Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 061724
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1224 PM EST Wed Dec 6 2017

.SYNOPSIS...
A cold front today will open the door to an increasingly cold
and wet pattern the remainder of the week into Saturday before a
drying trend begins Sunday. Frigidly cold air will close the
weekend out with widespread 20s Monday morning. Another cold
front next Tuesday may bring a reinforcement of cold air.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 930 AM Wednesday...First wave of light rain now moving NE
across the Cape Fear region. High-Res guidance shows more to
follow as a series of waves move along the cold front now
approaching the coast from the NW. This front should move across
the coastal counties and offshore sometime later this morning.
Latest obs show the front is within 20 miles of the coast. Have
tweaked precip and weather in the gridded database to fine-tune
timing of precip, otherwise forecast remains good to go. Still
anticipating this mornings temperatures will be the highest we
will see today as readings drop in the wake of the FROPA.
Previous discussion follows:

Today will be nothing less than a perfect day, for those who
get to stay inside. A cold front will sweep across the area this
morning leaving cloudy, rainy, and increasingly cold conditions
across the area.

Satellite and radar imagery tells the story this morning. An
area of showers ahead of a cold front is encroaching on the
I-95 corridor at this hour, with the surface boundary lagging
just a bit behind that. Well aloft, latest WV imagery shows a
pronounced moisture tap feeding into the Carolinas which can be
traced all the way back into the tropical Pacific Ocean. Also
clearly evident is a deep cyclone across the southern Hudson Bay
of Canada, around which a mid-level trough is digging into the
eastern CONUS. These features together will create a cloud and
unsettled day, with temperatures dropping through the period.

Ahead of this cold front, showers will continue to advect east
into a warm (the last time this word will be used for a while)
and moist airmass. Latest forecast profiles suggest PWATs
climbing to near 1.6 inches by daybreak, supporting the
persistence of the showers ahead of the front, and have carried
likely to categorical POP through late morning. Once the front
pushes offshore, which is expected to occur before noon, winds
will abruptly shift to the north as high pressure expands from
the Midwest. While cold fronts can frequently be drying
features, the main trough axis aloft remains well to our west,
so moist SW flow will continue despite the surface northerly
surge. This of course creates an overrunning event, and although
a period of drying is progged this aftn, isentropic lift along
the 300K surface begins to increase and maximize this evening
and tonight. A tight moisture gradient will exist from East to
West, and the coast has the best chance for increasing
stratiform rain the latter half of the near term, but as
isentropic lift persists overnight the entire area may again get
into a steady stratiform rain.

Despite the subtle drying likely this aftn, clouds will persist
as moisture remains trapped beneath a near surface inversion
behind the front. A few showers are possible at any time as well
thanks to weak impulses rotating up from the base of the
longwave trough, although QPF will be light. Still, the
combination of cool north winds, clouds, and showers, will
actually cause temps to drop through the aftn, so today`s highs
are occurring presently, with afternoon "highs" expected to be
in the 50s, low 60s far southern zones. There will be little
change in the conditions tonight, and a damp, cold, and cloudy
night is forecast with mins falling back to near 40.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 330 AM Wednesday...Chief caption this period, `Cold
Rain`. A moisture rich, equatorial Pacific tap caught in an
amplifying upper trough will overspread a cold and moist SFC-850
layer. Several waves of upper support and enhanced kinetic
energy aloft will traverse early Thursday, and again on Friday,
very likely enhancing rainfall rates as isentropic lift peaks.
The jetlets will bring average 50 KT H7-H8 winds during these
times. QPF trends have become even more impressive now,
accumulating rain totals for both THU/FRI between 1-2 inches.
Highs Thursday not cracking 50 in most spots, will turn colder
Friday. Surface temperatures in the low to middle 30s over the
interior of SE NC late Friday night, may result in a -RA/-SN
mix, accumulations not expected at this time. The veering flow
aloft to westerly above the cold layer should lessen isentropic
omega and PCPN rates are expected to trend lighter Friday night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 3 PM Tuesday...850mb temperatures remain below 0C on
Saturday as we remain in westerly mid level flow and between the
offshore front and a moisture-starved front approaching from
the NW. A very impressive disturbance (100kt and 35s-1 vort at
500mb) sharpens the upper trough on Sunday, pushing even colder
air into the region. Some recovery should then be slated for
Monday as the eastern trough deamplifies (while still remaining
huge in expanse). This may be short-lived however as energy
appears to be digging into its western edge.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 18Z...MVFR cigs will improve to VFR this afternoon at both
KLBT and KFLO and then the coastal terminals around 00Z. Mid level
cigs then expected the remainder of the TAF valid period.
Precipitation will persist the entire period but be light. There
should be sufficient surface wind speeds to prevent any fog issues.

Extended Outlook...MVFR/IFR due to SHRA Friday mainly coastal
terminals. MVFR showers ending Sat. VFR Sun/Mon.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 930 AM Wednesday...Cold front still approaching the
coastal waters from the NW and should move across the forecast
area later this morning. Periods of rain are still expected
today and tonight. No changes needed to the forecast with the
latest update. Previous discussion follows:

A cold front approaching from the west will cross the waters
late this morning before stalling offshore. Ahead of this front,
SW winds will slowly climb towards 15-20 kts before abruptly
shifting to the NW this aftn and then N tonight. A brief
reprieve in speeds is forecast this aftn before a surge occurs
tonight, pushing wind speeds up again near 20 kts with higher
gusts. Latest buoy obs show seas of 2-4 ft, and a brief uptick
to 3-5 ft is possible just ahead of the FROPA. Seas will remain
primarily 2-4 ft however, and that is true even post FROPA,
until the northerly surge tonight drives wave heights to 4-5 ft.
These gusty winds combined with the higher seas, confused
spectrum, and periods of moderate rainfall will create hazardous
marine conditions much of the period, and a SCEC has been
hoisted for all waters beginning at midnight and persisting into
Thursday.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 330 AM Wednesday...This is going to be a difficult marine
period due to unrelenting north winds around 20 KT, at times
gusting higher, and 4-5 foot seas offshore. Dominant wave
periods every 5-6 seconds from the N-NE will result in steep
waves and bumpy navigation for small craft this period, and an
underlying 1-2 ft SSE swell every 8 seconds will add turmoil.
Rain periodically will reduce visibility to below 2 NM. At a
minimum expect `Exercise Caution` conditions, but an `Advisory`
could be required for portions of this period, given the gust
potential as cold air surges across the waters.


LONG TERM /SATURDAY THROUGH SUNDAY/...
As of 3 PM Tuesday...Additional turning to W or even WSW then
slated for Saturday, the latter depending on the strength the
troughiness associated with the next approaching cold front.
Behind this boundary wind turns back to the NW on Sunday along
with a slight increase in wind speed and possibly wave height as
cold air gets re-enforced across the region.

&&

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

&&

$$
SYNOPSIS...99
NEAR TERM...REK/JDW
SHORT TERM...MJC
LONG TERM...MBB
AVIATION...MRR
MARINE...MJC/REK/JDW/MBB



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