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000
FXUS61 KAKQ 240017
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
817 PM EDT FRI SEP 23 2016

.SYNOPSIS...
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High pressure moves across the area tonight. A backdoor cold
front drops south across the region Saturday. High pressure
tracks across Southeast Canada early next week.
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&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Update...Only minor tweaks made to ongoing forecast. Overall,
expect mostly clear skies overnight with patchy fog developing
after midnight. High clouds should start streaming into far nrn
counties closer to sunrise as a backdoor front approaches the
region (see short term discussion below).

Previous discussion (334 PM)...
Latest MSAS showing low pressure and weakening sfc trof off the
Carolina coast with high pressure building over the Mid Atlantic
region. Meanwhile, a backdoor cold front drops south into
northern VA by 12Z Sat. Lows in the mid-upr 60s except near 70 at
the coast.
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&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
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1025+ mb high moving across southern Canada pushes a backdoor cold
front across the region Sat. Day starts off partly to mostly sunny
then quickly clouds up post fropa as the winds shift to the N-NE
during the afternoon. NAM slowest with the fropa thus most
aggressive with sct convection developing along the boundary.
GFS/SREF keep it dry across AKQ FA but do develop some upslope
shwrs across the mts after 21z. Will maintain a dry forecast on
Sat. Tmps tricky and will depend on timing of front. Highs in the
mid to upr 70s ern shore to mid 80s swrn zones.

Front continues to push south into the Carolinas Saturday night in
response to high pressure sliding across Southeast Canada. This
high extends south across the Mid Atlantic Region Sunday and
Sunday night. Latest data continues to focus on increasing low
level moisture and weak isentropic lift Saturday night into Sunday
night. The depth of moisture is rather shallow...favoring only low
end pcpn chances for pockets of light rain or drizzle mainly along
and west of the I-95 corridor. Kept slght chc pops (stratiform
rain rather than showers) across the Piedmont. The onshore flow
results in mostly cloudy/overcast skies for areas mainly west of
the Bay during this same time and partly cloudy for the Eastern
Shore. Lows Sat night in the mid 50s north to mid 60s south. Highs
Sun 70-75. Lows Sun night in the mid 50s to lwr 60s. If it clears
early enough...SBY could drop to near 50 by 12Z Mon.

High pressure moves north of New England Monday with the next
front approaching from the west during the afternoon. Slght chc
shwrs across the Piedmont ahead of the front. Onshore flow and
clouds keeps it cool with highs in the low to mid 70s.
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&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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Medium range period has become somewhat clearer with the latest
12Z model suite trending further into at least modest agreement.
There are still significant timing differences that exist
regarding a cold frontal passage Tue into early Wed followed by a
large area of High pressure building into the local area from the
west as an upper level trough becomes centered over eastern Canada
and the NE CONUS/New England Tue/Tue night, then shifts off the E
coast by Thu. Have raised POPS Tue/Tue night to 30-40% with the
front, along with a chc for tstms Tue aftn/evening. Beyond that,
will linger 20-30% POPS mainly along the coast Wed in case the
front trends slower, with mainly dry conditions expected Wed night
through Fri. Temperatures will avg close to seasonal averages,
with highs Tue ranging from the mid 70s NW to around 80 F S/SE
(where more sun may occur ahead of the front). Highs Wed-Fri
generally in the 70s with lows in the 50s, except in the 60s SE.
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&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Mostly clear skies overnight as weak high pressure slides over the
area...allowing patchy fog to develop after 24/0900Z. Visibilities
should generally be 3-5SM...except KSBY and KECG where
visibilities could drop as low as 2SM with SCT stratus around
400ft AGL. A backdoor cold front then drops south through the
region on Saturday...primarily spreading widespread high clouds
across the area during the day. Given the abundant/recent rainfall
from the past several days and persistent onshore/ne winds, expect
SCT cumulus to develop during the aftn...especially near coastal
sites. KSBY will likely experience MVFR cigs given how early the
front comes through there and overall proximity to the frontal
boundary throughout the day.

The front pushes south of Albemarle Sound after midnight Saturday
night with stronger central high pressure sliding across Southeast
Canada and building down into the Mid Atlantic Region through
Sunday night before sliding off the New England coast early next
week. Patchy fog may be possible once again late Saturday night
into early Sunday morning, otherwise VFR conditions will prevail.
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&&

.MARINE...
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Latest obs continue to depict diminishing NE flow across the
waters, generally 5-10 KT. Seas avg 3-4 ft with 10-12 second
dominant periods and wave in the Bay are 1-2 ft. Trends are slower
with the approaching cold front from the N later tonight into Sat,
now the winds tonight will avg 5-10 Kt or less and gradually
shifting to the SSW after midnight.

On Sat, front progged to push through the waters from N to S,
pushing into NC by late afternoon. Did not raise SCA headlines as
winds should stay below thresholds, but there will probably be
about a 3 hr period with occasional gusts to 20 KT. Waves in the
Bay should build to 2-3 ft by late morning/early aftn and to 2 ft
in the rivers so still not ideal boating conditions even without
headlines (may need to issue an MWS). For the coastal waters,
distant tropical Cyclone Karl Invof Bermuda looks to aid in seas
building to 4-5 ft. Trends in wavewatch are slower and slightly
weaker however, so did not issue SCA headlines as this is marginal
and will be late 2nd period (will allow next shift to determine if
seas ever do reach a widespread 5 ft). Wavewatch and NWPS both
depict seas subsiding once again for Sunday through Sunday night.
Next cold front approaching from the NW will shift winds back to
the SE on Mon and increase from the S Mon night/Tue. Still some
models differences/uncertainties but could see marginal SCA
conditions in the Bay Mon night/Tue and probably will have SCA
conditions behind the front sometime midweek as significantly
cooler airmass and strong high pressure builds in from the NW.
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&&

.HYDROLOGY...
The Cashie River at Windsor continues to fall but remains in the
moderate flood range. The river is forecast to slowly fall below
flood stage late Sunday night. See FLSAKQ for details.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...None.

&&

$$
SYNOPSIS...MPR
NEAR TERM...BMD/MPR
SHORT TERM...JDM/MPR
LONG TERM...LKB
AVIATION...AJB
MARINE...LKB
HYDROLOGY...AKQ