Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 192001
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
301 PM EST Sun Nov 19 2017

.SYNOPSIS...
High pressure will build to our south tonight through Monday
night. The high will move offshore Tuesday and a cold front will
pass through Tuesday night into Wednesday. High pressure will
build back overhead later Wednesday through Thanksgiving Day.
Coastal low pressure will likely move well out to sea Friday and
a cold front will pass through Saturday.

&&

.NEAR TERM /THROUGH MONDAY/...
Current surface analysis reveals deepening low pressure over the
lowe St. Lawrence Valley heading northeast, with the cold front
which passed through the area early this morning now well off
the coast. High pressure remains centered well to the southwest
over Texas, however. Aloft, a deep longwave trough dominates the
eastern United States, with one shortwave crossing New England
and a second approaching our area from Ohio.

The approaching shortwave aloft and departing surface low will
continue to dominate our weather tonight. As the surface low
continues moving away, the gusty winds will continue slowly
diminishing, but we are unlikely to really get light overnight
as cold advection continues. As the shortwave passes, the snow
showers over the Allegheny Front are likely to reintensify, so
the winter weather advisory remains in effect for the higher
elevations of western Pendleton and western Grant counties. The
shortwave may in fact be enough of a forcing mechanism to get a
few flurries or sprinkles to travel east of the mountains, most
likely towards Martinsburg and Hagerstown, but possibly
approaching the metro itself. There should be no impact from
these except for a little wonder at seeing snowflakes for the
first time this season, if it happens.

Overnight, snow showers along the Allegheny Front should
quickly wind down behind the shortwave. Temps will bottom out
below freezing in most of the area, except the warmest urban
centers and along the warmer large bodies of water
(Potomac/Chesapeake).

On Monday, high pressure should continue building eastward,
reaching eastern North Carolina by day`s end. This will cause
winds to shift from northwest to southwest, but warm advection
will be slow, so we still expect Monday to be chilly, with highs
struggling to reach 50. The lighter winds and greater sunshine
under a shortwave ridge will likely make Monday feel a little
more comfortable, especially in the afternoon.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
High pressure will shift east off the coast Monday night and
Tuesday, allowing southwesterly flow to dominate. While Monday
night looks radiational thanks to diminishing winds and clear
skies near the center of the high, by Tuesday sunshine and
warmer air aloft will translate to warmer surface temps, with
most places rebounding 5-10 degrees above Monday`s expected
highs.

Tuesday night, a cold front will approach from the northwest
while a shortwave will spawn a coastal low near the Outer Banks.
Still some question regarding how far west the rain shield from
this low makes it, but most guidance now shows rain reaching
southern Maryland, and a fair number have rain reaching
Baltimore and Washington proper. Thus, have chance pops for the
big cities and likely in southern MD. Further west, odds are
considerably lower. It should overall be a milder night thanks
to the warm advection ahead of the cold front combined with
increased cloud cover, with lows mostly above freezing.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
High pressure will build into the region Wednesday through
Friday night. Dry conditions expected with plenty of sunshine
each day and mainly clear skies at night. Despite the daytime
sunshine, temperatures each period will be about 5 to 7 degrees
below average with highs in the upper 40s to near 50 and lows in
the upper 20s to near 30.

A storm system over eastern Canada will bring a cold front
toward and across the mid-Atlantic Saturday and Saturday night.
There is a chance for a few rain showers along the Mason-Dixon
region Saturday with a chance of rain and snow showers in the
Appalachians and along the Mason-Dixon regions Saturday night.
Temperatures will be closer to average.

A gusty northwest wind will usher in cold air into the region
Sunday. With that, a chance of snow showers are expected in the
Appalachian Mountains. Below average temperatures expected to
retake the region.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
VFR overall through the TAF period. There could be a stray
sprinkle or flurry, but really, the main concern tonight is the
slowly diminishing wind gusts. Gusts should mostly be below 30
knots this evening and may drop below 20 knots late tonight.
Winds may return to the 20 knot range during the day Monday.
Tuesday night is the only real chance of sub- VFR as a low
pressure system could bring a bit of rain, which may reduce cigs
and vis for a time. Still uncertain just how far west this
precip gets.

VFR conditions Wednesday through Thursday night. Winds
northwest 5 to 10 knots Wednesday. Winds northwest around 5
knots Wednesday night. Winds becoming light and variable
Thursday and Thursday night.

&&

.MARINE...
Gale warning remains in effect through 6PM. Some uncertainty for
the overnight given continued cold advection over warmer waters,
which could enhance mixing and bring some higher gusts back to
the surface. This might mean we need to extend the gale, but
with high uncertainty, have left it SCA for the time being to
give the evening shift one last look. SCA continues most waters
through Monday as high pressure shifts east to our south. Winds
probably go sub SCA on Monday night but may go back to SCA
Tuesday ahead of the next cold front, which passes late Tuesday
night.

SCA possible behind cold front Wednesday, may be diminishing
Wednesday night. Winds light and variable Thursday and Thursday
night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...Winter Weather Advisory until 11 PM EST this evening for
     WVZ501-505.
MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST Monday
     for ANZ530>534-537>543.
     Gale Warning until 6 PM EST this evening for ANZ530>543.
     Small Craft Advisory from 6 PM this evening to 10 AM EST
     Monday for ANZ535-536.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...KLW
AVIATION...RCM/KLW
MARINE...RCM/KLW


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