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209
FXUS61 KLWX 210920
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
420 AM EST Mon Jan 21 2019

.SYNOPSIS...
Arctic high pressure will build over the region through Tuesday,
before sliding off the Mid Atlantic coast Tuesday night. A cold
front will move into the Ohio Valley on Wednesday, as low
pressure riding along the boundary moves across the area
Wednesday night and into Thursday. Another cold front will
cross the area on Friday as high pressure builds back over the
region the first half of the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Arctic high pressure stretches from Ontario southward into the
Mississippi River Valley this morning, as low pressure over Nova
Scotia continues its track northward. The strong pressure
gradient between the building high and exiting low continues to
produce strong northwesterly winds across the Mid Atlantic,
with gusts of 25-35 mph being observed over the CWA. The main
story this morning, and really through tonight will be the very
cold temperatures being driven into the region. Observations
early this morning have temperatures in the single digits to
teens across the area. Factor in the winds mentioned above, wind
chill values are below zero for a majority of locations, with
some dangerously cold values as low as -25 to -30F along the
higher elevations of the Alleghenies. As such the Wind Chill
Warning remains in effect until this afternoon for the higher
elevations of the Alleghenies, and a Wind Chill Advisory
continues for everyone else through 11am.

Given the gradient remains strong with the exiting low and
building high, wind chills will hover around zero for much of
the day as highs likely hold in the teens, with low 20s along
our far southern zones. Did consider a potential Wind Advisory
this morning into early afternoon for portions of northern and
northeast MD, as we could see some gusts upwards of 40-45mph.
Don`t think the frequency of Advisory level gusts and the
overall likelihood is high enough at this time to warrant an
issuance. Regardless, a blustery and very cold day is in store
for the region, despite ample sunshine. Be sure to dress in
layers if you are planning on spending anytime outdoors today,
ensuring to protect any exposed skin.

High pressure will build overhead tonight, with clear skies and
a gradual decrease in winds. This will allow wind chills to
remain below Advisory levels, however low temperatures will be
exceptionally cold in the single digits for much of the area,
teens being observed in the cities and near the larger bodies of
water. Locations along the Alleghenies, Potomac Highlands, as
well as portions of the Shenandoah Valley will likely fall
below zero.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The high will begin to shift off the coast Tuesday afternoon
and Tuesday night as a return flow sets up over the area.
Temperatures will rebound on Tuesday back into the 30s under
mostly sunny skies, but remain below normal for the latter half
of January. Clouds will be on the increase Tuesday night as
southwest flow aloft and warm air advection improves ahead of a
frontal boundary cross the Mississippi Valley and low pressure
nears the Great Lakes. As clouds increase Tuesday night ahead of
the approaching system, some light wintry precipitation will be
possible across portions of western MD/WV in the predawn hours
Wednesday. Not expected much in the way of accumulation, but
some light freezing rain and/or sleet will be possible. Low
temperatures Tuesday night will range from the lower 20s to near
30 degrees.

The frontal boundary will near the area on Wednesday, bringing
rain to the region as warmer air wins out with highs in the
middle 40s to lower 50s. The boundary will linger across the
area Wednesday night as low pressure moves along it. This will
result in periods of moderate to heavy rainfall. As the low
nears the Delmarva late Wednesday night and early Thursday
morning, colder air will try to filter in on the backside to
bring a change over to rain/snow in the Alleghenies.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
A low pressure system will move across our region Thursday.
Rain, associated with the low, will be moderate to heavy at
times with the potential for a little snow on the back side
of this low. Once the low moves off the East Coast, drier air
will encompass much of the region with the possibility of some
upslope snow showers in the Potomac Highlands Thursday night.

Colder temperatures and drier air will ensue Friday and Friday
night before a brief cold front makes an attempt to cross the region
late Saturday into Saturday night. A couple of snow showers or
squalls could develop with this front.

An arctic high will build in behind this front and settle overhead,
briefly, late Saturday night into early Sunday. Another low pressure
system will develop to our south Sunday into Monday and move
northeast either over the Interior Southeast U.S. or near the East
Coast. Either way, this storm should be the one to watch throughout
the week as it has the potential to pull in colder air from the
northwest and enable the development of some accumulating snowfall.
The European model is hinting of this very thing. However; timing
and intensity of this storm system is how the GFS model is
differing from the European.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Gusty northwest winds and VFR conditions will persist today
across the terminals. As high pressure builds over the terminals
tonight, winds will abate, with clear skies and VFR conditions
persisting through Tuesday night.

A return to sub VFR conditions likely on Wednesday as a frontal
boundary and low pressure crosses the terminals through
Wednesday night with rain, at times heavy, expected.

IFR conditions possible Thursday with rain overspreading the region.
Conditions should improve to MVFR or VFR Thursday night as the low
pressure pulls away. Winds southwest shifting northwest 10 to 15
knots Thursday, diminishing Thursday night. VFR conditions Friday
and Friday night. Winds west around 10 knots becoming northwest 10
to 15 knots Friday night.

&&

.MARINE...
Gale Warnings remain in effect through this afternoon for all
waters. Small Craft Advisory conditions will linger tonight
before winds subside late as high pressure builds over the
waters.

With the high overhead, then shifting off the coast late
Tuesday, sub SCA conditions expected through this time. Winds
will increase late Tuesday night, and especially
Wednesday/Wednesday night as southerly flow increases and low
pressure nears the waters, with SCA conditions likely.

Small craft advisories likely Thursday. Winds southwest shifting
northwest 15 knots gusting to 25 knots. Small craft advisories
possible Thursday night through Friday night. Winds northwest
becoming west 10 to 15 knots with possible higher gusts.

&&

.TIDES/COASTAL FLOODING...
Persistent and strong northwest flow will yield blowout
conditions through tonight.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Wind Chill Advisory until 11 AM EST this morning for DCZ001.
MD...Wind Chill Warning until 1 PM EST this afternoon for MDZ501.
     Wind Chill Advisory until 11 AM EST this morning for
     MDZ003>006-011-013-014-016>018-502>508.
VA...Wind Chill Warning until 1 PM EST this afternoon for VAZ503-
     504.
     Wind Chill Advisory until 11 AM EST this morning for
     VAZ025>031-036>040-050>057-501-502-505>508.
WV...Wind Chill Warning until 1 PM EST this afternoon for WVZ501-
     503-505-506.
     Wind Chill Advisory until 11 AM EST this morning for
     WVZ050>053-055-502-504.
MARINE...Small Craft Advisory from 4 PM this afternoon to 6 AM EST
     Tuesday for ANZ530>543.
     Gale Warning until 4 PM EST this afternoon for ANZ530>543.

&&

$$
SYNOPSIS...BKF
NEAR TERM...BKF
SHORT TERM...BKF
LONG TERM...KLW
AVIATION...BKF/KLW
MARINE...BKF/KLW
TIDES/COASTAL FLOODING...BKF