FXUS62 KILM 251152
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
652 AM EST FRI DEC 25 2009
.SYNOPSIS...
A STRONG COLD FRONT WILL BRING RAIN AND GUSTY WINDS TODAY. COLD
AIR WILL BEGIN TO BUILD BACK SATURDAY NIGHT AND BE RE-ENFORCED ON
MONDAY. THE NEXT STORM SYSTEM MAY AFFECT THE REGION THURSDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM FRIDAY...COASTAL TROF/WARM FRONT WILL MOVE INLAND AS IT
LIFTS NORTH LATER TODAY. INITIALLY WEDGE HOLDS ON BUT IT WILL ERODE
DURING THE DAY. LIGHT RAIN WILL SLOWLY SPREAD FROM SOUTHWEST TO
NORTHEAST DURING THE NEXT FEW HOURS WITH MOST OF THE AREA SEEING
LIGHT RAIN BY DAY BREAK. LIGHT TO MODERATE RAIN TRANSITIONS TO
SHOWERS ONCE SOUTHEAST LOW LEVEL FLOW DEVELOPS BEHIND THE WARM
FRONT. INCREASED TEMPERATURES/DEWPOINTS SPREAD OVER THE AREA
PROVIDING A SLIGHT INCREASE IN INSTABILITY JUST AHEAD OF THE COLD
FRONT.
LINE OF CONVECTION ALONG THE FRONT WILL MOVE RAPIDLY ACROSS THE AREA
LATE THIS AFTERNOON AND MAY PRODUCE A SHORT LIVED SEVERE WEATHER
THREAT. NOT A LOT OF SURFACE BASED INSTABILITY TODAY WITH CAPE
VALUES GENERALLY UNDER 500. SOUNDINGS DO SHOW SOME MID LEVEL
INSTABILITY...BUT AS PAST EVENT HAVE SHOWN STABLE SURFACE/MARINE
LAYER HELP KEEP STRONG WINDS FROM REACHING THE SURFACE. SOUNDINGS DO
SUGGEST A BRIEF PERIOD LATE THIS AFTERNOON WHEN STRONGER WINDS ALOFT
MAY BE ABLE TO MIX TO THE SURFACE. HOWEVER...THE SOUNDINGS CONTINUE
TO SHOW A VERY SHALLOW STABLE LAYER WHICH MAY BE ENOUGH TO KEEP
DAMAGING WINDS ALOFT. THERE ARE ALSO SOME OUTRAGEOUS HELICITY VALUES
DUE TO THE COMBO OF STRONG WINDS AND MARGINAL DIRECTIONAL SHEAR
WHICH COULD ALSO PRODUCE TORNADOES...BUT AGAIN WE HAVE SEEN THESE
HIGH SHEAR/LOW CAPE EVENTS IN THE PAST AND TYPICALLY VERY LITTLE
HAPPENS. WITH THAT BEING SAID...THE SEVERE WEATHER THREAT REMAINS
QUITE REAL FOR TODAY WITH SPC KEEPING ALMOST THE ENTIRE FORECAST
AREA IN THE SLIGHT RISK AREA.
TEMPERATURES IN THE MID TO UPPER 60S TODAY COULD PUSH A BIT HIGHER
DEPENDING ON TIMING OF SURFACE FEATURES...DID NOT NEED TO MAKE ANY
MAJOR CHANGES TO HIGHS. COLD FRONT SWEEPING ACROSS THE AREA THIS
EVENING WILL CLEAR OUT CLOUDS AND PRECIP. TRIPLE POINT LOW WHICH
PASSES WEST OF THE AREA TODAY AS IT LIFTS NORTHEAST WILL FIRST
INDUCE WESTERLY AND THEN NORTHWESTERLY WINDS OVERNIGHT.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 3 AM FRIDAY...
SOUTHWESTERLY CYCLONIC FLOW AROUND DEEP GREAT LAKES VORTEX WILL LAST
THE ENTIRE SHORT TERM PERIOD. LOW LEVEL THERMAL RIDGE IS PUSHED TO
THE EAST BY THIS FEATURE SATURDAY NIGHT BRINGING AN END TO THE ABOVE
CLIMO TEMPS. SPOKES OF VORTICITY BEGIN TO LIFT THROUGH THIS
SOUTHWESTERLY FLOW SUNDAY NIGHT. GUIDANCE IS SHOWING AMPLE MOISTURE
AND LIFT ASSOCIATED WITH THESE SMALL SCALE FEATURES TO SUPPORT SOME
LIGHT PRECIPITATION. GIVEN THE FAIRLY DRY LOW LEVELS AND WEAK COLD
AIR ADVECTION LEADING TO DOWNWARD VERTICAL MOTION BENEATH THE MID
LEVEL LIFT PRECIP SEEMS LESS LIKELY THAN JUST AN INCREASE IN CLOUDS
AT THIS POINT.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 3 AM FRIDAY...ON MONDAY THE FINAL KICKER VORT SWINGS THROUGH
THE TROUGH THAT HAD BEEN IN PLACE OVER THE EASTERN FOR SEVERAL DAYS
PREVIOUS. BEHIND THIS FEATURE WILL COME A BATCH OF RENEWED COLD AIR
ADVECTION PUSHING H850 TEMPS DOWN TO -6 TO -8 DEG C ACCORDING TO
ECMWF BUT ONLY AROUND -2 DEG C ACCORD TO GFS. CAA TAPERS OFF ON
TUESDAY AND H850 TEMPS SHOULD BE WITHIN A FEW DEG OF FREEZING. WILL
UNDERCUT GUIDANCE SOME ON MONDAY AS A COMPROMISE BUT FOLLOW CLOSELY
NEXT FEW DAYS. HIGHS MIRED IN THE 40S FOR MON WITH A RUN AT 50 FOR
THE NEXT FEW. COASTAL TROUGHINESS AND/OR GULF OF MEXICO SYSTEM COULD
BRING INCREASING MOISTURE LOCALLY BY THURSDAY BUT MEASURABLE
RAINFALL WILL PROBABLY BE DELAYED JUST BEYOND THE LONG TERM.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 12Z...WARM FRONT WILL CROSS THE REGION THIS MORNING BRINGING
RAIN AND LOWERING CIGS. RAIN AND POTENTIAL THUNDERSTORMS WILL OCCUR
THIS AFTN IN ADVANCE OF A COLD FROPA THIS EVENING.
HIGH CONFIDENCE IN CHARACTERISTICS OF EVENT TODAY...WITH LOW
CONFIDENCE IN TIMING. LARGE AREA OF STRATIFORM RAIN JUST TO THE SW
OF FLO THIS MORNING...AND THIS WILL SPREAD ACROSS THE AREA
THROUGH THE AFTN. ONCE RAIN BEGINS VSBYS AND CIGS WILL QUICKLY DROP
TO MVFR...WITH IFR CIGS DEVELOPING A SHORT TIME AFTER. AS IS TYPICAL
IN THESE OVERRUNNING SITUATIONS THE COLUMN SATURATES FROM TOP DOWN
AND IFR CIGS DEVELOP FREQUENTLY...SO AM FAIRLY CONFIDENT IN IFR
TODAY. WINDS WILL INCREASE THROUGH THE AFTN AS A STRONG 850MB JET OF
50 TO 60 KTS MOVES OVERHEAD. STRENGTH OF SURFACE WINDS WILL DEPEND
GREATLY ON LEVEL OF MIXING...BUT EXPECT SEVERAL HOURS OF 20 TO 30 KT
GUSTS AS THE WINDS VEER TO THE SOUTH THROUGH THE AFTN.
RAIN TYPE WILL BECOME MORE CONVECTIVE THIS AFTN AS COLD FRONT
APPROACHES. WITH SIGNIFICANT SHEAR DUE TO THE LLJ SOME
THUNDERSTORMS...POTENTIALLY SEVERE...ARE POSSIBLE FOR A SHORT
DURATION THIS AFTN. VERY LOW CONFIDENCE IN THIS PART OF THE FORECAST
BUT ANY THUNDER WILL LIKELY OCCUR AFTER NEXT TAF ISSUANCE SO THERE
IS SOME TIME TO UPDATE. FOR NOW HAVE VCTS WITH 1K FOOT CB IN THE
TAFS TO REFLECT POTENTIAL. ONCE COLD FRONT COMES THROUGH THIS
EVENING WINDS WILL BEGIN TO DECREASE AND SHOULD EASE SIGNIFICANTLY
TONIGHT. HAVE INTRODUCED LLWS ONLY AT ILM DUE TO THEIR PROXIMITY TO
THE LLJ AS IT PULLS AWAY TONIGHT. GUIDANCE SPLIT ON CLEARING
TONIGHT...BUT WITH SIGNIFICANT LL MOISTURE THINK THERE IS A GOOD
CHANCE FOR IFR STRATUS AT ALL THE TERMINALS TOWARD THE END OF THIS
TAF PERIOD.
EXTENDED OUTLOOK...VFR SUNDAY. SLIGHT POTENTIAL FOR MVFR CIGS WITH
LOW PRESSURE TROUGH MONDAY. VFR TUESDAY.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM FRIDAY...COASTAL TROF/WARM FRONT CURRENTLY BISECTS THE
WATERS WITH 41013 REPORTING ESE(110 DEG) WINDS AND 41038 REPORTING
ENE(060 DEG). FRONT WILL MAKE ITS WAY TO THE COAST LATER TODAY WITH
WINDS ACROSS THE WATERS BECOMING ESE AND INCREASE TO 25 TO 30 KT.
CONDITIONS WILL BE VERY CLOSE TO GALE WARNING CRITERIA...BUT COOLER
SHELF WATERS WILL MAKE IT DIFFICULT FOR STRONGEST WINDS ALOFT TO
REACH THE SURFACE. ANY STORMS THAT DEVELOP WILL LIKELY HAVE MUCH
STRONGER WINDS WITHIN THEM...LATEST GUIDANCE IS SHOWING 50 TO 60 KT
IN THE LOWEST 3K FT...AND COULD POSE A SIGNIFICANT RISK TO MARINERS.
SEAS CURRENTLY 6 TO 8 FT WILL CONTINUE TO BUILD TODAY...ULTIMATELY
APPROACHING 15 FT NEAR 41013. COLD FRONT WILL MOVE ACROSS THE WATERS
SHORTLY AFTER 00Z WITH OFFSHORE FLOW DEVELOPING...WORKING TO KNOCK
BACK SEAS. OFFSHORE FLOW BEHIND THE FRONT IS NOT VERY STRONG...SO IT
MAY TAKE A WHILE FOR SEAS TO FALL BELOW 6 FT. WENT AHEAD AND
EXTENDED THE SCA TO 12Z BASED ON LATEST FROM SWAN/WW3.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 3 AM FRIDAY...
WEST TO NORTHWEST WINDS THROUGH THE PERIOD AS HIGH PRESSURE BUILDS
IN FROM THE WEST BEHIND COLD FRONT. THE PROLONGED OFFSHORE FLOW WILL
OPEN UP A RANGE IN SEAS FROM NEARSHORE TO OFFSHORE...GENERALLY
AVERAGING 3 TO 5 FT FOR SATURDAY AND SUBSIDING TO 2 TO 4 FT ON
SUNDAY IN A SHORT PERIOD WIND WAVE DOMINATED SEA STATE.
LONG TERM /MONDAY THROUGH TUESDAY/...
AS OF 3 AM FRIDAY...
UPPER LEVEL DISTURBANCE SWINGS THROUGH ON MONDAY BRINGING A
FORTIFIED SURGE OF COLD AIR. NW WINDS WILL INCREASE AS HIGHER
PRESSURES AGAIN BEGIN TO BUILD ACROSS THE WATERS. ADVISORIES NOT
ANTICIPATED AT THIS TIME BUT CAUTIONARY HEADLINES NOT OUT OF THE
QUESTION. BOTH WINDS AND SEAS WILL ABATE ON TUESDAY AS GRADIENT
DECREASES.
&&
.HYDROLOGY...
ALL RIVERS IN THE RIVER DISTRICT ARE BELOW FLOOD STAGE.
THE WACCAMAW RIVER AT CONWAY IS CURRENTLY AT ACTION STAGE AND
FORECAST TO HOLD STEADY DURING THE PERIOD.
A CLOSE WATCH IS WARRANTED FOR THE GREAT PEE DEE AT PEE DEE...NOW A
HAIR BELOW ACTION STAGE OF 18 FEET AND FORECAST TO HOLD STEADY UNTIL
THE AM...THEN SLOWLY RECEDE. THE LITTLE PEE DEE AT GALIVANTS FERRY
IS ABOVE ACTION STAGE BUT FORECAST TO HOLD STEADY THROUGH THE
FORECAST PERIOD.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST SATURDAY FOR AMZ250-252-
254-256.
&&
$$
SYNOPSIS...MBB
NEAR TERM...III
SHORT TERM...MBB
LONG TERM...MBB
AVIATION...JDW
HYDROLOGY...MDC
