Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 050744 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 344 AM EDT SAT SEP 5 2015 .SYNOPSIS... HIGH PRESSURE WILL RIDGE DOWN FROM NEW ENGLAND TODAY BRINGING COOLER TEMPERATURES. THIS HIGH PRESSURE WILL PERSIST INTO EARLY NEXT WEEK CONTINUING SOMEWHAT BELOW NORMAL TEMPERATURES...BUT WITH INCREASING CHANCES FOR SHOWERS. A RETURN TO MORE TYPICAL LATE SUMMER WEATHER WILL DEVELOP TUESDAY AND PERSIST THROUGH THE END OF THE WEEK. A COLD FRONT WILL APPROACH BY NEXT WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SATURDAY...THE CAROLINAS ARE ON THE SOUTHERN EDGE OF 1026 MB HIGH PRESSURE CENTERED OVER NEW ENGLAND. THE NORTHEAST SURGE THAT SPREAD SOUTHWARD ACROSS THE AREA OVER THE PAST FEW HOURS WASN`T A TRUE COLD FRONT SINCE THERE IS VIRTUALLY NO AIRMASS CHANGE TAKING PLACE. 850 MB TEMPS OF +17 TO +18C YESTERDAY WILL FALL BY 1-2 DEG C TODAY WHICH SHOULD RESULT IN COOLER HIGH TEMPERATURES...85-89 WITH THE WARMEST READINGS IN THE FLORENCE/DARLINGTON AREA. 00Z MODELS WERE TIGHTLY CLUSTERED WITH REGARD TO MASS/WIND FIELDS IN THE LOW LEVELS TODAY AND TONIGHT. THE BIGGEST FORECAST QUESTION CONCERNS CONVECTIVE CHANCES TODAY. IN THE 850-700 MB LAYER THE AIR THAT WILL BE OVER OUR AREA THIS AFTERNOON IS CURRENTLY OVER AND JUST EAST OF THE NORTHERN OUTER BANKS. MODELS ANALYZE THIS AS A RATHER DRY SLUG OF AIR...ESPECIALLY JUST ABOVE THE DEPTH OF THE ANTICIPATED DAYTIME MIXED LAYER. THIS SHOULD SERVE TO DILUTE/MIX OUT GROWING CUMULUS TOWERS AND REDUCE THE ULTIMATE NUMBER OF SHOWERS OR STORMS THAT FORM. THIS EFFECT SHOULD BE MOST PRONOUNCED ACROSS THE SC PEE DEE REGION WHERE THE CORE OF THE DRY AIR WILL BE PASSING OVER DURING THE MID AFTERNOON. SURFACE TEMPERATURES SHOULD POKE HIGH ENOUGH INLAND TO ENHANCE CONVERGENCE NEAR THE COAST THROUGH A WEAK SEABREEZE CIRCULATION. SEVERAL OF THE HIGH RES MODELS (NSSL WRF, WRF-NMM, OPERATIONAL NAM) HIGHLIGHT THIS ZONE FROM 5-25 MILES INLAND WITH A HIGHER POTENTIAL FOR PRECIP THIS AFTERNOON. MY FORECAST POPS RANGE FROM 10 PERCENT IN THE FLORENCE- DARLINGTON AREA TO 30 PERCENT FROM BURGAW AND WHITEVILLE TO CONWAY. ISOLATED SHOWERS MAY CONTINUE THROUGH TONIGHT AS CONDITIONALLY UNSTABLE AIR ALOFT ADVECTS ACROSS ON NE WINDS. PERHAPS MORE CERTAIN IS THAT LOW STRATUS WILL DEVELOP LATE TONIGHT AS RADIATIONAL COOLING SATURATES THE BOUNDARY LAYER BUT 15-20 KT WINDS JUST ABOVE THE SURFACE DON`T ALLOW FOG. LOWS NEAR 70 EXCEPT A FEW DEGREES WARMER AT THE BEACHES. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY...UPPER TROUGH WILL CLOSE OFF AND BE FORCED TO RETROGRADE FROM THE WESTERN ATLANTIC OCEAN BACK ACROSS THE SOUTHEAST THIS PERIOD AS LARGE RIDGING BLOCKS ITS PROGRESSION TO THE NORTH OR EAST. BENEATH THIS FEATURE...A SURFACE TROUGH WILL ALSO BACK IN FROM THE ATLANTIC AND INTO THE CAROLINAS SUNDAY INTO MONDAY...ALONG WITH HIGHER PRECIPITABLE WATERS FROM REMNANT TROPICAL MOISTURE POOLED FROM EX-TROPICAL STORM ERIKA. ALL OF THESE FEATURES TOGETHER WILL CREATE A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS...ESPECIALLY DURING THE AFTNS WHEN HEATING OF THE DAY WILL HELP TRIGGER CONVECTION ALONG THE SURFACE TROUGH. HOWEVER...AT LEAST SCHC POP WILL BE CARRIED EVEN AT NIGHT DUE TO HIGH COLUMN MOISTURE...THE SURFACE FEATURE...AND RELATIVELY STEEPER LAPSE RATES THANKS TO THE 500MB TROUGH OVERHEAD. TEMPS BOTH DAYS WILL LIKELY FEATURE LOW DIURNAL RANGES AS CLOUD COVER AND PRECIP KEEPS MINS ABOVE NORMAL AND HIGHS BELOW. EXPECT LOWS EACH NIGHT TO DROP TO 68-72...WARMEST AT THE COAST...WITH HIGHS IN THE LOW 80S AT THE COAST...MID 80S WELL INLAND. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 AM SATURDAY...UPPER TROUGH PLAGUING THE SOUTHEAST THE SEVERAL DAYS LEADING UP TO THIS PERIOD WILL SLOWLY FILL AND DISSIPATE BY MID-WEEK AS RIDGING DEVELOPS NEAR FLORIDA AND EXPANDS TO THE NORTH. WHILE OVERALL THICKNESS INCREASE WILL BE MARGINAL...THE EROSION OF THE SURFACE TROUGH ASSOCIATED WITH THE BUILDING HEIGHTS COMBINED WITH BERMUDA-TYPE RIDGING WILL BRING DRIER AND WARMER CONDITIONS MUCH OF NEXT WEEK. TUESDAY MAY STILL FEATURE ABOVE-CLIMO PRECIP CHANCES AS IT IS THE TRANSITION DAY...BUT WED-FRI WILL BE MORE SUMMER-LIKE WITH TYPICAL DIURNAL CONVECTIVE CHANCES AND TEMPS SEVERAL DEGREES ABOVE CLIMO FOR BOTH HIGHS AND LOWS. A COLD FRONT WILL APPROACH LATE IN THE PERIOD BUT FOR NOW WILL KEEP IT JUST NW OF THE AREA UNTIL THE WEEKEND. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... AS OF 06Z...MAINLY VFR CONDITIONS TO PREVAIL ACROSS ALL LOCATIONS DURING THE 06Z ISSUANCE PERIOD...WITH THE EXCEPTION OF THE FOLLOWING. THE PRE-DAWN SAT HRS AND CONTINUING INTO THE EARLY DAYLIGHT SAT HRS...THE AREA TERMINALS WILL BE UNDER MVFR TO POSSIBLY IFR CONDITIONS FROM LOW STRATUS...MAINLY BETWEEN 500 TO 1200 FEET. THIS LOW LEVEL MOISTURE IS TRAPPED BELOW A WEAK SFC BASED INVERSION THAT SHOULD BREAK BY MID DAYLIGHT SAT MORNING. ALTHOUGH THE AREA TERMINALS WILL BE UNDER SFC HIGH PRESSURE RIDGING SOUTHWARD FROM ITS CENTER ACROSS NEW ENGLAND...ENOUGH HEATING AND LEFTOVER MOISTURE IN THE LOW LEVELS WILL ALLOW FOR DIURNAL CU TO DEVELOP ESPECIALLY AWAY FROM THE IMMEDIATE COAST. WITH THE ILM CWA ONLY RANGING FROM SEA LEVEL AT THE COAST TO ROUGHLY 300-400 FT ACROSS OUR FAR WESTERN INLAND LOCATIONS. BY NO MEANS THE INCREASE IN HEIGHTS ACROSS THE ILM CWA ARE LIKE THE DISTANCE TRAVELED FROM THE CENTRAL TO THE WESTERN CAROLINAS...BUT YOU COULD ALMOST CALL IT VERY WEAK OROGRAPHIC UPLIFT GIVEN THE NE-E WINDS IN THE LOWER LEVELS PROGGED FOR SAT. WITH ALL THAT SAID...WILL JUST INCLUDE VCTS ACROSS OUR ONLY INLAND TERMINALS...AND LEAVE THE COASTAL TERMS CONVECTION FREE FOR NOW. OVERALL...THE DIURNAL CU WILL REMAIN WITHIN VFR HEIGHTS...WITH THE EXCEPTION IF 1 OF OUR INLAND TERMINALS EXPERIENCES CONVECTION. WITH MAX TEMPS EXPECTED ONLY IN THE 80S OVER LAND AREAS...AND LOCAL SSTS IN THE 80S...NOT MUCH OF A DIFFERENCE EXISTS BETWEEN THE 2 TEMPS AND WILL THEREFORE ONLY INDICATE A WEAK INLAND PROGRESSING SFC RESULTANT WIND BOUNDARY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SATURDAY...THE CAROLINAS ARE ON THE SOUTHERN EDGE OF 1026 MB HIGH PRESSURE CENTERED OVER NEW ENGLAND. THE PRESSURE GRADIENT BETWEEN THIS HIGH AND A WEAK TROUGH OF LOW PRESSURE EXTENDING EAST OFF THE FLORIDA COAST WILL MAINTAIN A NORTHEAST WIND TODAY AND TONIGHT. WIND SPEEDS SHOULD BE STRONGEST THIS MORNING... 14-17 KNOTS SUSTAINED...WITH WIND SPEEDS DIMINISHING BY SEVERAL KNOTS THIS AFTERNOON. 00Z COMPUTER MODELS ARE IN GOOD AGREEMENT WITH WIND SPEED AND DIRECTION. SEAS CURRENTLY 1-2 FEET SHOULD BUILD THE MOST NEAR AND EAST OF CAPE FEAR DUE TO THE NORTHEAST FETCH...WITH 3 FOOT SEAS EXPECTED BY 8-10 AM. SEAS SHOULD DIMINISH BACK TOWARD 2 FEET TONIGHT. ISOLATED SHOWERS MAY DEVELOP LATER TODAY...WITH BETTER CHANCES TONIGHT. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM FRIDAY...SURFACE RIDGE OF HIGH PRESSURE WILL BUILD DOWN THE COAST THROUGH THE SHORT TERM...WHILE A COASTAL TROUGH PUSHES SLOWLY INLAND BENEATH A MID-LEVEL TROUGH. THIS WILL MAINTAIN NE WINDS SUNDAY AND MUCH OF MONDAY...WITH SLIGHT VEERING TO MORE EASTERLY WINDS LATE MONDAY AS THE SURFACE TROUGH PUSHES INLAND. HIGHEST SPEEDS THIS PERIOD WILL BE SUNDAY WHEN THE RIDGE IS STRONGEST AND THE GRADIENT IS PINCHED...AS WINDS REACH 15-20 KTS BEFORE FALLING BACK TO 10-15 KTS BY MONDAY...AND THEN BELOW 10 KTS MONDAY NIGHT. THE SEA SPECTRUM WILL BE DOMINATED BY A 5-6 SEC NE WIND WAVE WHICH WILL EASE AND LENGTHEN INTO MONDAY...CREATING 3-4 FT SEAS SUNDAY...DROPPING TO 1-3 FT ON MONDAY. LONG TERM /TUESDAY THROUGH WEDNESDAY/... AS OF 300 AM SATURDAY...HIGH PRESSURE EXPANDING OFF THE FLORIDA COAST WILL DRIVE A RETURN TO MORE TYPICAL SUMMERTIME CONDITIONS THROUGH MID WEEK. TUESDAY WILL BE THE TRANSITION DAY AS WINDS VEER BETWEEN E/NE EARLY TO SOUTH LATE...AND THEN EVEN FURTHER TO SW ON WEDNESDAY THANKS TO RETURN FLOW DEVELOPING AROUND THE SURFACE HIGH. ALTHOUGH THIS VARIETY OF WIND DIRECTION MAY CAUSE A CONFUSED SPECTRUM TUESDAY...WIND SPEEDS WILL BE LIGHT AROUND 10 KTS...SO WAVE AMPLITUDES WILL BE 1-3 FT TUESDAY. AS THE SW WINDS BECOME DOMINANT WEDNESDAY...SEAS WILL REMAIN 1-3 FT BUT A GROUND SWELL WILL BEGIN TO INCREASE IN AMPLITUDE WITHIN THE SPECTRUM. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...JDW NEAR TERM...TRA SHORT TERM...JDW LONG TERM...JDW AVIATION...TRA MARINE...TRA/JDW

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