Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 260252 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 952 PM EST TUE NOV 25 2014 .SYNOPSIS... RAIN WILL CONTINUE TONIGHT INTO WEDNESDAY MORNING AS LOW PRESSURE MOVES UP THE SOUTHEAST COAST. SKIES WILL CLEAR OUT BY THANKSGIVING DAY...WITH TEMPERATURES RUNNING SEVERAL DEGREES BELOW NORMAL INTO THE WEEKEND BEFORE WARMER TEMPERATURES RETURN EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... AS OF 1000 PM TUESDAY...SO FAR SO GOOD WITH THE EARLIER CHANGES TO QPF AMOUNTS. WITH THE EXCEPTION OF A NARROW BAND OVER WILMINGTON WHICH IS DROPPING FAIRLY HEAVY RAIN NOW...RATES ARE 0.05 INCHES PER HOUR OR LESS ACROSS THE BULK OF THE FORECAST AREA. RADAR COMPOSITES SOUTH TO THE FLORIDA GEORGIA LINE SHOW A SIZABLE GAP IN RAINFALL... PERHAPS KEEPING THOSE RED CLAY ROADS A LITTLE LESS MUDDY THAN THEY OTHERWISE MIGHT BE. DEEP CONVECTION CONTINUES ACROSS CENTRAL FLORIDA AND OFF THE FLORIDA EAST COAST AND THIS SHOULD CONTINUE TO NEGATIVELY IMPACT OUR PRECIPITATION INTENSITY FOR THE NEXT 3-5 HOURS. LATEST HRRR MODEL RUNS SHOW THE SYNOPTIC LOW MAY ACTUALLY MOVE INLAND BRIEFLY ACROSS SE NORTH CAROLINA AROUND 11-12Z WED. A TRACK THIS FAR WEST WOULD KEEP LOW TEMPERATURES IN WILMINGTON IN THE 60S DUE TO ONSHORE EASTERLY FLOW. I HAVE TWEAKED THE IMPLIED SYNOPTIC LOW TRACK A LITTLE CLOSER TO THE COAST...JUST NICKING BALD HEAD ISLAND BEFORE DAYBREAK. PREVIOUS DISCUSSION FROM 700 PM FOLLOWS... WE ARE ENTERING THE PERIOD OF WHAT SHOULD BE THE STRONGEST UPPER LEVEL DIVERGENCE AND LOW-TO-MID LEVEL ISENTROPIC LIFT NOW. 305K-310K ISENTROPIC LIFT FORECASTS FROM THE 18Z NAM OR GFS SUGGEST IT SHOULD BE POURING EVERYWHERE! HOWEVER THE BROAD-SCALE RADAR COMPOSITE SHOWS THE FORECAST PROBLEM FOR TONIGHT: WIDESPREAD DEEP CONVECTION ACROSS THE FLORIDA PENINSULA AND OFFSHORE EAST OF JAX IS PRODUCING DOWNSTREAM MID-LEVEL WARMING AND DRYING THAT IS NEGATIVELY IMPACTING PRECIPITATION COVERAGE ACROSS SOUTH GEORGIA AND THE CAROLINAS. THIS IS A CLASSIC PROBLEM WE SEE LOCALLY DURING THE COOL SEASON THAT HAS FRANKLY NEVER BEEN HANDLED WELL BY THE SYNOPTIC MODELS. BOTH THE HRRR AND HRRRX (AN EXPERIMENTAL VERSION AVAILABLE ON THE RAPIDREFRESH.NOAA.GOV SERVER) ARE INITIALIZING WITH THE CORRECT "HOLE" IN THE PRECIPITATION SHIELD AND SHOW THIS ANOMALY MAY CONTINUE TO PLAGUE THE REGION`S RAINFALL FORECAST THROUGH THE NIGHT. THE 18Z SYNOPTIC RAINFALL GUIDANCE FROM WPC ALSO SEEMS TO AGREE WITH THIS IDEA OF LESSER RAINFALL TOTALS THAN ORIGINALLY THOUGHT. WITH THIS IN MIND I HAVE KEPT FORECAST POPS AT 100% (EVERYONE WILL GET AT LEAST 0.01 INCHES OF RAIN) BUT I HAVE TRIMMED BACK FORECAST RAINFALL AMOUNTS SUBSTANTIALLY. FROM RIGHT NOW THROUGH THE END OF THE EVENT LATE WEDNESDAY MORNING IT APPEARS TOTALS SHOULD AVERAGE HALF OF AN INCH...PERHAPS APPROACHING AN INCH ALONG THE COAST IF RAINFALL RATES CAN INCREASE TOWARD THE END OF THE EVENT WEDNESDAY MORNING. OVER THE PAST FEW DAYS SYNOPTIC GUIDANCE HAS TRENDED FARTHER WEST WITH THE FORECAST PATH OF THE LOW MOVING NORTH FROM FLORIDA. 18Z MODELS CONTINUED THIS TREND AND I HAVE SHIFTED THE IMPLIED TRACK OF THE LOW IN THE FORECAST WIND GRIDS TO ONLY ABOUT 10 MILES EAST OF CAPE FEAR LATE TONIGHT. THIS WILL HAVE THE ADDED IMPACT OF MAINTAINING A WARMER AIRMASS NEAR THE COAST...PARTICULARLY SE NORTH CAROLINA...AND I HAVE RAISED FORECAST LOWS BY SEVERAL DEGREES HERE. FARTHER INLAND THE COLD AIR SHOULD BEGIN TO BLEED IN FROM THE NW SHORTLY AND VERY FEW CHANGES WERE NEEDED TO THE OVERALL TEMP/WIND FORECAST. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...LOW PRESSURE HUGGING THE COAST WILL BE MOVING N OF THE WATERS WEDNESDAY MORNING. AS THE LOW MOVES UP THE NORTH CAROLINA AND MID ATLANTIC COAST WED...THE RAIN WILL SHUT OFF FROM SSW TO NNE. PERIODS OF HEAVY RAIN ARE STILL POSSIBLE WED MORNING...BUT EXPECT BY AFTERNOON...THE RISK FOR RAINFALL WILL HAVE ENDED ACROSS ALL BUT THE CAPE FEAR AREA WHERE A SLIGHT RISK OF AFTERNOON RAIN WILL STILL BE POSSIBLE. WILL INCLUDE CATEGORICAL POPS WED MORNING THROUGHOUT. CONVECTION IS EXPECTED TO STAY OFFSHORE... EAST OF THE LOW CENTER WHERE THERE WILL BE AN INFLUX OF WARMER AND MORE UNSTABLE AIR. ONE VERY POTENT MID-LEVEL SHORTWAVE TROUGH WILL PIVOT ACROSS THE FORECAST AREA WED AFTERNOON WHILE ANOTHER SKIRTS OUR FORECAST AREA TO THE N LATE WED NIGHT AND THU MORNING BEFORE LIFTING OUT. THE INFLUX OF COLDER AND DRIER AIR WORKING INTO THE EASTERN CAROLINAS ON THE BACKSIDE OF FIRST SHORTWAVE WILL HELP TO SIGNIFICANTLY DRY THE COLUMN WITH PRECIPITABLE WATER VALUES DROPPING TO LESS THAN HALF AN INCH. THIS WILL HELP TO PROMOTE DECREASING AFTERNOON CLOUDINESS... ESPECIALLY ACROSS SOUTHERN AND WESTERN ZONES. THE SECOND SHORTWAVE MAY ACTUALLY BRING A BRIEF INCREASE IN CLOUD COVER...BUT PRECIPITATION IS EXPECTED TO REMAIN TO OUR N. TEMPS ON WED WILL NOT MOVE MUCH AS COLD AIR ADVECTION GETS UNDERWAY. IN FACT HIGHS WILL BE ACHIEVED IN MANY CASES PRIOR TO OR AROUND SUNRISE. WE EXPECT HIGHS TO BE IN THE LOWER TO MID 50S ON THE COAST WITH UPPER 40S TO AROUND 50 FROM EYF TO HYW AND POINTS W. DAYTIME TEMPS WILL HOLD STEADY OF NOT DROP A DEGREE OR TWO. TEMPS WED NIGHT WILL DROP INTO THE 30S TO AROUND 40. EVEN THE COLDEST SPOTS SHOULD NOT REACH THE FREEZING MARK GIVEN THE LACK OF RADIATIONAL COOLING. CHILLY HIGH PRESSURE WORKING TO THE COAST FROM THE W WILL ALLOW THE PRESSURE GRADIENT TO LOOSEN THU NIGHT. THE COOLEST TEMPS AT 850 MB THU WILL BE OFFSET BY SUNSHINE AND WE DO EXPECT HIGHS TO STILL REACH THE MID 50S. RADIATIONAL COOLING WILL DEVELOP THU NIGHT WHICH SHOULD ALLOW LOWS TO DROP INTO THE UPPER 20S TO LOWER 30S OVERNIGHT. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 PM TUESDAY...LONG TERM PERIOD WILL REMAIN DRY WITH MID LEVEL FLOW BECOMING PROGRESSIVE. COLD ADVECTION WILL BE WINDING DOWN FRI...BUT TEMPS STILL END UP WELL BELOW CLIMO. DEEP WESTERLY FLOW WILL BE QUICK TO SHIFT THE CENTER OF THE MODIFYING HIGH OFF THE COAST WITH RETURN FLOW DEVELOPING SAT. TEMPS REMAIN BELOW CLIMO SAT BUT WILL BE WARMER THAN FRI. EARLY NEXT WEEK 5H RIDGE TRIES TO BUILD NORTH FROM THE EASTERN GOMEX AND FL. BUILDING HEIGHTS AND INCREASING SOUTHWEST FLOW EARLY NEXT WEEK WILL PUSH TEMPS ABOVE CLIMO. BACKDOOR COLD FRONT DEPICTED IN MEDIUM RANGE GUIDANCE YESTERDAY NOW LOOKS TIMED TO CROSS THE AREA TUE MORNING...WITH BOTH GFS/ECMWF IN DECENT AGREEMENT. FRONT WILL PASS DRY FOLLOWED BY WEAK COLD ADVECTION WITH TEMPS DROPPING BACK NEAR CLIMO. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 00Z...EXPECT VFR/MVFR CONDITIONS EARLY THIS EVENING TO DETERIORATE TO IFR AS RAIN CONTINUES THROUGH THE OVERNIGHT HOURS. A SHALLOW LAYER OF LIGHT NORTHEAST WINDS BEHIND THE FRONT WILL HELP TO PROMOTE IFR STRATUS AS MOISTURE IS TRAPPED BENEATH A LOW-LEVEL INVERSION. MEANWHILE...A DEVELOPING AREA OF LOW PRESSURE ALONG THE FRONT WILL MOVE UP THE SOUTHEAST COAST OVERNIGHT... BRINGING MORE PERSISTENT RAIN THAT MAY LOWER VSBYS TO MVFR/IFR LEVELS AT TIMES. LIGHT NORTHEAST WINDS WILL BECOME MORE NORTHERLY AFTER MIDNIGHT... AND THEN NORTHWEST BY 12Z ON THE BACK SIDE OF THE LOW AS IT MOVES UP THE MID-ATLANTIC COAST. THE ENHANCED GRADIENT WILL RESULT IN GUSTY NORTHWEST WINDS 15-20 KT DURING THE MORNING/EARLY AFTN HOURS. CONDITIONS WILL IMPROVE FROM SW TO NE ACROSS OUR AREA DURING THE AFTN AS THE LOW RACES AWAY AND DRIER AIR IS PULLED INTO THE CAROLINAS. RAIN SHOULD END BY 18Z AS MVFR CIGS GRADUALLY IMPROVE TO VFR BY THE END OF THE PERIOD. EXTENDED OUTLOOK...VFR CONDITIONS EXPECTED THURSDAY THROUGH SUNDAY. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 1000 PM TUESDAY...LATEST HRRR MODEL RUNS SHOW THE LOW TRACKING A BIT FARTHER WEST THAN THE AFTERNOON MODELS INDICATED. I HAVE TWEAKED THE IMPLIED TRACK OF THE LOW ANOTHER 5 MILES WEST IN THE LATEST GRIDDED WIND FORECAST...JUST NICKING BALD HEAD ISLAND BEFORE DAYBREAK. THIS WOULD BRING SOUTHERLY WINDS ACROSS MOST OF THE COASTAL WATERS NORTH OF CAPE FEAR LATE TONIGHT. OTHERWISE FEW CHANGES WERE NEEDED TO THE FORECAST THIS EVENING. PREVIOUS DISCUSSION FROM 700 PM FOLLOWS... THE CAROLINA COASTAL WATERS ARE IN A LULL CURRENTLY AS LOW PRESSURE DEVELOPS ALONG A FRONT STALLED ACROSS THE FLORIDA PENINSULA. THIS FRONT EXTENDS NORTHEASTWARD TO VERY NEAR CAPE FEAR WHICH EXPLAINS THE WEAK PRESSURE GRADIENT WE SEE ON SURFACE CHARTS. AS THE NIGHT PROGRESSES THE LOW SHOULD FOLLOW THE FRONT NORTH-NORTHEASTWARD...GRADUALLY DEEPENING AND PASSING JUST EAST OF CAPE FEAR BEFORE DAYBREAK WEDNESDAY MORNING. WITH THE FRONT REMAINING JUST OFF THE COAST WE SHOULD NOT SEE VERY STRONG WINDS ACROSS THE COASTAL WATERS TONIGHT...15 KNOTS OR LESS THROUGH EARLY WEDNESDAY MORNING. THE EXCEPTION TO THIS MAY BE ACROSS THE WATERS 10-20 MILES EAST OF CAPE FEAR WHERE STRONG SOUTH WINDS DEVELOPING AROUND MIDNIGHT AHEAD OF THE INTENSIFYING LOW COULD REACH 25 KNOTS. CERTAINLY OFFSHORE BEYOND 20 MILES WINDS ARE GOING TO INTENSIFY QUITE A BIT OVER THE NEXT 6 HOURS AHEAD OF THE LOW. THIS WILL BE IMPORTANT SINCE SEAS WILL BUILD QUITE SUBSTANTIALLY OFFSHORE...AND A GOOD DEAL OF SOUTHERLY SWELL ENERGY SHOULD PROPAGATE INTO THE COASTAL WATERS BEGINNING LATE THIS EVENING. FOR THIS REASON THE SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT FOR THESE 4-6 FOOT SEAS DEVELOPING AFTER MIDNIGHT. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE THROUGH THE DAY WED. WE DO THINK THESE CONDITIONS MAY WANE WED EVE. HOWEVER...IT IS POSSIBLE THAT SMALL CRAFT ADVISORY CONDITIONS REDEVELOP FOR A TIME LATE WED NIGHT AND THU AS BACKSWELL FROM COASTAL LOW PRESSURE WELL NORTH OF THE AREA WORKS DOWN THE COAST. ALSO...THE PRESSURE GRADIENT BETWEEN HIGH PRESSURE TO OUR W AND COASTAL LOW WILL HELP TO INCREASE LOW-LEVEL WIND SPEEDS AS SURGE OF COLDEST AIR ARRIVES ACROSS THE WATERS. THE WIND DIRECTION WILL BE NW OR TRANSITIONING TO NW WED MORNING AS THE LOW MOVES FURTHER UP THE COAST. THE DIRECTION WILL THEN BACK TO A MORE WESTERLY DIRECTION WED NIGHT AND THU. AS HIGH PRESSURE TO THE W BEGINS TO ASSERT ITSELF LATE THU AND THU NIGHT...THE WIND DIRECTION WILL VEER TO NW AND THEN N. HIGHEST WIND SPEEDS THIS PERIOD WILL BE UP TO 20 TO 25 KT AND SEAS UP TO 5 TO 8 FT. LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 300 PM TUESDAY...DECREASING NORTHWEST FLOW ON FRI WILL BECOME LIGHT AND VARIABLE FRI NIGHT INTO SAT AS SURFACE RIDGE AXIS MOVES OVERHEAD. LIGHT SOUTHERLY FLOW DEVELOPS SAT AFTERNOON AS THE CENTER OF THE HIGH PUSHES EAST OF THE WATERS. GRADIENT BECOMES A LITTLE MORE DEFINED LATER SAT WITH SOUTHWEST FLOW INCREASING TO 10 TO 15 KT SAT NIGHT AND SUN. SEAS 2 TO 4 FT FRI MORNING DROP TO 2 TO 3 FT FRI NIGHT AND 2 FT OR LESS SAT AND SUN. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EST WEDNESDAY FOR AMZ250-252-254-256. && $$ NEAR TERM...TRA SHORT TERM...RJD LONG TERM...III AVIATION...BJR

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