Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 190845
AFDLWX

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

.SYNOPSIS...
A strong cold front will move off to the east today and 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. Canadian high pressure will build
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 TONIGHT/...
Deepening low pressure center near the east end of Lake Ontario
early this morning will track northeastward through the day
reaching eastern Quebec by tonight.

An associated strong cold front is crossing the region as of this
typing (330am) and it will be clearing east of the Chesapeake
Bay by 7 AM. Widespread rain showers expected out ahead of the
front, along with gusty south/southwest winds. As the front
passes, expect a sharp turn to the west/northwest and surge in
wind speed to the 40- 50 mph range.

Rain showers will change to snow showers along and west of the
Allegheny Front as cold air rushes behind the cold front, and
upslope snow showers will persist through the day and into
tonight. The intensity and coverage of the upslope snow
showers will vary through the day, with the first heavy surge
occurring between 4 AM and 10 AM, followed by a second surge
between 4 PM and Midnight tonight as a potent upper level
shortwave crosses the region and moisture deepens again. A
Winter Weather Advisory remains in effect for western Grant and
western Pendleton Counties for 3-6" of snow.

The other main story for today will be gusty west/northwest
winds. Aside from gusts associated with frontal passage, the
most widespread and strongest winds will occur just after
sunrise (7am) through 12 noon or so when the best overlap of the
wind field aloft and low level mixing occurs. Have maintained
the Wind Advisory for much of the area aside from portions of
central Virginia for gusts up to around 50 mph. Winds will
lessen during the afternoon and evening hours.

Temperatures today will not follow the usual diurnal curve with
early morning mild temperatures falling after frontal passage,
and then remaining steady or recovering slightly through the
day. The after sunrise highs should range in the 40s/50s,
locally near 60F south/east and in the 30s in the higher
elevations.

A potent upper level shortwave and secondary cold front will
then cross the region late today into tonight. While passage
should be mainly dry, enough moisture and even a small amount of
instability may get picked up ahead of the front for a few
flurries/snow showers to make it downwind of the mountain chain
and into northwestern VA, the eastern panhandle of WV, and into
central/northern MD.

Lows tonight in the 20s/30s.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
High pressure will build south of the region on Monday leading to
fair skies and dry weather. West/northwest winds in the morning
will lessen and turn southerly by days end. Highs Monday
within a few degrees of 50F.

Warm air advection and southwest flow returns for Monday night
and Tuesday ahead of the next northern stream shortwave.
Uneventful weather expected during this time with lows Monday
night in the 20s/30s and highs Tuesday warming back up through
the 50s and approaching 60F.

The shortwave is progged to cross the region Tuesday night with
the potential for some showers. As southern stream energy also
moves through the southeastern US, cyclogenesis does look to
take place off the coast of the Carolinas, but looks to stay
mainly S/E of the region at this point.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A cold front will move off to our south Wednesday while Canadian
high pressure approaches from the north and west. The high will
build overhead Wednesday night through Thanksgiving
Day...bringing dry and chilly conditions.

Shortwave energy in the southern branch of the jetstream will
cause low pressure to develop over the Gulf of Mexico toward
Florida Thanksgiving Day. The low is expected to track north and
east...but latest guidance continues to suggest that it will be
far enough out to sea so it has no impact on our weather. Will
continue to monitor trends in guidance over the next few days. A
northwest shift would have a significant impact on the forecast
for Friday. As of now...it appears that a return flow around a
departing surface high will bring somewhat milder conditions
along with some sunshine.

A cold front will approach Friday night before passing through
Saturday. Blustery and much colder conditions are expected
behind the cold front later Saturday and Sunday. Upslope snow
showers are possible along/west of the Allegheny Front. A few
flurries could even spill east of the mountains but confidence
is low at this time.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
Main aviation weather concern through today will be gusty west
to northwesterly winds. South/southwest winds early this
morning will turn sharply to the west/northwest following a
frontal passage with gusts 30-40 knots expected this morning.
Winds will gradually lessen during the afternoon hours. Along
the front, a brief period of MVFR is also possible in low clouds
and rain.

Otherwise, mainly VFR is expected through Tuesday. The next
chance of any precipitation and possible restrictions will
come Tuesday night with the next system.

High pressure will bring VFR conditions Wednesday through
Thanksgiving Day. Coastal low pressure is expected to move out
to sea Friday so more VFR conditions are likely. However...the
track of this low will have to be monitored closely.

&&

.MARINE...
A Gale Warning remains in effect through today for all waters. Gusty
south/southwest winds early this morning will turn sharply to the
west/northwest following a frontal passage with gusts to 30-40 knots
expected this morning, gradually lessening during the afternoon
hours.

Small Craft Advisories are then in place for tonight and into Monday
as northwest winds gradually abate. Sub-SCA winds are then expected
Monday night, before the next chance for SCA winds arrive on
Tuesday/Tuesday night ahead of the next system.

High pressure will build overhead Wednesday through Thanksgiving
Day. A Small Craft Advisory may be needed for portions of the
waters Wednesday into Wednesday night. Still watching for the
potential of a coastal low Friday. As of now...it appears that
the track will be well out to sea so the most likely scenario is
for it to not have any impact.

&&

.TIDES/COASTAL FLOODING...
Water levels are around 1 to 1.5 feet above normal due to a strong
southerly flow. These anomalies may creep up a bit before a cold
front moves through between 5 am and 8 am. Will have to keep an
eye out for Annapolis.

Strong offshore flow behind the front will cause anomalies to
sharply fall through this afternoon. Tidal blowout conditions are
possible tonight.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Wind Advisory until 3 PM EST this afternoon for DCZ001.
MD...Wind Advisory until 3 PM EST this afternoon for MDZ003-501-502.
     Wind Advisory until 3 PM EST this afternoon for MDZ004>006-011-
     013-014-016>018-503>508.
VA...Wind Advisory until 3 PM EST this afternoon for VAZ025>031-503-
     504-507-508.
     Wind Advisory until 3 PM EST this afternoon for VAZ040-052>054-
     501-505-506.
WV...Wind Advisory until 3 PM EST this afternoon for WVZ050>053-055-
     501>506.
     Winter Weather Advisory until 11 PM EST this evening for
     WVZ501-505.
MARINE...Gale Warning until 6 PM EST this evening for ANZ530>543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...MM
SHORT TERM...MM
LONG TERM...BJL
AVIATION...BJL/MM
MARINE...BJL/MM
TIDES/COASTAL FLOODING...BJL



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