Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 151521
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1021 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.
.NEAR TERM /THROUGH TONIGHT/...
Rain will continue to move south of the Mid-Atlantic region this
morning as a southern stream disturbance moves to our south. A
cold front is moving through the outlook area this morning.
Isolated to scattered snow showers are across Central PA and
dropping south into the Mid-Atlantic. Snow showers have been
observed across the higher elevations on the Allegheny Front
this morning causing a dusting. Further east...temperatures have
climbed into the upper 30s and low 40s. Rain was reported at
HGR and MRB. The showers with the front will continue to move
eastward however most activity should stay north of I-66 this
morning and early afternoon. Expect gusty winds behind the front
as gusts near 30 mph have been reported behind the front.
Steepening lapse rates are expected behind the front resulting
in good mixing and gusty winds. Expect gusts up to 30 mph. Isolated
showers are expected this afternoon. Even with temperatures
reaching the low to mid 40s cant rule out snow or rain changing
to snow. Gusty winds will likely also increase within showers
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 limited...as
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.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Cold air advection continues Thursday...as 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.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
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.
.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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 until 6 PM EST Thursday for ANZ530>543.