Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 232350 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 750 PM EDT WED JUL 23 2014 .SYNOPSIS... BERMUDA HIGH PRESSURE WILL GIVE WAY TO A A COLD FRONT APPROACHING FROM THE NORTHWEST TOMORROW. THIS FRONT WILL BECOME STATIONARY OVER THE REGION THIS WEEKEND. A SECOND COLD FRONT WILL APPROACH THE REGION MONDAY NIGHT INTO TUESDAY AND IT TO WILL STALL ALONG THE COAST LATE TUESDAY AND WEDNESDAY. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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AS OF 715 PM WEDNESDAY...DIURNALLY DRIVEN POPCORN TYPE SHOWERS AND THUNDERSTORMS EARLY THIS EVENING...WILL SLOWLY DISSIPATE THE REMAINDER OF THIS EVENING IN RESPONSE TO THE LOSS OF DAYTIME HEATING. COLLIDING OUTFLOW BOUNDARIES MAY AID IN CONTINUING CONVECTION SEVERAL HOURS AFTER SUNSET. DURING THE PROGRESSION OF THE OVERNIGHT PERIOD...THE LONGWAVE TROF THATS BEEN PLAGUEING THE EASTERN 1/3RD OF THE U.S. FOR A COUPLE WEEKS NOW...WILL SLIGHTLY AMPLIFY DUE TO A MID-LEVEL S/W TROF DROPPING ACROSS THE FA LATE TONIGHT BUT MAINLY DURING THURSDAY. THE NE-SW ORIENTED TROF AXIS TO REMAIN POSITIVELY TILTED AND WEST OF THE FA. CURRENT MIN TEMP FORECAST OF GENERALLY MID 70S LOOKS AOK...WITH ISOLATED LOWER 70S WELL INLAND...AND UPPER 70S ALONG THE IMMEDIATE COAST. PREVIOUS DISCUSSION............................................ AS OF 320 PM WEDNESDAY...PURELY SUNSHINE-DRIVEN CONVECTION IS OCCURRING ACROSS EASTERN NORTH AND SOUTH CAROLINA THIS AFTERNOON. EXCEPT FOR A "DRY" LAYER OF 60% RELATIVE HUMIDITY NEAR 700 MB THE TROPOSPHERE IS VERY HUMID THROUGH ITS DEPTH AND PRECIPITABLE WATER VALUES ARE NEAR 2.0 INCHES. TEMPERATURES IN THE UPPER 80S AND LOWER 90S ARE GENERATING SURFACE-BASED CAPE NEAR 2000 J/KG AND LIFTED INDICES AROUND -5 WITH NO CAPPING. LACK OF WIND SHEAR IS FAVORING SINGLE-CELL STORMS WITH NO ORGANIZATION...AND THE BIGGEST THREAT TODAY`S CONVECTION POSES IS BRIEF HEAVY RAINFALL AND LIGHTNING. ACTIVITY SHOULD CONTINUE AS LONG AS THERE IS SURFACE- BASED INSTABILITY PRESENT...LARGELY DECAYING IN THE 6-9 PM TIME FRAME. THE UPPER LOW THAT DIRECTED THE PLUME OF HUMID TROPICAL AIR NORTHWARD INTO THE CAROLINAS EARLIER IN THE WEEK IS RETROGRADING UNDERNEATH THE SOUTHWESTERN U.S. RIDGE AND IS NO LONGER A FACTOR IN OUR WEATHER. HUMID AIR IS STILL SWINGING AROUND THE BERMUDA HIGH AND ITS UPPER LEVEL CENTER OVER THE EASTERN BAHAMAS. WESTERLY FLOW ACROSS THE SOUTHERN APPALACHIANS IS INDUCING DOWNSTREAM SURFACE TROUGHING...AND THE PRESSURE PATTERN BETWEEN THIS SURFACE TROUGH OVER THE PIEDMONT AND THE BERMUDA HIGH OFFSHORE WILL ENSURE A SOUTHWEST WIND OVERNIGHT. STRENGTHENING WINDS JUST ABOVE THE SURFACE SHOULD MAKE FOG LESS LIKELY TONIGHT THAN EARLIER IN THE WEEK. LOWS SHOULD REACH A MUGGY 73-74 INLAND...AND 75-77 AT THE COAST.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... AS OF 320 PM WEDNESDAY...THURSDAY IS SETTING UP TO BE A HOT AND STORMY AFTERNOON AND EVENING. THE THE SYNOPTIC SCALE A 500 MB TROUGH AXIS WILL SHIFT TOWARD THE COASTAL CAROLINAS AND FORECAST AREA WILL BE ON THE EAST SIDE OF THE TROUGH THROUGH THE PERIOD. AT THE SURFACE A COLD FRONT IS EXPECTED TO SHIFT TO THE COAST FRIDAY EVENING. AHEAD OF THIS FRONT WITH A WEST SOUTHWESTERLY WINDS TEMPERATURES ARE EXPECTED TO REACH MID 90S ESPECIALLY IN INLAND NORTHEAST SOUTH CAROLINA. THESE TEMPERATURES COMBINED WITH THE DEW POINT IN THE LOWER 70S WILL PRODUCE HEAT INDICES VALUES IN THE 100 TO 103 DEGREE RANGE ESPECIALLY INLAND AREAS. FOR STORMS WITH THE FRONTAL BOUNDARY COMING ACROSS A A WEAK MID LEVEL JET CAN NOT RULE OUT STRONG WINDS WITH THE STORMS BUT THE HIGH PRECIPTABLE WATERS OF OVER 2 INCHES WILL ME HEAVY DOWNPOURS ARE POSSIBLE AND ISOLATED FLOODING IS POSSIBLE. FOR FRIDAY...WITH THE FRONT IN THE REGION AND CLOUD COVER EXPECT A CHANCE OF THUNDERSTORMS BUT HIGH TEMPERATURES WILL BE IN THE UPPER 80S TO NEAR 90. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 320 PM WEDNESDAY...A WEAK UPPER IMPULSE CROSSES THE REGION ON SATURDAY WHILE PIEDMONT TROUGH/FRONTAL REMAINS SIT TO OUR WEST. TOUGH TO COMPLETELY RULE OUT ISO CONVECTION IN SUCH A SETUP BUT MID LEVELS REMAIN TOO DRY FOR ANY MORE COVERAGE THAN THAT. MUCH THE SAME WILL APPLY ON SUNDAY...AND BOTH DAYS WILL LIKELY OFFER UP FAIRLY SEASONABLE TEMPERATURES. SUNDAY NIGHT INTO MONDAY MAY START GETTING ACTIVE AS MID LEVEL CYCLONIC FLOW AND SURFACE COLD FRONT APPROACH FROM THE NW...BOTH IN RESPONSE TO UNSEASONABLY STRONG TROUGHINESS DEVELOPING IN THE GREAT LAKES. THIS FRONT PUSHES THROUGH MONDAY NIGHT INTO TUESDAY MORNING. SOME COOLER AND DRIER AIR WILL THEN FILTER IN BEHIND IT FOR THE MIDWEEK PERIOD. EXCEPTION MAY BE ALONG THE COAST WHERE SUFFICIENT MOISTURE MAY LINGER FOR SMALL RAIN CHANCES. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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AS OF 00Z...ISOLATED SHRA/TSRA CONTINUE LARGELY BETWEEN THE TERMINALS EARLY THIS EVENING. VCTS COULD OCCUR AT KFLO/KLBT UNTIL CONVECTION GRADUALLY TAPERS OFF OVER THE NEXT SEVERAL HOURS...BUT CONFIDENCE IS LOW. ISOLATED SHOWERS REMAIN POSSIBLE UNTIL MIDNIGHT AT KFLO/KLBT AND THE COASTAL TERMINALS UNTIL SUNRISE TOMORROW...BUT CONFIDENCE IS LOW DUE TO LACK OF LIFT AND INCREASED DRYING IN THE MID/UPPER LEVELS. WINDS WILL STAY ELEVATED OVERNIGHT FROM THE SW. THIS SHOULD WORK AGAINST ANY FOG FORMATION...BUT COULD STILL SEE TEMPO MVFR VSBYS/SCT STRATUS AT KFLO/KLBT IN THE PRE-DAWN HOURS. COASTAL TERMINALS SHOULD REMAIN VFR. SW WINDS SHOULD INCREASE BY MID MORNING TO 10-20KT AT THE COASTAL TERMINALS AND AROUND 10KT AT KFLO/KLBT. EXPECT A DECENT CHANCE OF TEMPO TSRA/MVFR BY 18Z. EXTENDED OUTLOOK...SHOWERS/TSTMS/TEMPO MVFR POSSIBLE THROUGH FRIDAY...AS WELL AS SUNDAY AND MONDAY.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 730 PM WEDNESDAY...PRESSURE PATTERN AND TIGHTENING GRADIENT OVERNIGHT WILL YIELD SW WINDS INCREASING TO 10 TO 15 KT...OR POSSIBLY A SOLID 15 KT. THIS IN RESPONSE TO THE SFC PG TIGHTENING SOME BETWEEN BERMUDA HIGH PRESSURE CENTERED WELL OFFSHORE AND THE PIEDMONT TROF ACROSS THE CAROLINAS WHICH GETS CONSUMED BY THE APPROACHING COLD FRONT FROM THE NW DURING THURSDAY. SIGNIFICANT SEAS WILL BE THE COMBINATION OF 2 ENTITIES...1. AN ESE TO SE 1-3 FOOT GROUND SWELL EXHIBITING 7 TO 9 SECOND PERIODS. ...AND 2. LOCALLY PRODUCED 1-3 FOOT SW WIND DRIVEN WAVES EXHIBITING 3 TO 5 SECOND PERIODS. EITHER 1 OF THESE ENTITIES COULD DOMINATE THE SIGNIFICANT SEAS AT ANY 1 TIME. IE. THE AFTN/EVENG SEA BREEZE CIRCULATION FOR DOMINATING WIND DRIVEN WAVES. PREVIOUS DISCUSSION................................................ AS OF 320 PM WEDNESDAY...BERMUDA HIGH PRESSURE WELL OFF THE SOUTHEAST COAST HAS TURNED OUR SURFACE WINDS SOUTH-SOUTHWESTERLY THIS AFTERNOON...AND A STEADY SOUTHWEST WIND IS EXPECTED TO CONTINUE OVERNIGHT. WIND SPEEDS AT THE BEACHES SHOULD INCREASE TO 12-15 KNOTS LATE THIS AFTERNOON WITH THE SEABREEZE...AND A SOLID 15 KNOTS IS EXPECTED OVERNIGHT AWAY FROM SHORE DUE TO THE STRONGER GRADIENT BETWEEN THE HIGH OFFSHORE AND A LOW PRESSURE TROUGH ACROSS THE NC/SC PIEDMONT REGION. SEAS CURRENTLY 2-3 FEET IN A COMBINATION OF AN 8 SECOND SOUTHEAST SWELL AND SHORTER PERIOD WIND WAVES MAY BUILD TO 4 FEET OVERNIGHT...ESPECIALLY EAST OF CAPE FEAR WHERE THE WIND FETCH WILL BE LONGEST. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 320 PM WEDNESDAY...WINDS WILL BE FROM THE SOUTHWEST THROUGH THE PERIOD WITH AN INCREASE IN WINDS AS A SURFACE COLD FRONT APPROACHES THE WATERS BUT STALLS JUST ON SHORE. WHEN THE FRONT STALL THE WINDS WILL WEAKEN JUST A BIT. A SEA HEIGHTS ARE EXPECTED TO INCREASE TO 3 TO 4 FEET ON THURSDAY AND THEN SETTLE BACK TO 2 TO 3 FEET RANGE ON FRIDAY. LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 320 PM WEDNESDAY...SATURDAY WILL BRING FAIRLY TYPICAL CONDITIONS FOR THE TIME OF YEAR...A SOUTHWESTERLY FLOW RESULTING FROM WEST ATLANTIC HIGH PRESSURE AND A WEAK PIEDMONT TROUGH/FRONTAL BOUNDARY INLAND. A SHARPENING OF THE LATTER ON SUNDAY WILL TIGHTEN THE FLOW AND SEAS COULD BUILD TO ADVISORY LEVELS. THE APPROACH OF AN UNSEASONABLY STRONG COLD FRONT ON MONDAY WILL FURTHER TIGHTEN THE GRADIENT AND AN ADVISORY APPEARS EVEN MORE LIKELY. BOTH DAYS ARE A TOUGHER CALL OVER SRN ZONES WHERE 6 FT SEAS MAY HAVE A HARDER TIME GETTING CLOSE ENOUGH TO SHORE TO BE IN THE 20NM FORECAST ZONES.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...DRH NEAR TERM...DCH/TRA SHORT TERM...DRH LONG TERM...MBB AVIATION...MRR

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