Area Forecast Discussion
Issued by NWS Wakefield, VA

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629
FXUS61 KAKQ 090259
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
959 PM EST Thu Dec 8 2016

.SYNOPSIS...

Canadian high pressure builds into the Mid-Atlantic overnight
into Friday, and settles over the region Friday night into
Saturday. The high slides offshore Sunday. Low pressure will
push north of the area on Monday...with the associated cold
front crossing the region Monday night. Another strong cold
front impacts the region during the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...

Mid-evening GOES WV imagery continues to feature broad cyclonic
flow aloft over the east-central CONUS, in association w/a deep
cold upper low situated over ern Quebec. The surface cold front
is now oriented along the coast of SE VA back into eastern NC at
03z, and is primarily indicated by a sharp drop in dewpoints from
the low to mid 30s to the upper teens to low 20s back in the
piedmont (with dewpoints in the single digits to low teens just
upstream).

The primary CAA arrives late tonight as strong Canadian high
pressure spreads ewd through the Ohio Valley and into the Mid-
Atlantic. Temperatures have already dropped into the mid to upper
30s inland, upper 30s to low 40s Se coast. LAV and RAP have
handled temps well thus far and have leaned in its direction for
the overnight. Look for temps to eventually settle into the
mid/upper 20s late tonight/early Friday morning, with low 30s for
coastal se VA/ne NC.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
A cold/brisk day is anticipated Friday as the Arctic high builds
from the Central Plains toward the southern Appalachians. 850mb
temps drop to around -10C (-2 st dev) Friday afternoon. Steady 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 will trend toward
cooler thickness regressions. 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 and will 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 westerly wind.

Cold high pressure remains over the region Saturday night.
Meanwhile, a nrn stream trough dives into the Great Lakes region,
which could result in increasing high clouds late, especially
across the north. There should still be several hours of rather
ideal radiational cooling conditions and lows should once again
drop at least into the low/mid 20s. The initial wave pushes north
of the region Sunday with a secondary wave diving tracking into
the Ohio Valley, with the surface high sliding offshore. Clouds
should thicken and mixing will be limited, so highs will still be
below normal and moderate only into the mid 40s to low 50s se.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Sfc high pressure slides offshore by Sun aftn and winds become
more sly on Sun. The combination of a weak coastal trough
developing off the Carolina Coast Sun night and a warm front
lifting north through the area should bring rain up along the Mid
Atlantic coastal areas Sun night into Mon morning with a brief
period of drying during the day on Mon as the region becomes
warm-sectored. A cold front associated with low pressure tracking
along the St Lawrence River Valley is then expected to cross the
region Mon night and exit the coast by Tue morning. Winds
generally sw ahead of the front...becoming nly Tue. The cooler air
behind the cold front is much more modified and what would be
typical breezy conditions along the coast are not anticipated at
this time. Sfc high pressure returns Tue/Tue night...followed by
what could be a developing coastal low off the Southeast into Mid
Atlantic coasts on Wed.

A brief warm-up should be anticipated as the aforementioned warm
front lifts through the region Sun night into early Mon. Areas
north of the warm front should remain wedged and keep cooler air
in place prior to the initial onset of precip. This could result
in a rain/snow mix quickly transitioning to all rain overnight.
Precip should remain as rain through Monday. Temperatures
generally at to slightly below normal throughout the period.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Canadian high pressure will begin to build over the Mid Atlantic
States tonight. Patches of high clouds early Thursday evening
will clear overnight with the sky remaining mostly clear Friday.
Winds will remain from the northwest through the 00Z TAF period.

OUTLOOK...High pressure builds into the area through Saturday.
High pressure slides offshore Sunday. There will be a chance for
rain Monday as a cold front approaches from the west. Following
the passage of the cold front Monday night...dry weather returns
for Tuesday.

&&

.MARINE...
Have started all SCA flags for the waters with the aftn forecast
issuance since winds are expected to increase in the next 3-6 hrs.
A strong cold front will cross the waters this evening...followed
by a rapidly tightening pressure gradient, strong cold air
advection, and a strong 140-160kt jet streak impacting the waters
in the post-frontal environment. Overall wind forecast over the
waters is on track with w-nw winds increasing to 15-25kt this
evening with gusts around 30kt over the ocean/Ches Bay overnight.
Speeds stabilize Fri morning (still sustained 15-20kt), and a
brief lull in winds to 10-15kt can be anticipated on the rivers
during this time. This will be short-lived as a secondary surge in
colder air/wind speeds is expected to occur Fri evening...with
speeds/gusts increasing by roughly 5kt. Seas build to 4-6ft this
evening and overnight... hovering around 4-5ft through early Sat
morning. Waves will average 3-4ft during SCA and may also drop to
a solid 3ft during the brief lull in winds Fri morning.

The cold air finally begins to equalize and the pressure gradient
slowly relaxes after midnight Fri night into early Sat as sfc high
pressure builds across the OH/TN Valleys and inches closer to the
Mid Atlantic Region. The high slides overhead Sat night into Sun
morning with light and variable winds. The high then slides
offshore by Sun aftn and winds become more sly aob 15kt on Sun.
The combination of a weak coastal trough developing off the
Carolina coast Sun night and a warm front lifting north through
the area should bring rain up along the Mid Atlantic coast Sun
night into Mon morning with a brief period of drying during the
day on Mon. A cold front associated with low pressure tracking
along the St Lawrence River Valley is then expected to cross the
waters Mon night and exit the coast by Tue morning. Winds
generally sw aob 15kt ahead of the front...becoming nly Tue. The
cooler air behind the cold front is much more modified and SCA
conditions are not anticipated at this time. Seas average 2-3ft
Sat night through Mon and may build up to 5ft briefly on Tue.
Waves 1-2ft.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory until 10 PM EST Friday for ANZ635-636-638.
     Small Craft Advisory until 4 AM EST Friday for ANZ637.
     Small Craft Advisory until 7 AM EST Saturday for ANZ630>632-
     634.
     Small Craft Advisory until 4 AM EST Saturday for ANZ633-650-
     652-654-656-658.

&&

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



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