FXUS62 KILM 260801
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
301 AM EST SAT DEC 26 2009
.SYNOPSIS...
MILD AIR WILL REMAIN ACROSS THE REGION UNTIL PUSHED OUT BY A COLD
FRONT MONDAY NIGHT. COOL WEATHER WILL LAST INTO MID WEEK AT WHICH
TIME MOISTURE WILL BE INCREASING. RAIN CHANCES BEGINNING ON
WEDNESDAY MAY LAST INTO FRIDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM SATURDAY...SURFACE HIGH CURRENTLY OVER THE GULF COAST
WILL BUILD INTO THE AREA TODAY AND TONIGHT. VERY DRY AIR OVER THE
SOUTHEAST TODAY AND TONIGHT...PRECIPITATELY WATER VALUES TOP OUT
AROUND 0.40 INCH AT THE END OF THE PERIOD...WILL MAKE PRECIP A NON
FACTOR. WEAK COLD ADVECTION DURING THE 24 HOURS OR SO WILL DROP 500
HEIGHTS AND 1K TO 500 MB THICKNESS VALUES A LITTLE...BUT IMPACT ON
TEMPS WILL BE MINIMAL.
MOSTLY SUNNY TODAY WITH SOME LATE HIGH CLOUDS AS MOISTURE INCREASES
IN THE 400 TO 500 MB LAYER AHEAD OF WEAK SHORTWAVE OVER THE NORTHERN
GULF. AFTERNOON TEMPS WILL TOP OUT IN THE UPPER 50S TO LOWER 60S.
SHOULD BE ENOUGH OFFSHORE FLOW TO KEEP ALL BUT THE IMMEDIATE COAST
FROM FEELING LOWER TO MID 50S WATER TEMPS. LOW TEMPS ARE A LITTLE
MORE IN QUESTION. WEAK TO CALM LOW AND MID LEVEL WINDS ALONG WITH
VERY DRY AIR ALOFT WOULD SUGGEST A GOOD RADIATIONAL COOLING NIGHT.
PRESENCE OF HIGH CLOUD WILL DETERMINE EFFECTIVENESS OF COOLING. IT
LOOKS LIKE A MAJORITY OF THE UPPER MOISTURE/HIGH CLOUD WILL PASS
EAST OF THE AREA ALLOWING MORE COOLING THAT WHAT MOS IS SUGGESTING.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 3 AM SATURDAY...SOUTHWESTERLY MID LEVEL FLOW SUNDAY AROUND
DEEP CUTOFF IN THE OHIO VALLEY WHILE SMALL SCALE SURFACE HIGH BUILDS
IN FROM THE WEST. 850MB TEMPERATURE 3-4 DEG C BUT MIXING WILL BE A
BIT SHALLOWER...PROBABLY CLOSER TO 900 OR 925 MB WHERE TEMPS CLOSER
TO 5.5C. THIS SHOULD BRING HIGHS IN THE LOW 60S. LOW LEVEL THERMAL
TROUGH BEINGS TO COLD ADVECT INTO THE AREA SUNDAY NIGHT BRINGING LOW
TEMPS BACK TO CLIMO. SURFACE TROUGH/COLD FRONT THEN COMES THROUGH
JUST PRIOR TO 12Z MONDAY AS MID LEVEL VORT MAX CROSSES THE REGION
FINALLY LIFTING OUT THE OHIO VALLEY VORTEX. THIS WILL SETUP A STRONG
BUT SHORT-LIVED PERIOD OF STRONG COLD AIR ADVECTION MONDAY THAT
SHOULD KEEP HIGH TEMPERATURES STUCK IN THE UPPER 40S UNLESS THEY
MANAGE TO REACH THE LOWER 50S EARLY ENOUGH BEFORE FALLING IN THE
AFTERNOON AS 850MB TEMPS PLUMMET TO -8C BY 00Z. THERMAL TROUGH
PASSES TO THE EAST BY WEDNESDAY NIGHT AND LOW LEVEL TEMPS WARM EVEN
THOUGH NWRLY FLOW CONTINUES. AT THE SURFACE WINDS APPEAR LIGHT
ENOUGH TO PREVENT APPRECIABLE MIXING BUT NOT WEAK ENOUGH FOR A GOOD
RADIATIONAL COOLING NIGHT. LOWS COULD STILL END UP IN THE MID 20S
PER CONTINUITY OR BE CLOSER TO 30/LOW 30S PER NEW 00Z MEX GUIDANCE.
WILL SPLIT THE DIFF FOR NOW.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 3 AM SATURDAY...TEMPERATURES REBOUND SLIGHTLY ON
TUESDAY...PROBABLY BACK TO AROUND CLIMO. LOW AMPLITUDE MID LVL RIDGE
BUILDS BUT SFC HIGH WEDGING ALSO DEVELOPING. THIS WEDGE WILL REMAIN
IN PLACE WEDNESDAY AND THURSDAY AS A TROUGH DEVELOPS OFF THE COAST.
YET ANOTHER OVERRUNNING SCENARIO WILL ALSO BE DEVELOPING AS LOW
PRESSURE BEGINS TO FORM IN THE GULF OF MEXICO. LOW END CHANCE POPS
BEGIN ON WEDNESDAY BUT GUIDANCE HAS USUALLY BEEN TOO FAST WITH THESE
SYSTEMS AS THEY UNDERESTIMATE THE DRYNESS OF THE WEDGE. PRETTY
IMPOSSIBLE TO RESOLVE OVERALL TIMING DIFFERENCES OF THE
SYSTEM...WITH WET WEATHER POSSIBLE RIGHT THROUGH FRIDAY ALTHOUGH GFS
IS CONSIDERABLY QUICKER.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AS OF 08Z...COLD FRONT HAS EXITED WITH WEAK WESTERLY FLOW
DEVELOPING. LOW LEVEL MOISTURE IS HOLDING ON WHICH HAS CREATE
TRANSIENT IFR CEILINGS AND/OR VISIBILITIES. LOW CONFIDENCE FORECAST
THROUGH THE REMAINDER OF THE OVERNIGHT. FORECAST SOUNDINGS SUGGEST
CLEARING SKIES AND INCREASING VIS WHILE IN REALITY THE EXACT
OPPOSITE HAS BEEN HAPPENING...ALBEIT BRIEFLY. ONCE SUN COMES UP
FORECAST CONFIDENCE INCREASES WITH ALL SITES BECOMING VFR AND
REMAINING THERE THROUGH THE PERIOD. UPPER LEVEL MOISTURE LATE TODAY
AND TONIGHT MAY LEAD TO SOME CIRRUS AROUND 25K FT...BUT THINK THE
BULK OF THIS CLOUD WILL BE SOUTH AND EAST OF THE SITES.
EXTENDED OUTLOOK...MEDIUM CONFIDENCE FOR DRY AIR AND HIGH PRESSURE
FOR VFR SUNDAY. POSSIBLE MVFR FOR MONDAY. TUESDAY AND WEDNESDAY VFR.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM SATURDAY...SCA CONTINUES FOR ALL WATERS BUT THE DOWNWARD
TREND HAS BEGUN. 41110 RECENTLY REPORTED 8 FT SEAS WITH 11 FT AT
41013. WEAK OFFSHORE FLOW IS ALLOWING SEAS TO STAY UP LONGER THAN
TYPICAL...BUT SCA ENDING TIME AROUND 8 AM STILL LOOKS TO BE ON
TRACK. SEAS WILL CONTINUE TO DECREASE THROUGH THE PERIOD AS HIGH
PRESSURE TO THE SOUTHWEST BUILDS IN. GRADIENT SLOWLY WEAKENS THROUGH
THE PERIOD...RESULTING IN OFFSHORE FLOW UNDER 10 KT TONIGHT.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 3 AM SATURDAY...OFFSHORE WINDS EXPECTED FOR THE DURATION OF
THE PERIOD. AS A MID LEVEL TROUGH AXIS SWINGS ACROSS THE FORECAST
AREA ON MONDAY A MODERATELY STRONG COLD SURGE WILL BOLSTER WINDS AND
SEAS. A BRIEF SMALL CRAFT ADVISORY APPEARS POSSIBLE DURING THE PEAK
OF THE SURGE AT WHICH TIME SOME 6FT SEAS MAY AFFECT MAINLY THE OUTER
REACHES OF THE FORECAST ZONES.
LONG TERM /TUESDAY THROUGH WEDNESDAY/...
AS OF 3 AM SATURDAY...HIGH PRESSURE PREVIOUSLY TO THE NORTHWEST
BECOMES SITUATED MORE TO THE NORTH BY TUESDAY. THIS WILL VEER WINDS
TO A MORE NORTHERLY DIRECTION. AT THE SAME TIME THE INCREASING
PRESSURES WILL DECREASE THE GRADIENT ACROSS THE SOUTHEAST AND WIND
SPEEDS AND RESULTING SEAS WILL DIMINISH. COASTAL TROUGHINESS TO
BRING ADDITIONAL VEERING IN DIRECTION AND MAYBE INCREASED SPEEDS
AGAIN. A FAIRLY ENERGETIC GULF OF MEXICO SYSTEM WILL BE DEVELOPING
AND WILL AFFECT THE REGION EVENTUALLY BUT ITS TIMING IS HIGHLY
UNCERTAIN AT THIS TIME.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EST THIS MORNING FOR AMZ250-
252-254-256.
&&
$$
SYNOPSIS...MBB
NEAR TERM...III
SHORT TERM...MBB
LONG TERM...MBB
AVIATION...III/MDC
