Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 150217
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
917 PM EST Sun Jan 14 2018

.SYNOPSIS...
Canadian high pressure will settle over the eastern U.S.
overnight before sliding to our east later Monday. A clipper
system will bring a cold front through the area Tue night into
Wednesday. Low pressure will develop offshore late Wednesday
into Thursday before high pressure settles to our south late in
the week.

&&

.NEAR TERM /THROUGH MONDAY/...
High pressure will remain overhead overnight. Winds will remain
light and north to northeasterly. Aside from some high clouds
streaming across the region from southwest to northeast, dry
conditions will prevail. Tonight`s temperatures will drop into
the single digits in colder valleys and rural areas, while the
suburbs and metro areas will have lows in the teens.

A low pressure system will move from near Chicago early Monday
morning to Lake Erie by later in the day Monday. This low will
be accompanied by some moderately-strong upper level energy that
will move across lower Michigan during the day. As previously
mentioned, a jetmax will arrive during the same time and could
bring us more in the way of cloud cover. There may be just
enough lift that we can`t rule out a couple of flurries or
perhaps a brief period of very light snow in parts of the
region mainly east and southeast of I-95. Any flurries or very
light snow that does reach the ground would be from about mid-
morning to mid-afternoon. High temperatures Monday may only
reach the upper 20s and lower 30s.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
The moderately-strong upper level energy and jetmax should move
off to the north Monday night. A cold front will approach from
the Ohio Valley and a southerly flow will allow for relatively
milder conditions compared to Sunday night...but it will still
be cold.

A potent upper-level low will slowly pass through the eastern
Great Lakes Tuesday through Tuesday night. This system will be
strong enough for surface low pressure to develop over the same
area. The upper-level trough axis associated with this system
will swing closer towards neutral tilt during this time. A
strengthening jet will cause a band of precipitation to develop
Tuesday and it will slowly move south and east into our area.
Exact timing remains uncertain due to divergence in the
guidance. For now...the timing of snow is a blend between the
faster GFS and the slower ECMWF/NAM which is close to the GEFS
which lies in between. This means that the best chance for
accumulating snow Tuesday morning will be in the Potomac
Highlands...but it may make a run south and east toward the I-95
Corridor by Tuesday evening. There is a better chance for snow
later Tuesday night near and south/east of the I-95 corridor.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Light snow may be ongoing Wednesday as an upper trough and jet
max aloft move across the area and induce cyclogenesis off of
the eastern US coastline. Much of the precipitation tied to the
coastal low now appears to remain offshore, however upper level
forcing and jet dynamics still favor a period of snow
Wednesday. Some accumulation is likely, although timing and
amounts are still uncertain as non-trivial model differences
still exist.

Very cold and blustery conditions will then again follow behind the
departing system for later Wednesday, Wednesday night, and lasting
into Thursday morning. High pressure will then build south of the
region from Thursday through Saturday, which will promote southerly
flow and moderating temperatures over the Mid-Atlantic. A fast
moving upper level shortwave will race across the northern tier of
the country and into the northeast on Friday, and this may bring a
chance of some light precipitation.

By next Sunday, a low pressure system will be developing in the
central/southern Plains states and eject northeastward towards the
Great Lakes. This will further increase warm air advection and
southerly flow across the area.

Temperatures during the extended period will start quite cold with
highs in the 20s on Wednesday, and lows in the teens Wednesday
night. A gradual moderation is expected for the end of the week and
weekend with 30s for highs Thursday, 40s Friday, and then likely
breaking into the 50s by Saturday and Sunday.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR conditions are expected overnight. Warm advection behind
high pressure sliding east Monday will cause lower clouds to
develop across the eastern terminals. MVFR conditions are likely
for KBWI and KMTN...KDCA and possible for KIAD. A few flurries
are possible Monday across the same terminals. MVFR cigs may
continue Monday night across the eastern terminals.

A cold front along with low pressure will cause a band of snow
to develop Tuesday morning to the north and west. The snow will
slowly slide south and east...impacting the terminals later
Tuesday and Tuesday night. The snow may hang around for much of
Wednesday as well...especially across the eastern terminals.
Exact timing is uncertain but confidence has increased for a
period of accumulating snow during this time.

Primarily VFR will return for Wednesday night through Friday,
although some light precipitation is also possible Friday. Gusty
northwest winds are also expected to develop Wednesday into
Thursday.

&&

.MARINE...
High pressure will remain over the waters overnight...but a
weak pressure surge will cause northerly winds to channel down
the Bay/lower Tidal Potomac River. A Small Craft Advisory
remains in effect for the lower Tidal Potomac River and Maryland
Chesapeake Bay south of Smith Point. Weak high pressure will
remain just offshore Monday through Tuesday night. Winds should
remain below SCA criteria during this time.

Sub-SCA conditions are likely Wednesday into Thursday behind a
departing low offshore. Another period of SCA conditions are
possible on Friday with a weak system.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ533-534-537-
     543.

&&

$$
SYNOPSIS...KLW
NEAR TERM...BJL/KLW
SHORT TERM...BJL/KLW
LONG TERM...MM
AVIATION...BJL/MM/KLW
MARINE...BJL/MM/KLW


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