Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 022306 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 706 PM EDT WED SEP 2 2015 .SYNOPSIS... ABOVE NORMAL TEMPERATURES ARE EXPECTED THROUGH FRIDAY. A WEAK TROUGH WILL LINGER IN THE AREA THROUGH EARLY FRIDAY. A RIDGE OF HIGH PRESSURE WILL BUILD IN FROM THE NORTH BEHIND A COLD FRONT BY THIS WEEKEND...BRINGING UNSETTLED WEATHER AND COOLER TEMPERATURES THROUGH EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... AS OF 730 PM WEDNESDAY...CLOSELY WATCHING SCATTERED CONVECTIVE SHOWERS AND STORMS ACROSS THE NORTHWESTERN HALF OF NC SINKING SOUTHEASTWARD. WHILE THE 500 MB COLD POOL CENTERED OVER VIRGINIA SHOULD NOT DIVE THIS FAR SOUTH...A SURPRISING NUMBER OF MODELS STILL SHOW SHOWERS MAKING IT INTO SE NORTH CAROLINA STARTING AROUND 3-4 AM. FORECAST SOUNDINGS SHOW THIS WOULD NOT BE SURFACE- BASED CONVECTION BUT INSTEAD ROOTED IN A LAYER AROUND 7000 FEET UP. LAPSE RATES BETWEEN 800-400 MB ARE STEEP ENOUGH THAT SHOULD ANYTHING SURVIVE THAT LATE IT COULD STILL HAVE THUNDER. TO BLEND WITH NWS RAH AND MHX I HAVE ADDED A 20 POP LATE TONIGHT FROM LUMBERTON TO ELIZABETHTOWN TO BURGAW...OTHERWISE VERY FEW CHANGES WERE NEEDED TO THE FORECAST WITH THIS EARLY EVENING UPDATE. DISCUSSION FROM 300 PM FOLLOWS... A SUMMER LIKE AIR MASS HOLDING OVER THE AREA TODAY WITH WEAK HIGH PRESSURE MAINTAINING LIGHT AND MORE VARIABLE WINDS. WITH STRONG HEATING AND DECENT DOWNSLOPE FLOW THROUGH THE LOW LEVELS...TEMPS SOARED ABOVE 90 MOST PLACES...WITH SEA BREEZE DOMINATING THIS AFTERNOON NEAR SHORE. AS THE SEA BREEZE PUSHES SLOWLY INLAND SLOWLY IT WILL REMAIN THE FOCAL POINT FOR LOW LEVEL CONVERGENCE...BUT PLENTY OF DRY AIR ALOFT WILL KEEP SHWRS AT BAY FOR THE MOST PART. OVERALL...EXPECT FLATTER CU TO MIX WITH MAINLY SUNNY SKIES ACROSS THE AREA. MOISTURE WILL INCREASE GRADUALLY THROUGH THE ATMOSPHERE INTO TONIGHT....MAINLY VISIBLE IN THE MID TO UPPER LEVELS DUE TO A SHORTWAVE TRACKING DOWN FROM THE NW. MODELS SHOW ASSOCIATED CONVECTION WITH SHORTWAVE UPSTREAM OVER NC/VA BORDER EARLY THIS EVENING THEN DIMINISHING AS IT REACHES OUR NW CWA BOUNDARY LATE EVENING...CLOSER TO MIDNIGHT. THEREFORE MAY SEE A FEW STRAY SHWRS/TSTMS REACH OUR NORTHERN TIER BUT OVERALL EXPECT MAINLY CLOUDS MOVING DOWN OVER THE AREA. TEMPS HOLDING UP IN THE 70S MOST PLACES OVERNIGHT IN A WARM AND HUMID AIR MASS. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...UPPER RIDGE BUILDS STRONGLY ACROSS MIDDLE AMERICA AND THIS WILL RESULT IN A TROUGH DIGGING DOWN THE EAST COAST THU INTO FRI. DEVELOPING NW FLOW ALOFT WILL ALLOW WEAK MID- LEVEL DISTURBANCES...EMBEDDED IN FLOW...TO IMPACT THE EASTERN CAROLINAS. THE STRONGEST OF THESE FEATURES DURING THIS TIME FRAME WILL REACH THE AREA LATER THU AFTERNOON AND THU NIGHT. AT THE SURFACE...HIGH PRESSURE WILL ASSERT A STRONG ENOUGH PUSH TO BRING A BACKDOOR COLD FRONT ACROSS THE AREA FRIDAY NIGHT. THE PIEDMONT TROUGH AND SEABREEZE BOUNDARIES WILL STRENGTHEN THU AFTERNOON AND THESE MESOSCALE BOUNDARIES SHOULD PROVIDE SOME MODEST LIFT...THUS ALLOWING SOME CONVECTION TO DEVELOP AS STRONG HEATING INCREASES THE INSTABILITY. THE HIGHEST PRECIPITABLE WATER VALUES AND THE GREATEST MOISTURE DEPTH ARE STILL EXPECTED THU/THU NIGHT...ALTHOUGH NOT THAT IMPRESSIVE EVEN FOR EARLY SEPTEMBER. AT THIS TIME...WILL KEEP POPS IN THE SLIGHT CHANCE/CHANCE CATEGORY. HOWEVER...HIGHER POPS MAY BE WARRANTED AS WE PROGRESS THROUGH LATE WEEK AND ARE BETTER ABLE TO NAIL DOWN THE TIMING OF THE VARIOUS FEATURES PREVIOUSLY DISCUSSED. THE WARMEST DAY WILL BE THU WHEN HIGHS ARE EXPECTED MAINLY IN THE MID 90S WITH LOWER 90S VERY NEAR THE COAST AND UPPER 80S AT THE BEACHES. HIGHS ON FRI WILL BE MAINLY IN THE LOWER 90S...STILL ABOVE NORMAL...UPPER 80S AT THE BEACHES. LOWS WILL BE IN THE LOWER 70S THU NIGHT AND UPPER 60S TO LOWER 70S FRI NIGHT. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 300 PM WEDNESDAY...COMPLEX MID-LEVEL PATTERN WILL LEAD TO A CHALLENGING FORECAST WITH LIKELY AN EXTENDED PERIOD OF UNSETTLED WEATHER ACROSS THE SOUTHEAST. GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT THROUGH THE EXTENDED WHICH CREATES HIGHER CONFIDENCE THIS PERIOD...AND IT APPEARS MUCH OF THE EXTENDED WILL BE UNSETTLED WITH BELOW NORMAL HIGHS AND SEASONABLE LOWS. LARGE UPPER RIDGE WILL BUILD ACROSS THE NORTHEAST FROM THE GULF COAST...DRIVING A SURFACE RIDGE DOWN THE EASTERN SEABOARD. AS THIS OCCURS...A BACK DOOR TYPE FRONT WILL STALL SOUTH OF THE AREA...AS A WEAKNESS IN THE PRESSURE FIELD STRENGTHENS AND EXPANDS FROM THE NE...SOUTH OF THE RIDGE. THIS UPPER TROUGH WILL SHARPEN AND CUT OFF ACROSS THE SOUTHEAST...AND THEN SIT BASICALLY IN PLACE THROUGH TUESDAY AS IT IS BLOCKED BY RIDGING ON ALL SIDES. BENEATH THIS TROUGH...THE REMNANTS OF ERIKA WILL MEANDER NEAR THE SOUTHEAST COAST MAINTAINING CLOUDS...SHOWERS...AND COOL TEMPERATURES...ESPECIALLY ALONG THE COAST. STILL SOME UNCERTAINTY INTO HOW MUCH QPF IS EXPECTED SINCE FORCING IS WEAK...BUT TROPICAL MOISTURE IN THE VICINITY OF ERIKAS REMNANTS WILL CREATE THE POTENTIAL FOR SHOWERS...SOME OF WHICH MAY BE HEAVY AT TIMES...ESPECIALLY SUNDAY THROUGH TUESDAY. WPC QPF SHOWS 1-2 INCHES THROUGH THE PERIOD...HEAVIEST ALONG THE COAST. GUIDANCE SUGGESTS ERIKAS REMNANTS WILL FINALLY DISSIPATE ENTIRELY BY WEDNESDAY AND LIFT TO THE NORTH AS THE BLOCKING RIDGE WEAKENS...THIS WILL LEAD TO IMPROVING AND MORE SEASONABLE WEATHER AT THE END OF THE EXTENDED. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... AS OF 00Z...THE LIGHT SOUTHEAST RESULTANT WILL GIVE WAY TO A NEARLY CALM SOUTHWEST FLOW IN A COUPLE OF HOURS. A VORT MAX IN VIRGINIA WILL DROP SOUTHWARD OVERNIGHT AND WILL HAVE SCATTERED CONVECTION WITH IT. THIS CONVECTION MAY GET CLOSE ENOUGH TO OUR NORTHERN TERMINALS TO WARRANT A VCSH MENTION. THE CONVECTION WILL LIKELY DISSIPATE BY 09Z. THIS IS MAINLY LEANING ON THE NAM MODEL AS THE GFS SHIFTS THE PRECIP OFFSHORE BEFORE IT GETS HERE. THURSDAY...ANOTHER HOT DAY WITH WEST NORTHWEST FLOW. SOME SCATTERED CONVECTION MAY DEVELOP AROUND MAX HEATING. EXTENDED OUTLOOK...PREDOMINATELY VFR WITH BRIEF MORNING FOG AND ISOLATED/SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 730 PM WEDNESDAY...VIRTUALLY NO CHANGES WERE NEEDED TO THE FORECAST WITH THIS EARLY EVENING UPDATE. DISCUSSION FROM 300 PM FOLLOWS... A TROUGH WILL BE STRUNG OUT FROM WEST TO EAST SOUTH OF OUR LOCAL WATERS BUT WEAK HIGH PRESSURE WILL HOLD LOCALLY THROUGH TODAY. BASICALLY FLOW WILL BE DOMINATED BY THE SEA BREEZE THIS AFTERNOON WITH ON SHORE GUSTIER WINDS...BASICALLY SE-S. WITH WINDS GENERALLY 10 KT OR LESS...SEAS WILL REMAIN 2 FT OR LESS. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... AS OF 300 PM WEDNESDAY...THE SLACK PRESSURE GRADIENT...WHICH HAS BEEN IN PLACE FOR SEVERAL DAYS...WILL FINALLY BEGIN TO TIGHTEN... AND WITH THAT WE WILL SEE WIND SPEEDS INCREASING. THE HIGHEST WINDS THIS PERIOD ARE EXPECTED IN THE WAKE OF A BACKDOOR COLD FRONT FRI NIGHT. WIND SPEEDS FRI NIGHT ARE EXPECTED TO BE UP TO 15 TO 20 KT AS A NE SURGE EXPANDS SOUTHWARD ACROSS THE WATERS AS HIGH PRESSURE BUILDS FROM THE N. A LAND BREEZE WILL ALLOW FOR A LIGHT OFFSHORE WIND THU MORNING. THE SEABREEZE AND PIEDMONT TROUGH WILL INCREASE SW WINDS TO AROUND 10 KT THU AFTERNOON AND EVE. SEAS WILL BE 2 FT OR LESS WITH 3 FT SEAS EXPANDING SOUTHWARD ACROSS THE WATERS FRI NIGHT. LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 300 PM WEDNESDAY...HIGH PRESSURE WILL RIDGE DOWN THE COAST STRONGLY SAT/SUN BEFORE SLOWLY WEAKENING EARLY NEXT WEEK. AS THIS HIGH BUILDS SW FROM NEW ENGLAND...IT WILL BE ACCOMPANIED BY A NE SURGE...DRIVING WINDS UP TO AROUND 15 KT SATURDAY AND SUNDAY. WINDS WILL VEER SLOWLY ON MONDAY TO BECOME MORE EASTERLY AS THE RIDGE WEAKENS...WITH SPEEDS DROPPING TO AROUND 10 KT AT THE END OF THE PERIOD. THE SEA SPECTRUM WILL BE SIGNIFICANTLY DOMINATED BY A NE WIND WAVE THROUGH THE PERIOD...WHICH WILL MASK A LOW-AMPLITUDE SE SWELL. WAVE HEIGHTS WILL BE 2-3 FT EARLY SATURDAY...RISING TO 3-4 FT LATE SATURDAY AND SUNDAY AS THE NE FETCH PERSISTS. WAVE HEIGHTS WILL THEN EASE A BIT MONDAY ON THE SLACKENING WINDS. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...RJD NEAR TERM...TRA/RGZ SHORT TERM...RJD LONG TERM...JDW AVIATION...SHK

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