FXUS62 KILM 230147
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
847 PM EST TUE DEC 22 2009

.SYNOPSIS...
FAIR AND COOL WEATHER WILL CONTINUE THROUGH CHRISTMAS EVE AS HIGH 
PRESSURE AND A DRY AIR MASS HOLD OVER THE REGION. PRECIPITATION 
CHANCES WILL INCREASE INTO CHRISTMAS DAY...ALONG WITH A GRADUAL 
WARMING TREND...AS A FRONT APPROACHES FROM THE SOUTHWEST. A 
CLEARING...COOLING AND DRYING TREND IS EXPECTED IN THE WAKE OF THIS 
SYSTEM HEADING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 9 PM TUESDAY...1035 MB HIGH PRESSURE OVER THE SOUTHERN CANADA  
EXTENDS A RIDGE AXIS SOUTHWARD TO A SECONDARY HIGH (1025 MB) 
ANALYZED OVER EASTERN NORTH CAROLINA. TEMPERATURES FELL OF A 
FIGURATIVE CLIFF THIS EVENING AS THE SUN SET...AND WE ARE ALREADY 
WITHIN 5-7 DEGREES OF FORECAST LOWS IN MANY LOCATIONS. FORECAST 
SOUNDINGS FROM THE NAM AND GFS ARE IN EXCELLENT AGREEMENT WITH 1000 
FT TEMPERATURES FALLING TO AROUND 40 DEGREES F BY DAYBREAK. IN 
SIMILAR SITUATIONS IN THE PAST (MAINLY CLEAR SKIES...NEUTRAL THERMAL 
ADVECTION...LIGHT LOW-LEVEL WINDS...AND DRY AIR) THIS TRANSLATED TO 
LOWS 13 DEGREES BELOW 1000 FT TEMPS...OR UPPER 20S FOR TONIGHT. THIS 
IS IN AGREEMENT WITH THE 12Z NAM MOS AND IS ONLY SLIGHTLY BELOW THE 
12 AND 18Z RUNS OF THE GFS MOS. WE HAVE TWEAKED LOWS DOWN 1-2 
DEGREES IN MOST LOCATIONS BUT OTHERWISE THE FORECAST REMAINS 
UNCHANGED. SOME SWAMPY AREAS OF SOUTHEAST NC WITH ORGANIC 'MUCK' 
SOIL TYPE COULD HAVE LOWS AROUND 20 DEGREES TONIGHT.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 226 PM TUESDAY...WEDNESDAY AND JUST ABOUT ALL OF THURSDAY
WILL FEATURE VERY DRY AIR BETWEEN 925 AND 600 MILLIBARS...THUS
LITTLE IN THE WAY OF SENSIBLE WEATHER IS EXPECTED ASIDE FROM
OCCASIONAL CIRRO-STRATUS OVERHEAD IN GENERALLY A WESTERLY FLOW
ALOFT...WITH SURFACE HIGH PRESSURE WEDGED INTO THE REGION ALONG
THE LEE OF THE APPALACHIANS PRODUCING LOW LEVEL NE FLOW BOTH DAYS.
THE WEDGE WILL BE A LONG WAY FROM EROSION THROUGH THURSDAY SO 
MAXIMUM TEMPS BOTH DAYS SHOULD HOLD PRIMARILY IN THE 50S. 

CHANGES THURSDAY EVENING BEGIN TO IMPACT SENSIBLE WEATHER...AS
INCREASING AND VEERING ONSHORE WIND FLOW SETS UP DEVELOPING MOISTURE
CONVERGENCE OFFSHORE...WHILE ISENTROPIC LIFT AND INCREASING COLUMN
MOISTURE BEGIN TO EXPAND FROM SW TO NE OVER THE AREA AHEAD OF A
FRONTAL SYSTEM EMERGING FROM THE CENTRAL GULF STATES. MOST OF THE
PRECIPITATION IF ANY THOUGH THURSDAY DAYBREAK WILL BE CONFINED
AFTER MIDNIGHT WEDNESDAY...AND WILL LIKELY BE SPATIALLY CONFINED
ALONG THE COAST IN LIGHT SHOWERS FROM THE LOW LEVEL CONVERGENCE.
MEANWHILE ISENTROPIC RAINS WILL BE INCREASING IN AERIAL COVERAGE
AFTER DAYBREAK THURSDAY ASSOCIATED WITH AN APPROACHING WARM FRONT
GLIDING OVER THE TENACIOUS WEDGE...SATURATING THE COLUMN TOP-DOWN.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 226 PM TUESDAY...PRECIPITATION PROBABLY ONGOING AT THE START 
OF THE PD. WARM FRONT PUSHING INTO SOUTHERN ZONES FRIDAY MORNING 
MEETING SOME RESISTANCE BY SURFACE WEDGE BEING RE-ENFORCED BY THE 
PRECIP. MEANWHILE 40-50KT 850MB JET BEGINS TO OVERRUN THE SURFACE 
LAYER. GUIDANCE NOT IN VERY GOOD AGREEMENT AS TO WHETHER OR NOT THE 
WEDGE BREAKS BY MIDDAY. THE WRF IS SLOWER...SHOWING ONLY A MINOR 
EROSION OF THE WEDGE BY 00Z WHEREAS THE GFS IS QUICKER AND MORE 
AGGRESSIVE. USUALLY GUIDANCE IS TOO QUICK IN DOING SO AND THUS THE 
WRF IS PREFERRED. GFS IS ALSO QUICKER IN TAKING THE PLUME OF DEEP 
MOISTURE OFFSHORE. HOW THESE INGREDIENTS ALL COME TOGETHER WILL 
DICTATE WHETHER OR NOT A SEVERE WEATHER THREAT MATERIALIZES AND 
RIGHT NOW ITS JUST TOO EARLY TO TELL. RAINFALL TOTALS MAY BE 
APPRECIABLE THOUGH WITH EARLY INDICATIONS THAT UP TO AN INCH OR SO 
MAY FALL. FORECAST HIGH TEMPERATURE ON FRIDAY ALSO VERY MUCH HINGING 
UPON THE EROSION OF THE WEDGE. RIGHT NOW STILL LIKE THE WARM 
ADVERTISED TEMPS IN THE LOW 60S EVEN THOUGH THEY MAY NOT COME TIL 
AFTER DARK AND MOST OF THE DAYTIME HOURS ARE IN THE 40S AND 50S. 
SATURDAY THROUGH MONDAY WILL BRING A DRY WSW MID LEVEL FLOW AROUND 
GREAT LAKES VORTEX. CAA TEMPERED BY THE LOW AMPLITUDE BUT STILL 
ENOUGH TO KEEP TEMPS BELOW CLIMO...A FEW DEGREES BY DAY AND ABOUT A 
CATEGORY EACH NIGHT. TROUGH FINALLY BELLIES UNDER
THE VORTEX MONDAY NIGHT CAUSING IT TO OPEN UP AND LIFT EASTWARD. 
THIS WOULD STRENGTHEN CAA LOCALLY FOR A CHILLIER TUESDAY.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
SURFACE RIDGE WILL CONTINUE TO DOMINATE THE WEATHER WITH 
PREDOMINATELY VFR CONDITIONS. SOME LIGHT FOG IS POSSIBLE AROUND 
SUNRISE...WITH GOOD RADIATIONAL COOLING CONDITIONS. A LIGHT 
NORTHEAST FLOW WILL BECOME EASTERLY AT THE MYRTLES WITH THE MARINE 
LAYER. 

EXTENDED OUTLOOK...HIGH CONFIDENCE IN VFR WEDNESDAY EVENING. 
INCREASING CONFIDENCE IN PERIODS OF IFR LATE THURSDAY AND FRIDAY 
WITH RAIN AND LOW CEILINGS. VFR SATURDAY.

&&

.MARINE...

NEAR TERM /THROUGH TONIGHT/...
AS OF 9 PM TUESDAY...A SURFACE HIGH OVER SOUTHERN CANADA EXTENDS A 
RIDGE AXIS DOWN TO A SECONDARY CENTER OVER EASTERN NORTH CAROLINA. 
PRESSURES FALL OFF TO THE EAST OVER THE WARMER ATLANTIC WATERS...AND 
WE ARE LEFT WITH A STEADY NORTH WIND OVER THE COASTAL WATERS. AS 
PRESSURES RISE OVER THE LANDMASS DUE TO NOCTURNAL COOLING WE SHOULD 
SEE THE PRESSURE GRADIENT TIGHTEN ALONG THE COAST WITH A MODERATE 
NOCTURNAL SURGE OF NORTHERLY WINDS. WIND SPEEDS ARE CURRENTLY AROUND 
10 KNOTS...AND SHOULD INCREASE TO 12-15 KNOTS AFTER 2 AM. THIS IS 
PERFECTLY IN LINE WITH PREVIOUS FORECASTS AND NO CHANGES ARE PLANNED.

REPORTS FROM BUOYS SHOW SEAS AVERAGING 2 FT WITH A FEW 1 FT REPORTS 
AT NEARSHORE LOCATIONS. THIS MAY BUILD TOWARD 3 FT OUT BEYOND 10 
MILES FROM SHORE LATE WHEN WIND SPEEDS INCREASE.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 226 PM TUESDAY...THE MAIN MARINE WEATHER THEME FOR THIS TIME
PERIOD WILL BE AN INCREASING NE WIND FLOW WEDNESDAY AND THURSDAY. 
WEDNESDAY LOOKS OK IN LIGHT TO MODERATE NE WIND SPEEDS...BUT BY LATE
WEDNESDAY NIGHT AND ESPECIALLY INTO THURSDAY...SMALL CRAFT ADVISORY
SPEEDS WILL BE APPROACHED. BY THURSDAY...SEAS WILL RESPOND AND COULD
REACH WAVE HEIGHTS OF 4-7 FEET...HIGHEST OFFSHORE THURSDAY AFTERNOON.
PRIMARY WAVE DIRECTION AT PEAK OF SEAS LOOKS TO BE FROM ALMOST DUE 
EAST WITH DOMINANT WAVE PERIODS CENTERED AT 6-7 SECONDS THEN...MAKING
FOR MODERATELY STEEP SEAS THURSDAY AND THURSDAY NIGHT. IT APPEARS A
SMALL CRAFT ADVISORY WILL BE NEEDED SOMETIME THURSDAY. 

LONG TERM /FRIDAY THROUGH SUNDAY/... 
AS OF 226 PM TUESDAY...SMALL CRAFT ADVISORY LIKELY TO START THE 
PERIOD. STRONG GRADIENT WINDS ASSOCIATED WITH COLD AIR SURFACE WEDGE 
AND DEVELOPING SURFACE TROUGH ALONG THE COAST. PINNING DOWN WIND 
DIRECTION BEING MADE PROBLEMATIC AS THE WEDGE SHOULD BREAK DOWN AT 
SOME POINT AND YIELD A SWITCH FROM STRONG NE TO STRONG SE OR EVEN S 
WINDS. THE TURN TO ONSHORE SHOULD ALLOW LARGER WIND WAVES TO BE 
ADVECTED INTO THE FORECAST WATERS BUT IT IS UNCERTAIN AS TO WHETHER 
THAT OCCURS AROUND MIDDAY OR NOT TIL FRIDAY NIGHT. CONVERSELY THERE 
IS BETTER CONFIDENCE IN A COLD FRONTAL PASSAGE BY 06Z SATURDAY 
MORNING WHEN WEST WINDS WILL SPREAD ACROSS THE WATERS. FLOW JUST 
ABOVE THE SURFACE REMAINS SOUTHWESTERLY HOWEVER AND THAT SHOULD 
PREVENT STRONG GUSTINESS. HIGH PRESSURE BUILDING IN FROM THE 
WEST-SOUTHWEST WILL KEEP A WESTERLY WIND IN THE FORECAST THAT WILL 
TEND TO DIMINISH TOWARDS THE END OF THE PERIOD AS THE CENTER OF THE 
RIDGE APPROACHES.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...

SC...NONE.
NC...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS...MJC
NEAR TERM...TRA
SHORT TERM...MJC
LONG TERM...MBB
AVIATION...43