Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 180328
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1028 PM EST Sat Feb 17 2018

.SYNOPSIS...
Weak high pressure will break down this evening. A modest cold
front will approach from the NW late tonight and push across and
south of the local waters early Sunday before temporarily
stalling. High pressure will temporarily build in from the N
thru NE Sunday thru Sunday night. The earlier stalled front
will return back to the north as a warm front and push across
the area early Monday. Bermuda High pressure will follow and
build across the waters late Monday and prevail through
Thursday of next week.

.NEAR TERM /THROUGH SUNDAY/...
As of 1000 PM Saturday...Quick changes with the addition of
patchy fog across all locations based on latest sfc obs trends.
Sfc dewpoints are progged to increase into the 50s which is not
high enough for sea fog to develop when passing across SSTs that
are now in the mid to upper 50s. Enough low level moisture will
advect inland with both stratus and patchy ground fog possible.
The low temps for tonight will basically occur by late this
evening, and then slowly increase due to WAA from SE to S flow.
Did not change any POPs. Have kept the previous pcpn type and
coverage and continued with low QPF ie. less than 0.05 inches.

Previous.......................................................
As of 300 PM Saturday...Front that was stalled south of the
area has begun lifting back north as a warm front. Weak surface
wave moving northeast along the boundary is helping lift the
front back into the forecast area. Shallow layer of near
saturation, from roughly 2k ft to 6k ft, is starting to show up
as echos on KLTX. Thus far rain is not being reported in any
locations. As the front returns north this evening there will be
a narrow window where the layer below 6k ft will be nearly
saturated. However, the lack of forcing coupled with the short
duration of the event suggests a low chance of measurable
rainfall. Cannot rule out a few areas measuring a hundredth to
two this evening into tonight but suspect most of what falls
from the sky will lead to dampness with only a few areas ending
up wet. Still this is likely to be the best chance for
measurable rainfall during the period. Front`s northward
progression is limited and short- lived. The surface wave moves
off to the northeast this evening, opening the door for the
return of high pressure. The north winds on the backside of the
exiting low coupled with northerly flow around the east side of
the building high helps drive the front to the south in the pre-
dawn hours. Low tonight will once again hinge upon how quickly
the cooler air arrives. Warmer solution worked out better this
morning and is likely to be the way to go tomorrow morning as
well. Lows will range from upper 40s to lower 50s.

Front pushes well south of the area tomorrow morning, aided by
stretched shortwave pushing off the coast late tonight. High
pressure builds in from the northwest and quickly shifts east, a
result of the flat flow aloft. Forecast area will experience
significant low level drying and skies are likely to be partly to
mostly sunny tomorrow. Despite light northeast flow, becoming
onshore in the afternoon, the abundance of sunshine coupled with
limited cold advection results in highs above climo. Away from the
immediate coast highs will be in the mid 60s, with highs at the
coast likely to be mid to upper 50s. Any rain chances end with the
passing of the front and tomorrow will be dry.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM Saturday...A cloudy yet warming period on tap for the
short term. Warm front lifting through late Sunday night into Monday
morning to yield warm and moist advection. Ascent will be very
sloped and gentle though so rainfall chances will remain very low
and QPF prospects negligible. Mid level ridge starts building into
the area from offshore late Monday night helping to start decreasing
cloud cover.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...An exceptionally strong upper level
ridge is expected to develop next week off the East Coast. 500
mb heights up to 591 dam would be above normal in August, and
should be among the highest values ever observed locally this
early in the season according to the SPC sounding climatology
webpage. The Penn State GEFS ensemble viewer
(http:/cms.met.psu.edu/sref/GEFS) shows 500 mb height
forecasts nearly 3 standard deviations above normal for several
days next week. This should be a vertically stacked high with
deep southerly flow transporting an unseasonably warm and humid
subtropical airmass across the Carolinas.

High temperatures are expected to reach 80-83 degrees Tuesday
through Thursday inland, with somewhat cooler readings expected
near the coast due to nearshore water temperatures still in the
50s. The warmest days are expected to be Wednesday and Thursday
where record highs are currently forecast in Florence and
Wilmington. Thursday should be the warmest day near the coast as
an upper level trough passes through New England, veering
surface winds a bit more westerly which will delay/suppress the
seabreeze and its cooler, maritime influence. I think Thursday
may have the best potential for Myrtle Beach to achieve a record
high.

As the trough passes through New England and Canadian high
pressure advances eastward across the Great Lakes, a backdoor
cold front will get shoved southward into the Carolinas Thursday
night. To be a day 6 forecast there is surprising agreement
among the GFS/ECMWF/Canadian models with the timing of this
front. Cooler northeasterly winds behind the front should
suppress temperatures by 5-10 degrees on Friday. As the ridge
rebuilds again Friday night the front should return north with
our temperatures rising well above normal again on Saturday.

I`ve kept the forecast dry through the period as it appears each
day`s cumulus field should be capped off by a subsidence
inversion 6000-9000 feet AGL associated with the strong upper
ridge. While it`s possible a sprinkle or light shower could
develop from shallow diurnal convection beneath this inversion,
coverage of rain should be less than 10 percent each day. The
best potential for a shower might be on Wednesday as both the
GFS and ECMWF show a pocket of enhanced mid-level moisture
passing across the central and western Carolinas during the day.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
As of 00Z...Messy conditions in the region as a litany of
fronts and pressure systems remain in the area. Expect IFR to
MVFR conditions for the next several hours as a more pronounced
front will move across from the west slowly eliminating the
moisture. Not a sudden change in conditions so IFR to MVFR could
linger well into the morning hours especially along the coast.
VFR conditions should develop later Sunday.


Extended Outlook...Sun morning becoming VFR. Tempo MVFR/IFR/SHRA
cig/vsby Sun night/Mon. Becoming VFR Tue. VFR/SHRA Wed. VFR Thur.

&&

.MARINE...
NEAR TERM /THROUGH SUNDAY/...
As of 1000 PM Saturday...Progressive wx features to continue.
Mesoscale warm front at the same time will push inland while
lifting to the north. Winds will veer to the SE-S 10-15 kt by
midnight and further veer to the SW at 15 to 20 kt by daybreak
as the sfc pg tightenes ahead of the fast approaching cold
front.

Ocean Sfc Dewpoints are not progged to reach widespread 60s
which is needed with latest SSTS having recently risen to the
mid and upper 50s. As a result, have cut down on the sea fog
however area inlets and the intra-coastal waterway will see
some reductions in vsby from land based fog.

Significant seas will run 2 to 3 ft with 4 footers possible by
morning. Short period and choppy wind driven waves will
dominate the sig. seas.

Previous....................................................
As of 300 PM Saturday...Northeast surge has weakened
considerably during the last 2 hours or so and the SCA was
allowed to expire at 2 PM. Surface high continues to build down
the coast but as its influence weakens a front, stalled south of
the area, will lift north later this afternoon and evening as
weak low pressure in eastern GA moves northeast. The front is
expected to lift north and west of the waters tonight with a
brief period of enhanced southerly flow around midnight. Speeds
may briefly touch 20 kt but not for a long enough duration to
warrant any headlines. The exiting low will be followed by a
cold front, pushed well south of the waters a little after
daybreak Sun. Cold advection behind the front does not appear
particularly strong however, the gradient will result in wind
speeds on the high end of the 15 to 20 kt range. Seas falling to
2 to 3 ft overnight will start to build as northeast flow
develops and then increases Sun. Most areas will experience 2 to
4 ft seas but isolated portions of NC zones could see 5 ft late
in the period.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM Saturday...Wind turns onshore Sunday night as a warm
front approaches the coast. Then on Monday a turn to SE expected as
the boundary moves northward. High pressure center shifting from our
north to west Atlantic Monday night will turn winds southerly. Wind
speed and seas will show a gradual downward trend for the entire
period.

LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 300 PM Saturday...Strong high pressure will build off the
East Coast next week, bringing gentle southerly winds Tuesday
and Wednesday. By Thursday winds should veer more southwesterly
in advance of a backdoor cold front that is expected to reach
the Cape Fear area sometime Thursday night. This should be a
very warm airmass, perhaps too warm for any sea fog to develop
despite an otherwise favorable situation.

A large region of easterly and southeasterly winds south of the
big Atlantic high should produce a 9-second southeasterly swell
that could reach 3 feet out at 20 miles distance from shore.
Shorter period wind waves of 1-2 feet are also expected.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.

&&

$$
SYNOPSIS...DCH
NEAR TERM...DCH/III
SHORT TERM...TRA
LONG TERM...MBB
AVIATION...SHK
MARINE...


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