Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KAKQ 241740
Area Forecast Discussion
National Weather Service Wakefield VA
140 PM EDT SAT SEP 24 2016
A backdoor cold front drops south across the region today. High
pressure tracks across Southeast Canada early next week. A second,
stronger cold front will cross the region later Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
Backdoor cold front rather easy to identify late this morning as
it begins to move south across the lwr MD ern shore. Winds shift
to the NNE along with a BKN-OVC ST deck between 1K to 1.5K ft.
This trend expected to continue thru out the day as the front sags
south. Plenty of heating ahead of it allows temps to rise into the
80s under mstly sunny skies. Tmps tricky post fropa as readings
may hold steady or fall due to the cloud coverage and wind shift,
especially across the lwr MD ern shore.
High-res models continue to show an area of rather shallow lift
along the front as it drops across the southern half of the area
from late aftn through about midnight. Expect most areas to remain
dry, but thnk sct showers will be possible after 18Z, mainly across
the piedmont and I-85 corridor. QPF will be minimal with still
relatively dry air aloft. and only weak isentropic lift.
Front drops south of the area late tonight, with sct showers
along the boundary likely lingering into the morning hours. Clouds
will be on the increase post-frontal, especially inland with post
frontal nne flow as high pressure ridges down and cool air wedge
begins to set up. Accordingly beefed up sky cover tonight and into
Sunday. Lows Sat night in the mid 50s north to mid 60s south.
.SHORT TERM /SUNDAY THROUGH MONDAY/...
Front continues to push south into the Carolinas Sunday in
response to high pressure sliding across Southeast Canada. This
high extends south across the Mid Atlantic Region Sunday and
Sunday night. Have again increased SKY cover to account for
increasing low level moisture/ongoing weak isentropic upglide.
Overcast conditions and pockets of light rain or drizzle remain a
good bet along and west of the I-95 corridor. Pops remain only in
slight chc range with minimal chances for measuring pcpn.
Nonetheless, drizzly and overcast inland...a mix of some sun along
with clouds along the coast. Highs Sun 70-75. Lows Sun night in
the mid 50s to lwr 60s. Cooler readings in the lower 50s with
clearing sky across Eastern shore.
Upper ridge pivots to the coast on Monday, before sliding offshore
Monday night. At the sfc, high pressure moves north of New
England Monday with the next front approaching from the west
during the afternoon. Across the piedmont, cool air wedge will
hold on one more day...with lingering clouds, onshore flow
maintaining cool temps. Monday highs generally in the low to mid
70s, upper 70s to around 80 along the SE coast.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Strong cold front progged to drop into the region Monday night ahead
of a potent northern stream trough. Latest deterministic and
ensemble guidance in good agreement with pushing the front across
the region late Monday night through Tuesday. Moisture increases
along the front with precipitable waters climbing above 1.75 inches.
Instability progged to be marginal ahead of the front due to cloud
cover and poor lapse rates, However, will keep mention of slight
chance thunder in the area of highest showalter values (elevated
instability) and shear around 40 knots. Both GFS and ECMWF models
push the front across the region rather quickly Tuesday with much of
the area seeing a decent chance for shower. Have capped at high end
chance. High pressure builds in from the west late Tuesday and
Tuesday night. Will linger POPs over the southeast half of the
forecast area, but expect much of the precip to push offshore by
late Tuesday night. High pressure prevails through the end of the
week and into the weekend.
Temperatures will average close to seasonable averages, with highs
Tuesday ranging from the mid 70`s northwest to around 80 southeast.
Highs Wednesday through Friday generally in the 70`s with lows in
the 50`s, expect in the 60`s southeast. Based on the latest
statistical guidance, the Piedmont may see some readings in the
40`s Thursday morning.
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --Backdoor cold front moving south across the region this afternoon.
Wind shift to the north well ahead of it, but the boundary is
denoted by a BKN-OVC ST layer between 1.5-2.5K ft. This cloud
deck will lift a bit (btwn 3-4K ft) as it drifts south across the
region over the next several hours. The MVFR conditions along with
NNE winds at 10 mph or less continue through most of the forecast
period west of the Ches Bay. Model data indicating drier air from
the north begins to work its way south along the Delmarva late
tonight with SCT-BKN cloud coverage. Latest data continues to
support VFR conditions at SBY after 12Z Sun.
A light shwr/sprnkl possible at RIC tonite as the wedge sets up,
but coverage not widespread enuf to include in forecast attm. Fog
not expected to be an issue tonight, but local MVFR VSBYS (3-5SM)
possible towards sunrise.
The next chc for sgnfcnt pcpn comes late Monday night and Tuesday
ahead and along the next cold front.
-- End Changed Discussion --
Weak pressure gradient observed over the waters early this morning
as a cold front drops into the northern Mid-Atlantic region. Winds
are generally out of the west-southwest at or below 10 knots. Seas 3-
4 feet and waves 1-2 feet. The weak front drops southward over the
waters today, with flow becoming northernly. 850mb temps dip
slightly behind the front, but a lack of low level cold air
advection and weak gradient winds expected to keep winds sub-SCA
this afternoon. Hi-resolution guidance has trended lower on speeds
as well. Waves build to 2-3 feet late morning/early afternoon. For
the coastal water, distant tropical cyclone Karl will aid in
building seas to 4-5 feet this afternoon through tonight. Have
raised SCA headlines for all coastal waters as a result. Expect a
few gusts to around 20 knots, so have opted against SCA for
hazardous seas. High pressure builds southward over the waters
tonight, with northernly winds diminishing to around 10-15 knots.
Seas subside to 3-4 feet Sunday afternoon. Waves 1-2 feet.
The next cold front approaching from the northwest will shift winds
back to the south to southeast Monday. Marginal southerly SCA
conditions are possible ahead of the front late Monday and Monday
night behind a lifting warm front. The front progged to reach the
waters Tuesday morning, pushing offshore Tuesday afternoon. SCA
conditions expected behind the front as a significantly cooler air
mass and strong high pressure builds in from the northwest.
-- Changed Discussion --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 Sunday evening. See FLSAKQ for details.
-- End Changed Discussion --
MARINE...Small Craft Advisory until 10 AM EDT Sunday for ANZ650-652-654-