FXUS62 KILM 241138
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
638 AM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE WILL BE LOSING ITS GRIP OVER THE SOUTHEAST THROUGH
FRIDAY. WARM AIR WILL STREAM ACROSS THE REGION ON FRIDAY AHEAD OF
A STRONG COLD FRONT. COLD AIR WILL BEGIN TO RETURN SATURDAY NIGHT
AND REMAIN WELL INTO NEXT WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM THURSDAY...HIGH PRESSURE CONTINUES TO WEDGE DOWN THE EAST
COAST WITH DEWPOINTS ACROSS MOST OF THE AREA CURRENTLY IN THE UPPER
20S TO LOW 30S. THIS IS SIGNIFICANT BECAUSE BOTH THE 00Z NAM AND GFS
ARE ALREADY RUNNING 5 TO 10 DEGREES HIGHER AS OF 06Z. SO IT
CERTAINLY APPEARS THAT GUIDANCE IS YET AGAIN UNDER ESTIMATING THE
STRENGTH OF THE WEDGE. NAM/GFS SOUNDINGS AND TIME/HEIGHT CROSS
SECTIONS SHOW MOISTURE BELOW 700 MB INCREASING OVERNIGHT AS MID
LEVEL SOUTHERLY FLOW INCREASES AND BOUNDARY LAYER FLOW BECOMES
SOUTHEAST AFTER MIDNIGHT. LOW LEVEL MOISTURE IS ABUNDANT THERE IS
BASICALLY NO INSTABILITY UNTIL AFTER THE END OF THE PERIOD. WEAK
ISENTROPIC LIFT STARTS TO SPREAD OVER THE INLAND SC COUNTIES BETWEEN
09Z AND 12Z FRI AS WARM FRONT PUSHES NORTH. IF STRENGTH OF WEDGE
CONTINUES TO BE UNDER FORECAST IT IS POSSIBLE LIGHT DRIZZLE/RAIN
COULD START EARLIER...BETTER ISENTROPIC LIFT EARLIER...BUT LOWER
LEVELS WOULD ALSO BE DRY AND TAKE A LITTLE LONGER TO MOISTEN UP. DID
BACK OFF ON POPS A LITTLE THU NIGHT/FRI MORNING BUT IT MAY NOT BE
ENOUGH.
WILD CARD FOR TODAY REMAINS THE COASTAL TROF AND WHETHER IT MOVES
INLAND. LOCATION OF SURFACE LOW OVER THE ARKLATEX REGION USUALLY
HELPS PULL THE TROF ONSHORE...AND GUIDANCE DOES SHOW THIS HAPPENING
AFTER 00Z. PROBLEM IS THE WEDGE HAS TO WEAKEN FOR THIS TO HAPPEN. DO
NOT THINK IT WILL WEAKEN ENOUGH BEFORE THE WARM FRONT ARRIVES LATE
IN THE PERIOD. KEEPING SLIGHT CHANCE ALONG THE COAST SPREADING
INLAND AFTER 00Z.
HIGHS TODAY SHOULD BE SIMILAR TO YESTERDAY...MAYBE A DEGREE OR TWO
WARMER. THICKNESS/HEIGHTS DO EXPERIENCE A MARGINAL INCREASE...THOUGH
INCREASING HIGH CLOUD WILL HELP OFFSET SOME OF THAT. BIG DIFFERENCE
WILL BE OVERNIGHT WHERE TEMPS WILL BE MUCH WARMER THAN THE PAST
SEVERAL NIGHTS. TEMPS WILL DROP AFTER SUNSET...BUT INCREASING CLOUDS
AND SURFACE WINDS WILL CAUSE TEMPS TO FLATLINE AROUND MIDNIGHT.
WARMEST AREAS WILL BE ALONG THE COAST...AROUND 50 DECREASING TO
LOWER 40S INLAND. IF COASTAL TROF DOES MOVE ONSHORE...AREAS BEHIND
THE TROF COULD PUSH INTO THE MID.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 3 AM THURSDAY...STRONG ISENTROPIC UPGLIDE SPREADS OVER THE
REGION IN THE 12Z TO 18Z TIMEFRAME. THERE ARE STILL SOME DIFFERENCES
IN GUIDANCE REGARDING WHEN MEASURABLE RAINFALL BREAKS OUT ACROSS THE
REGION AND THE RIBBON OF DEEP MOISTURE WILL BE QUITE NARROW. TIMING
ISSUES ASIDE...RAINFALL CHANCES JUST ABOUT 100 PERCENT AT SOME POINT
FRIDAY. MODELS HAVE COME INTO BETTER AGREEMENT IN THE WEDGE EROSION
AND NOW SHOW A SOUTHERLY COMPONENT TO WINDS AREA-WIDE BY 18Z. SEVERE
WEATHER THREAT APPEARS QUITE LOW BUT NONZERO DUE TO TYPICAL COLD
SEASON HIGH SHEAR-LOW CAPE SETUP. DRY MID LEVEL AIR SWEEPS IN FROM
THE SOUTHWEST BY 06Z AS SURFACE FRONT MOVES INTO WESTERN COUNTIES.
JUST OFF THE SURFACE HOWEVER DEEPLY ALIGNED SOUTHWESTERLY FLOW WILL
HOLD BACK LOW LEVEL COLD ADVECTION SATURDAY AND ANOTHER MILD
AFTERNOON EXPECTED. WINDS VEER JUST ENOUGH SATURDAY NIGHT TO ALLOW
COLD AIR ADVECTION TO KICK IN.
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 3 AM THURSDAY...DEEP MID LEVEL VORTEX SPINS SLOWLY ACROSS THE
GREAT LAKES SUNDAY INTO MONDAY. THIS WILL BRING DRY AND COLD
ADVECTION LOCALLY WITH AFTERNOON HIGHS STRUGGLING INTO THE LOW 50S
IN A WELL MIXED ENVIRONMENT. TROUGH AXIS SWINGS THROUGH LATER MONDAY
FORTIFYING THE CAA TUESDAY AND WEDNESDAY. HIGH BOTH DAYS MAY
STRUGGLE TO REACH 50 ALL BUT SOUTHERNMOST ZONES WHERE LOW 50S
EXPECTED. CLOUD COVER GENERALLY AT A MINIMUM SAVE FOR MID OR HIGH
LEVEL MOISTURE ON WEDNESDAY WELL AHEAD OF DEVELOPING GULF OF MEXICO
SYSTEM.
&&
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AS OF 12Z...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 AFTN AS WINDS TURN MORE
EASTERLY AND INCREASE IN SPEED. RAIN WILL BEGIN TO AFFECT THE AREA
BY LATE IN THE TAF PERIOD.
LOW CONFIDENCE FORECAST AT THE COASTAL TERMINALS TODAY WITH MODERATE
CONFIDENCE INLAND. CURRENT SATELLITE IMAGERY DEPICTING MOSTLY CLEAR
SKY CONDITIONS...NOT EVEN ANY CIRRUS...BUT SOME LOW STRATUS
AFFECTING MYR/CRE ASSOCIATED WITH THE COASTAL TROUGH. BELIEVE THIS
HAS POTENTIAL TO CONTINUE AND SPREAD TO FLO THROUGH THE
MORNING...BUT IS HIGHLY DEPENDENT ON WESTWARD ADVANCE OF COASTAL
TROUGH. FOR NOW HAVE SCT AT 4K FEET MYR/CRE WITH FEW AT FLO BUT
COULD SEE SOME TEMPO BKN CIGS DEVELOP. ILM/LBT ARE MUCH LESS LIKELY
TO SEE ANY OF THIS LOW STRATUS TODAY AND HAVE NOT INCLUDED MENTION
OF ANY IN THE TAFS. SURFACE PRESSURE GRADIENT IS CONTINUING TO
STRENGTHEN...AND ONCE THE INVERSION BREAKS AFTER SUNRISE WINDS WILL
QUICKLY BEGIN TO GUST TO AROUND 20 KT AT ALL TERMINALS. WARM FRONT
AND OVERRUNNING PRECIP WILL APPROACH FIRST AT FLO AFTER 06Z AND
SPREAD NE ACROSS THE AREA. THESE HIGH PRESSURE WEDGES ARE NORMALLY
UNDERDONE BY GUIDANCE...SO HAVE SLOWED ONSET OF PRECIP FROM PROGS
AND ILM/LBT MAY NOT SEE ANY RAIN UNTIL AFTER THIS VALID TAF PERIOD.
WILL UPDATE RAIN CHANCES MORE SPECIFICALLY AT NEXT TAF ISSUANCE.
HIGH CONFIDENCE IN LOWERING CIGS TO MVFR AS WARM FRONT
ADVANCES...BUT LOW CONFIDENCE IN EXACT TIMING OF RAIN AND EVENTUAL
DEVELOPMENT OF IFR CIGS.
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 AM THURSDAY...NO CHANGES TO CURRENT HEADLINES. NORTHEAST
FLOW WILL INCREASE TODAY AS GRADIENT OVER THE WATERS STARTS TO
TIGHTEN IN RESPONSE TO DEVELOPING LOW OVER THE SOUTHERN PART OF THE
COUNTRY. SEAS SHOULD REACH 6 FT BY AFTERNOON...AMZ254 MAY LAG BY A
FEW MORE HOURS BEING MOSTLY SHELTERED FROM THE NE. NORTHEAST WINDS
EVENTUALLY COME AROUND TO MORE ONSHORE AT SOME POINT THIS EVENING OR
OVERNIGHT...BUT TIMING REMAINS AN ISSUE. COASTAL TROF MOVES TO THE
COAST OVERNIGHT...AND MAY PUSH FARTHER INLAND...ALLOWING FIRST EAST
AND THEN SOUTHEASTERLY FLOW TO DEVELOP OVER THE WATERS. GRADIENT
REMAINS TIGHT WITH SPEEDS IN EXCESS OF 20 KT. SEAS ABOVE 6 FT
CONTINUE THROUGH THE PERIOD...TOPPING OUT BETWEEN 9 AND 10 FT BY THE
END OF THE PERIOD.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 3 AM THURSDAY...SMALL CRAFT ADVISORY EXPECTED ON FRIDAY IN
STRONG PREFRONTAL REGIME. GALE FORCE GUSTS APPEAR POSSIBLE. IF
ONSHORE FLOW PERSISTS LONG ENOUGH TO SLOSH WARMER SSTS BACK INTO THE
FORECAST AREA THEN MIXING MAY BE STRONGER THAN CURRENTLY FORECASTED
AND SHORT FUSED GALE WARNING MAY BE NEEDED. SHARP VEER TO WEST WITH
FROPA FRIDAY NIGHT ACCOMPANIED BY DECREASE IN SPEEDS. NEAR SHORE
SEAS WILL BE BEATEN DOWN FIRST BY THE SHIFT TO OFFSHORE DIRECTION
AND CONDITIONS AWAY FROM SHORE WILL IMPROVE THEREAFTER. SATURDAY
AFTERNOON/EVENING APPEARS TO BE THE TIMEFRAME DURING WHICH SMALL
CRAFT ADVISORY CAN BE LOWERED.
LONG TERM /SUNDAY THROUGH MONDAY/...
AS OF 3 AM THURSDAY...LONG TERM PERIOD FEATURES COLD HIGH PRESSURE
BUILDING IN FROM THE NORTHWEST. THIS WILL BRING NORTHWESTERLY TO
WESTERLY WINDS THAT COULD BE QUITE GUSTY ON ACCOUNT OF GOOD
DIRECTIONAL ALIGNMENT IN THE LOW LAYERS JUST ABOVE THE SURFACE. THE
OFFSHORE WINDS WILL KEEP THE SHORT PERIOD WAVES FROM BUILDING
SIGNIFICANTLY WITHIN 20NM BUT SOME PERIODS OF SCEC WINDS NOT OUT OF
THE QUESTION.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 6 AM EST SATURDAY
FOR AMZ250-252-254-256.
&&
$$
SYNOPSIS...MBB
NEAR TERM...III
SHORT TERM...MBB
LONG TERM...MBB
AVIATION...JDW
