Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 250156
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
856 PM EST Wed Feb 24 2021

.SYNOPSIS...
A cold front will pass through the area tonight and high
pressure will build in behind the boundary through Friday. A
multi-low system will impact the region late Friday and through
this weekend. High pressure returns for early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A cold front that extends from western Maryland through West
Virginia this evening will continue to drop south and east,
passing through our area tonight. A few showers are expected in
the Allegheny Highlands, and perhaps into eastern West
Virginia, western and north-central Maryland, and the northern
Shenandoah Valley. However, dry conditions are most likely to
persist farther southeast as the boundary outruns the upper-
level support well to our north. Having that been said, a
sprinkle or stray shower cannot be completely ruled out, but
confidence is too low to introduce into the forecast at this
time.

A southwest flow has allowed for unusually mild conditions this
evening. However, a northwest flow overnight will bring a return
of more seasonable temperatures along with gusty winds. Bumped
up wind speeds overnight to gust around 25 to 40 mph behind the
boundary. Latest bufkit guidance does show a small stable layer
near the surface, which would keep the strongest winds over the
ridges. However, given the cold and dry advection combined with
the pressure rises, latest thinking is that these winds will
make it into the valleys and Wash/Balt metro areas as well.
Therefore, the latest forecast has been updated to reflect that,
with the strongest winds over the northern and central portions
of the CWA where the pressure surge behind the cold front will
be strongest.

Precipitation may change to scattered snow showers along and
west of the Allegheny Front before ending late tonight. Any snow
accumulation will be light, but with temps falling below
freezing there may be slippery areas by the morning along the
ridges.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
The cold front will pass southeast of our region by early Thursday
morning. Behind the frontal passage, winds will become west to
northwesterly leading to advection of cooler and drier air into our
region. Skies will become mostly clear with cooler afternoon temps
in the mid to upper 40s to low 50s. Overnight lows will be chilly in
the 20s and lower 30s.

High pressure will build into our region Thursday afternoon and
remain situated over the region through Friday. Temperatures will
moderate through this period with near normal temps in the upper 40s
to lower 50s. The high pressure overhead and will shift eastward off
the eastern seaboard Friday afternoon.  A multi low frontal system
will pass to the south of our region late Friday and into Saturday.
A coastal low will form along this frontal system and move north
into our region on Saturday. The initial precipitation associated
with this system will impact our region early on Saturday morning.
Wintry precipitation during the initial onset (especially near
the Mason-Dixon Line and along the ridges) is possible, but the
high pressure becoming situated off the coast will lead to a
east to southeasterly flow which will advect in warmer and more
moist air into our region and limit below freezing conditions.
Therefore, confidence for wintry precipitation in the valleys
lowers. Overnight lows will hover in the 30s with near freezing
temps mainly along the Allegheny front and along the ridge tops
in the Potomac Highlands and Blue Ridge Mountains.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Wet weather appears in store for Sunday and Mon as series of upper
level disturbances move across the region north of a stationary
front along the NC/VA border. There could multiple periods of rain
or repeated activity as front remains stationary, but lack of
instability suggests rain will be stratiform limiting rainfall
rates, and thus, potential for any flooding. EPS reasonable worst
case scenario is for amounts ranging from an inch across the north
to inch and half across the south.

High pressure builds for Mon night before another low pressure
impacts the area next Wednesday.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
A cold front will pass through the terminals tonight. Strong
northwest winds are likely to develop behind the boundary with
gusts around 25 to 30 knots (with even a few gusts around 35
knots possible). The strongest winds are expected after 02z at
KMRB, and after 05z across the rest of the terminals. Gusty
winds will continue into Thursday morning before diminishing
later Thursday as high pressure draws closer. High pressure will
bring VFR conditions through Thursday night.

A brief period of VFR overcast conditions will be possible
Friday morning as an upper level jet passes overhead. Winds will
become east to southeasterly on Friday with gusts of 10 to 15
knots.

Flight restrictions likely Sunday into Monday.

&&

.MARINE...
A south to southwest flow will continue through this evening
with a few gusts near SCA criteria. However, a cold front will
pass through the waters overnight, and strong northwest winds
are expected behind the boundary. Frequent gusts around 25 to 30
knots are expected (especially after 05z from northwest to
southeast). An SCA is in effect for all of the waters. Gale
force gusts are possible during this time, but confidence is too
low for a Gale Warning since the strongest wind field aloft
will occur when air temperatures are still a little warmer than
the water temperatures (despite cold advection). This will have
to be monitored closely because a Gale Warning may be needed
briefly overnight.

Winds will gradually diminish Thursday as high pressure draws
closer. SubSCA conditions likely Thursday evening into Friday.

SCA conditions do not appear likely as area remains stable north of
a surface front.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 11 AM EST Thursday for ANZ531-538-
     539.
     Small Craft Advisory until 1 PM EST Thursday for ANZ532>534-
     537-540>543.
     Small Craft Advisory from 1 AM to 11 AM EST Thursday for
     ANZ530-535-536.

&&

$$
SYNOPSIS...JMG
NEAR TERM...BJL/JMG
SHORT TERM...JMG
LONG TERM...LFR
AVIATION...BJL/LFR/JMG
MARINE...BJL/LFR/JMG


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