Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 172317 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 717 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/...
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AS OF 730 PM WEDNESDAY...CHANGES TO THE FORECAST EARLY THIS EVENING CENTER ON OBSERVED RADAR TRENDS. CONVECTION IS FINALLY DIMINISHING IN INTENSITY AND COVERAGE ACROSS THE CAPE FEAR AREA...BUT A RENEWED CLUSTER OF STORMS IS CROSSING THE SANTEE RIVER WITH ITS SIGHTS SET ON GEORGETOWN IN THE NEXT HOUR. STORM MOTION IS BEING DRIVEN PRIMARILY BY BOUNDARIES AND COLD POOL INTERACTIONS...ALTHOUGH A TREND NOTED WITH THE TALLER MORE SIGNIFICANT THUNDERSTORMS HAS BEEN TO ACCELERATE EASTWARD DUE TO STRONG WEST WINDS UP ABOVE 600 MB THAT THE SHALLOWER LESS SIGNIFICANT CONVECTION ISN`T BEING AFFECTED BY. THE SPC MESOANALYSIS PAGE SHOWS SURFACE-BASED CAPE IS AROUND 1500 J/KG WITH FAVORABLE MID-LEVEL LAPSE RATES AROUND 6 DEG C/KM. CONVECTIVE TRENDS THIS EVENING SHOULD BE TOWARD A SLOW DECREASE IN ACTIVITY AS THE SURFACE COOLS. PLENTY OF DRY AIR ABOVE 700 MB HAS BEEN HELPING PRODUCE CONVECTIVE OUTFLOW BOUNDARIES DUE TO ENTRAINMENT INTO DOWNDRAFTS. THE LATEST FEW HRRR RUNS SHOW THERE MAY BE A FEW LINGERING SHOWERS ACROSS NE SOUTH CAROLINA ROOTED IN A LAYER OF UNSTABLE AIR AT 950-925 MB PERSISTING AFTER MIDNIGHT. I`LL KEEP SOME 20 POPS GOING FROM MYRTLE BEACH AND MARION SOUTHWARD BETWEEN 03-06Z TO ACCOUNT FOR THIS POTENTIAL. NO SIGNIFICANT CHANGES HAVE BEEN MADE TO OTHER FORECAST ELEMENTS. LOWS SHOULD STILL FALL INTO THE LOWER TO MID 60S FOR MOST AREAS AS WEAK COOL ADVECTION DEVELOPS OVERNIGHT ON LIGHT NE WINDS BELOW 850 MB. LINGERING LOW-LEVEL MOISTURE WILL ALMOST CERTAINLY CREATE LOW STRATUS AND FOG LATE TONIGHT...ESPECIALLY INLAND FROM THE COAST.
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&& .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 /00Z THURSDAY THROUGH MONDAY/...
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AS OF 00Z...CONVECTION ASSOCIATED WITH AN UPPER TROUGH MOVING OVERHEAD IS WANING THIS EVENING. WILL MONITOR FOR ANY DEVELOPMENT ALONG THE OUTFLOW BOUNDARY MOVING TOWARD KCRE/KMYR...BUT ATTM NO STORMS POSE A THREAT TO ANY TAF SITE. FOG/STRATUS WILL BECOME AN INCREASING CONCERN OVERNIGHT...ESPECIALLY INLAND AT KFLO/KLBT. THESE SITES COULD SEE MVFR VSBYS BY 06Z...WITH IFR/LIFR CIGS/VSBYS DEVELOPING IN THE PRE-DAWN HOURS BEGINNING AROUND 09Z. ALONG THE COAST...NORTHEAST WINDS AOB 5 KT SHOULD KEEP VSBYS FROM DROPPING BELOW MVFR LEVELS. BUT STILL EXPECT MVFR/TEMPO IFR CIGS TO DEVELOP AT KILM/KCRE/KMYR BY DAYBREAK...THOUGH CONFIDENCE IS SLIGHTLY LOWER THAN FOR THE INLAND TERMINALS. ANY LINGERING MVFR CIGS AFTER 13Z SHOULD IMPROVE TO VFR BY MIDDAY. NORTHEAST WINDS AOB 10 KT WILL PREVAIL ON THU...BECOMING MORE EAST IN THE AFTERNOON. EXTENDED OUTLOOK...GUSTY NORTHEAST WINDS EXPECTED FRI/SAT AS COOL HIGH PRESSURE EXTENDS SOUTHWARD INTO THE CAROLINAS. EARLY MORNING MVFR/IFR STRATUS POSSIBLE SAT/SUN MORNING. OTHERWISE VFR.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 730 PM WEDNESDAY...WEAK LOW PRESSURE WELL OFF THE SC COAST WILL MAINTAIN A LIGHT NE WIND OVERNIGHT. HIGH PRESSURE NORTH OF THE GREAT LAKES WILL BEGIN TO RIDGE SOUTHWARD LATE TONIGHT. A SLIGHT NE SURGE TONIGHT WILL INCREASE WIND SPEEDS UP TO 10 TO 15 KT. EASTERLY SWELL FROM DISTANT HURRICANE EDOUARD WILL ALLOW SEAS TO BE CONSIDERABLY HIGHER THAN THE WIND SPEEDS WOULD OTHERWISE INDICATE... 3 TO 4 FT OUTSIDE OF SHOALING/NEARSHORE INFLUENCES...WITH DOMINANT PERIODS OF 12 TO 13 SECONDS. 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.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ NEAR TERM...TRA SHORT TERM...RGZ LONG TERM...JDW AVIATION...BJR

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