Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 150836

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
336 AM EST Wed Feb 15 2017

A cold front will pass through the region this morning. High
pressure builds overhead through Friday and then remains nearby
into early next week.


Precipitation shield associated with the southern stream disturbance
will clip the southern third of the forecast area this morning. With
measurable precipitation remaining near/south of Washington DC.
Likely PoPs across central VA into S MD...with up to a quarter inch
of rainfall there (further north near DC less than a tenth of an
inch). Precipitation associated with this feature should begin to
push out of S MD by late morning.

Cold front associated with northern stream upper-level trough
crosses the area early this morning with gusty NW winds (20-30 mph)
developing in its wake. Potent vorticity maxima rotates around the
base of upper-level trough as it approaches our area later this
morning. This will help to induce scattered showers across the Mid-
Atlantic near midday. High-resolution guidance is hinting at the
potential for a broken line (or line) of showers to develop. If a
quasilinear feature can materialize/organize...then gusty
convectively induced showers would be possible. Steep low-level
lapse rates suggest that some of these showers N/W of I95 could be
snow despite near surface temperatures AOA 40F. Shallow nature of
the convection would preclude lightning for all areas but the wind
turbine belt across the Allegheny Front where snow is expected to be
the dominate P-Type. Any activity east of the Allegheny Front should
diminish by early evening.

Burst of heavier snow possible along the Allegheny Front this
evening through early tomorrow morning as upslope flow induces lift
within saturated DGZ. Window for accumulation rather
inversion quickly lowers by morning. Maximum 12-hour accumulation
just above 2 inches...with 95th percentile near 2.5 inches. Thus,
probability of reaching advisory criteria very low and held off on
any advisories across this area.


Cold air advection continues high pressure starts to
build toward the area. Gusty winds will redevelop by morning as
diurnal mixing increases and then continue through afternoon. Highs
generally in the upper 30s/lower 40s.

High pressure slides to our south Friday...with slight moderation of
temperatures back to seasonable norms and relatively light winds.
While current forecast remains dry...a few members of the GFS family
continue to suggest some light precipitation as subtle shortwave
crosses the area.


A large ridge of high pressure will build across the eastern
portion of the United States for the extended forecast period.
As a result, expect warm and benign conditions. There are a
couple of things to monitor though. First will be a southern
stream shortwave undercutting the forecast area Saturday night
into Sunday morning. Have a period of partly cloudy skies at the
moment. Depending on this path and strength, this potentially
could result in a few showers, mainly for central Virginia and
southern Maryland. The other feature at the moment is a northern
stream disturbance on Tuesday. Guidance right now is keeping
most of this precip north of the area. That too could change.
Considering current temperature forecasts though, any
precipitation would be just rain. Very un-February-like...10-15
degrees above normal.


While VFR conditions prevail through Friday night...gusty NW winds
(~25-30 knots) develop later this morning behind frontal passage.
The gusty winds abate some tonight (though gusts 15-20 kts possible
overnight at DCA/BWI/MRB/MTN). Gusty W/NW winds redevelop Thursday
morning as diurnal mixing increases...gusts ~25-30 kts possible.
Gusty winds will subside Thursday night.

VFR conditions anticipated this weekend, with lighter winds.


Solid SCA criteria northwesterly winds develop later this morning in
cold air advection behind cold front. By early afternoon...expect a
line (or broken line) of scattered showers (perhaps with some snow
across the northern Chesapeake Bay) to traverse the waters...which
could lead to some isolated gale force wind gusts. Current thinking
is coverage would be too temporally limited at any one given
location for a Gale Warning and that if these gusty showers
develop that they could be handled with Special Marine Warnings
(if needed)...though this will continue to be evaluated.

Wind field strengthens further tonight...though reduced mixing
should limit wind gusts to high-end SCA criteria. Despite increased
mixing Thursday...wind field begins to weaken enough to keep gusts
mostly high-end SCA. While a low-end Gale Warning remains possible
Thursday...probability is currently low. Extended current SCA
headline through Thursday evening. SCA may need to be extended
further into Thursday night for portions of the Chesapeake Bay.
Winds abate early Friday as high pressure builds overhead.

Winds anticipated to be mostly 10 kt or less this weekend.


MARINE...Small Craft Advisory from 9 AM this morning to 6 PM EST
     Thursday for ANZ530>543.


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