FXUS62 KILM 250156
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
856 PM EST THU DEC 24 2009

.SYNOPSIS...
LOW PRESSURE WILL DEVELOP OVER THE DEEP SOUTH TONIGHT...AND BRING
WARMER TEMPERATURES AND SOAKING RAINS AS IT LIFTS NORTHEAST ACROSS 
THE CAROLINAS CHRISTMAS DAY AND NIGHT. HIGH PRESSURE WILL BUILD FROM 
THE NORTHWEST BEGINNING SATURDAY...WITH COLD TEMPERATURES RETURNING 
SUNDAY THROUGH WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
AS OF 8 PM THURSDAY...A WARM FRONT ACROSS THE OFFSHORE ATLANTIC 
WATERS IS FORECAST TO MOVE INLAND LATE TONIGHT...BRINGING A MUCH 
WARMER AND MORE HUMID AIRMASS TO THE COASTAL CAROLINAS. COLD...DRY 
HIGH PRESSURE CENTERED OVER THE MID-ATLANTIC STATES IS PUSHING AN 
ARCTIC AIRMASS INTO VIRGINIA AND NORTHWESTERN NORTH CAROLINA...BUT 
NORTHEASTERLY FLOW HERE AT THE COAST VEERS SOUTHEASTERLY BEHIND THE 
WARM FRONT WITH MODIFIED SUBTROPICAL AIR STREAMING IN. 

LOW TEMPERATURES HAVE LIKELY BEEN ACHIEVED ALREADY THIS EVENING IN 
MANY LOCATIONS...WITH A STEADY TEMPERATURE CURVE EXPECTED OVERNIGHT 
FOR INLAND AREAS. ALONG THE COAST TEMPERATURES SHOULD STEADILY RISE 
OVERNIGHT...PERHAPS REACHING 55-60 DEGREES BEFORE DAYBREAK CHRISTMAS 
MORNING. 

THE ONE POINT THE MODELS MAY BE STRUGGLING WITH THIS EVENING IS THE 
LARGE AREA OF MODERATE RAINFALL OVER GEORGIA. THE 12 AND 18Z RUNS OF 
THE NAM DID NOT GIVE THIS AREA SIGNIFICANT LIFT OR PRODUCE 
SUFFICIENT QPF GIVEN CURRENT RADAR AND OBSERVATIONAL TRENDS. THE 18Z 
GFS APPEARS TO HAVE A BETTER HANDLE ON THIS AREA OF PRECIPITATION... 
AND ALSO WITH THE AREA OF MAINLY LIGHT RAIN DEVELOPING ALONG THE 
SOUTH CAROLINA COAST. THE GFS SUGGESTS AREAS ALONG AND WEST OF I-95 
SHOULD RECEIVE MEASURABLE RAIN...MAINLY AFTER MIDNIGHT. POPS 
FOR KINGSTREE...FLORENCE...DARLINGTON AND BENNETTSVILLE HAVE BEEN 
RAISED TO THE LIKELY CATEGORY. ALONG THE CAPE FEAR COAST IT APPEARS 
THAT RAIN MAY HOLD OFF UNTIL AFTER DAYBREAK...SO POPS HAVE BEEN 
LOWERED SLIGHTLY HERE.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
AS OF 3 PM THURSDAY...MAIN CHALLENGE WILL BE THE QUESTION OF
SEVERE WEATHER AS LOW PRESSURE MOVES OUT OF THE DEEP SOUTH AND
CROSSES THE CAROLINAS ON AN INLAND TRACK ON FRIDAY. THIS WILL BE
A VERY DYNAMIC STORM SYSTEM WITH DIFLUENCE ALOFT...AND STRONG LOW-
LEVEL JETTING WITH 850MB WINDS PROGGED TO INCREASE TO 55-60
KT...PROVIDING STRONG DEEP-LAYER DIRECTIONAL AND SPEED SHEAR. SPC
DAY 2 OUTLOOK HAS THE ILM CWA AT THE NORTHERN END OF A SLIGHT RISK
AREA. BIGGEST NEGATIVE FOR SEVERE WEATHER IS THE LACK OF
INSTABILITY...AS CAPE IS NEGLIGIBLE AND LIFTED INDICES BARELY GO
NEGATIVE IF AT ALL. FOR NOW WILL JUST MENTION THE SLIGHT RISK IN
THE HWO...AS I BELIEVE THAT EVEN THUNDER WILL BE DIFFICULT TO COME
BY.

MINOR TIMING DIFFERENCES BETWEEN THE MODELS RAISE AN INTERESTING
QUESTION OF HOW DEEP INTO FRI EVENING POPS WILL NEED TO BE
CARRIED. GFS HAS THE LOW-LEVEL JET EXITING TO THE NORTHEAST BY
00Z...WHILE THE NAM IS A FEW HOURS SLOWER. FOR NOW WILL TAPER FRI
EVENING POPS FROM HIGH CHANCE ALONG THE NC COAST TO SLIGHT CHANCE
IN THE WESTERN ZONES...ROUGHLY SPLITTING THE DIFFERENCE. HOWEVER
WE DID LEAN TOWARD THE WARMER NAM MOS GUIDANCE FOR MIN TEMPS AS
THE GFS SEEMS A BIT TOO BULLISH WITH THE COLD AIR.  

COLD ADVECTION HOLDS OFF FOR MOST OF SATURDAY...SO EXPECT QUITE A
MILD DAY WITH TEMPS GETTING INTO THE 60S ACROSS MUCH OF THE ILM
CWA. CHILLIER AIR MASS FINALLY STARTS TO GET IN HERE SAT NIGHT
WITH TEMPS BACK TO THE LOW SIDE OF CLIMO...BASICALLY SPLITTING THE
DIFFERENCE BETWEEN MOS GUIDANCE NUMBERS.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 3 PM THURSDAY...DEEP-LAYER CYCLONE WILL PIVOT TOWARDS THE SRN 
GREAT LAKES REGION ON SUNDAY...THEN OPEN UP AND LIFT OUT BEGINNING 
SUNDAY NIGHT. GFS AND TO A LESSER EXTENT THE ECMWF ARE SUGGESTING 
SOME GULF MOISTURE WILL BE PICKED UP IN SW FLOW AND STREAM OVER THE 
EASTERN CAROLINAS SUNDAY/SUNDAY NIGHT. 24/12Z MEX GUIDANCE HAS 
RAMPED UP POPS SIGNIFICANTLY OVER PREVIOUS RUNS DURING THIS TIME 
FRAME...SO THINK AT LEAST A LOW CHANCE POP IS WARRANTED AT THIS TIME.

SHORTWAVE WILL PUSH OFF THE COAST MONDAY AFTERNOON...AND COLD HIGH 
PRESSURE WILL BUILD IN THROUGH MIDWEEK. MODELS AGREE IN THE 
DEVELOPMENT OF A COASTAL TROUGH WEDNESDAY...WITH A SURFACE LOW 
EITHER RIDING UP FROM THE GULF OR DEVELOPING OFF THE SC COAST BY 
THURSDAY. EITHER SCENARIO WILL LEAD TO INCREASED CHANCE FOR A RAIN 
EVENT LATE IN THE WEEK.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 00Z...BIG CHANGES COMING. CLEAR...CRISP DAYS LEAVE AS HIGH 
PRESSURE WEDGE RECEDES AND ANOTHER STRONG LOW PRESSURE MOVES THROUGH 
THE EASTERN HALF OF THE US. THIS TIME THE LOW MOVES UP THE WEST SIDE 
OF THE APPALACHIAN MOUNTAINS...CURRENTLY MOVING THROUGH ARKANSAS. 
THE ASSOCIATED FRONTS WILL AFFECT THE TERMINALS WITH INCREASED 
CLOUDINESS...RAIN AND BREEZY EASTERLY WINDS.

VFR FOR ALL TERMINALS TO START. SC TAF SITES BECOME MVFR BY 04Z WITH 
CEILING BELOW 3000 FEET. LBT/ILM FOLLOW SUIT BY 08Z. AS THE WARM 
FRONT APPROACHES...RAIN BEGINS BY 10Z AT FLO AND SLOWLY ENGULFS THE 
TERMINAL AREA WITH CEILINGS LOWERING TO 2000 FEET AND VISIBILITY 
DROPS TO MVFR RANGE. FLO/LBT IFR WITH CEILINGS BY 14Z. CONFIDENCE 
DROPS LATE IN THE PERIOD AS TO WHEN WARM FRONT MOVES THROUGH THE 
TERMINAL AREA...AROUND 20Z. SHOWERS WILL THEN MOVE INTO THE AREA 
WITH THE POSSIBILITY OF A THUNDERSTORM...NOT ENOUGH CONFIDENCE TO 
ADD TO TAFS WITH HIGH SHEAR BUT LOW CAPE...WILL ADDRESS IN NEXT SET. 
WIND CONTINUES GUSTY THROUGH THE PERIOD FROM THE EAST 10 TO 20 KNOTS 
WITH GUSTS TO 25 KNOTS. WIND VEERS MORE SOUTHERLY AND LESS BREEZY 
LATE IN THE PERIOD.

EXTENDED OUTLOOK...MEDIUM CONFIDENCE FOR DRY AIR TO QUICKLY REPLACE 
MOIST AIR MASS FOR VFR SATURDAY. SUNDAY A DIFFERENT STORY WITH MOIST 
AIR BACK BRINGING POSSIBLE IFR CONDITIONS...AND BACK TO VFR MONDAY
AND TUESDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 8 PM THURSDAY...THE COASTAL FRONT/WARM FRONT OFFSHORE WILL 
PICK UP THE PACE AND PUSH WESTWARD OVERNIGHT...REACHING LAND BEFORE 
DAYBREAK. EAST-NORTHEAST WIND TRAJECTORIES WILL TURN MORE 
SOUTHEASTERLY WITH A MUCH WARMER AND MORE HUMID AIRMASS ADVECTING IN 
FROM THE SUBTROPICAL ATLANTIC. MODELS ARE DOING AN OUTSTANDING JOB 
FORECASTING THE STRONG WINDS BEING EXPERIENCED CURRENTLY. SUSTAINED 
WIND SPEEDS AROUND 25 KT ARE GUSTING TO 30 KNOTS FROM THE OFFSHORE 
WATERS ALL THE WAY UP TO THE BEACHES. SEAS HAVE BUILT TO 6-7 FT AND 
SHOULD BUILD ANOTHER FOOT OR SO OVERNIGHT. WIND SPEEDS BEHIND THE 
WARM FRONT MAY TEMPORARILY DECREASE BY 5-10 KNOTS LATE TONIGHT... 
BUT SHOULD INCREASE AGAIN TOMORROW. ALL THESE TRENDS ARE WELL 
HANDLED BY THE PREVIOUS FORECAST AND NO SIGNIFICANT CHANGES WERE 
NEEDED FOR THE EVENING UPDATE.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 3 PM THURSDAY...MAIN CHALLENGE IS HOW STRONG THE WINDS WILL
GET ON FRIDAY WITH THE LOW-LEVEL JET TRANSLATING ACROSS THE
WATERS. WINDS AT 850MB WILL CRANK UP TO 55-60 KT FRI
AFTERNOON...BUT STABILITY WILL LIMIT SFC WINDS TO A SOLID 25 KT. A
FEW GALE FORCE GUSTS WILL BE QUITE LIKELY...BUT NOT WITH THE
PERSISTENCE OR FREQUENCY TO MERIT A WARNING. THESE WINDS WILL BE
ENOUGH TO DEVELOP SEAS AS HIGH AS 8-10 FT AWAY FROM SHORE. THIS IS
SLIGHTLY UNDER THE SWAN OUTPUT...WHICH SEEMS TO DEVELOP SEAS TOO
FAST EVEN IN THIS ONSHORE FLOW REGIME.

BY FRI EVENING THE LOW-LEVEL JET SHIFTS NORTH AND EAST OF THE
WATERS...ALLOWING WINDS TO VEER TO WESTERLY AND DIMINISH
SUBSTANTIALLY. OFFSHORE TRAJECTORY WILL KNOCK SEAS DOWN FAIRLY
QUICKLY. EXPECT TO FALL BELOW SCA THRESHOLDS SOMETIME AFTER
MIDNIGHT...BUT WILL KEEP STATUS QUO WITH THE ADVISORY GOING THRU
6AM SAT.  

BENIGN W-NW WINDS AND SUBSIDING SEAS EXPECTED SAT AND SAT NIGHT AS
HIGH PRESSURE AND AN INITIALLY MILD AIR MASS SPREAD IN. 

LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 3 PM THURSDAY...WEAK SURFACE HIGH IS EXPECTED TO BE OVER SE GA 
EARLY SUNDAY WITH A RATHER WEAK GRADIENT OVER THE CAROLINA COASTAL 
WATERS. RESULT WILL BE NW FLOW 10 KT...PERHAPS BECOMING VARIABLE 
LATE SUNDAY AS THE HIGH FADES. STRONGER HIGH PRESSURE WILL BUILD IN 
FROM THE WEST BEGINNING SUNDAY NIGHT. NW FLOW WILL INCREASE TO 
AROUND 20 KT BY EARLY MONDAY...THEN DIMINISH AND BECOME MORE 
NORTHERLY BY TUESDAY AFTN AS THE HIGH CENTER SHIFTS TOWARD THE 
MID-ATLANTIC REGION.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST SATURDAY FOR AMZ250-252-
     254-256.

&&

$$

NEAR TERM...TRA
SHORT TERM...RAS
LONG TERM...CRM
AVIATION...MDC