE SYSTEM PROGGED TO DEVELOP ALONG A STALLED COLD FRONT OFF THE COAST. STILL SIGNIFICANT UNCERTAINTY INTO THE STRENGTH AND EXACT PLACEMENT OF THIS FEATURE...BUT AT LEAST SOME IMPACTS ARE EXPECTED LOCALLY. THIS LOW PRESSURE WILL MAKES ITS CLOSEST APPROACH TO THE WATERS ON SATURDAY...PRODUCING ENHANCED NE WINDS OF 15-20 KTS...POSSIBLY HIGHER IF THE LOW IS CLOSER/STRONGER THAN CURRENTLY FORECAST. WINDS THEN BECOME VARIABLE ON SUNDAY AS A WEAK RIDGE OF HIGH PRESSURE BUILDS TOWARDS THE AREA...BEFORE TURNING TO THE SW WIND SW ON MONDAY...WITH SPEEDS RISING BACK TO 10-15 KTS. WAVES WILL BE PRIMARILY NE-WIND-WAVE DRIVEN ON SATURDAY WITH HEIGHTS 4-5 FT...BUT AGAIN...IF THE SYSTEM IS STRONGER OR CLOSER AN SCA MAY BE NEEDED. THEREAFTER...WAVE HEIGHTS FALL TO 2-4 FT ON SUNDAY...AND THEN 1-3 ON MONDAY WITH A SW WIND WAVE AND WEAK SE SWELL FORMING IN THE SPECTRUM. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...RJD SHORT TERM...RGZ LONG TERM...JDW AVIATION...RJD/MRR

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