Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 170256 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1056 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/...
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AS OF 1030 PM TUESDAY...QUITE A LINE OF CONVECTION HAS DEVELOPED OVER THE PAST FEW HOURS EXTENDING FROM THE SOUTH SIDE OF CHARLOTTE EASTWARD ACROSS ROCKINGHAM...FAYETTEVILLE...AND APPROACHING CLINTON. SPC MESOANALYSIS INDICATES SURFACE-BASED PARCELS ARE CAPPED...WHICH MAKES SENSE GIVEN SURFACE TEMPERATURES IN THE LOWER 70S. ELEVATED CAPE OF 750-1000 J/KG WITH MINIMAL CAPPING IS AVAILABLE WHEN PARCELS AROUND 950-925 MB ARE CONSIDERED. MID-LEVEL LAPSE RATES ARE RATHER STEEP AT 6 DEG C/KM. ALTHOUGH CONVECTION HAS MERGED INTO A LINE EARLIER THERE WERE HINTS OF SUPERCELLULAR CHARACTERISTICS AS A BELT OF STRONGER MID-LEVEL FLOW ACROSS NORTH-CENTRAL NORTH CAROLINA IS PRODUCING 0-6 KM BULK SHEAR VALUES NEAR 30 KNOTS. THE SURFACE COLD FRONT IS LOCATED 50-100 MILES BEHIND THE CONVECTION...CURRENTLY EXTENDING ACROSS THE NORTHERNMOST ROW OF COUNTIES IN NORTH CAROLINA. ALTHOUGH PRESSURES ARE CURRENTLY STEADY ACROSS THE AREA WE ANTICIPATE FALLING PRESSURES TO DEVELOP ALONG THE COAST AND OFFSHORE SHORTLY AS LOW PRESSURE DEVELOPS. THIS LOW WILL PULL THE FRONT DOWN LATE TONIGHT AND OFFSHORE BY DAYBREAK. SINCE THE CONVECTION IS ELEVATED AND BASED WITHIN A UNIFORM 950-900 MB LAYER IT SHOULD RESPOND MORE TO OVERALL SYNOPTIC FORCING THAN TO ANYTHING GOING ON HERE AT THE SURFACE. THE UPPER DISTURBANCE IS LOCATED NEAR I-77 NORTH OF CHARLOTTE AND SHOULD MOVE EAST-NORTHEASTWARD THROUGH THE NIGHT. AS THE STORMS DRIFT SOUTH THEY WILL MOVE OUT OF THE INFLUENCE OF THE UPPER TROUGH AND SHOULD WEAKEN. THIS IS SHOWN BY THE 23Z RUN OF THE HRRR...WHICH ALSO INDICATES THE CONVECTION MAY JUMP WILMINGTON AND SOUTHPORT...REDEVELOPING OFFSHORE AFTER 2-3 A.M. WITHIN A REGION OF SURFACE-BASED INSTABILITY OVER THE WARM OCEAN WATER. NO CHANGES HAVE BEEN MADE TO FORECAST LOWS...STILL ANTICIPATED TO RANGE FROM THE UPPER 60S INLAND TO THE LOWER 70S AT THE COAST.
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&& .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...
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NEAR TERM /THROUGH TONIGHT/... AS OF 1030 PM TUESDAY...WINDS ACROSS THE NC WATERS ARE GENERALLY FROM THE SOUTH OR SOUTHEAST WITH A MORE VARIABLE PATTERN NOTED ACROSS THE SOUTH CAROLINA WATERS. PRESSURES SHOULD BEGIN TO FALL SHORTLY ALONG THE COAST AS LOW PRESSURE DEVELOPS OFFSHORE. THIS LOW WILL PULL THE COLD FRONT...CURRENTLY ACROSS NORTHERN NORTH CAROLINA...SOUTHWARD AND OFF THE COAST BY DAYBREAK WITH NORTHERLY WINDS EXPECTED TO DEVELOP. A LINE OF THUNDERSTORMS ACROSS THE INTERIOR COASTAL PLAIN WILL PROBABLY WEAKEN BEFORE MAKING IT TO THE BEACHES...HOWEVER CONDITIONS FAVOR THE DEVELOPMENT OF SCATTERED THUNDERSTORMS OUT AHEAD OF THIS LINE AFTER MIDNIGHT...MOST LIKELY IN THE 2-4 AM TIME FRAME. SEAS CURRENTLY 1-2 FT MAY BEGIN TO BUILD TOWARD 3 FEET ACROSS THE OUTERMOST PORTION OF THE COASTAL WATERS LATE TONIGHT AS SWELL FROM DISTANT HURRICANE EDOUARD FINALLY MAKES IT TO THE COAST. 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.
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&& .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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