Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 200018 CCA

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
818 PM EDT Mon Mar 19 2018

Low pressure over southern Missouri will push across the Tennessee
Valley later tonight. A coastal low will develop along the mid-
Atlantic Coast Tuesday ahead of this main low pressure system. A
second low pressure system will develop off of the Tidewater of
Virginia Tuesday night and move northeast Wednesday. Canadian high
pressure returns for the latter half of the work week.


A large area of stratiform rain is pivoting across the Ohio
Valley this evening. Expect this to move into the area after
midnight for the western ridges, then progress eastward toward
the metros by daybreak. Precipitation should start as all rain
except over western Maryland and parts of the eastern West
Virginia panhandle where it will be cold enough for a wintry
mix of snow and sleet. An east-southeast flow at the surface
will gradually back around to the northeast as energy from the
western low transfers to the coast. Temperatures will be in the
lower to middle 30s for the most part. Rain amounts will
average one tenth to one quarter of an inch in northeastern
zones and one quarter to one half inch in southwestern zones.
Any ice accumulation will range from trace to a few hundredths
of an inch and be mainly over the Appalachian Front, eastern
West Virginia and western Maryland.


As the first storm, coastal low, develops nearshore Tidewater of
Virginia, a transition from a wintry mix will become more of a
snow and sleet mix Tuesday morning and continue through the
remainder of day mainly west of the Blue Ridge. Significant snow
and sleet accumulations are expected over the Potomac Highlands,
with a glaze of ice expected as well across the Shenandoah
Valley, Blue Ridge and northern Maryland.

There should still be a lull in precipitation late Tuesday
afternoon into Tuesday evening but with some uncertainties as
to how long in time and coverage. Once the lull is over, an
enhancement of precipitation will start up again sometime
Tuesday afternoon and should be in the form of mainly snow. Some
sleet may mix in at times.

As it will be snowing in most areas to the north and west of the
Metropolitan areas, a second coastal low will develop near the
Delmarva Peninsula late Tuesday into Tuesday evening. As this
low moves northeastward Tuesday night and early Wednesday, low
pressure will reside at the surface and aloft over West Virginia,
helping spread snowfall across much of the CWA.

Overall we have increased precipitation amounts for our entire
CWA through Wednesday. The models have trended toward a more wet
and colder solution for the second of the two storms.

The second low will pull away from the coast on Wednesday,
bringing an end to precipitation by the evening. Temperatures
through the period will remain below normal as cold air
advection wins out along with precipitation and ample cloud
cover affecting the region.


A high pressure system will be in control of our forecast area
Thursday into Friday night allowing for dry conditions over
most of our region. Northwesterly winds during these days could
bring additional snow showers west of the Allegheny Front,
mainly on Thursday. A boundary and low pressure system may
affect us during the weekend bringing additional snow/rain to
the area but there is still uncertainty on track and timing.


MVFR/IFR VIS and CIGs expected to overtake the terminals
toward daybreak as low pressure approaches from the west,
bringing precipitation from south to north. A break in
precipitation Tuesday afternoon could provide some improving
conditions, but likely remain MVFR/IFR.

Another low pressure area poised to bring wintry precipitation
to the terminals Tuesday night and early Wednesday, resulting
in continued MVFR/IFR VIS and CIGs. Winds are expected to be
east southeast this afternoon, backing out of the north to
northeast tonight, remaining at 10 knots or less.

VFR conditions expected over the terminals on Thursday and
Friday with high pressure in control. Breezy conditions expected
on Thursday with gusts reaching up to 20 kts. Saturday
conditions will depend on the track and timing of another low
pressure system that could affect our area.


Low pressure will move south of our area tonight and redevelop
off the coast early Tuesday. This will bring SCA conditions
across our waters starting tonight. A Gale Warning has been
issued for the lower Chesapeake as the low strengthens and
passes to our east, delivering a strong pressure gradient over
the waters. Small Craft Advisories to perhaps Gale Warnings are
anticipated through the day Tuesday and will likely be required
through the day on Wednesday as another low pressure area
approaches the waters from the south.

Wind gusts will be above small craft criteria on Thursday,
therefore a small craft advisory is likely. Winds should remain
below criteria Friday and Saturday.


Two areas of low pressure will pass off the coast Tuesday and
Wednesday, resulting in prolonged onshore flow. Water levels
will be rising during this time, with minor flooding becoming
possible by Wednesday. Exact projections are still uncertain at
this time though.


DC...Winter Storm Watch from late Tuesday night through Wednesday
     evening for DCZ001.
MD...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for
     Winter Storm Watch from late Tuesday night through Wednesday
     evening for MDZ003>006-011-013-014-503>508.
     Winter Storm Warning from 5 AM to 8 PM EDT Tuesday for MDZ501-
     Winter Storm Watch from Tuesday evening through Wednesday
     afternoon for MDZ501-502.
     Winter Storm Watch from Wednesday morning through Wednesday
     evening for MDZ016>018.
VA...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for
     Winter Storm Watch from late Tuesday night through Wednesday
     evening for VAZ025>031-040-052>054-501-503>508.
WV...Winter Weather Advisory from 6 AM to 6 PM EDT Tuesday for
     Winter Storm Watch from late Tuesday night through Wednesday
     evening for WVZ051>053.
     Winter Storm Warning from 5 AM to 8 PM EDT Tuesday for WVZ050-
     Winter Storm Watch from Tuesday evening through Wednesday
     afternoon for WVZ050-055-501>506.
MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT
     Wednesday for ANZ531>533-537-539>542.
     Small Craft Advisory from 6 AM Tuesday to 6 PM EDT Wednesday
     for ANZ530-535-536-538.
     Small Craft Advisory from midnight tonight to 6 AM EDT Tuesday
     for ANZ543.
     Small Craft Advisory from 6 PM Tuesday to 6 PM EDT Wednesday
     for ANZ534-543.
     Gale Warning from 6 AM to 6 PM EDT Tuesday for ANZ534-543.
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ534.


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