Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 222007

Area Forecast Discussion
National Weather Service Wakefield VA
407 PM EDT Tue Aug 22 2017

High pressure remains centered off the Mid Atlantic coast
through tonight as a cold front begins to approach from the
west. The front crosses the area late Wednesday afternoon
through Wednesday night, with strong high pressure building
north of the area from Thursday into the upcoming weekend.


Latest surface analysis centers high pressure over the western
Atlantic, with a lee/thermal trough over the Piedmont. Isolated
to widely scattered showers and thunderstorms have spread into
interior portions of northeast North Carolina, but the overall
trend is for the activity is to dissipate as it moves northeast.
Activity will dissipate this evening as instability wanes.

Warm/humid tonight with little chance for
any rain under a SW wind of 10 mph. Lows mainly in the mid to
upper 70s. Clouds increase across the north ahead of the
approaching cold front and lead shortwave. Have introduced a
slight chance PoP for the Maryland Eastern Shore late tonight,
but best chances for measurable precipitation remain north and
west of the local area.


Models in good agreement with dropping the cold front into the
local area Wednesday morning, then pushing the front across the
area through Wednesday afternoon. Shearing vort lobe progged to
ride along the front as winds increase aloft. The added forcing
along the boundary along a narrow ribbon of high precipitable
waters will result in scattered to numerous showers and
thunderstorms Wednesday afternoon. Downslope flow from 1-3km
will limit the coverage over the Piedmont, but hi-res and course
resolution guidance indicates that the activity should become
more organized central Virginia eastward as it interacts a
moderately unstable air mass (mixed-layer CAPE values 500-1500
J/kg) and marginal shear (25-30 knots). Dry mid levels and an
inverted V sounding indicate the main threat will be damaging
winds and frequent lightning. SPC maintains a marginal risk for
severe weather across the southeast half of the local area.
Heavy rainfall is also possible as the cold front slows as it
reaches southeast Virginia and northeast North Carolina
Wednesday afternoon. Precipitable water values progged around 2
to 2.25 inches. Westerly flow in the mid levels indicates that
the motion should prevent widespread heavy rainfall, but some
areas could see periods of heavy rainfall. No headlines planned
at this time. Flow becomes north to northeast behind the front,
as dry air spreads into the area from the northwest. The front
and upper wave push offshore Wednesday evening. Guidance
indicates a wave of low pressure develops along the front over
the Carolinas, keeping rain chances in northeast North Carolina
and far southeast Virginia through Wednesday night. Highs
Wednesday range from the mid 80`s northwest to around 90
southeast. Lows Wednesday night in the low to mid 60`s inland to
the low 70`s near the coast.

High pressure builds in from the northwest Thursday as the front
stalls along the Southeast coast. Will keep low chance PoPs
across northeast North Carolina Thursday nearest the front and
deepest moisture. Otherwise, dry, cooler and less humid
conditions expected. Highs Thursday forecast in the low to mid
80`s under a partly cloudy sky.


Cooler and drier for the late week period courtesy of building
longwave upper level trough over the eastern United States.
Meanwhile, broad 1024+ mb surface high pressure builds south over
the interior northeast from Great Lakes Thursday and Friday,
eventually setting up over New England and ridging down the east
coast over the weekend into early next week. Forecast remains mostly
dry, although a few showers possible along the coast in persistent
onshore flow.

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 Fri-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.


VFR and dry conditions prevail to begin the 18Z TAF period as
high pressure remains centered just offshore. Scattered cu with
decks around 3 to 4k feet AGL has developed across the region.
South to southwest winds generally 10-15 knots. Few gusts to 20
knots inland. Not much chance for any tstms today or this

A cold front approaches the region late tonight, but with a
continued SW flow, expect VFR conditions tonight/early wed
morning with fog/low stratus unlikely. Flight restrictions will
be possible with the front later on Wednesday...mainly in the
afternoon and through Wednesday night due to showers and
thunderstorms. The front should exit the coast Thursday morning
with lingering showers possible across far SE VA/NE NC.
Conditions are anticipated to improve Thursday afternoon into
Friday as the front shifts farther southeast and high pressure
builds north of the region. Breezy NE winds expected near the
coast Thursday and Friday.


A cold front will approach the waters from the northwest tonight,
crossing the area Wednesday through Wednesday night. Winds will
increase tonight ahead of the cold front with SSW winds of 15 to 20
knots possible across both the bay and ocean. A few wind gusts of 25
knots will also be possible across the northern ocean and bay zones.
As a result, went ahead and issued a Small Craft Advisory for the
Chesapeake Bay tonight into early Wednesday morning. Waves will
build to 2 to 3 feet in the bay and seas will build to 3 to 5 feet
in the northern zones. Winds shift to the N/NE 10 to 15 knots behind
the front by Wednesday afternoon through early Thursday morning.

Strong high pressure builds north of the region Thursday and into
the weekend. Expect wind speeds of 10 to 15 knots with a few
occasional gusts to 20 knots, particularly early Thursday morning as
the gradient tightens. Waves will be 1 to 3 feet and seas will be 2
to 4 feet.

Onshore (E-NE) flow for the late week period as high pressure builds
NNW of the local area. Winds remain elevated 10 to 15, occasional
gusts to ~20 kt through the late week period as a couple of waves
move across the stalled front to the south across the Carolinas.
Seas remain choppy for the late week period into the weekend with
the persistent onshore flow, remaining 2-4 ft northern waters...4-
5ft southern waters.


MARINE...Small Craft Advisory from 10 PM this evening to 6 AM EDT
     Wednesday for ANZ630>632-634-650-652.


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