Issued by NWS Wilmington, NC
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS62 KILM 212335 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 635 PM EST SAT NOV 21 2009 .SYNOPSIS...-- Changed Discussion --INCREASING MOISTURE FROM THE GULF OF MEXICO WILL ENTER THE CAROLINAS SUNDAY INTO MONDAY WITH WIDESPREAD RAIN EXPECTED. A BRIEF WARM UP IS EXPECTED MID WEEK. A STRONG COLD FRONT THURSDAY WILL USHER IN SOME COLDER AIR FOR NEXT WEEKEND.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... AS OF 3 PM SATURDAY...MULTI-LAYERED CLOUDINESS IS INCREASING OVER THE CAROLINAS FROM THE SOUTH AS AN UPPER TROUGH OVER LOUISIANA ADVECTS GULF MOISTURE INTO THE AREA. ASIDE FROM SOME CLOUDS TRAPPED UNDER A SUBSIDENCE INVERSION AROUND 800 MB...THE BULK OF THIS MOISTURE IS AT AND ABOVE THE 500 MB LEVEL CURRENTLY. MODELS SHOW THE DEPTH OF MOISTURE INCREASING THROUGH THE NIGHT AS SURFACE LOW PRESSURE NEAR THE MOUTH OF THE MISSISSIPPI RIVER MOVES INTO SOUTHERN ALABAMA LATE. THE 12Z RUNS OF THE NAM AND GFS SHOW MEASURABLE PRECIPITATION SHOULD HOLD OFF UNTIL DURING THE DAY SUNDAY. THIS IDEA IS SUPPORTED BY RECENT RADAR COMPOSITES SHOWING THE FRONT EDGE OF THE PRECIPITATION EXTENDING NO FARTHER EAST THAN BILOXI MS CURRENTLY. LOW TEMPERATURES TONIGHT PRESENT AN INTERESTING PROBLEM. MOS GUIDANCE SUGGESTS WE WILL REACH THE MID 40S IN MOST AREAS WHILE THE RAW NAM AND GFS MODELS SHOW LOWS IN THE 50-55 RANGE. THE 12Z CANADIAN IS IN BETWEEN THESE TWO EXTREMES. INSULATING INFLUENCE FROM CLOUDS WILL BE PARTIALLY OFFSET BY WEAK COOL ADVECTION BELOW 850 MB. OUR FORECAST IS FOR UPPER 40S INLAND AND AROUND 50 AT THE COAST. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... AS OF 3 PM SATURDAY...NEARLY ALL OF THE GUIDANCE HAS DELAYED ARRIVAL OF THE PRECIP ON SUN...WITH LIGHT PRECIP NOW SPREADING OVER THE SOUTHWEST PORTIONS OF THE FORECAST AREA SUN MORNING. LIGHT PRECIP WILL CONTINUE TO SPREAD NORTH DURING THE AFTERNOON HOURS...COVERING ALL OF THE AREA BY LATE AFTERNOON. HEAVIEST RAIN ARRIVES SUN NIGHT INTO MON WITH INCREASE IN ISENTROPIC LIFT. DELAYED ARRIVAL OF CATEGORICAL POPS TO ACCOUNT FOR SLOWER EVOLUTION OF THE SYSTEM. LOW PRESSURE DEVELOPING OFF THE GA/SC COAST SUN NIGHT WILL TRACK NORTHEAST...PASSING JUST EAST OF CAPE FEAR ON MON. FORECAST SOUNDINGS AND CROSS SECTIONS SHOW PLENTY OF DRY AIR ABOVE 850 MB SPREADING OVER THE AREA MON MORNING. SUBSIDENCE IN THE WAKE OF EXITING LOW AND UPPER LEVEL SHORT WAVE COMBINED WITH DRY AIR WILL BRING AN END TO MEASURABLE PRECIP. HAVE EXTENDED HIGHER POPS INTO MON...BUT THINK MOST OF THE ACTION WILL BE OVER BY LATE MORNING. AREA REMAINS UNDER THE INFLUENCE OF THE WEDGE FOR THE REMAINDER OF MON AND THROUGH MON NIGHT WITH SOUTHWEST FLOW JUST ABOVE THE SURFACE. WEAK OVERRUNNING WILL KEEP LOW CLOUD COVER IN PLACE WITH SOME PATCHES OF DRIZZLE THROUGH THE AFTERNOON AND OVERNIGHT. AT THIS POINT IT DOES NOT LOOK LIKE THIS BATCH OF PRECIP WILL MEASURE. TEMPERATURES WILL REMAIN BELOW CLIMO DURING THE DAY...THOUGH COASTAL SITE MAY FLIRT WITH CLIMO ON MON DEPENDING ON HOW CLOSE THE LOW GETS TO THE COAST. CLOUD COVER AND MOISTURE WILL HELP KEEP OVERNIGHT LOWS ABOVE TO WELL ABOVE CLIMO BOTH NIGHT. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 3 PM SATURDAY...WEAK HIGH PRESSURE WILL BE IN PLACE ACROSS COASTAL CAROLINAS TUES THROUGH WED. PCP WATER VALUES WILL BE DOWN CLOSER TO A HALF INCH WITH PLENTY OF DRY AIR ALOFT...BUT MOISTURE PROFILES CONTINUE TO SHOW A VERY SHALLOW LAYER OF MOISTURE HOLDING ON THROUGH WED MORNING. WITH SHALLOW COOL AIR IN PLACE AND DECENT SUBSIDENCE AND DRY AIR IN PLACE ABOVE WILL HOLD ON TO LOW CLOUDS THROUGH MUCH OF TUES. PATTERN REMAINS FAIRLY FLAT IN THE MID TO UPPER LEVELS THROUGH MID WEEK UNTIL THURS INTO FRI WHEN MORE SIGNIFICANT TROUGH APPROACHES AND MOVES THROUGH. DRIER WESTERLY FLOW TAKES OVER THROUGH MID WEEK. A COLD FRONT OR PRE FRONTAL TROUGH MOVES INTO THE COASTAL CAROLINAS LATE WED INTO THURS AS COASTAL TROUGH DEVELOPS OFF THE SOUTHEAST COAST. LOOKING AT MID TO UPPER LEVELS..MAY SEE A SHORTWAVE MOVE THROUGH LONGER WAVE H5 TROUGH GIVING PUSH OF DRIER AIR INITIALLY...BUT THEN WINDS BACK ON THURS TAPPING INTO A LITTLE GULF MOISTURE. THIS REMAINS MAINLY OFF SHORE...BUT MAY BE JUST CLOSE ENOUGH TO PRODUCE SOME PCP FOR THURS AFTN. THEREFORE WILL HOLD ONTO LOW END POPS FOR THURS. THEN PLENTY OF DRY AIR WILL MOVE IN BEHIND STRONG COLD FRONT LATE THURS INTO FRI. BY FRI HIGH AMPLITUDE MID TO UPPER TROUGH SWINGS ACROSS THE EAST COAST SCOURING OUT ALL THE WEATHER AND BRINGING DRY AND COOL HIGH PRESSURE FOR THE WEEKEND. MID TO UPPER LEVEL FLOW WILL REMAIN MORE WESTERLY THROUGH FRI NIGHT BUT BY SAT AFTN SHOULD GET STRONGER AND DEEPER LAYER COLD AIR STREAMING INTO THE CAROLINAS IN A DEEP LAYER NW FLOW AS H5 TROUGH CLEARS THE COAST. EXPECT DRY BUT COLD WEATHER THROUGH THE WEEKEND. TEMPS WILL HOLD AROUND NORMAL OR ABOVE WITH SUNNIEST AND WARMEST DAY EXPECTED ON WED. BY LATE THURS INTO FRI COLD AND DRY HIGH PRESSURE WILL BUILD IN BEHIND STRONG COLD FRONTAL PASSAGE. 850 TEMPS DROP BELOW 0C BY FRI EVENING AND WITH PLENTY OF DRY AIR IN PLACE...EXPECT TEMPS DOWN IN THE 30S FOR OVERNIGHT LOWS BOTH FRI NIGHT AND SAT NIGHT. DAY TIME HIGHS FRI AND SAT WILL BE BELOW NORMAL...BELOW 60 INLAND TO JUST NEAR 60 ALONG THE COAST. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...-- Changed Discussion --SURFACE HIGH PRESSURE OVER THE TERMINALS IS PROVIDING A DRY NORTHEAST FLOW IN THE LOW LEVELS. THIS IS EXPECTED TO CONTINUE THROUGH SUNRISE RESULTING IN VFR CONDITIONS. MOISTURE NEAR AN INVERSION AROUND 5K COULD RESULT IN AT LEAST SCATTERED TO TEMPO CEILINGS AT THAT LEVEL OVERNIGHT. OTHERWISE OVERNIGHT...SCATTERED MID LEVEL CLOUDS AND BROKEN HIGH LEVEL CLOUDS ARE EXPECTED. AFTER SUNRISE VFR IS EXPECTED THROUGH 18Z AT THE TERMINALS WITH MID LEVEL CEILINGS 8-12K DEVELOPING AS VIRGA OVERSPREADS THE TERMINALS FROM SOUTHWEST TO NORTHEAST. EVENTUALLY THE RAIN WILL DEVELOP CEILINGS 4-5K AS MOISTURE POOLS AT THE INVERSION LEVEL. AFTER 18Z SHOULD SEE A BETTER CHANCE OF MVFR CEILINGS DEVELOPING AS THE LOWER LEVELS CONTINUE TO MOISTEN UP. ALTHOUGH THERE IS A SLIGHT CHANCE OF IFR CEILINGS BY LATE AFTERNOON AT FLO/CRE/MYR...WIDESPREAD IFR CEILINGS SHOULD HOLD OFF UNTIL AFTER THIS TAF VALID PERIOD. EXTENDED OUTLOOK...WIDESPREAD IFR MONDAY. IFR DUE TO FOG POSSIBLE TUESDAY AND WEDNESDAY MORNINGS.-- End Changed Discussion --&& .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 3 PM SATURDAY...A STATIONARY FRONT NEARLY 500 MILES OFF THE CAROLINA COAST DEVELOPED A WEAK LOW PRESSURE CENTER EARLY THIS MORNING. THIS LOW IS STILL OUT THERE ALTHOUGH ITS INFLUENCE ON OUR WEATHER IS BECOMING SMALLER. ATTENTION IS NOW SHIFTING TO THE GULF COAST WHERE A NEW LOW IS DEVELOPING OVER COASTAL LOUISIANA. THIS LOW WILL MOVE EAST TO AROUND MOBILE AL BY DAYBREAK SUNDAY. THE PRESSURE GRADIENT BETWEEN THIS LOW AND HIGH PRESSURE OVER NEW ENGLAND AND THE EASTERN GREAT LAKES WILL KEEP A HEALTHY NE WIND BLOWING THROUGH THE NIGHT INTO SUNDAY. WIND SPEEDS SHOULD AVERAGE 15-20 KT WITH SOME 25 KT GUSTS POSSIBLE...ESPECIALLY IN THE FRYING PAN SHOALS VICINITY. OUTPUT FROM OUR LOCAL SWAN WAVE MODEL WAS ALMOST PERFECT ON INITIALIZATION AND WILL BE USED FOR THE FORECAST TONIGHT. A SMALL CRAFT ADVISORY WILL REMAIN POSTED FOR THE NC WATERS FOR 6 FT SEAS OUT BEYOND 15 MILES FROM SHORE. WE WILL ALSO KEEP AN ADVISORY GOING THROUGH THE EVENING SOUTH OF MURRELLS INLET UNTIL THE 6 FT SEAS DIE AWAY THERE. ANY SIGNIFICANT RAINFALL SHOULD HOLD OFF UNTIL SOMETIME DURING THE DAY SUNDAY. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 3 PM SATURDAY...NORTHEAST FLOW CONTINUES THROUGH THE PERIOD WITH SURFACE LOW PROGGED TO PASS EAST OF THE WATERS SUN NIGHT INTO MON. PINCHED GRADIENT ON SUN WILL KEEP WINDS AROUND 20 KT WITH SEAS 4 TO 6 FT INTO SUN NIGHT. STRONGEST WINDS AND HIGHEST SEAS WILL BE ACROSS NC WATERS...SO WILL CONTINUE SCA FOR ZONES 250 AND 252. WILL LIKELY NEED A SCEC FOR SC ZONES WHEN THE TIME COMES. GRADIENT RELAXES WHEN SURFACE LOW PASSES THE WATERS EARLY MON. HIGH PRESSURE CONTINUES TO RIDGE DOWN THE EAST COAST AS THE LOW MOVES OFF TO THE NORTHEAST ON MON...KEEPING LOW LEVEL FLOW OUT OF THE NORTH. LIGHTER WINDS...10 TO 15 KT MON AND MON NIGHT...AND A SLIGHT OFFSHORE COMPONENT WILL ALLOW SEAS TO FALL PRETTY QUICKLY...TO 2 TO 4 FT BY MON EVENING. LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 3 PM SATURDAY...WEAK HIGH PRESSURE OVER WATERS THROUGH MID WEEK WITH BENIGN WINDS AND SEAS EXPECTED. OVERALL EXPECT LIGHT OFF SHORE FLOW 10 KTS OR LESS THROUGH EARLY THURS WITH SEAS LESS THAN 3 FT. BY THURS AFTN GRADIENT MAY INCREASE AS COLD FRONT PUSHES INTO THE CAROLINAS FROM THE WEST AND COASTAL TROUGH DEVELOPS TO THE SOUTH. EXPECT WINDS AND SEAS TO INCREASE THROUGH LATE THURS INTO FRI AS COLD FRONT APPROACHES AND MOVES THROUGH. MAY SEE SEAS UP NEAR 4 TO 5 FT IN OUTER WATERS IN STRONGER WESTERLY FLOW THURS NIGHT INTO FRI MORNING. && .ILM WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --SC...NONE. NC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST MONDAY FOR AMZ250-252-256. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST MONDAY FOR AMZ254.-- End Changed Discussion --&& $$ NEAR TERM...TRA SHORT TERM...III LONG TERM...RGZ AVIATION...MRR
