Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 180521 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 121 AM EDT THU SEP 18 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 1:30 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: ISOLATED CONVECTION HAS CONTINUED ACROSS ROBESON COUNTY AND ALSO JUST OFF THE NEW HANOVER COUNTY BEACHES THIS EVENING. WITH SURFACE TEMPERATURES NOW 70-74 DEGREES IN MOST LOCATIONS SURFACE-BASED CAPE IS BELOW 1000 J/KG WITH 20-40 J/KG OF CONVECTIVE INHIBITION TO DEAL WITH. HOWEVER LIFTING PARCELS FROM 925 MB GIVES ABOUT THE SAME INSTABILITY WITH NO SIGNIFICANT CAPPING. THIS IS LIKELY THE SOURCE REGION FOR THE ONGOING SHOWERS AND THUNDERSTORMS. ACTIVITY APPEARS TO BE FOCUSED ALONG AN INVERTED TROUGH THAT IS THE LEADING EDGE OF A MODEST NORTHEASTERLY SURGE OVER EASTERN NORTH CAROLINA. GIVEN THE VERY MOIST AIRMASS UP THROUGH 850 MB THERE IS NO REASON THIS INVERTED TROUGH/SURGE LINE CANNOT SERVE AS THE FOCUS FOR ADDITIONAL SHOWERS OR THUNDERSTORMS ALL THE WAY THROUGH THE NIGHT AS IT MOVES SOUTHWESTWARD THROUGH EASTERN SOUTH CAROLINA. IN AGREEMENT WITH THE LATEST HRRR (NCEP PARALLEL VERSION) WILL MAINTAIN 20-30 POPS ACROSS MOST OF EASTERN SOUTH CAROLINA THROUGH THE NIGHT. THIS MAY HAVE SOME NEGATIVE IMPACT ON THE DEVELOPMENT OF FOG AND LOW STRATUS LATE TONIGHT...BUT NO SIGNIFICANT CHANGES WERE MADE TO THAT PORTION OF THE FORECAST. PREVIOUS DISCUSSION FROM 730 PM FOLLOWS... 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 /FRIDAY 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 /05Z THURSDAY THROUGH MONDAY/...
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AS OF 06Z...EXPECT IFR/LIFR BR/STRATUS TO DEVELOP AT KFLO AND KLBT AFTER 09Z WITH LIGHT/CALM WINDS AND DECREASING CLOUD COVER. ALONG THE COAST...SLIGHTLY STRONGER NORTHEAST FLOW WILL LIKELY KEEP VSBYS FROM DROPPING BELOW MVFR LEVELS BEFORE 12Z. THERE IS A CHANCE THAT SOME TEMPO IFR CIGS COULD DEVELOP AT KCRE/KMYR BETWEEN 10-12Z...BUT CONFIDENCE IS LOW SO WILL KEEP IFR STRATUS SCT ATTM. MVFR CIGS SEEM MORE LIKELY FOR KILM/KCRE/KMYR JUST AFTER DAYBREAK. PATCHES OF MVFR CIGS MAY LINGER THROUGH THE LATE MORNING...BUT EXPECT VFR AT ALL TAF SITES BY MIDDAY. THEN VFR SHOULD PREVAIL THROUGH THE REST OF THE PERIOD. NORTHEAST WINDS AOB 10 KT WILL BECOME MORE EASTERLY AFTER 18Z. DO NOT ANTICIPATE MUCH...IF ANY...PCPN DURING THE DAY GIVEN THE DRY AIR ALOFT SEEN IN THE FCST SOUNDINGS. 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 1:30 AM THURSDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: WINDS ACROSS THE COASTAL WATERS NORTH OF CAPE FEAR ARE A LITTLE STRONGER THAN ANTICIPATED EARLIER. THIS IS LIKELY DUE TO A TIGHTENING PRESSURE GRADIENT BEHIND A MODEST SURGE LINE/INVERTED TROUGH THAT IS DROPPING SLOWLY SOUTHWESTWARD ALONG THE COAST. WIND GUSTS UP TO 21 KNOTS HAVE BEEN MEASURED AT CAPE LOOKOUT AND WRIGHTSVILLE BEACH WITHIN THE PAST HOUR. NO MODEL HAS WINDS THIS STRONG CURRENTLY...BUT I HAVE BUMPED WIND SPEED FORECASTS UP TO A SOLID 15 KNOTS NORTH OF CAPE FEAR...AND 10-15 KNOTS SOUTH OF CAPE FEAR TO NEAR MYRTLE BEACH. SEAS ARE UP TO A SOLID 4 FEET NORTH OF CAPE FEAR IN A COMBINATION OF SWELL AND WIND WAVES. PREVIOUS DISCUSSION FROM 730 PM FOLLOWS... 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. && $$ SYNOPSIS...RGZ NEAR TERM...REK/RJD SHORT TERM...RGZ LONG TERM...JDW AVIATION...BJR MARINE...REK/RJD/JDW/RGZ

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