Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 170836
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
336 AM EST Fri Nov 17 2017

.SYNOPSIS...
High pressure will build overhead through this afternoon before
moving offshore tonight through Saturday. A strong cold front
will cross the area late Saturday night. High pressure will
build to the south of the region late Sunday through Monday
before moving offshore Tuesday. Another cold front will pass
through Tuesday night into Wednesday and Canadian High pressure
is likely to build overhead for Thanksgiving Day.

&&

.NEAR TERM /THROUGH TODAY/...
High pressure will gradually build overhead through the day
today, leading to dry weather and mostly sunny skies. Still
seeing some strato-cumulus out there early this morning in the
northwest flow, but these will dissipate through the morning
hours as northwest winds gradually weaken through the day. High
temperatures expected to reach the 50s area-wide.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
Active weather expected for the weekend as surface high pressure
slides offshore and low pressure exits the Plains states, moves
towards the Great Lakes, and exits through the Saint Lawrence
Valley, deepening to a ~980mb low in the process.

Quiet weather is expected for much of tonight with the region
still under control of the departing surface high. Light
southerly flow and high clouds will both be on the increase as a
warm front moves towards the region, associated with the
aforementioned low pressure system. A light rain shower or two
are possible towards morning across western MD and WV. Lows
tonight in the 30s to around 40F.

Low level southwest flow will increase rapidly on Saturday as
warm frontal zone moves across. Some rain showers are likely,
mainly north across MD and eastern WV and mostly in the first
half of the day as the strongest forcing lifts northward into
PA/NY. Otherwise, south to southwest surface winds will increase
through the day with gusts up 35 mph possible by late in the
afternoon, likely higher across the higher elevations where wind
advisories may be necessary by evening as 850mb winds approach
50 knots. Highs Saturday 50-60F.

Strong cold front will cross the region Saturday night, with a
period of rain showers and increasing winds. A Wind Advisory will
likely be required for winds to 50 mph for at least the higher
elevations, and it may be necessary area-wide as winds increase
just ahead of the front out of the southwest and again behind
the front out of the northwest. Can`t rule out a fine line with
focused area of gusty winds immediately along the front either.

Behind the front, low level temperature profiles will crash, with
precipitation changing to snow and taking on an upslope
characterization as northwest winds increase. Lows 30s/40s.

On Sunday, gusty northwest winds will continue with gusts up to 50
mph possible, especially in the morning and over the higher terrain.
Upslope snow showers will continue along the Allegheny Front, with
some also possible downwind as upper trough moves overhead. Several
inches of snow accumulation are likely in the higher elevations near
and along the Allegheny Front. Highs Sunday stuck in the 30s in the
higher elevations, with 40s to low 50s elsewhere.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
High pressure centered to the south Monday will move offshore
Tuesday. Dry conditions are expected during this time. Monday
will turn out chilly and Tuesday will be a bit milder due to a
return southwest flow around the departing high.

A cold front will pass through late Tuesday night into
Wednesday. Little moisture will be associated with the boundary.
An isolated shower cannot be ruled out with the frontal
passage...but most places will be dry and any precipitation
that does occur will be light.

Canadian high pressure will build overhead later Wednesday
through Thanksgiving Day...bringing dry and chilly conditions.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
VFR expected through tonight with strato-cumulus early this
morning scattering out, replaced by increasing high clouds
tonight. A period of sub-VFR conditions are possible Saturday
night as a cold front moves across the region bringing a period
of rain showers.

Main aviation weather concern however will be increasing low
level wind field Saturday and Sunday. This will bring wind
gusts out of the southwest Saturday afternoon and evening up to
30-35 knots, and up to 40 knots behind the front late Saturday
night into Sunday. Low level wind shear will also be a concern
before winds gust on Saturday.

Winds will gradually lessen late Sunday and Sunday night.

VFR conditions are most likely for Monday and Tuesday.

&&

.MARINE...
Small Craft Advisory remains in effect for all waters through
noon today for gusty northwest winds. It continues through 6
PM for the lower Tidal Potomac and parts of the Chesapeake,
however winds will be lessening as high pressure moves overhead,
and it may be able to be cancelled early.

Sub-SCA winds then expected for much of tonight. Early Saturday
morning will see an increase in southerly winds, and SCA winds
are expected to develop after 4 AM Saturday across portions of
the waters, with SCA in effect for all waters after 8 AM
Saturday. Winds will increase through the day, and a Gale
Warning may be necessary by late Saturday afternoon and Saturday
evening. Gales then become more likely out of the southwest
Saturday night and northwest Sunday as winds increase further
associated with a potent frontal passage.

Winds gradually lessen late Sunday and Sunday night, however
SCA level winds still likely.

High pressure centered to the south of the waters Monday will
move offshore Tuesday. A cold front will pass through late
Tuesday night into Wednesday. A Small Craft Advisory may be
needed for portions of the waters Monday through Wednesday.

&&

.TIDES/COASTAL FLOODING...
Anomalies have dropped due to an offshore flow. However...there
are anomalies around 1 to 1.5 feet in the southern portion of
the Bay. The northwest flow will decrease today and then turn to
the southwest tonight. This will allow for those anomalies to
return north into our area. Latest forecast blends toward the
ETSS and ESTOFS which keeps water levels well below minor
flooding...but if all that water does return then minor
flooding could take place during the high tide cycle tonight
into early Saturday.

A southerly flow will strengthen Saturday and Saturday night
ahead of a cold front. There is a better chance for minor
flooding during this time near high tide. A strong offshore flow
will likely cause blowout conditions Sunday into Sunday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until noon EST today for ANZ530>532-535-
     536-538>540.
     Small Craft Advisory until 6 PM EST this evening for ANZ533-
     534-537-541>543.

&&

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



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