Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231456 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1056 AM EDT TUE SEP 23 2014 .SYNOPSIS... A COASTAL TROUGH JUST OFFSHORE WILL BRING INCREASING RAINFALL TO THE AREA TODAY THROUGH WEDNESDAY...ALONG WITH WELL BELOW NORMAL TEMPERATURES. RAINFALL CHANCES WILL DIMINISH LATE IN THE WEEK. A WARMING AND DRYING TREND IS EXPECTED OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1000 AM TUESDAY...UPPER LOW TAKING SHAPE OVER THE SE STATES ...AND HAS BASICALLY BROKE OFF FROM THE MAIN BELT OF POLAR WESTERLIES...VIA WATER VAPOR IMAGERY TRENDS. ATLANTIC AND GULF OF MEXICO MOISTURE WILL GET ENTRAINED INTO THIS LOW. DYNAMICS FROM THIS UPPER LOW INCLUDING MID-LEVEL VORTS/IMPULSES ROTATING THRU IT...WILL PROVIDE ADDITIONAL MEANS OF SYNOPTIC/MESOSCALE LIFT. OVERALL...HAVE KEPT CATEGORICAL POPS AT THE COAST....WITH A SLOW DECLINE AS 1 PROGRESSES INLAND. USING THE I-95 CORRIDOR AS A DIVIDING LINE BETWEEN THE BEST/HIER POP CHANCES EAST TO THE COAST...WITH CHANCE ALONG AND WEST OF THE I-95 CORRIDOR. THE COASTAL TROF/FRONT TO REMAIN JUST OFFSHORE AND WILL BE A FOCUS FOR THUNDERSTORM ACTIVITY DUE TO THE INCREASING INSTABILITY. HOWEVER...ELSWHERE AND OVER LAND AREAS HAVE INDICATED STRATIFORM TYPE LIGHT RAINS TO DOMINATE. HAVE LOWERED AFTN MAXES ALREADY AND MAY NEED TO LOWER AGAIN GIVEN THE LACK OF INCREASE TREND TO THE LOCAL TEMPS. PREVIOUS DISCUSSION........................................... AS OF 630 AM TUESDAY...IF THERE WAS ANY DOUBT IN YOUR MIND THAT SUMMER IS OVER...TODAY SHOULD ERASE IT. CANADIAN HIGH PRESSURE OVER OH-PA WILL SHOVE A COOL DRY AIRMASS SOUTHWARD INTO THE CAROLINAS. THE COLD FRONT AT THE LEADING EDGE OF THIS NEW AIRMASS IS STALLING OUT OVER THE GULF STREAM. AN UPPER LEVEL LOW HAS CUT OFF ACROSS FAR-WESTERN SOUTH CAROLINA...AND THE CIRCULATION AROUND THIS FEATURE WILL DRAW A STREAM OF MID-LEVEL MOISTURE BACK OVER THE FRONT AND ACROSS THE AREA TODAY. WEAK LOW PRESSURE WILL ATTEMPT TO CLOSE OFF A CENTER ALONG THE FRONT ALONG THE GA/SC COAST TONIGHT...BUT MODEL CONSENSUS SAYS IT SHOULD REMAIN AN OPEN WAVE. HOWEVER THE LOWERING PRESSURES HERE WILL CONTRAST QUITE STRONGLY WITH THE HIGH OFF TO THE NORTH...CREATING HEALTHY NORTHEAST WINDS THAT WILL INCREASE TONIGHT TO 15-20 MPH INLAND WITH GUSTS APPROACHING 30 MPH ON THE BEACHES. A LARGE AREA OF RAIN WITH EMBEDDED CONVECTIVE SHOWERS HAS DEVELOPED OVER THE COASTAL WATERS AND SHOULD SPREAD INLAND THIS MORNING. POPS FOR THE COASTAL CITIES OF WILMINGTON...SOUTHPORT AND MYRTLE BEACH HAVE BEEN INCREASED TO 80-90 PERCENT. FARTHER INLAND WHERE DRY AIR IS QUITE A BIT BETTER ENTRENCHED MUCH OF THE PRECIPITATION SHOULD EVAPORATE AND POPS ARE ONLY IN THE 30-50 PERCENT RANGE. THERE SHOULD BE A FAIRLY TIGHT GRADIENT IN ACTUAL RAINFALL AMOUNTS JUST OFF THE COAST WITH NO MORE THAN 0.50 INCHES EXPECTED TO FALL ON THE BEACHES...BUT BETTER THAN ONE INCH PREDICTED JUST 15 OR 20 MILES OFF CAPE FEAR. FARTHER INLAND FORECAST RAINFALL AMOUNTS ARE MUCH LOWER...A TENTH OF AN INCH OR LESS ALONG AND WEST OF I-95. ALL THIS CLOUD COVER AND RAIN SHOULD REALLY KEEP TEMPERATURES DOWN. THE PATTERN LOOKS LIKE A CLASSIC MID-WINTER WEDGE DESPITE TEMPERATURES A GOOD 25-30 DEGREES WARMER. STILL...HIGHS IN THE UPPER 60S TO LOWER 70S IN SEPTEMBER ARE NOTHING TO SNEEZE AT. THE 00Z AND 06Z GFS MOS LOOKS MUCH CLOSER TO REALITY THAN THE NAM...BUT EVEN IT IS PROBABLY A LITTLE TOO WARM IN MOST AREAS. AFTER A RELATIVE LULL IN PRECIPITATION COVERAGE LATE THIS AFTERNOON AND THIS EVENING...SUBSTANTIAL RAINFALL MAY AGAIN SURGE ONTO THE COAST OVERNIGHT AS STRONGER LOW-LEVEL WIND FIELDS DEVELOP AND ISENTROPIC LIFT INCREASES. PRECIP SHOULDN`T PENETRATE QUITE AS FAR INLAND HOWEVER DUE TO A MORE BACKED/NORTHERLY LOW-LEVEL WIND DIRECTION...AND MY FORECAST POPS RANGE FROM 60-80 PERCENT ON THE COAST TO 20-30 PERCENT ALONG THE I-95 CORRIDOR. UNDER CLOUDS AND A STIFF NORTHEAST WIND LOWS SHOULD FALL INTO THE UPPER 50S INLAND AND LOWER 60S NEAR THE COAST.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 AM TUESDAY...VERY UNSETTLED DURING THE SHORT TERM AS A STAGNANT PATTERN CONTINUES ACROSS THE CONUS. ALOFT...AN UPPER LEVEL LOW CLOSED OFF ACROSS SC WILL ONLY SLOWLY FILL AND LIFT...LIKELY MAINTAINING AT LEAST SOME SEMBLANCE OF AN UPPER TROUGH THROUGH THURSDAY NIGHT. THIS IS DUE TO A HIGHLY AMPLIFIED RIDGE ACROSS THE ATLANTIC...AS WELL AS GROWING RIDGING ACROSS THE CENTER PART OF THE COUNTRY FORCING SYSTEMS TO GRIND TO A HALT. AT THE SURFACE...A VERY STRONG 1035+ MB SURFACE HIGH WILL WEDGE DOWN FROM NEW ENGLAND WHILE A COASTAL TROUGH SHARPENS AND LURKS OFFSHORE...ALONG WITH VERY STRONG MOIST ADVECTION. THESE FEATURES TOGETHER WILL CREATE AN EXTENDED PERIOD OF COOL TEMPS WITH WIDESPREAD SHOWERS AND CLOUDS...AS WELL AS GUSTY NE WINDS. WHILE THERE IS STILL CONSIDERABLE SPREAD AMONG THE VARIOUS GUIDANCE INTO HOW FAR WESTWARD THE COASTAL TROUGH WILL LIFT...AND THUS HOW HEAVY THE RAIN WILL BE...IT SEEMS ALMOST CERTAIN THAT THE COAST WILL SEE RAIN DURING THIS PERIOD...WITH A SHARP GRADIENT TOWARDS I-95. THE INTERACTION OF THE UPPER LOW WITH THE COASTAL TROUGH WILL SHARPEN THE TROUGH ON WEDNESDAY...AND MAY EVEN SPAWN A WEAK LOW MOVING JUST ALONG THE COAST INTO THURSDAY. THIS COMBINED WITH DEEP MOIST ADVECTION ON EASTERLY FLOW...DRIVING INCREASING ISENTROPIC LIFT ATOP THE COASTAL BOUNDARY...SUGGESTS AT LEAST PERIODS OF HEAVY RAIN POSSIBLE ALONG THE IMMEDIATE COAST WEDNESDAY...DECREASING SOMEWHAT INTO THURSDAY. AGAIN...HOW FAR INLAND THE RAIN WILL PENETRATE IS STILL UNCERTAIN...BUT THE HEAVIEST RAIN AND HIGHEST POP WILL CERTAINLY BE RIGHT ALONG THE IMMEDIATE COAST. TEMPS BOTH WED AND THU WILL STAY WELL BELOW CLIMO WITH HIGHS ONLY IN THE LOW/MID 70S...MADE TO FEEL EVEN MORE RAW BY NE WINDS AND RAIN. LOWS AT NIGHT HOWEVER WILL BE SOMEWHAT HELD IN CHECK BY THE SAME CLOUDS AND RAIN...SO EVEN WITH COOL NE WINDS PERSISTING OVERNIGHT...MINS WILL BE JUST ABOVE CLIMO IN THE LOW/MID 60S. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 300 AM TUESDAY...THE EXTENDED BEGINS COOL AND UNSETTLED...MAYBE UNSURPRISINGLY BY THIS POINT...AS THE PERSISTENT COASTAL TROUGH REMAINS JUST OFFSHORE WHILE HIGH PRESSURE REORGANIZES ACROSS THE GREAT LAKES. LOW PRESSURE ALONG THE OFFSHORE BOUNDARY MOVING NEAR NEW ENGLAND WILL PUSH NORTHEAST AWAY FROM THE AREA BY SATURDAY...WHICH IN CONJUNCTION WITH THE EXPANSION OF THE MIDWEST HIGH WILL DRIVE THE OFFSHORE BOUNDARY WELL EAST BY THE WKND. ALOFT...THE QUASI-STATIONARY TROUGH WILL FILL AS RIDGING BLOSSOMS ACROSS THE MIDDLE OF THE COUNTRY...BEFORE PUSHING OVERHEAD DURING THE WKND. THESE FEATURES COMBINED SUGGEST A DRYING TREND...ESPECIALLY FROM SATURDAY INTO MONDAY...ALONG WITH TEMPS WARMING TO SEASONABLE OR ABOVE...AND THE FIRST WKND OF FALL WILL FEATURE PLEASANT WEATHER ACROSS THE AREA. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... AS OF 12Z...EXPECT PERIODS OF -RA/RA THROUGH THE DAY AS AN UPPER LOW TO OUR WEST DRAWS MOISTURE OVER A STALLED FRONT OFFSHORE. RADAR IMAGERY THIS MORNING SHOWS SHRA OFF THE COAST WITH -RA/DZ MOVING OVER OUR SOUTHERN TERMINALS. PCPN COVERAGE WILL INCREASE THROUGH THE LATE MORNING/EARLY AFTN HOURS...WITH CIGS LIKELY LOWERING TO MVFR AT THE COASTAL SITES WHERE RAIN WILL BE MORE PERSISTENT. THE INLAND TERMINALS COULD SEE TEMPO MVFR LATER TODAY...BUT VFR WILL PREVAIL AT KFLO/KLBT. BRIEF VSBY RESTRICTIONS ARE POSSIBLE ALONG THE COAST IF CONVECTIVE SHOWERS MOVE ONSHORE...BUT HAVE ONLY INCLUDED VCSH ATTM AS THIS ACTIVITY WILL MOSTLY REMAIN OFFSHORE. NORTHEAST WINDS WILL BE 10-12 KT TODAY WITH HIGHER GUSTS POSSIBLE IN THE AFTN. THE MODELS INDICATE A BRIEF LULL IN PCPN THIS EVENING...BUT EXPECT MORE -RA AT KILM/KCRE/KMYR AFTER 06Z. LOWEST CIGS OVERNIGHT WILL BE AT THE COAST...MVFR AND PERHAPS IFR NEAR THE END OF THE PERIOD. NORTHEAST WINDS STRENGTHEN TONIGHT AS THE COASTAL TROUGH SHARPENS...BECOMING AROUND 15 KT WITH 20+ KT GUSTS EARLY WED MORNING. EXTENDED OUTLOOK...PERIODS OF RAIN AND MVFR/IFR CONDITIONS EXPECTED THROUGH THURSDAY. CHANCE OF SHOWERS FRIDAY...MAINLY ALONG THE COAST. VFR ON SATURDAY. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 1000 AM TUESDAY...THE COASTAL WATERS WILL REMAIN WEST OF THE INVERTED COASTAL TROF/FRONT DURING THIS EVENT. A PINCHED GRADIENT WILL DEVELOP BETWEEN THE STRONG RIDGING DOWN THE EAST COAST AND THE INVERTED TROF/FRONT. THIS HAS ALREADY RESULTED WITH NE WINDS HAVING INCREASED TO SCA VALUES...AND BUILDING SIGNIFICANT SEAS. SEAS COULD PEAK AROUND 8 FT OUTER WATERS OFF CAPE FEAR...AND OFF THE MOUTH OF WINYAH BAY. DOMINANT PERIODS WILL HOVER AROUND 6 SECONDS INDICATIVE OF WIND DRIVEN WAVES THE DOMINANT WAVE TYPE. PREVIOUS DISCUSSION............................................ AS OF 630 AM TUESDAY...THIS MORNING`S SUITE OF MODEL RUNS HAVE UNFORTUNATELY ALL TRENDED TOWARD STRONGER WIND SPEEDS AND HIGHER SEAS DEVELOPING OVER THE NEXT 24 HOURS. A STALLED FRONT OUT OVER THE GULF STREAM WILL DEVELOP A WAVE OF LOW PRESSURE ALONG IT TONIGHT ALONG THE GEORGIA AND SOUTH CAROLINA COAST. CANADIAN HIGH PRESSURE WILL ALSO TRY TO RIDGE SOUTHWARD FROM NEW ENGLAND. THIS WILL PINCH THE PRESSURE GRADIENT RATHER SIGNIFICANTLY ALONG THE CAROLINA COAST...WITH DETERIORATING WEATHER CONDITIONS THE RESULT. WINDS CURRENTLY ARE NORTHERLY AT 10-15 KNOTS ACROSS THE SC WATERS BUT HAVE VEERED NORTHEASTERLY NEAR 20 KNOTS ACROSS THE NC WATERS. THIS SURGE OF NORTHEASTERLY WINDS SHOULD MOVE DOWN THE COAST OVER THE NEXT FEW HOURS...WITH 25 KNOT WINDS DEVELOPING THIS AFTERNOON. THE WORST CONDITIONS ARE EXPECTED TO OCCUR TONIGHT WHEN WINDS COULD REACH 30 KNOTS. ONE CONCERN IS THE NORMALLY QUITE RELIABLE GFS MODEL IS SHOWING WINDS JUST 1000 FEET ALOFT ACCELERATING TO 35 KNOTS OVERNIGHT ALONG THE SOUTH CAROLINA COAST. DEPENDING ON HOW MUCH HEAT FROM THE WARM OCEAN SURFACE CAN WARM THE AIRMASS...WE COULD CONCEIVABLY SEE THESE GALE-FORCE WINDS COME DOWN TO THE SURFACE AT LEAST IN GUSTS. SEAS CURRENTLY ONLY 2-4 FEET SHOULD BUILD STEADILY IN RESPONSE TO THE WINDS...REACHING AS HIGH AS 6-8 FEET TONIGHT. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 AM TUESDAY...HIGH PRESSURE WILL WEDGE DOWN THE COAST THROUGH THE SHORT TERM...WHILE A COASTAL TROUGH REMAINS JUST OFFSHORE THE CAROLINAS. THIS WILL PRODUCE CONSISTENT NE WINDS THROUGH THE PERIOD...WITH THE HIGHEST SPEEDS OCCURRING ON WEDNESDAY AS A WAVE OF LOW PRESSURE MOVES ALONG THE TROUGH...PINCHING THE GRADIENT. NE WINDS MAY EXCEED 25 KTS THE FIRST HALF OF WEDNESDAY...WITH GUSTS APPROACHING GALE FORCE. THESE WINDS WILL EASE SLOWLY WED NIGHT AND THE FIRST PART OF THURSDAY...BECOMING 15-20 KTS...BEFORE SLOWLY RAMPING UPWARD AGAIN THURSDAY NIGHT. THESE WINDS WILL KEEP WAVE AMPLITUDES ELEVATED...4-7 FT EXPECTED WED AND THU. THERE MAY BE A BRIEF PERIOD WED NIGHT INTO THURSDAY WHEN WAVE HEIGHTS DROP BELOW SCA THRESHOLDS...BUT EVEN SO...EXPECT HEADLINES TO BE IN EFFECT THE ENTIRETY OF THE PERIOD. LONG TERM /FRIDAY THROUGH SATURDAY/... AS OF 300 AM TUESDAY..HIGH PRESSURE WILL SOMEWHAT RE-ORIENT ITSELF INTO THE WKND...BECOMING CENTERED ACROSS THE GREAT LAKES INSTEAD OF NEW ENGLAND. WHILE THIS LEAVES A WEDGE IN PLACE LOCALLY...IT WILL BE OF DECREASED STRENGTH...AND THUS NE WINDS WILL BE SOMEWHAT LOWER THAN EARLIER IN THE WEEK...15-20 KTS INTO THE WKND. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR AT LEAST A PORTION OF THE EXTENDED...LIKELY MOST OF FRIDAY...FOR 4-6 FT SEAS...BEFORE AMPLITUDES WANE ON SATURDAY.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT WEDNESDAY FOR AMZ250-252- 254-256.
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&& $$ SYNOPSIS...JDW NEAR TERM...DCH/TRA SHORT TERM...JDW LONG TERM...JDW AVIATION...TRA

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