FXUS62 KILM 221926
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
226 PM EST TUE DEC 22 2009
.SYNOPSIS...
FAIR AND COOL WEATHER WILL CONTINUE THROUGH THURSDAY AS HIGH
PRESSURE AND A DRY AIR MASS HOLD OVER THE REGION. PRECIPITATION
CHANCES WILL INCREASE THURSDAY NIGHT THROUGH FRIDAY NIGHT...ALONG
WITH A GRADUAL WARMING TREND...AS A FRONTAL SYSTEM APPROACHES FROM
THE SOUTHWEST. A CLEARING...COOLING AND DRYING TREND IS EXPECTED
IN THE WAKE OF THIS SYSTEM HEADING INTO THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 226 PM TUESDAY...THE ONLY GAME IN TOWN IS THE TEMPERATURE
FORECAST WHICH IS ESSENTIALLY THE SAME AS LAST NIGHT. ALTHOUGH
850MB TEMPERATURES WARM SLIGHTLY...THE AXIS OF SURFACE HIGH
PRESSURE WILL REMAIN OVERHEAD ALLOWING IDEAL RADIATIONAL
CONDITIONS TO PREVAIL. HAVE FOLLOWED THE SAME PATTERN OF THE
PREVIOUS MORNINGS UNDERCUTTING GUIDANCE BY A DEGREE OR TWO
INLAND...GOING SLIGHTLY ABOVE AT MYR AND RIGHT ON THE MAV NUMBERS
AT ILM. CHANNELED VORTICITY MOVING ACROSS THE MIDWEST MAY ALLOW A
FEW HIGH CLOUDS TO SNEAK IN LATE TONIGHT...BUT THESE WILL HAVE NO
APPRECIABLE AFFECT ON TEMPERATURES OR SKYCOVER CATEGORIES.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 226 PM TUESDAY...WEDNESDAY AND JUST ABOUT ALL OF THURSDAY
WILL FEATURE VERY DRY AIR BETWEEN 925 AND 600 MILLIBARS...THUS
LITTLE IN THE WAY OF SENSIBLE WEATHER IS EXPECTED ASIDE FROM
OCCASIONAL CIRRO-STRATUS OVERHEAD IN GENERALLY A WESTERLY FLOW
ALOFT...WITH SURFACE HIGH PRESSURE WEDGED INTO THE REGION ALONG
THE LEE OF THE APPALACHIANS PRODUCING LOW LEVEL NE FLOW BOTH DAYS.
THE WEDGE WILL BE A LONG WAY FROM EROSION THROUGH THURSDAY SO
MAXIMUM TEMPS BOTH DAYS SHOULD HOLD PRIMARILY IN THE 50S.
CHANGES THURSDAY EVENING BEGIN TO IMPACT SENSIBLE WEATHER...AS
INCREASING AND VEERING ONSHORE WIND FLOW SETS UP DEVELOPING MOISTURE
CONVERGENCE OFFSHORE...WHILE ISENTROPIC LIFT AND INCREASING COLUMN
MOISTURE BEGIN TO EXPAND FROM SW TO NE OVER THE AREA AHEAD OF A
FRONTAL SYSTEM EMERGING FROM THE CENTRAL GULF STATES. MOST OF THE
PRECIPITATION IF ANY THOUGH THURSDAY DAYBREAK WILL BE CONFINED
AFTER MIDNIGHT WEDNESDAY...AND WILL LIKELY BE SPATIALLY CONFINED
ALONG THE COAST IN LIGHT SHOWERS FROM THE LOW LEVEL CONVERGENCE.
MEANWHILE ISENTROPIC RAINS WILL BE INCREASING IN AERIAL COVERAGE
AFTER DAYBREAK THURSDAY ASSOCIATED WITH AN APPROACHING WARM FRONT
GLIDING OVER THE TENACIOUS WEDGE...SATURATING THE COLUMN TOP-DOWN.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 226 PM TUESDAY...PRECIPITATION PROBABLY ONGOING AT THE START OF
THE PD. WARM FRONT PUSHING INTO SOUTHERN ZONES FRIDAY MORNING
MEETING SOME RESISTANCE BY SURFACE WEDGE BEING RE-ENFORCED BY THE
PRECIP. MEANWHILE 40-50KT 850MB JET BEGINS TO OVERRUN THE SURFACE
LAYER. GUIDANCE NOT IN VERY GOOD AGREEMENT AS TO WHETHER OR NOT THE
WEDGE BREAKS BY MIDDAY. THE WRF IS SLOWER...SHOWING ONLY A MINOR
EROSION OF THE WEDGE BY 00Z WHEREAS THE GFS IS QUICKER AND MORE
AGGRESSIVE. USUALLY GUIDANCE IS TOO QUICK IN DOING SO AND THUS THE
WRF IS PREFERRED. GFS IS ALSO QUICKER IN TAKING THE PLUME OF DEEP
MOISTURE OFFSHORE. HOW THESE INGREDIENTS ALL COME TOGETHER WILL
DICTATE WHETHER OR NOT A SEVERE WEATHER THREAT MATERIALIZES AND
RIGHT NOW ITS JUST TOO EARLY TO TELL. RAINFALL TOTALS MAY BE
APPRECIABLE THOUGH WITH EARLY INDICATIONS THAT UP TO AN INCH OR SO
MAY FALL. FORECAST HIGH TEMPERATURE ON FRIDAY ALSO VERY MUCH HINGING
UPON THE EROSION OF THE WEDGE. RIGHT NOW STILL LIKE THE WARM
ADVERTISED TEMPS IN THE LOW 60S EVEN THOUGH THEY MAY NOT COME TIL
AFTER DARK AND MOST OF THE DAYTIME HOURS ARE IN THE 40S AND 50S.
SATURDAY THROUGH MONDAY WILL BRING A DRY WSW MID LEVEL FLOW AROUND
GREAT LAKES VORTEX. CAA TEMPERED BY THE LOW AMPLITUDE BUT STILL
ENOUGH TO KEEP TEMPS BELOW CLIMO...A FEW DEGREES BY DAY AND ABOUT A
CATEGORY EACH NIGHT. TROUGH FINALLY BELLIES UNDER
THE VORTEX MONDAY NIGHT CAUSING IT TO OPEN UP AND LIFT EASTWARD.
THIS WOULD STRENGTHEN CAA LOCALLY FOR A CHILLIER TUESDAY.
&&
.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
AS OF 19Z...SURFACE RIDGE OF HIGH PRESSURE WILL DOMINATE THE
SENSIBLE WEATHER WITH LIGHT WINDS AND MOSTLY CLEAR SKY CONDITIONS.
HIGH CONFIDENCE IN VFR THROUGH THE PERIOD AT ALL TERMINALS. SKC AT
ALL TERMINALS THIS AFTN...BUT HAVE INTRODUCED A FEW CIRRUS AT 25K
FEET THIS EVENING TO ACCOUNT FOR INCREASING UPPER LEVEL MOISTURE
DEPICTED ON WV IMAGERY AND TIME HEIGHTS. MODELS HAVING A DIFFICULT
TIME DETERMINING A PREDOMINATE WIND DIRECTION DUE TO THE LIGHT
GRADIENT...BUT EXPECT PRIMARILY LIGHT NORTH WINDS AROUND 5 KT AS THE
HIGH SETTLES TO THE SOUTH. WINDS WILL DECOUPLE TONIGHT WITH THE
DEVELOPMENT OF THE NOCTURNAL INVERSION BUT NO FOG IS EXPECTED SINCE
LOW LEVELS OF THE ATMOSPHERE WILL REMAIN DRY. TOMORROW WILL FEATURE
MORE OF THE SAME...WITH THE ONLY NOTICEABLE DIFFERENCE BEING AN
INCREASE IN CIRRUS COVERAGE WITH SCT TO POTENTIALLY BKN CIGS AT 25K
FEET.
EXTENDED OUTLOOK...HIGH CONFIDENCE IN VFR WEDNESDAY. INCREASING
CONFIDENCE IN PERIODS OF IFR LATE THURSDAY AND FRIDAY WITH RAIN AND
LOW CEILINGS. VFR SATURDAY.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 226 PM TUESDAY...AXIS OF HIGH PRESSURE WILL CONTINUE TO RIDGE
DOWN ACROSS THE WATERS THROUGH THE AFTERNOON AND OVERNIGHT HOURS.
LITTLE CHANGE IN THE GRADIENT WITH ONLY A SUBTLE INCREASE FROM 0600
UTC ON. FORECAST TRENDS IN THIS DIRECTION WITH WINDS INCREASING A
COUPLE OF KNOTS AFTER MIDNIGHT. WILL USE AROUND 10 KNOTS THIS
AFTERNOON PER BUOY OBSERVATIONS INCREASING TO A RANGE OF 10-15 KNOTS
TONIGHT. A SUBTLE INCREASE IN SEAS IS ALSO OBSERVED IN THE LATEST
SWAN DATA...ALTHOUGH TWO FEET SHOULD SUFFICE FOR THE PERIOD.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 226 PM TUESDAY...THE MAIN MARINE WEATHER THEME FOR THIS TIME
PERIOD WILL BE AN INCREASING NE WIND FLOW WEDNESDAY AND THURSDAY.
WEDNESDAY LOOKS OK IN LIGHT TO MODERATE NE WIND SPEEDS...BUT BY LATE
WEDNESDAY NIGHT AND ESPECIALLY INTO THURSDAY...SMALL CRAFT ADVISORY
SPEEDS WILL BE APPROACHED. BY THURSDAY...SEAS WILL RESPOND AND COULD
REACH WAVE HEIGHTS OF 4-7 FEET...HIGHEST OFFSHORE THURSDAY AFTERNOON.
PRIMARY WAVE DIRECTION AT PEAK OF SEAS LOOKS TO BE FROM ALMOST DUE
EAST WITH DOMINANT WAVE PERIODS CENTERED AT 6-7 SECONDS THEN...MAKING
FOR MODERATELY STEEP SEAS THURSDAY AND THURSDAY NIGHT. IT APPEARS A
SMALL CRAFT ADVISORY WILL BE NEEDED SOMETIME THURSDAY.
LONG TERM /FRIDAY THROUGH SUNDAY/...
AS OF 226 PM TUESDAY...SMALL CRAFT ADVISORY LIKELY TO START THE
PERIOD. STRONG GRADIENT WINDS ASSOCIATED WITH COLD AIR SURFACE WEDGE
AND DEVELOPING SURFACE TROUGH ALONG THE COAST. PINNING DOWN WIND
DIRECTION BEING MADE PROBLEMATIC AS THE WEDGE SHOULD BREAK DOWN AT
SOME POINT AND YIELD A SWITCH FROM STRONG NE TO STRONG SE OR EVEN S
WINDS. THE TURN TO ONSHORE SHOULD ALLOW LARGER WIND WAVES TO BE
ADVECTED INTO THE FORECAST WATERS BUT IT IS UNCERTAIN AS TO WHETHER
THAT OCCURS AROUND MIDDAY OR NOT TIL FRIDAY NIGHT. CONVERSELY THERE
IS BETTER CONFIDENCE IN A COLD FRONTAL PASSAGE BY 06Z SATURDAY
MORNING WHEN WEST WINDS WILL SPREAD ACROSS THE WATERS. FLOW JUST
ABOVE THE SURFACE REMAINS SOUTHWESTERLY HOWEVER AND THAT SHOULD
PREVENT STRONG GUSTINESS. HIGH PRESSURE BUILDING IN FROM THE
WEST-SOUTHWEST WILL KEEP A WESTERLY WIND IN THE FORECAST THAT WILL
TEND TO DIMINISH TOWARDS THE END OF THE PERIOD AS THE CENTER OF THE
RIDGE APPROACHES.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...NONE.
&&
$$
SYNOPSIS...MJC
NEAR TERM...SHK
SHORT TERM...MJC
LONG TERM...MBB
AVIATION...JDW
