FXUS62 KILM 242010
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
310 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 FRIDAY AND FRIDAY NIGHT. HIGH PRESSURE WILL BUILD
FROM THE NORTHWEST BEGINNING SATURDAY...WITH COLD TEMPERATURES
RETURNING SUNDAY THROUGH WEDNESDAY.
&&
.NEAR TERM /THROUGH 6 AM FRIDAY/...
AS OF 3 PM THURSDAY...HIGH PRESSURE CONTINUES TO NOSE DOWN INTO
THE AREA ALTHOUGH PRESSURES HAVE STABILIZED AND MODELS ARE
ADVERTISING PRESSURES TO FALL FROM THIS POINT ON. THE LOWER
TROPOSPHERE REMAINS MOISTURE CHALLENGED VIA VISIBLE SATELLITE
LOOPS AND SURFACE OBSERVATIONS SHOWING DEWPOINTS IN THE LOWER 30S
AND EVEN A SMALL AREA OF UPPER 20S IN OUR NORTHEASTERN COUNTIES.
WITH THIS TREND AND CONSIDERING THE MODELS HAVE BEEN TRENDING
SLOWER WITH THE PROGRESSION OF THE COLD FRONT ASSOCIATED WITH THE
POWERFUL CYCLONE ACROSS THE CENTRAL UNITED STATES...HAVE
DRAMATICALLY SCALED BACK POPS AND CLOUD COVER FOR THE FIRST 12
HOURS OF THE NEAR TERM. THE LONG ADVERTISED COASTAL TROUGH HAS YET
TO MATERIALIZE AND CONSIDERING THE MOISTURE PROFILES...THE MAIN
FRONT WHICH IS SLATED TO ARRIVE LATER FRIDAY WILL...MOST LIKELY BE
THE FORCING MECHANISM FOR MEASURABLE RAIN. OVERNIGHT LOWS WILL
CHALLENGING AND WILL BE AT THE MERCY OF LOW LEVEL WARM ADVECTION
WHICH WILL COINCIDE WITH THE INCREASE IN CLOUD COVER. OVERALL THE
COOLER MAV NUMBERS SEEM THE BEST BET...REACHED EARLY WITH WARMING
TEMPERATURES AFTER 0800/0900 UTC.
&&
.SHORT TERM /FRIDAY 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 /20Z THURSDAY THROUGH TUESDAY/...
AS OF 18Z...HIGH PRESSURE WEDGE WILL SLOWLY GIVE WAY TO ADVANCING
WARM FRONT THROUGH THE PERIOD. WEAK TROUGH OFFSHORE MAY AFFECT THE
COASTAL TERMINALS WITH LOW CLOUDS THIS EVENING AS WINDS TURN MORE
EASTERLY AND INCREASE IN SPEED. RAIN WILL BEGIN TO AFFECT THE AREA
BY LATE IN THE TAF PERIOD.
HIGH CONFIDENCE FORECAST EARLY IN THE PERIOD BECOMING LOW CONFIDENCE
OVERNIGHT DUE TO TIMING OF OVERRUNNING PRECIP AND LOWERING
CIGS. FOR THIS AFTN...VFR ALL TERMINALS WITH MOSTLY CLEAR SKY
CONDITIONS AND ONLY FEW/SCT 4K FOOT STRATUS ADVECTING ACROSS
CRE/MYR/FLO. THIS STRATUS IS ASSOCIATED WITH A COASTAL TROUGH AND IS
BEING PUSHED ONSHORE BY WINDS WITH AN INCREASINGLY EASTERLY
COMPONENT. THE WEDGE IS HANGING ON STRONGER THAN PROGGED...AS
EXPECTED...AND HENCE CLOUD COVER IS REALLY HAVING A DIFFICULT TIME
DEVELOPING ACROSS THE TERMINALS. HIGH CIRRUS IS ENCROACHING FROM THE
WEST HOWEVER...AND ALL TERMINALS WILL DEVELOP OVC CI CIGS BY
TONIGHT. THIS IS WHERE THE CONFIDENCE BEGINS TO DECREASE. WITH A
STRONGER WEDGE...PRECIP WILL HAVE A DIFFICULT TIME SATURATING THE
COLUMN TO REACH THE GROUND. GUIDANCE CONTINUALLY SLOWING ONSET OF
PRECIP AND HAVE SLOWED ONSET IN THE TAFS EVEN FURTHER...BUT TIMING
IS VERY TRICKY WITH AN OVERRUNNING EVENT INTO A DRY COLUMN. HIGH
CONFIDENCE IN DEVELOPMENT OF MVFR CIGS OVERNIGHT INTO THE
MORNING...BUT EXACTLY WHEN IS VERY TOUGH TO DETERMINE ATTM. EXPECT
RAIN TO REACH FLO AROUND 09Z AND SPREAD TO ILM BY 14Z. ONCE RAIN
BEGINS VSBYS WILL DROP TO AT LEAST MVFR AND CIGS POTENTIALLY TO
IFR...BUT SINCE THIS IS VERY LATE IN THE TAF PERIOD THERE IS TIME
FOR FUTURE ADJUSTMENT WITH UPDATED GUIDANCE. WINDS WILL SLOWLY VEER
TO THE E/SE AND INCREASE THROUGH THE PERIOD...GUSTING TO 20 KT OR
MORE BY LATE TONIGHT.
EXTENDED OUTLOOK...MODERATE CONFIDENCE IN PERIODS OF IFR THROUGH
SATURDAY MORNING WITH RAIN AND LOW CEILINGS. SOME FOG ALSO POSSIBLE
SATURDAY MORNING. VFR SUNDAY AND MONDAY.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 3 PM THURSDAY...WINDS AND SEAS CONTINUE ON THE UPTREND THIS
AFTERNOON WITH 41013 REPORTING 21 KNOTS THE PAST COUPLE OF HOURS AND
SEAS UP TO ALMOST SIX FEET. 41110 IS ECLIPSING FIVE FEET AS WELL.
WINDS WILL CONTINUE IN A RANGE OF 20-25 KNOTS FOR THE OVERNIGHT
HOURS AND VEER TO THE EAST AND FINALLY SOUTHEAST BY MORNING AS THE
WEDGE BREAKS. SWAN INITIALIZED THE SEAS ALMOST PERFECT AND SEE NO
REASON TO DEVIATE FROM THESE VALUES THROUGH THE NEAR TERM. BY EARLY
FRIDAY MORNING WE SHOULD SEE A SOLID 6-8 FEET IN THE COASTAL ZONES
WITH SOME 10 FOOTERS POSSIBLE FOR 41013. SMALL CRAFT CONDITIONS
CONTINUE FOR ALL WATERS.
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...SHK
SHORT TERM...RAS
LONG TERM...CRM
AVIATION...JDW
