FXUS62 KILM 160531
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1230 AM EST WED DEC 16 2009
.SYNOPSIS...
ARCTIC HIGH PRESSURE WILL BUILD ACROSS THE AREA THROUGH FRIDAY.
A STORM SYSTEM WILL SKIRT THE SOUTHERN SIDE OF THIS HIGH FRIDAY
NIGHT INTO SATURDAY AND SHOULD BRING A VERY CHILLY RAIN AND A SMALL
CHANCE FOR SOME LIGHT WINTRY MIXED PRECIPITATION WELL INLAND. CHILLY
HIGH PRESSURE WILL THEN REASSERT ITSELF FOR THE REMAINDER OF THE
FORECAST PERIOD INTO NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
AS OF 9 PM TUESDAY...AT THE MOMENT...LATEST SFC ANALYSIS PLACES THE
COLD FRONT BETWEEN FLORENCE AND ELIZABETHTOWN. EXPECT GUSTY NW-N
WINDS...10 TO 15 MPH WITH GUSTS TO 20 MPH IMMEDIATELY AND UP TO A
FEW HRS AFTER THE CFP. NOTICEABLE DRYING WILL ALSO IMMEDIATELY
FOLLOW AS INDICATIVE OF THE LOWER DEWPOINT PUSH WITH LOWER 60S AT
THE MOMENT AHEAD OF THE FRONT...AND WHICH HAVE ALREADY DECREASED TO
AROUND 50 ACROSS THE NW PORTIONS OF THE ILM CWA. SKIES DURING THE
POST FRONTAL TIME LINE THROUGH DAYBREAK WEDNESDAY WILL OBSERVE
PLENTY OF CI AND WILL THERE4 NOT ENTIRELY CLEAR OUT SKIES OVERNIGHT
INTO WEDNESDAY...WITH THE LATEST NAMBUFR TIME HT AND SOUNDINGS
INDICATIVE OF THIS. CURRENT FCST OF OVERNIGHT MINS AND THE HRLY TEMP
PROGRESSION ACROSS THE ILM CWA LOOKING AOK WITH AN OCCASIONAL TWEAK
NEEDED TO ACCOMMODATE SLOWER/FASTER SURGES. THE SAME HOLDS TRUE WITH
THE DRIER AIR...IE THE LOWER DEW POINT PROGRESSION.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 PM TUESDAY...DRY WEST-NW MID LEVEL FLOW ON WEDNESDAY AS
STRONG 1030MB SURFACE HIGH BUILDS IN FROM THE NORTH. COLD AIR
ADVECTION WILL PUSH H850 TEMPERATURES DOWN TO WITHIN A DEGREE OR
TWO OF 0C YIELDING HIGHS IN THE LOW/MID 50S IN A WELL MIXED
COLUMN. VERY GOOD RADIATIONAL COOLING CONDITIONS WEDNESDAY NIGHT
AS SURFACE HIGH BUILDS IN CLOSE ENOUGH TO COLLAPSE WINDS. SHOULD A
FEW MPH BREEZE KEEP UP THEN LOWS GENERALLY IN THE UPPER 20
EXPECTED...LOW 30S COAST. A FEW HOURS OF CALM WINDS COULD LEAD TO
COLDER READINGS. COLD AIR ADVECTION EITHER TO SHUT DOWN AND GO
NEUTRAL THURSDAY OR EVEN TURN VERY WEAKLY WARM. THIS WILL BE
NEGATED HOWEVER BY THE HIGH BEING RIDGED ENOUGH INTO THE FORECAST
AREA TO CAUSE SHALLOWER MIXING THAN WEDNESDAY AND HIGHS WILL ONCE
AGAIN BE MIRED IN THE LOW TO MID 50S. THE WEAK WARM ADVECTION
PAIRED WITH GRADUALLY INCREASING CLOUDS THURSDAY NIGHT WILL BRING
LOW TEMPERATURES A CATEGORY OR MORE MILDER THAN WEDNESDAY NIGHT
WITH LOW 30S GENERALLY EXPECTED.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 3 PM TUESDAY...MAIN FORECAST CONCERN IS GULF COAST LOW AND ITS
IMPACT ON THE REGION FRI INTO SUN. FAIRLY GOOD AGREEMENT BETWEEN THE
ECMWF/GFS/CANADIAN WITH RESPECT TO PRESENCE OF THE LOW...BUT STILL A
LOT OF VARIANCE IN THE FINER DETAILS. THE OPERATIONAL GFS IS COLDER
THAN ITS ENSEMBLE MEMBERS...BY AS MUCH AS 20 DEGREES IN SOME CASES.
ALSO WORTH NOTING THAT THE CANADIAN/ECMWF ARE WARMER THAN THE GFS.
SO WHILE POPS HAVE BEEN INCREASED FRI NIGHT AND SAT HAVE NOT YET
MENTIONED ANY PRECIP TYPE OTHER THAN LIQUID. FROZEN PRECIP REMAINS A
POSSIBILITY...BUT THE LOCATION OF THE SURFACE HIGH TO THE NORTH IS
NOT FAVORABLE FOR KEEPING COLD/DRY LOW LEVEL AIR IN PLACE.
LOW EXITS OFF TO THE NORTHEAST SAT NIGHT INTO SUN WITH GFS SHOWING
IMPRESSIVE SHORTWAVE TROF MOVING ACROSS THE AREA EARLY SUN. IF THIS
FEATURE PANS OUT...IT WOULD LIKELY PRODUCE SOME FLURRIES AS IT
PASSES. HOWEVER...THIS FEATURE IS NOT PRESENT IN THE LATEST ECMWF OR
CANADIAN AND IS BEING IGNORED FOR NOW.
TEMPERATURES WILL REMAIN BELOW TO WELL BELOW CLIMO THROUGH THE
PERIOD...HOWEVER FORECAST IS NOT QUITE AS COLD AS THE LATEST
EXTENDED MOS GUIDANCE.
&&
.AVIATION /06Z WEDNESDAY THROUGH SATURDAY/...
COLD FRONT WELL E OF THE AREA AT 05Z. ARCTIC HIGH PRESSURE WILL
CONTINUE TO BUILD ACROSS THE AREA. VFR CONDITIONS THROUGH THE TAF
PERIOD. GUSTY N WINDS WILL BE STRONGEST THROUGH WED MORNING AND THEN
BEGIN TO DIMINISH AS THE CENTER OF STRONG HIGH PRESSURE NEARS.
EXTENDED OUTLOOK...VFR THROUGH FRIDAY. CHANCE OF IFR WITH RAIN
SATURDAY.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 9 PM TUESDAY...THE OVERNIGHTS DILEMMA IS 2 FOLD. THE TIMING
OF THE COLD FRONTAL PASSAGE...FOLLOWED BY THE WIND SHIFT AND THE
STRENGTH OF THE WINDS. HAVE GONE WITH THE NAMS CFP PORTRAYAL BETWEEN
03Z-05Z WHERE A WIND SHIFT WILL OCCUR...FROM 270ISH TO 330ISH.
AFTER 05Z...EXCELLENT COLD AIR ADVECTION...DRIER AIR...AND A
TIGHTENED SFC PRESSURE GRADIENT WILL ALL COMBINE TO PRODUCE 360ISH
WIND DIRECTIONS WITH 20-30 KT SPEEDS AND OCCASIONAL GUSTS OVER 35 KT
...ESPECIALLY ACROSS THOSE WARMER SST WATERS. HAVE UPPED THE SEAS BY
A FOOT ACROSS THE NORTHERLY FETCH DIRECTION AREAS...BUT WILL STILL
LIMIT OVERALL SEA HEIGHTS DUE TO THE MOSTLY OFFSHORE DIRECTION
WITHIN THE WIND TRAJECTORY.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 PM TUESDAY...MODERATELY PINCHED GRADIENT IN STRONG COLD
AIR ADVECTION REGIME ON WEDNESDAY. THE BEST SURFACE-BASED MIXING
WILL LAG IN TIME BEHIND THE STRONGEST LOW LEVEL WIND FIELDS. THIS
IS CASTING SOME UNCERTAINTY REGARDING THE CURRENT SMALL CRAFT
ADVISORY AS TO WHETHER OR NOT 25 KT AND/OR 6 FT WILL MATERIALIZE
FOR LONG INTO THE PERIOD. INITIAL IMPRESSION IS THAT THE ADVISORY
WILL BE ABLE TO BE CANCELLED EARLY. IN FACT BOTH NEWEST WNA
GUIDANCE AND LOCAL SWAN DATA SHOW NO 6 FT SEAS AS OF 12Z WED. IN
LIGHT OF SOME UNCERTAINTIES THOUGH...HAVE NOT MESSED WITH THE
EXPIRATION TIME OF 20Z AT THIS TIME. HIGH PRESSURE BUILDS IN MUCH
CLOSER TO THE FORECAST AREA FOR THE REMAINDER OF THE PD. THIS WILL
KEEP N TO NE WINDS VERY LIGHT AS SEAS CONTINUE TO SUBSIDE.
LONG TERM /FRIDAY THROUGH SUNDAY/...
AS OF 3 PM TUESDAY...LOW PRESSURE OVER THE NORTHEAST GULF OF
MEXICO WILL MOVE ACROSS NORTHERN FL FRI NIGHT AND UP THE SOUTHEAST
COAST SAT INTO SUN. TRACK OF LOW WILL DETERMINE WIND DIRECTION
OVER THE NEARSHORE WATERS...AND IT APPEARS THAT RIGHT NOW THE LOW
WILL PASS EAST OF THE WATERS. THIS WOULD RESULT IN PROLONGED
STRONG NORTHEAST FLOW AND LIKELY REQUIRE AT LEAST AN SCA. SPEEDS
MAY OR MAY NOT EXCEED 25 KT...BUT EXTENDED PERIOD WITH NORTHEAST
WINDS WILL PUSH SEAS OVER 6 FT ACROSS ANY UNSHELTERED WATERS.
STRENGTH OF LOW AS IT PASSES WILL DETERMINE IF GALE WATCH/WARNING
IS NEEDED...AND IT CERTAINLY SEEMS POSSIBLE.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 3 PM EST WEDNESDAY FOR
AMZ250-252-254-256.
&&
$$
NEAR TERM...DCH
SHORT TERM...MBB
LONG TERM...III
AVIATION...RJD/HDL
