Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 250533 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1233 AM EST TUE NOV 25 2014 .SYNOPSIS...
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UNSETTLED WEATHER IS EXPECTED OVERNIGHT AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH THE AREA ON TUESDAY MORNING. COOL AND WET CONDITIONS ARE EXPECTED TUESDAY NIGHT AND WEDNESDAY AS A DEEPENING LOW PRESSURE SYSTEM MOVES NORTH ALONG THE FRONT STALLED OFFSHORE. SKIES WILL CLEAR OUT ON THANKSGIVING DAY...WITH TEMPERATURES RUNNING SEVERAL DEGREES BELOW NORMAL INTO THE COMING WEEKEND.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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AS OF 1230 AM TUESDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: THE SURFACE COLD FRONT EXTENDS FROM NORTH- CENTRAL GEORGIA ACROSS THE NC/TN BORDER REGION. EAST OF THIS FRONT A SOUTHERLY WIND CONTINUES FROM FLORIDA AND THE BAHAMAS INTO THE EASTERN CAROLINAS. IN THE UPPER LEVELS A STRIPE OF DIFLUENCE EXISTS EXTENDING FROM THE FLORIDA PANHANDLE INTO EAST-CENTRAL NORTH CAROLINA...THE RESULT OF ACCELERATING FLOW INTO THE RIGHT- ENTRANCE REGION OF A 250 MB JET STREAK FROM ARKANSAS INTO NEW YORK STATE. THIS DIVERGENCE HAS SUPPORTED A NARROW BUT PERSISTENT REGION OF RAINFALL (AND EARLIER ELEVATED CONVECTION) ACROSS THE SC PEE DEE REGION INTO LUMBERTON. LATEST HIGH-RES HRRR RUNS SHOW WE SHOULD ENTER A RELATIVE LULL IN PRECIPITATION COVERAGE OVER THE NEXT 2-4 HOURS...BUT INCREASING SOUTHERLY FLOW AND ISENTROPIC LIFT CENTERED ON THE 305K ISENTROPIC SURFACE (~750 MB OR 8000 FEET AGL) SHOULD LEAD TO INCREASING COVERAGE OF RAIN AGAIN LATE TONIGHT INTO THE DAYLIGHT HOURS TUESDAY. ALTHOUGH THE 18Z GFS HAD A FAIRLY FAST EASTWARD MOVEMENT OF THE COLD FRONT OFF THE COAST LATE TONIGHT WITH NW WINDS DEPICTED OVER THE COASTAL WATERS BY 12Z TUE...THE BULK OF THE OTHER GUIDANCE SHOWS A MUCH SLOWER EASTWARD MOVEMENT OF THE BOUNDARY WITH SW WINDS CONTINUING. GIVEN THE CURRENT POSITION OF THE FRONT I AM INCLINED TO BELIEVE THE SLOWER GUIDANCE...AND HAVE ADJUSTED FORECAST WINDS & TEMPS ACCORDINGLY.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY NIGHT/... AS OF 3 PM MONDAY...INCREASED CONFIDENCE IN SUBSTANTIAL RAINFALL ESPECIALLY ALONG THE COAST THROUGH THE PERIOD. COLD FRONT PUSHES OFF THE COAST AND DECELERATES EARLY TUESDAY. THE COLD AIR ADVECTION AND DEEP MOISTURE BOTH LAG BEHIND AND THERE SHOULD BE JUST ENOUGH STRUNG OUT VORTICITY AND LOW LEVEL CONVERGENCE FOR OCCASIONAL LIGHT RAIN THROUGH THE DAY. TEMPS WILL BE FAIRLY CLOSE TO CLIMO DESPITE THE WIDESPREAD CLOUDS AND RAINFALL. SEVERAL INGREDIENTS THEN COME TOGETHER TUESDAY NIGHT FOR SOME RATHER IMPRESSIVE DYNAMICS AND POTENTIAL HEAVY RAIN. MID LEVEL IMPULSE CURRENTLY OVER SRN TX SWINGS THROUGH THE TROUGH AND GIVES IT A WEAK NEGATIVE TILT. SURFACE LOW DEVELOPS ALONG THE FRONT OFFSHORE. STRONG SSWRLY LOW LEVEL JET DEVELOPS IN ASSOC WITH THIS WAVE WHILE WEAK ISALLOBARIC COMPONENT TURNS FLOW INTO THE LOW WEST OF IT...I.E. OVER LANDMASS. THIS RESULTS IN AN IMPRESSIVE THERMAL GRADIENT...850MB TEMPS NEAR 15C JUST OFF COAST AND DOWN TO 2 C OVER WRN ZONES BY 12Z WED. THE RESULTING LOW LEVEL FRONTOGENESIS IS SOME OF THE STRONGEST I`VE SEEN IN A WHILE...WITH THE GFS FORECASTING VALUES OF 100-200 UNITS. IT IS ALSO TOUGH TO RULE OUT A NARROW ZONE OF CONDITIONAL SYMMETRIC INSTABILITY DEVELOPING RIGHT OVER THE IMMEDIATE (MAINLY NC) COAST AND ADJACENT WATERS. DURING THE OVERNIGHT HOURS THIS LOW LEVEL FORCING MAY EVEN COUPLE WITH DEEPER ASCENT FROM THE DEVELOPING UPPER JET CONFIGURATION AS THE RIGHT ENTRANCE OF A 190KT UPPER JET MOVES INTO PA. IN FACT GFS CROSS SECTIONS FOR A TIME SHOW ASCENT CLEAR THROUGH THE DEPTH OF THE COLUMN. WITH AT LEAST SOME CONNECTION TO GOMEX MOISTURE THIS SETUP COULD EASILY YIELD 2-2.5 INCHES OF RAINFALL ALONG THE IMMEDIATE COAST BEFORE THE RAIN TAPERS OFF MIDDAY WEDNESDAY OR WEDNESDAY AFTERNOON. THE BULK OF THE RAIN WILL FALL OVERNIGHT TUESDAY TO PERHAPS AS LATE AS DAYBREAK WED. THEREAFTER THE DEEP MOISTURE AND UPPER FORCING SHIFT OFFSHORE. LIGHTER RAIN WED MORNING THEN GIVES WAY TO A DRYING TREND AS COLD AIR ADVECTION BEGINS CRANKING UP BY 18Z. WEDNESDAY AFTERNOON HIGHS WILL NOT BE MUCH HIGHER THAN TUESDAY NIGHT LOWS. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 3 PM MONDAY...MID LEVEL TROUGHING OVER THE SOUTHEAST AT THE START OF THE PERIOD WILL LIFT NORTHEAST FRI WITH PROGRESSIVE FLOW DEVELOPING FOR THE WEEKEND. MID LEVEL TROUGH HELPS PUSH REMAINS OF DRY COLD FRONT THROUGH EARLY FRI WITH HIGH PRESSURE BUILDING IN FOR THE WEEKEND. PROGRESSIVE FLOW QUICKLY PUSHES THE CENTER OF THE HIGH OFFSHORE WITH RETURN FLOW DEVELOPING AS EARLY AS MIDDAY SAT. DEEP DRY WESTERLY FLOW WILL HELP KEEP THE REGION DRY THROUGH THE END OF THE PERIOD. TEMPERATURES BELOW CLIMO FOR THE FIRST HALF OF THE PERIOD WILL START A STEADY CLIMB BACK TO CLIMO EARLY NEXT WEEK AS HIGH MOVES FARTHER OFF THE COAST AND RETURN FLOW STRENGTHENS. LATE IN THE PERIOD A WEAK BACKDOOR COLD FRONT WILL TRY TO MOVE SOUTH ACROSS THE AREA. LATEST GFS KEEPS THIS FEATURE NORTH WHILE ECMWF PUSHES IT SOUTH. WILL FAVOR THE ECMWF SOLUTION...WHICH IS FAVORED BY WPC...FOR NOW BUT CONFIDENCE IS LOW. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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AS OF 06Z...EXPECT CIGS TO LOWER TO MVFR/IFR LEVELS THIS MORNING AS A COLD FRONT MAKES ITS WAY ACROSS THE CWA. PERIODS OF -RA WILL CONTINUE STREAMING OVERHEAD WITHIN THE SOUTHWEST FLOW AHEAD OF THE FRONT. THE LATEST NAM GUIDANCE HAS BACKED OFF IFR BEFORE 12Z... COMING INTO BETTER AGREEMENT WITH THE EARLIER GFS SOUNDINGS. THEREFORE...HAVE ONLY INCLUDED MVFR CIGS OVERNIGHT AT THE COASTAL TERMINALS. WINDS WILL GRADUALLY VEER FROM SW TO NW AFTER SUNRISE FOLLOWING FROPA...AND POST-FRONTAL IFR STRATUS APPEARS MOST LIKELY ALONG THE COAST AFTER 12Z. DEEP MOISTURE AND UPPER SUPPORT WILL CONTINUE TO PROMOTE -RA THROUGH MUCH OF THE DAY EVEN BEHIND THE FRONT. EXPECT IFR CIGS TO PREVAIL ALONG THE COAST DURING THE DAY AND MVFR INLAND. PCPN COVERAGE AND INTENSITY SHOULD INCREASE AFTER 00Z WED AS LOW PRESSURE DEVELOPS ALONG THE STALLED FRONT OFFSHORE. WIDESPREAD IFR CIGS APPEAR INCREASINGLY LIKELY AFTER 00Z WED WITH N-NE WINDS AOB 10 KT. EXTENDED OUTLOOK...RAIN WITH MVFR/IFR CIGS WILL PERSIST INTO WED AFTN...ESPECIALLY ALONG THE COAST. EXPECT GUSTY WINDS LATE TUE/EARLY WED...IN ADDITION TO HEAVIER PCPN THAT WILL REDUCE VSBYS TO MVFR/IFR AT TIMES. VFR LATE WED THROUGH SAT.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 1230 AM TUESDAY...NO CHANGES TO THE FORECAST WITH THE LATEST UPDATE. PREVIOUS DISCUSSION FOLLOWS: A COLD FRONT IS ANALYZED EXTENDING FROM NORTH-CENTRAL GEORGIA NORTHWARD ACROSS THE NC-TN BORDER REGION. THE BOUNDARY WILL MOVE STEADILY EASTWARD TONIGHT BUT SHOULD REMAIN INLAND FROM THE COAST EVEN AT DAYBREAK TUESDAY. SOUTH-SOUTHWEST WINDS CONTINUE ACROSS THE AREA BRINGING UNSEASONABLY HUMID AIR NORTHWARD FROM FLORIDA AND THE BAHAMAS. AS THIS SUBTROPICAL AIR CROSSES THE CHILLY NEARSHORE OCEAN PATCHY SEA FOG HAS DEVELOPED... MAINLY ALONG THE SC COAST ALTHOUGH PATCHY SEA FOG IS ALSO POSSIBLE ALONG THE BRUNSWICK COUNTY COAST AND POINTS NORTH AS WELL. THE BULK OF THE RAINFALL SHOULD REMAIN INLAND TONIGHT..ALTHOUGH TOWARD DAYBREAK RAIN CHANCES WILL INCREASE FROM SOUTH TO NORTH LEADING UP TO A RATHER SUBSTANTIAL TWO-DAY HEAVY RAINFALL EVENT TUE-WED. SEAS REMAIN QUITE LARGE ESPECIALLY GIVEN THE WIND SPEEDS WE ARE OBSERVING. THIS IS MAINLY DUE TO SOUTHERLY SWELL FROM THE RELATIVELY LONG FETCH OF STRONG WINDS FROM THE BAHAMAS TO THE CAROLINAS OVER THE PAST THREE DAYS. A SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT FOR THESE SEAS TONIGHT. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... AS OF 3 PM MONDAY...COLD FRONT PUSHES THROUGH EARLY TUESDAY WITH LITTLE FANFARE OTHER THAN A WIND SHIFT BUT A VERY DYNAMIC SETUP ALOFT WILL LEAD TO A RAPID DECAY IN CONDITIONS TUESDAY NIGHT. LIGHT OFFSHORE WINDS MUCH OF THE DAY TUESDAY AS THE FRONT SLOWS. STRONG SYSTEM SWINGING OUT OF SOUTHERN TEXAS TO THEN CAUSE FAIRLY RAPID PRESSURE FALLS ALONG THE BOUNDARY TUESDAY NIGHT INTO WEDNESDAY. AS THIS LOW CRANKS UP AND MOVES BY CONDITIONS SHOULD RAMP UP TO SMALL CRAFT ADVISORY LEVELS. BY WEDNESDAY MORNING THE STILL DEEPENING LOW ACCELERATES OFF TO OUR NORTH AND EAST. STRONG OFFSHORE WINDS STILL LIKELY WORTHY OF AN ADVISORY LIKELY CONTINUE IN THE ENSUING COLD SURGE AND SEAS WILL SIMILARLY BE HESITANT TO FALL BELOW CRITERIA BEFORE WEDNESDAY NIGHT. LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 3 PM MONDAY...PINCHED GRADIENT THU INTO FRI WILL MAINTAIN OFFSHORE FLOW IN THE 15 TO 20 KT RANGE INTO FRI. GRADIENT WEAKENS MIDDAY FRI FOLLOWING PASSAGE OF REMAINS OF DRY COLD FRONT. NORTH TO NORTHWEST FLOW ON FRI WILL WEAKEN AS SURFACE HIGH BUILDS INTO THE REGION...MOVING OVERHEAD LATE IN THE DAY. WINDS WILL BECOME LIGHT AND VARIABLE LATER FRI AND SAT AS THE SURFACE RIDGE AXIS LINGERS IN THE REGION. SEAS 2 TO 4 FT THU INTO FRI WILL DROP TO 2 FT OR LESS AS WINDS BECOME LIGHT AND VARIABLE.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR AMZ250-252-254-256.
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&& $$ SYNOPSIS...MBB NEAR TERM...REK/TRA/RGZ SHORT TERM...MBB LONG TERM...III AVIATION...BJR MARINE...REK/TRA/III/MBB/RGZ

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