Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 151854
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
154 PM EST Mon Jan 15 2018

.SYNOPSIS...
High pressure will weaken and slide toward the east coast through
tonight. A cold front will approach the area Tuesday before
passing through Tuesday night into Wednesday. Low pressure will
develop along this boundary offshore later Wednesday before high
pressure settles to our south Thursday. High pressure will remain
to our south through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Clouds are building from both the east and the west this
afternoon in response to a shortwave aloft and low-level onshore
flow. These clouds will stick around through the night as high
pressure continues to weaken and move away and troughing
approaches from the west. Another cold night is expected despite
the clouds with lows generally in the 20s. Light snow likely
moves in/develops over the western ridges and into northwestern
Maryland by daybreak.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The much awaited cold front associated with the approaching
trough will move slowly eastward into the area during the day
Tuesday. As heights fall and lift increases, anticipate snow
(mainly light) to continue developing eastward, eventually
reaching the NW suburbs of DC/Baltimore after dark. There is
still some uncertainty in timing, but the most likely scenario
is one where snow moves into the Shenandoah Valley and parts of
north-central Maryland (northern Baltimore to Frederick County
MD) between 4 and 7 PM, pushing across I-95 between 8 and 11 PM.

The steadiest snow from the Shenandoah Valley eastward to the
metro areas should be between late Tuesday evening and early
Wednesday morning, likely impacting the Wednesday morning
commute. Steadier snow should enhance/linger across portions of
central Virginia (the Charlottesville area) to southern Maryland
through Wednesday morning as a wave of low pressure develops
offshore. Meanwhile, dry air advecting in from the northwest
should cause snow to cease across much of eastern West Virginia,
northern Virginia and northern Maryland by mid-morning
Wednesday. In general, anticipating 1-2 inches across much of
the area, with 2-4 inches across the higher elevations and
central Shenandoah Valley into parts of central Virginia where
higher ratios/stronger forcing and moisture will be juxtaposed.

Have issued an advisory across the Allegheny Front and northern
Maryland/eastern West Virginia where confidence is highest, and
hoisted a Special Weather Statement for a potentially hazardous
Wednesday morning commute for the I-95 corridor.

Clearing and breezy conditions are expected Wednesday night as the
cold front pushes east, ushering in another Arctic airmass. Cold
wind chills are possible again over the higher elevations which
could warrant an advisory Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
High pressure will remain to our south over the southeastern CONUS
into the Atlantic Thursday through the weekend. A west to southwest
flow will allow for a moderating trend in temperatures. In
fact...this weekend max temps in the 50s are most likely. Dry
conditions will likely persist during this time as well.

Overall there is good pattern agreement amongst guidance for the
long term period. On Thursday morning, the upper level trough will
be exiting the east coast, giving way to a shortwave ridge and
surface high pressure building across the Mid South. While high
temperatures will return closer to seasonal normals, Thursday night
will likely be cold (teens/20s) again with light winds and mostly
clear skies.

Low pressure will track into the Great Lakes later Sunday into
Monday. The cold front associated with the low will approach our
area during this time. A southwest flow will continue to usher in
milder conditions...but increased moisture from the Gulf of Mexico
and the forcing from the front will cause increasing chances for
precipitation. Timing is uncertain this far out.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
MVFR cigs expected to persist through tonight for eastern
terminals in onshore flow. -SN with possible restrictions likely
reaches MRB around daybreak. Patchy fog is hinted at east of the
Blue Ridge tonight by some guidance, but left out for now given
seemingly low likelihood with cloud cover, though non-zero
potential given onshore flow.

Sub-VFR (IFR possible at times) likely Tuesday night in -SN. VFR
should return by midday Wednesday. Winds should be light today
through Tuesday, then become NW and blustery by Wednesday.

High pressure will settle to the south and east for Thursday
through Saturday. A west to southwest flow is expected during this
time. VFR conditions are most likely during this time.

&&

.MARINE...
Generally light winds expected through Tuesday. NW winds
increase likely to SCA levels early Wednesday morning. High
pressure  will settle off to the south and east Thursday
through the weekend. A west to southwest flow is most likely
during this time. A Small Craft Advisory may be needed for
portions of the waters Thursday. Winds may approach SCA criteria
Friday into the weekend as well, but confidence is low.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for
     MDZ003-501-502.
     Winter Weather Advisory from 4 PM Tuesday to 7 AM EST
     Wednesday for MDZ004>006-507.
VA...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for
     VAZ503.
WV...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for
     WVZ050>053-055-501>505.
MARINE...None.

&&

$$
SYNOPSIS...BJL
NEAR TERM...DHOF
SHORT TERM...DHOF
LONG TERM...BJL
AVIATION...DHOF
MARINE...DHOF



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