Area Forecast Discussion
Issued by NWS Wilmington, NC

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151 FXUS62 KILM 071129 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 629 AM EST SUN FEB 7 2016 .SYNOPSIS... A LOW PRESSURE SYSTEM WILL RAPIDLY INTENSIFY AS IT TRACKS NORTHEAST OFFSHORE OF THE CAROLINAS TODAY. THIS SYSTEM MAY BRING A MIX OF RAIN AND SNOW TO INLAND LOCATIONS TODAY. THE STRONG LOW WILL TRACK FARTHER OUT TO SEA TONIGHT THRU MONDAY. WEAK HIGH PRESSURE WILL PREVAIL MONDAY FOLLOWED BY A COLD FRONTAL PASSAGE MONDAY NIGHT. A DRY ARCTIC AIR MASS WILL FOLLOW INTO MID WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 630 AM SUNDAY...THE POTENT MID-LEVEL S/W TROF IS NOW MOVING OFF THE NORTHERN FLORIDA COAST AND AIDING THE FURTHER DEVELOPMENT OF THE ALREADY DEEPENING SFC LOW OFFSHORE FROM THE GA COAST. IN ADDITION TO THESE DYNAMICS...THE 300 MB JET WILL POSITION ITSELF ACROSS THE SE U.S. COAST WHEREBY THE EASTERN CAROLINAS WILL BE IN THE LEFT FRONT QUADRANT OF THIS JET RESULTING WITH SYNOPTIC LIFT. THE UPPER JET DYNAMICS AND THE POTENT MID-LEVEL S/W TROF WILL COMBINE FORCES TO PRODUCE A MONSTER COASTAL LOW THAT WILL RAPIDLY DEEPEN FROM AROUND 1005 MB ATTM...TO THE 980S MB BY THIS EVENING. THE ONE CAVEAT THOUGH...IS THAT THE AIRMASS IS PROGGED TO REMAIN TOO MILD FOR FROZEN OR FREEZING PCPN FOR THE ILM CWA. COOLING ON THE BACKSIDE OF THE LOW REMAINS SUSPECT...WITH PROGGED 850 TEMPS REMAINING ABOVE 0 AND PARTIAL THICKNESS 1000-850MB ABOVE 1300M... THE THRESHOLD FOR SNOW. THEREFORE...HAVE REMOVED THE THREAT FOR FROZEN/FREEZING PCPN FOR TODAY. THERE ARE SEVERAL ADVISORIES...WATCHES AND WARNINGS ASSOCIATED WITH THIS DEEPENING AND POWERFUL LOW PRESSURE SYSTEM. THE 1ST IS THE FLOOD WATCH FOR THE COASTAL COUNTIES OF THE ILM CWA BI-STATE REGION. STILL LOOKING AT STORM TOTALS OF 1 TO 2 INCHES OF ADDITIONAL RAINFALL FROM THIS SYSTEM ACROSS LOCATIONS THAT EXPERIENCED 2 TO 5 INCHES OF RAINFALL LATE LAST WEEK. THE GROUNDS ACROSS THE WATCH AREA REMAIN SATURATED WITH SOME LOCATIONS STILL EXPERIENCING STANDING WATER. ON A SIDE NOTE...THE FA WILL EXPERIENCE ROUGHLY 12 TO 18 HRS OF STRATIFORM TYPE RAINS TOTALING UP TO 1 TO 2 INCHES. NORMALLY...THESE VALUES FALLING DURING THIS TIME FRAME DO NOT TRIGGER A FLOOD WATCH. THE ANTECEDENT CONDITIONS ACROSS THE FA ARE WHATS DRIVING THIS FLOOD WATCH. AND THE 2ND IS THE WIND ADVISORY FOR THIS MORNING THRU THE MID- EVENING HOURS...FOR THE IMMEDIATE COAST. MODEL MOS GUIDANCE CONTINUES TO PAINT PEAK SUSTAINED WINDS JUST SHY OF 30 KT FOR THE COASTAL LOCATIONS. IN ADDITION...WITH A STORM WARNING IN EFFECT FOR THE ADJACENT COASTAL AND OFFSHORE WATERS...IT WOULD BE PRUDENT TO INCLUDE THE COASTAL COUNTIES WITHIN ATLEAST A WIND ADVISORY. WITH AN OFFSHORE TRAJECTORY...NNE BACKING TO NW...DOMINATING THE WINDS. WIND SPEEDS WILL BE A PERCENTAGE LOWER THAN IF THE DOMINATING DIRECTIONS CONSISTED OF AN ONSHORE COMPONENT. GFS MOS AND NAM MOS GUIDANCE FOR LOCATIONS WITHIN THE COASTAL WATERS... INDICATE 40+ MPH SUSTAINED WINDS. WIND ADV THRESHOLDS ARE 1 HOUR OF SUSTAINED 31 TO 39 MPH OR WIND GUSTS TO 46+ MPH. THE THINKING IS THAT THE IMMEDIATE COAST WILL LIKELY OBSERVE WIND GUSTS THAT SATISFY THE VALIDITY OF THIS WIND ADVISORY. AS FOR TEMPERATURES...TODAYS HIGHS WILL LIKELY RUN IN THE UPPER 30S TO MID 40S...WITH THE MID 40S PUSHING IT. SOME COOLING ON THE BACKSIDE OF THE LOW...WILL PUSH TEMPS TO THE LOWER 30S FOR TONIGHTS LOWS. THESE LOWS WILL OCCUR WELL AFTER WHEN PCPN HAD ENDED. MAY NEED A STATEMENT ON BLACK ICE FOR TONIGHT WITH ROADWAYS HAVING NOT ENOUGH TIME TO DRY PRIOR TO THE ONSET OF FREEZING TEMPS.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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AS OF 3 AM SUNDAY...IMPRESSIVE SHORTWAVE DROPPING SOUTH THROUGH THE UPPER MIDWEST SUN INTO MON WILL BRING ANOTHER CHANCE OF WINTRY PRECIP TO THE AREA LATE MON AND MON NIGHT. DYNAMICS WITH THE SHORTWAVE ARE IMPRESSIVE...AS IS THE ABUNDANCE OF THE COLD AIR. THE ONLY LIMITING FACTOR WILL BE THE AMOUNT OF MOISTURE...SPECIFICALLY THE LOW LEVEL MOISTURE. FORECAST SOUNDINGS SHOW STRONG UPWARD MOTION IN THE DENDRITIC GROWTH ZONE WITHIN A LAYER OF INCREASED MOISTURE. HOWEVER...BELOW 5K FT OR SO THE DRY AIR BECOMES AN OBSTACLE. STRONG SHORTWAVES ALWAYS MANAGE TO WRING WHAT LITTLE MOISTURE IS AVAILABLE OUT OF THE ATMOSPHERE BUT IN THIS CASE THE QPF IS GOING TO BE RATHER LOW. SO WHILE THERE IS POTENTIAL FOR RAIN...POSSIBLY WITH SNOW SHOWERS MIXED IN...DO NOT THINK EVENT WILL BE THAT SIGNIFICANT. LATEST SOUNDINGS SUGGEST ALL RAIN FOR THE FORECAST AREA BUT THE COLD AIR IS NOT FAR AWAY AND GIVEN THE STRENGTH OF THE WAVE THERE IS DEFINITELY POTENTIAL FOR DYNAMIC COOLING. WILL KEEP FORECAST ALL RAIN FOR NOW (ESPECIALLY SINCE LOCAL TOP DOWN METHODOLOGIES YIELD ALL RAIN) BUT CANNOT RULE OUT THE ADDITION OF SNOW AS ZERO HOUR APPROACHES. WILL CONTINUE TO CARRY LOW CHC POP WITH MINIMAL QPF. SHORTWAVE HELPS DRIVE THE FIRST OF 2 COLD FRONT ACROSS THE AREA MON NIGHT. NEAR CLIMO TEMPS MON DROP BELOW CLIMO MON NIGHT AS COLD ADVECTION GETS GOING. CONTINUED STRONG COLD ADVECTION TUE AND TUE NIGHT WILL RESULT IN TEMPERATURES BELOW TO WELL BELOW CLIMO FOR THE SECOND HALF OF THE PERIOD. SECOND COLD FRONT CROSSES THE AREA LATER TUE REINFORCING THE ALREADY COLD AIR MASS IN PLACE. THIS COLD FRONT IS BEING DRIVEN BY ANOTHER SHORTWAVE ROTATING AROUND THE BASE OF THE TROUGH. ALTHOUGH LOW LEVEL MOISTURE REMAINS QUITE LIMITED THERE WILL BE ENOUGH MID LEVEL MOISTURE TO SUPPORT AN INCREASE IN CLOUD COVER AND POSSIBLY SOME VIRGA.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 3 AM SUNDAY...REGION WILL BE IN THE GRIP OF AN ARCTIC AIR MASS AS THE PERIOD BEGINS. BROAD 5H TROUGH OVER THE EASTERN CONUS WED INTO THU WILL MAINTAIN TEMPERATURES 10 TO 15 DEGREES BELOW CLIMO. HIGHS EACH DAY WILL STRUGGLE TO REACH MID 40S. LOWS AT NIGHT WILL NOT BE QUITE AS COLD AS ONE WOULD EXPECT GIVEN 850 TEMPS APPROACHING -14C AT TIMES. CENTER OF THE SURFACE HIGH NEVER SETTLES OVER THE AREA WITH THE BITTERLY COLD AIR IN PLACE. SO WHILE THIS MEANS COLD ADVECTION NEVER WANES IT ALSO MEANS BOUNDARY LAYER MIXING NEVER CEASES. LOWS WILL END UP IN THE MID 20S WED NIGHT. RATHER BALMY COMPARED TO WHAT -14C 850 TEMP ON A STRONG RADIATIONAL COOLING NIGHT WOULD YIELD...LOWS APPROACHING SINGLE DIGITS. THE MIXING WILL COME AT A PRICE THOUGH...WIND CHILL VALUES WILL DROP WELL INTO THE TEENS. MID LEVEL PATTERN REMAINS AMPLIFIED THU THOUGH HEIGHTS STARTS BUILDING AS SHORTWAVE EXITS. AIR MASS STARTS TO MODIFY BUT THE SURFACE LAYER WILL REMAIN ISOLATED AND SENSIBLE WARMING IS NOT LIKELY TO BE REALIZED UNTIL THU NIGHT AT THE EARLIEST. BRIEF PERIOD OF RETURN FLOW LATER THU AND THU NIGHT ENDS WITH COLD FRONT CROSSING THE AREA DURING FRI. THIS FRONT IS FOLLOWED BY ANOTHER ROUND OF ARCTIC AIR AS THE PERIOD ENDS. THE BEST...AND REALLY ONLY CHANCE FOR PRECIP WILL BE LATE IN THE PERIOD AHEAD OF THE AFOREMENTIONED COLD FRONT. ALTHOUGH SYSTEM DOES NOT APPEAR TO BE ALL THAT SPECIAL A COLD FRONT/SHORTWAVE COMBO WITH MOISTURE IS USUALLY A RECIPE FOR AT LEAST SOME LIGHT PRECIP. WILL CARRY A SILENT POP LATE IN THE PERIOD FOR NOW. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/... AS OF 06Z...SHOULD BE AN INTERESTING NEXT 24 HOURS TO SAY THE LEAST. CURRENTLY...SURFACE CYCLOGENESIS OCCURRING OFFSHORE FROM THE FLORIDA EAST COAST. A STRONG UPPER TROF WILL CATCH UP WITH THE SFC LOW THIS MORNING...RESULTING IN EXPLOSIVE DEEPENING OF THE SFC LOW JUST OFFSHORE FROM THE NC AND SC COASTS THRU THIS AFTERNOON AND EVENING. LOOK AT INITIALLY REDUCED VISIBILITY FROM LIGHT RAIN...VFR TO MVFR...WITH POCKETS OF MODERATE TO HEAVY RAIN...MVFR TO IFR... REDUCING VSBY TO LESS THAN 1 MILE AND ASSOCIATED CEILINGS AT OR BELOW 1200 FT. THE HEAVIEST PCPN WILL OCCUR DURING DAYTIME SUNDAY MORNING THRU MID-AFTERNOON. THE HIGHER PCPN AMOUNTS WILL OCCUR CLOSER TO THE COAST...IE MYR...CRE AND ILM. SFC TEMPS AND THE LOW LEVELS REMAIN MILD ENOUGH TO KEEP THE PCPN TYPE TO JUST PLAIN RAIN. THE ENDING OF THIS PCPN COULD BE A MIXTURE OF RAIN OR SNOW OR POSSIBLY ALL SNOW DEPENDING ON HOW MUCH WRAP AROUND COLD AIR MAKES IT INTO THE AREA PRIOR TO THE DEPARTURE OF THE MOISTURE. FOR NOW...ENDING THE PCPN AS PLAIN RAIN. THE MAJOR EFFECTS FROM THIS STORM SYSTEM WILL BE THE GUSTY NE WINDS INITIALLY...BACKING TO THE NORTH TODAY...AND NW LATE THIS AFTERNOON AND EVENING. THE SFC PG WILL TIGHTEN RAPIDLY THIS MORNING AS THE SFC LOW NEARLY BOMBS JUST OFFSHORE FROM THE CAROLINAS LATER THIS MORNING AND AFTERNOON...AND PASSES BY CAPE FEAR EARLY THIS EVENING...AND OFF CAPE HATTERAS BY SUNRISE MON. PEAK GUSTS WILL RUN 20 TO 30 KT ACROSS THE INLAND TERMINALS... AND 30-40 KT ACROSS THE COASTAL TERMINALS...AND OCCUR LATE THIS MORNING THRU EARLY THIS EVENING. EXTENDED OUTLOOK...CONDITIONS IMPROVE TO VFR SUNDAY EVENING AND OVERNIGHT...AND CONTINUING THRU MON. A CHANCE OF PRECIPITATION WITH MVFR CONDITIONS POSSIBLE LATE MONDAY INTO TUESDAY. ARCTIC AIR MASS WILL PROVIDE VFR CONDITIONS WEDNESDAY AND THURSDAY. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 630 AM SUNDAY...A STORM WARNING REMAINS IN EFFECT FOR THE ILM WATERS. OF THE 3 BIG KAHUNA MODELS...GFS...EUROPEAN AND THE NAM...HAVE DECIDED TO FOLLOW THE NAM/EUROPEAN AND ITS SFC LOW EVOLUTION AND TRACK. THE NAM AND EUROPEAN POSITIONS THE SFC LOW CLOSER TO THE CAROLINA COASTS AS IT MOVES NORTHEASTWARD JUST OFFSHORE FROM THE LOCAL WATERS THIS AFTERNOON THRU THIS EVENING. IN ADDITION...THE NAM AND EUROPEAN RAPIDLY INTENSIFY THIS LOW INTO THE 980S BY LATE THIS AFTERNOON AND EARLY EVENING. THE INTENSE AND WELL TIGHTENED SFC PRESSURE GRADIENT ACROSS THE LOCAL WATERS...WILL RESULT IN 25 TO 40 KT SUSTAINED WINDS WITH GUSTS UP TO 50 KT FROM MID-DAY THRU EARLY THIS EVENING. WITH THE LOW STAYING EAST OF THE LOCAL WATERS...WIND DIRECTIONS WILL START FROM THE NNE THEN BACK TO THE NORTH AS THE LOW PARALLELS THE COASTAL WATERS...AND FINALLY BACK TO THE NW AS IT PULLS AWAY TONIGHT. SIGNIFICANT SEAS WILL QUICKLY BUILD TODAY...PEAKING ROUGHLY IN A 7 TO 11 FOOT RANGE FROM MIDDAY THRU EARLY THIS EVENING. THE WIND DIRECTIONS...NNE BACKING TO NW...WILL RESULT IN A LIMITED FETCH FOR WHICH THE SEAS TO BUILD UPON. NEVERTHELESS...SEAS PEAKING AT 7 TO 11 FT IS NOT BAD FOR BASICALLY A PREDOMINATE OFFSHORE WIND DIRECTION. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 300 AM SUNDAY...SOUTHWEST FLOW WILL DROP UNDER 20 KT FOR A PERIOD ON MON BUT APPROACH OF STRONG COLD FRONT LATE IN THE DAY WILL PUSH WINDS BACK OVER 20 KT BY LATE AFTERNOON. PASSAGE OF COLD FRONT MON NIGHT IS FOLLOWED BY DEVELOPMENT OF WESTERLY FLOW...ENHANCED BY PINCHED GRADIENT AND STRONG COLD ADVECTION. SPEEDS MON NIGHT WILL APPROACH 30 KT SUSTAINED WITH GUSTS OF 35 TO 40 KT. COLD ADVECTION CONTINUES TUE AND TUE NIGHT WITH WINDS REMAINING IN THE 25 TO 30 KT RANGE THROUGH THE END OF THE PERIOD. SEAS RANGING FROM 3 TO 6 FT MON MORNING START BUILDING IN THE AFTERNOON...PEAKING BETWEEN 4 AND 8 FT MON NIGHT AND STAYING 4 TO 8 FT THROUGH THE END OF THE PERIOD. LONG TERM /WEDNESDAY THROUGH THURSDAY/... AS OF 3 AM SUNDAY...STRONG WEST TO NORTHWEST FLOW CONTINUES ON WED THEN STARTS TO WEAKEN THU AS COLD ADVECTION WEAKENS AND GRADIENT RELAXES. OFFSHORE FLOW DURING THE FIRST HALF OF THE PERIOD WILL BE AROUND 25 KT WITH GUSTS APPROACHING GALE FORCE. ELONGATED SURFACE RIDGE STARTS BUILDING IN FROM THE WEST LATE WED NIGHT AND THU. SPEEDS DROP UNDER 20 KT WED NIGHT AND UNDER 15 KT BY THE END OF THU. ALTHOUGH FLOW WILL BE OFFSHORE ELEVATED WIND SPEEDS WILL KEEP SEAS OVER 6 FT THROUGH WED NIGHT. GRADUAL REDUCTION IN WIND SPEEDS LATE WED NIGHT AND THU ALLOWS SEAS TO DROP TO 2 TO 4 FT THU AND THU NIGHT.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...FLOOD WATCH THROUGH THIS EVENING FOR SCZ053>056. WIND ADVISORY UNTIL 10 PM EST THIS EVENING FOR SCZ053>056. NC...FLOOD WATCH THROUGH THIS EVENING FOR NCZ099-105>110. WIND ADVISORY UNTIL 10 PM EST THIS EVENING FOR NCZ105>110. MARINE...STORM WARNING UNTIL 10 PM EST THIS EVENING FOR AMZ250-252-254- 256. && $$ SYNOPSIS...III NEAR TERM...DCH SHORT TERM...III LONG TERM...III AVIATION...DCH

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