Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 231810
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
210 PM EDT Wed Aug 23 2017

.SYNOPSIS...
A cold front will cross the area this afternoon through tonight,
with strong high pressure building north of the area from
Thursday into the upcoming weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest surface analysis depicts a cold front over the northwest
Piedmont. Early morning showers have mostly dissipated over the
northern counties as the best forcing lags over the mountains.
Sunny conditions observed on visible satellite ahead of the
front, which will result in a quick warm up into early
afternoon. An already humid air mass is in place, with mixed-
layer CAPE values analyzed at 500-1000 J/kg already this morning
across southeast Virginia and northeast North Carolina. Across
the northwest, temperatures will hold nearly steady through the
afternoon.

The front slowly pushes across the local area through mid
afternoon, before slowly along the coast in southwest flow
aloft. The shearing vort lobe progged to ride along the front,
as winds increase aloft. The added forcing for ascent along the
boundary along with a narrow ribbon of high precipitable waters
will result in scattered to numerous showers and thunderstorms.
Westerly mid level flow and weak lapse rates will limit coverage
over the Piedmont, but as instability increases across central
Virginia eastward (mixed layer CAPE values of 1-2k J/kg), hi-res
guidance indicates that convection should become better
organized. Marginal shear (20-30 knots) expected as the best
upper level flow remains north of the region, but given
relatively dry mid-levels and an inverted-V sounding, damaging
winds are possible. The best chances for strong to severe storms
are across the southeast half of the local area where SPC
maintains a marginal risk for severe weather. Another concern
will be along the coast as the front slows and better upper
level support arrives. Impressive omega along the front along
with precipitable waters in excess of 2 inches and MBE vectors
at or below 10 knots will result in locally heavy rainfall.
Flash flood guidance across the southeast is around 2-3 inches,
but given the overall progressive nature of the system, do not
anticipate widespread impacts from flooding. Headlines are not
anticipated.

Flow becomes north to northeast behind the front, as drier air
starts to spread into the area from the northwest later this
afternoon into tonight. Guidance indicates some linger moisture
over the Piedmont into central Virginia behind the front as
another area of convergence could result in additional showers
into this evening. Have increased cloud cover inland late today
through this evening and lingered chance PoPs inland through the
evening hours. Showers/thunderstorms diminish along the coast
through the evening as instability wanes and the shortwave
pushes offshore.

Highs today will range from the low 80`s northwest to low 90`s
southeast. Low tonight generally in the low to mid 60`s
northwest to low 70`s southeast.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
The front and waves of low pressure will push SE of the region
and offshore overnight thru Thu. Those waves of low pressure
will maintain slgt chc to chc Pops over extrm SE VA and NE NC.
Lows tonight will range fm the lower 60s extrm NW counties, to
the lower 70s extrm SE VA and NE NC.

High pressure will slowly build in from the northwest Thu thru
Fri, with the front getting pushed well SE of the area off the
SE coast. This will result in dry, cooler and less humid
conditions for Thu night thru Fri. Highs on Thu in the lower
80s under a partly sunny sky. Lows Thu night in the 60s. Highs
on Fri in the upper 70s to lower 80s under a partly to mostly
sunny sky.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Cooler and drier for the most of the extended period, as high
pressure builds acrs the Great Lakes and New England Fri night
thru Mon, and ridges southward into the region. Low pressure
moving NNE off the SE coast could affect the area on Tue.

Medium range guidance in relatively good agreement with developing a
tropical system along and offshore of the southeast coast along the
old frontal boundary early next week. Kept weekend dry, with low
rain chances along the SE coast by Monday. Looking ahead, rain
chances look to improve into the middle of next week, with moisture
from the remnants of Harvey looming to the SW. For temperatures,
high temperatures Sat-Mon will be at or just slightly below
normal through the period, mainly in the upper 70s to low 80s.
Early morning lows in the 50s inland to mid 60s along the coast.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
A cold front is pushing across the local area to begin the 18Z
TAF period. Behind the front, scattered to numerous showers and
thunderstorms are developing across the Piedmont into central
Virginia in a warm, moist, and unstable air mass. Showers and
thunderstorms will push eastward through this evening, becoming
better organized across central and eastern Virginia. Locally
damaging winds, heavy rainfall, and frequent lightning are the
main threats. The front pushes offshore and south of the region
tonight, with lingering chances for showers along the coast.
Flight restrictions are possible under the strongest storms.
MVFR ceilings are possible across southern Virginia and
northeast North Carolina tonight. Wind becomes north to
northeast behind the front, generally at or below 10 knots.

High pressure builds in from the northwest on Thursday as the
front stalls along the Southeast coast. An uptick in northeast
winds is anticipated Thursday morning with a surge of cold
advection, but winds diminish mid to late morning. Flow also
results in broken to overcast skies near the coast Thursday with
lingering chances for showers across the far southeast.

High pressure slowly builds north of the region through
Saturday, with periods of clouds due to onshore flow. Winds
remain northeast.

&&

.MARINE...
A cold front will approach the waters from the northwest and
cross the area late this aftn through tonight. SW flow still
avearges 15-20 kt over the Bay and coastal waters, have the SCA
headlines through 7 am for the entire Bay and for the nrn coatl
waters. Waves avg 2 to 3 feet in the bay and seas acrs the N are
4-5 ft. Winds shift to the N/NE 10 to 15 knots behind the front
by late this morning N and by aftn farther S (and with
convection this aftn winds will be locally much stronger but
this will be handled w/ MWS/SMW`s as needed).

Strong high pressure builds north of the region Thursday and
into the weekend. Given the warm waters and some cold advection
late tonight/Thu morning, expect a marginal SCA event over at
least some of the Bay and probably the lower James Thu morning.
Did not raise any SCA headlines as this will be mainly a 3rd
period event (and still fairly marginal). Otherwise expect
diminishing winds later Thu aftn through Fri as sfc high
pressure builds a little farther south and the pressure gradient
weakens. Waves in the lower Bay may briefly build to 3-4 ft Thu
morning, then will subside to 1-2 ft with coastal seas 3-4 ft.

Onshore (E-NE) flow for the weekend as high pressure builds NNW
of the local area and then shifts east to New England. Winds
remain elevated 10 to 15, occasional gusts to ~20 kt Sat, and
then increase more significantly Sunday into next week as
stalled front to the south lifts back N with low pressure
developing along the boundary. Seas remain choppy Sat, and then
will build to 5-7 ft or greater late Sun into next week.

&&

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

&&

$$
SYNOPSIS...TMG
NEAR TERM...SAM
SHORT TERM...LKB/SAM/TMG
LONG TERM...MAM
AVIATION...SAM/TMG
MARINE...LKB



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