Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 080130
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
830 PM EST Wed Dec 7 2016

.SYNOPSIS...
Weak high pressure builds into the region tonight. Weak low
pressure tracks along the Virginia North Carolina border Thursday
morning through early afternoon, followed by a cold front later
Thursday afternoon. Canadian high pressure builds into the area
Friday through the weekend.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Current GOES WV imagery depicts a broad trough over much of the
Conus aside from the Southeast. A deep stacked low is centered
near James Bay, and strong wsw flow exists from the Desert
Southwest through the Mid-Atlantic, with an embedded shortwave
trough over the s-central Plains. At the surface, large sprawling
1056mb high pressure is centered over nw Canada and is ridging
sewd into the nrn and central plains, with an extension spilling
from the Ohio Valley into the Mid-Atlantic in the wake of low
pressure departing offshore.

This extension of high pressure will break off from the main high
and become centered over the Mid-Atlantic tonight as a cold front
becomes defined over the Lwr Great Lakes. Meanwhile, the s-central
plains trough will rapidly track ewd toward the srn Appalachians.
Locally the sky should be mostly clear this evening (after aftn
sc/cu over the Ern Shore dissipates). Clouds then increase after
midnight from w-e with most of the area becoming mostly cloudy to
overcast by morning. Temperatures drop quickly through the 40s this
evening, with overnight lows ranging from the low/mid 30s n, to the
upper 30s/around 40 s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
The aforementioned srn stream system quickly tracks across the
region in vicinity of the VA/NC border Thursday morning through
early aftn. A shear axis and strong flow aloft will provide subtle
forcing for ascent along with pw values of 0.5-0.9". Downslope
flow and marginal moisture return will be limiting factors for
pcpn. Forecast PoPs are 20-30% and highest over se VA/ne NC, with
any QPF on the order of a few hundredths of an inch. A vigorous
upper trough will dig over the Great Lakes Thursday and push the
aforementioned cold front through the Ohio Valley and into the
Mid-Atlantic region by late aftn. Mostly cloudy to overcast most
of the day with clearing arriving in the Piedmont by mid-late aftn
as the cold front pushes through. Cloud cover should hold highs in
the upper 40s to low 50s.

Much colder air surges into the region Thursday night as the large
arctic high continues to build through the central Conus and
nudges ewd into the Southeast. 850mb temperatures drop to -8 to
-10C (-1 to -2 st dev) late Thursday night. Lows drop into the
mid/upper 20s under a quickly clearing sky. A cold/brisk day is
anticipated Friday as the Arctic high builds from the Central
Plains toward the srn Appalachians. 850mb temps drop to around
-10C (-2 st dev) Friday afternoon. Strong CAA will prevent
temperatures from reaching their full potential Friday afternoon,
even with a sunny sky. MOS guidance continues to show highs
generally in the low/mid 40s, but these numbers seem on the
high-side. Some Piedmont locales may struggle to get out of the
30s, with around 40/low 40s elsewhere. A brisk northwest wind of
10-15 mph inland and 15 to 20 mph near the coast is expected to
keep wind chill values in the low to mid 30s.

The high builds into the region Friday night into Saturday. By
this point the airmass will have modified enough to lose its
arctic characteristics. Still cold and well below normal
nonetheless, with lows Friday night in the upper teens to low 20s
inland, to the low/mid 20s for se coastal locations. Limited
mixing Saturday will keep highs in the upper 30s to low 40s
despite some warming at 850mb. Sunny with a light nw wind becoming
sw.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Sfc high pressure slides overhead Sat night and offshore by Sun
morning. Winds become more southerly and breezy...especially as a
weak coastal trough begins to develop along the Carolina and Mid
Atlantic coasts Sun night. Meanwhile, another upper level trough
digs across the Midwest and Ohio Valley Sun/Sun night...followed
by a strong cold front pushing through the area Mon and a more
progressive, westerly flow pattern aloft for Tue/Wed.

A brief warm-up should be anticipated with the coastal trough Sun
night into early Mon...along with increasing chances of
precipitation Sun evening through Mon evening with the passage of
a cold front. The Piedmont may remain wedged and keep cooler air
in place prior to the initial onset of precip. This could result
in precip starting as light snow showers Sun evening before
quickly transitioning to all rain overnight. Precip should remain
as rain through Monday, however if any precipitation lingers into
Mon night, it could easily transition back to light snow showers
as another round of cooler, modified arctic air and sfc high
pressure return to the region Mon night through mid week.
Temperatures generally at to slightly below normal throughout the
period.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Weak high pressure over the area will dissipate overnight. Low
pressure over western North Carolina will move eastward late tonight
and move off the coast Thursday.

A mostly clear sky prevailed Wednesday evening. Some patchy ground
fog was occurring at SBY and may occur at other locations
especially PHF but widespread IFR is not indicated.

Any fog will likely dissipate as mid level clouds spread in from
the southwest... causing temperatures to start rising. Cloud
bases lower to 5K feet or lower Thursday morning. with a period of
MVFR ceilings late morning through afternoon. A period of light
rain is possible (20-30% chc). A secondary cold front will push
this system offshore and cross the region later Thursday aftn.

High pressure builds into the area Thursday night through Saturday.
High pressure slides offshore Sunday as another cold front
approaches from the west. This cold front crosses the region Sunday
night into Monday. with a chance for rain.

&&

.MARINE...
A weak cold front crosses the waters late this aftn into this
evening...with cooler air filtering down over the waters the rest
of tonight into Thu. Winds generally nw-n aob 15kt during this
timeframe. Seas have been slow to subside through today, and have
therefore extended SCA flags for ocean through 500 AM Thu morning
when seas finally drop below 5ft. Meanwhile, an upper level trough
sits just north of the region on Thu...slowly sagging swd Thu
night and then sliding across the area on Fri. Winds become more
wnw as the day progresses with speeds remaining aob 15kt. Wind
speeds increase to 15-20kt Thu evening for Bay/Ocean/Sound/Mouth
of James River as a strong 125-150kt jet sags south over the
waters in advance of the upper trough.

A much colder arctic airmass arrives after midnight Thu night as
the sfc pressure gradient tightens and speeds increase to 20-30kt
(aforementioned areas) and 15-20kt (Rivers); still w-nw direction.
SCA flags will likely be issued beginning with this initial surge
in winds. Gale force gusts may still be possible (especially as
skies clear with the strong jet streak overhead), however
confidence is low at this time. The cold air begins to equalize
and the sfc pressure gradient starts to relax late Fri night into
early Sat as sfc high pressure axis shifts ewd and closer to the
waters. Winds remain within solid SCA speeds through Sat morning
before diminishing below 15kt all waters by Sat aftn. Seas build
to 5-7ft north (possibly up to 8ft near 20nm Fri evening)/5-6ft
south by Fri morning and are expected remain steadfast through
early Sat morning before subsiding below 5ft by Sat aftn. The high
slides overhead Sat night (light/variable winds) and offshore by
Sun morning. Winds become more sly on Sun with a possible surge in
speeds to 10-15kt into Sun night as a weak coastal trough starts
to develop off the Carolina and Mid Atlantic coasts. The trough
axis is expected to stall just offshore on Mon with winds becoming
more sw-w aob 15kt. Seas average 2-3ft Sat night through Sun Night
and may build to 4ft near 20nm on Mon. Waves 1-2ft.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 5 AM EST Thursday for ANZ650-652-
     654-656-658.

&&

$$
SYNOPSIS...AJZ/SAM
NEAR TERM...AJZ
SHORT TERM...AJZ/SAM
LONG TERM...BMD
AVIATION...AJZ/LSA
MARINE...BMD


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