National Weather Service United States Department of Commerce

 


000
FXUS62 KILM 090927
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
427 AM EST TUE FEB 9 2016

.SYNOPSIS...
A CHILLY AIR MASS IN THE REGION TODAY WILL BE REINFORCED BY THE
PASSAGE OF A DRY ARCTIC FRONT WEDNESDAY. THE AREA WILL REMAIN DRY
WITH BELOW NORMAL TEMPERATURES THROUGHOUT THIS WEEK. ANOTHER
ARCTIC FRONT WILL CROSS THE AREA FRIDAY NIGHT WITH ARCTIC HIGH
PRESSURE MOVING OVER THE CAROLINAS FOR THE WEEKEND...AND THE START
OF NEXT WEEK. TEMPERATURES LATE IN THE WEEK COULD BE THE COLDEST
OF THE YEAR.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 4 AM TUESDAY...DYNAMICS FROM A WEAK DISTURBANCE ALOFT WILL
BE ENOUGH TO PRODUCE ISOLATED LIGHT SHOWERS EARLY THIS MORNING.
A TRACE AT BEST IS EXPECTED.

THE CHANGE TO THE LONGWAVE PATTERN HAS NOW BEEN ESTABLISHED...WITH
A LARGE AMPLITUDE UPPER TROF AFFECTING ROUGHLY THE EASTERN 1/2 OF
THE U.S. AND THE COMPLEMENT LARGE AMPLITUDE UPPER RIDGE AFFECTING
THE WESTERN 1/2 OF THE UNITED STATES. THIS WILL PAINT A COLD AND
DRY PICTURE FOR THIS PERIOD AND SUBSEQUENT PERIODS...THAT WILL
LIKELY CONTINUE THRU THE UPCOMING WEEKEND. THE LONGWAVE UPPER TROF
AXIS WILL NEARLY LIE OVERHEAD. IN THIS POSITION...ANY EMBEDDED
MID- LEVEL VORTS OR SHEARED VORTICITY WILL NOT BE ABLE TO TAP ANY
GULF MOISTURE AND FOR THE MOST PART ATLANTIC MOISTURE WHEN THEY
MOVE ACROSS THE ILM CWA. IN ADDITION...THE ILM CWA WILL BE UNDER
SYNOPTIC SUBSIDENCE ALOFT DUE TO THE ILM CWA LYING WITHIN THE LEFT
REAR QUADRANT OF THE 300MB JET AXIS THAT IS ORIENTED FROM SW TO NE
ACROSS THE ADJACENT ATLANTIC WATERS. AS A RESULT...THE EMBEDDED
MID-LEVEL S/W TROFS WILL HAVE TO RELY ON MOISTURE THAT ACCOMPANIES
THEM...HENCE THE STRATO-CU AND ALTO- CU BKN TO OVC CLOUD DECKS
THAT WILL OCCASIONALLY AFFECT THE ILM CWA THIS PERIOD. NO POPS
THIS PERIOD...WITH POSSIBLE PCPN REMAINING NORTH OF THE ILM CWA
AND ACROSS THE APPALACHIAN MOUNTAINS. ANOTHER REASON TO KEEP A
PCPN- FREE FORECAST IS THE DOWNSLOPE TRAJECTORY OFF THE MOUNTAINS
THAT WILL ACT TO SCOUR OUT MOISTURE.

MODELS INDICATE THE ILM CWA WILL LIE UNDER EXPANSIVE CYCLONIC FLOW
SFC AND ALOFT...WITH NO REAL LOCAL INFLUENCES FROM ANY SFC HIGHS OR
LOWS. WHAT WILL BE OCCURRING IS A TIGHTENED SFC PG AND CONTINUED
CAA...ESPECIALLY AT THE LOWER LEVELS...AS HEIGHTS CONTINUE TO FALL
ALOFT DUE TO THE UPPER TROF FURTHER AMPLIFYING. LOOKING AT THE OLD
FAITHFUL MODEL CONSENSUS OF THE 1000-500MB THICKNESS FIELD...
THICKNESSES DROP FROM 532-536DAM THIS MORNING TO 530-534DAM BY WED
DAYBREAK. HOWEVER...CAA AT THE LOWER LEVELS IS MORE PRONOUNCED...
TAKE THE 850MB MODEL CONSENSUS TEMP FCST THAT BASICALLY RANGES FROM
-3 TO -6 DEGREES CELSIUS THIS MORNING...AND DROPS TO ROUGHLY -9 TO -
11 DEGREES CELSIUS BY DAYBREAK WED. OVERALL...WILL STAY CLOSER TO
THE LOWER AVBL MOS GUIDANCE FOR BOTH MAX AND MIN TEMPS THIS PERIOD.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 AM TUESDAY...ANOMALOUSLY DEEP 5H CUTOFF OVER THE EASTERN
CONUS WILL BE IN THE PROCESS OF LIFTING NORTHEAST WED. THIS WILL
ALLOW FOR INCREASING HEIGHTS ALOFT DURING THE PERIOD...THOUGH THE
LONGWAVE 5H TROUGH WILL REMAIN IN PLACE. DESPITE THE INCREASE IN
HEIGHTS THE REGION WILL REMAIN IN THE CLUTCHES OF THE SHALLOW ARCTIC
AIR. HIGHS WED AND THU STRUGGLE TO REACH 40...WITH LOW LEVEL PARTIAL
THICKNESSES SUGGESTING HIGHS IN THE UPPER 30S. PERIOD WILL BE DRY
BUT PASSAGE OF SHORTWAVES THROUGH THE 5H TROUGH COULD LEAD TO BRIEF
PERIOD OF INCREASED CLOUD COVER WED AFTERNOON AND AGAIN LATER THU.

WIND CHILL VALUES WILL BE A CONCERN WED THROUGH THU GIVEN
TEMPERATURES RUNNING 15 DEGREES BELOW CLIMO AND THE ANTICIPATED
BREEZY CONDITIONS. WIND CHILLS DURING THE DAY WILL BE IN THE UPPER
TEENS TO LOWER 20S WITH VALUES APPROACHING SINGLE DIGITS IN PLACES
WED NIGHT. WINDS DO START TO EASE UP LATE THU AFTERNOON AS THE
SURFACE HIGH SETTLES IN. ALTHOUGH CONDITIONS WILL NOT BE IDEAL SOME
RADIATIONAL COOLING COMPONENT IS EXPECTED THU NIGHT WITH LOWS
DIPPING INTO THE LOW TO MID 20S.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 3 AM TUESDAY...MID LEVEL TROUGHING WILL BE A FIXTURE THROUGH
THE PERIOD WITH ONLY THE AMPLITUDE VARYING. SURFACE HIGH IN THE AREA
FRI IS PUSHED SOUTH BY PASSAGE OF STRONG COLD FRONT SAT
MORNING...DRIVEN SOUTH BY CLIPPER SYSTEM PASSING WELL NORTH OF THE
AREA. FRONT PASSES DRY BUT IS TRAILED BY ANOTHER BLAST OF ARCTIC
AIR. LATEST GFS/ECMWF HAVE 850 TEMPS DROPPING BY ALMOST 15C IN A 24
HOUR SPAN FRI NIGHT TO SAT NIGHT. THE COLD ADVECTION CONTINUES
THROUGH SAT NIGHT BEFORE EASING ON SUN AS THE CENTER OF THE ARCTIC
HIGH SETTLES OVERHEAD. ALTHOUGH CONFIDENCE IS LOW GUIDANCE IS
POINTING AT POTENTIAL FOR AN EXTENDED PERIOD OF TIME WITH
TEMPERATURES BELOW FREEZING...STARTING LATE SAT AFTERNOON AND
LASTING THROUGH MIDDAY MON. DID NOT GO QUITE THAT COLD BUT SOMETHING
TO WATCH FOR. CENTER OF SURFACE HIGH OVERHEAD SUN NIGHT WILL ALSO
OPEN UP THE POTENTIAL FOR RADIATIONAL COOLING WHICH COULD PRODUCE
THE COLDEST TEMPS OF THIS WINTER.

SURFACE HIGH MOVES OFF THE COAST DURING MON WITH RETURN FLOW
DEVELOPING AHEAD OF A SOUTHERN STREAM SYSTEM. THIS SYSTEM...WHICH
WOULD MOVE INTO THE AREA NEAR THE END OF THE PERIOD MAY BE
ACCOMPANIED BY SOME RAINFALL BUT CURRENT SOLUTIONS SHOW LIMITED
DYNAMICS. THERE ALSO APPEARS TO BE ONLY A BRIEF DURATION OF DEEP
MOISTURE RETURN IN THE WAKE OF THE ARCTIC HIGH. SO EVEN IF SOME
PRECIP DOES DEVELOP IT WOULD BE LIMITED IN COVERAGE. AS THIS EVENT
IS STILL 6 DAYS OUT NOT READY TO GO WITH A HIGH POP BUT WILL
INTRODUCE A SILENT 20 FOR MON. ALTHOUGH RETURN FLOW WILL DEVELOP ON
MON TEMPERATURES WILL STILL END UP WELL BELOW CLIMO GIVEN THE SLOW
RATE AT WHICH ARCTIC AIR MASSES MODIFY AND THE EXPECTED COLD START
MON MORNING.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
AS OF 06Z...THE COLD FRONT HAS PUSHED OFF THE COAST...WITH ALL
TERMINALS EXHIBITING WSW-W WINDS 5 TO 10 KT. LBT TERMINAL MAY
BRIEFLY OBSERVE GUSTS ABOVE 15 KT THRU 08Z BUT SHOULD SETTLE BACK
TO 10 KT OR LESS THERE-AFTER. A LARGE AMPLITUDE LONGWAVE UPPER
TROF IS NOW ENTRENCHED ACROSS THE EASTERN UNITED STATES. SOME
SHEARED VORTICITY IN THE MID-LEVELS...AND AVBL MOISTURE IN THE
LOW TO MID LEVELS...WILL RESULT IN OCCASIONAL STRATOCU AND ALTOCU
CLOUD DECKS THRUOUT THE 06Z TAF ISSUANCE PERIOD. THEIR RESPECTIVE
CEILINGS WILL REMAIN IN VFR TERRITORY. THE MAIN CONCERN FOR
AVIATORS WILL BE THE GUSTY WSW-W WINDS THAT WILL GET BUSY AN HOUR
OR 2 AFTER DAYBREAK TUE. DURING DAYLIGHT TUE...THE CAA WILL
COMBINE WITH A WELL TIGHTENED SFC PG AND PRODUCE WESTERLY WINDS
SUSTAINED AT 15 TO 20 KT...WITH GUSTS OF 25 TO 30+ KT. THE WINDS
WILL SUBSIDE AFTER SUNSET BUT REMAIN ACTIVE IN THE 10 TO 15 KT
RANGE THIS EVENING.

EXTENDED OUTLOOK...PREDOMINATELY VFR. EXPECT W TO NW WINDS GUSTING
TO 20 TO 30+ KT WEDNESDAY INTO EARLY THURSDAY...AND AGAIN LATE
SATURDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 3 AM TUESDAY...SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR
ALL WATERS...THROUGH THE MID-WEEK PERIOD. THIS A RESULT OF A
TIGHTENED SFC PG COMBINED WITH CONTINUED CAA SURGES. THIS
COLD/ARCTIC AIR WILL BE ADVECTING ACROSS SSTS IN THE 50S WHICH
WILL ALLOW STRONGER WINDS AND/OR GUSTS TO MIX DOWN TO THE OCEAN
SURFACE. WINDS WILL BASICALLY BE 250-270 DEGREES AT 15 TO 25
KT...AND OCCASIONALLY 20 TO 30 KT THRUOUT THIS PERIOD. THE HIGHER
WINDS WILL PRIMARILY OCCUR OVER THE OUTER WATERS WHERE SSTS ARE
SLIGHTLY WARMER...ALONG WITH LESS FRICTIONAL EFFECTS FROM LAND.

OF NOTE...THE WINDS WILL PRIMARILY BE OFFSHORE WITH THE EXCEPTION OF
THE WATERS THAT LIE BETWEEN CAPE FEAR SOUTH TO MURRELLS INLET WHERE
THEY ARE PARALLEL TO THE COASTLINE. WITH THIS IN MIND...SIGNIFICANT
SEAS WILL BE HIGHER IN THE FOREMENTIONED WATERS DUE TO A SLIGHTLY
BETTER FETCH FOR WHICH TO BUILD SEAS UPON. OVERALL...SEAS WILL RUN 3
TO 7 FT...WITH A FEW 8 FOOTERS POSSIBLE ACROSS THE OUTER WATERS OFF
CAPE FEAR. SHORT PERIOD WIND DRIVEN WAVES WILL DOMINATE THE
SIGNIFICANT SEAS SPECTRUM.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 AM TUESDAY...STRONG COLD ADVECTION WED WILL KEEP WESTERLY
FLOW AROUND 25 KT THROUGH WED NIGHT. ADVECTION STARTS TO WEAKEN ON
THU WHICH ALLOWS FOR A SLOW BUT STEADY DECREASE IN WEST TO
NORTHWEST WINDS THU AND THU NIGHT. LATE IN THE PERIOD HIGH
BUILDING IN FROM THE WEST WILL RESULT IN WINDS VEERING TO
NORTHEAST AND DROPPING TO 10 KT OR LESS. SEAS 4 TO 7 FT ON WED
WILL GRADUALLY START DECREASING LATE WED NIGHT AND CONTINUE
FALLING THROUGH THU AND THU NIGHT. BY THE END OF THE PERIOD SEAS
WILL BE 2 FT OR LESS.

LONG TERM /FRIDAY THROUGH SATURDAY/...
AS OF 3 AM TUESDAY...HIGH PRESSURE IN THE AREA FRI IS PUSHED TO
THE SOUTH LATE FRI NIGHT BY COLD FRONT SWEEPING ACROSS THE WATERS
SAT MORNING. SOUTHWEST FLOW FRI WILL INCREASE A LITTLE DURING THE
DAY AS THE FRONT APPROACHES BUT SIGNIFICANT WINDS ARE NOT EXPECTED
UNTIL LATER SAT. STRONG COLD ADVECTION WILL DEVELOP AROUND MIDDAY
SAT WITH NORTHWEST FLOW EXCEEDING 20 KT SAT AND 25 KT SAT NIGHT.
GUSTS LATE SAT NIGHT MAY APPROACH GALE FORCE. SEAS 2 TO 3 FT FRI
INTO SAT START BUILDING ON SAT...PEAKING IN THE 3 TO 6 FT RANGE
LATE SAT NIGHT.

&&

.TIDES/COASTAL FLOODING...
MODEL SURGE FORECASTS FOR THE DOWNTOWN WILMINGTON GAGE ON THE
LOWER CAPE FEAR RIVER...IS FORECAST TO CLIMB ABOVE 5.5 FT MLLW
THIS MORNING WHICH IS THE THRESHOLD FOR FLOODING ALONG THE LOWER
CAPE FEAR RIVER FROM WILMINGTON SOUTHWARD. FORECASTS INDICATE THE
GAGE WILL TOP 6.2 FT MLLW AT THE 10 AM HIGH TIDE THIS MORNING. AS
A RESULT...A COASTAL FLOOD ADVISORY WILL BE ISSUED.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST THURSDAY FOR AMZ250-252-
254-256.

&&

$$
SYNOPSIS...DCH
NEAR TERM...DCH
SHORT TERM...III
LONG TERM...III
AVIATION...DCH
TIDES/COASTAL FLOODING...DCH