Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211845 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 145 PM EST SUN DEC 21 2014 .SYNOPSIS... A WEDGE OF HIGH PRESSURE WILL KEEP CLOUDS AND RAIN CHANCES IN THE FORECAST TODAY. RAIN CHANCES INCREASE ON MONDAY AS LOW PRESSURE MOVES ALONG THE COAST. THE WEATHER WILL REMAIN UNSETTLED TUESDAY BUT GROW A BIT MORE SEASONABLE. A STRONG COLD FRONT WILL BRING SHOWERS AND MAYBE THUNDERSTORMS WEDNESDAY INTO WEDNESDAY NIGHT. SUNSHINE FINALLY RETURNS ON CHRISTMAS DAY WHILE IT TURNS COOLER. DRY AND FAIRLY SUNNY WEATHER SHOULD LAST INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 130 PM SUNDAY...CLOUD COVER HAS BEEN SOMEWHAT ERODED BY DRY AIR ALOFT MOVING IN FROM THE WEST-SOUTHWEST AND LOW LEVEL DRY AIR SPREADING OVER THE AREA FROM THE NORTH. HOWEVER A SURFACE LOW EMERGING FROM THE GULF OF MEXICO THIS EVENING WILL ENSURE CLOUD COVER RETURNS. THE LOW WILL MOVE NORTHEAST...PASSING JUST OFF THE GA/SC COAST OVERNIGHT AND DRAGGING A STALLED FRONT CLOSE TO THE AREA. AHEAD OF THE LOW DEEP MOISTURE WILL OVERSPREAD THE CAROLINAS. FORECAST SOUNDINGS PEAK PRECIPITABLE WATER VALUES AROUND 1.25 INCH CLOSE TO MIDNIGHT WITH ONLY A SLIGHT DROP IN PWATS THROUGH THE END OF THE PERIOD. GOOD ISENTROPIC LIFT WITHIN THIS AREA OF DEEP MOISTURE WILL LEAD TO LIGHT RAIN...POSSIBLY WITH BRIEF PERIOD OF MODERATE RAIN...DEVELOPING THIS EVENING AND OVERNIGHT. LOOKING AT THE ISENTROPIC FIELDS THERE MAY BE 2 DISTINCT PERIODS OF LIGHT RAIN OVERNIGHT. THE FIRST AROUND 00Z WITH A SECOND ROUND OVERNIGHT AND A PERIOD OF DRIZZLE BETWEEN THEM. INCREASING CLOUD COVER AND APPROACH OF SURFACE LOW OVERNIGHT WILL HELP KEEP LOWS NEAR TO SLIGHTLY ABOVE CLIMO. TEMP CURVE WILL NOT BE A TYPICAL ONE WITH LOWS LIKELY OCCURRING BEFORE MIDNIGHT THEN HOLDING STEADY OR GRADUALLY INCREASING.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 3 AM SUNDAY...CLOUDS HANG TOUGH MONDAY TO KEEP TEMPS BELOW CLIMATOLOGY ONCE AGAIN AS SURFACE WEDGE OF HIGH PRESSURE RIDGES IN FROM POINTS NORTH. FRONTAL BOUNDARY STALLED WELL OFFSHORE AND IT WILL HAVE A WAVE OF LOW PRESSURE RIDGE UP ALONG OUR LATITUDE LATE IN THE DAY. AS THIS OCCURS SOME AREAS MAY EXPERIENCE SOME WEAK ISENTROPIC UP-GLIDE THAT LEADS TO SOME LIGHT RAIN. WITH THIS FORCING VERY WEAK AND MOISTURE CONFINED TO RELATIVELY LOW LEVELS NON-MEASURABLE SPRINKLES SEEM JUST AS LIKELY AS MEASURABLE RAINFALL ESPECIALLY INLAND. THE WEDGE STARTS TO BREAK DOWN ON TUESDAY AND THE UPPER PATTERN WILL REALLY BE AMPLIFYING. THIS WILL CERTAINLY LEAD TO A MILDER AFTERNOON BUT THE INCREASED MOISTURE ADVECTION WILL KEEP THE SKY CLOUDY. RAIN CHANCES WILL ALSO INCREASE FAIRLY RAPIDLY...MORE-SO FROM MOISTURE ADVECTION RATHER THAN FORCING LEADING TO ASCENT. IN FACT IN SUCH A SITUATION MODELS ARE OFTEN A BIT FAST ON ADVECTING MEASURABLE RAINFALL AND SO THERE MAY BE A FEW RAIN-FREE HOURS EARLY TUESDAY. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 3 AM SUNDAY...WEDNESDAY PROBABLY REPRESENTS THE BEST RAIN CHANCES THAT THE AREA HAS SEEN AND POSSIBLY WILL SEE FOR QUITE SOME TIME. HIGHLY AMPLIFIED PATTERN TO DRIVE A COLD FRONT THROUGH BY WEDNESDAY NIGHT. THE AMPLITUDE OF THE SYSTEM WILL BE SUCH THAT IT WILL SCOOP UP PLENTY OF GULF MOISTURE. IN THE WAKE OF THIS SYSTEM CHRISTMAS IS SHAPING UP TO BE RATHER BRISK AND COOLER BUT WILL AT LEAST FEATURE A RETURN OF SUNSHINE WHICH BY THEN WILL HAVE BEEN ABSENT FOR SEVERAL DAYS. THIS COOL HIGH THEN WEAKENS AND MOVES INTO THE REGION BY FRIDAY WHICH SHOULD SHUT OFF THE COOL ADVECTION. SATURDAY MAY BE EITHER SEASONABLE OR A FEW DEGREES WARMER AS ANOTHER COLD FRONT APPROACHES FROM THE NW. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 18Z...SCT-BKN LOW/MID-LEVEL CLOUDS THIS AFTERNOON WITH THE MOST PERSISTENT MID-LEVEL CIGS AT THE COASTAL TERMINALS. A BIT OF LIGHT RAIN IS MOVING NE NEAR THE COASTAL TERMINALS. WINDS ARE NE AROUND 9 KT. EXPECT LOW-MID VFR CIGS THIS AFTERNOON. PERIODS OF LIGHT RAIN CAN BE EXPECTED THIS EVENING AND OVERNIGHT AS A LOW PRESSURE AREA MOVES NE JUST OFFSHORE. AS THE COASTAL TROUGH MOVES SLIGHTLY CLOSER TO THE COASTAL TERMINALS...AND AS THE RAIN FALLS INTO THE COLD AIR NEAR THE SURFACE...CIGS/VSBYS WILL EVENTUALLY LOWER TO MVFR THIS EVENING AND TO IFR/LIFR BY MIDNIGHT. IFR/LIFR CONDITIONS WILL LIKELY PERSIST THROUGH THE REMAINDER OF THE TAF VALID PERIOD. EXTENDED OUTLOOK...RAIN LIKELY WITH IFR CIGS IMPROVING TO MVFR MON. SHOWERS/TEMPO MVFR TUE. WED RAIN/MVFR/IFR AND GUSTY WINDS AHEAD OF A COLD FRONT. MVFR THU BECOMING VFR WITH GUSTY NW WINDS. VFR FRI. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 130 PM SUNDAY...SCEC WILL CONTINUE FOR ALL ZONES THROUGH 3 BUT PLAN TO UPGRADE TO A SCA FOR ALL WATERS FOR THE OVERNIGHT PERIOD. GRADIENT WILL REMAIN MORE OR LESS UNCHANGED FOR MUCH OF WITH HIGH BUILDING DOWN THE COAST AS SURFACE LOW MOVES NORTH. BUOY 41013 IS ALREADY REPORTING 7 FT SEAS AND PROLONGED NORTHEAST FLOW IN THE 15 TO 20 KT RANGE SHOULD PUSH SEAS OVER 6 FT INTO THE OUTER EDGES OF THE MARINE ZONES. THIS EVENT WILL BE ON THE MARGINAL SIDE WITH CONDITIONS NO WHERE NEAR SCA THRESHOLDS CLOSE TO THE COAST...ESPECIALLY IN AMZ252. SEAS WILL RANGE FROM 4 TO 6 FT WELL AWAY FROM SHORE AND IN WATERS EXPOSED TO EXTENDED NORTHEAST FETCH WHILE WATERS CLOSE TO SHORE AND SHELTERED FROM NORTHEAST FLOW WILL RUN 1 TO 3 FT. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 3 AM SUNDAY...NE WINDS ON MONDAY WILL VEER SLIGHTLY ON TUESDAY AS A WEDGE OF HIGH PRESSURE OVER LAND WEAKENS. MONDAY WILL ALSO BRING ABOUT 5KT OF HIGHER WIND SPEED AT TIMES AS LOW PRESSURE MOVES UP ALONG A FRONTAL BOUNDARY OFF THE COAST. TUESDAY NIGHT THE FLOW WILL VEER AGAIN MORE DECIDEDLY AS THE APPROACH OF A COLD FRONT AND DYNAMIC UPPER SYSTEM APPROACH. WINDS WILL ALSO INCREASE LATE TUESDAY NIGHT ABOVE THE BOUNDARY LAYER...THOUGH COOL SSTS MAY TEMPER THE INCREASE IN WINDS SOMEWHAT AT THE SURFACE EARLY IN THE NIGHT. THIS EFFECT HOWEVER WILL BE OVERWHELMED TOWARDS THE END OF THE PERIOD BY THE OVERALL INCREASE IN MOMENTUM OF THE ATMOSPHERE AND A SMALL CRAFT ADVISORY WILL BE NEEDED. LONG TERM /WEDNESDAY THROUGH THURSDAY/... AS OF 3 AM SUNDAY...STRONGLY FORCED COLD FRONT APPROACHING ON WEDNESDAY AND SOLID SMALL CRAFT ADVISORY IN EFFECT. SUSTAINED GALE FORCED WINDS WILL BE LURKING NOT TOO FAR ABOVE THE SURFACE AND AS THE EVENT GETS CLOSER ATTENTION WILL SHIFT TO HOW DEEP MOMENTUM TRANSFER OVER THE COOL SSTS WILL BE. SHOULD MIXING OVERWHELM THE STABILIZING EFFECT OF THE COOL WATERS THEN WINDS MAY BE HIGHER THAN CURRENTLY FORECAST, ALTHOUGH SURFACE GALES STILL SEEM RATHER UNLIKELY. SHARP VEER WED NIGHT WITH FROPA AND BOUNDARY LAYER WIND SPEEDS DROP OFF CONSIDERABLY BY THURSDAY.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...MBB NEAR TERM...III SHORT TERM...MBB LONG TERM...MBB AVIATION...MRR

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