Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 210220

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
920 PM EST Mon Feb 20 2017

High pressure will build overhead through tonight. Cooler air
will seep south tonight into Tuesday. A weak disturbance will
cross the area Tuesday night into Wednesday. High pressure will
be located off the southeast coast of the United States Thursday
through Friday. A cold front will pass through the area during
the weekend.


Backdoor cold front is shifting southwestward through the area
this evening, noted by wind shift to the northeast and falling
dew points, as ridge of high pressure builds over New England.

At the same time, a highly amplified upper level ridge is
building into the region from the west. High clouds will
gradually increase across the area tonight as they spill over
the ridge axis. A broken deck of lower clouds is also possible
overnight across the Shenandoah Valley into the Potomac
Highlands. precipitation is expected. Lows tonight
mainly in the 30s to near 40F.

The surface high will move off the New England coast
Tuesday...but it will continue to wedge into the Mid-Atlantic.
The upper-level ridge will also gradually move off to the east.
An onshore flow around the high will cause cooler conditions
compared to recent days...but max temps will still be above
climo. An upper-level disturbance will approach from the
west...bringing some clouds to the area but it should remain


An upper-level disturbance associated with the northern stream
of the jet will pass through our area Tuesday night into
Wednesday...but it will be weakening as it moves through. Cutoff
low pressure will develop in the southern stream of the
jet...but that should remain well off to our south. A couple
showers are possible Tuesday night into Wednesday...but with our
area split between the northern and southern stream of the jet
most areas may end up dry. The best chance for showers will be
in the Allegheny Highlands due to an upslope component to the
low-level flow.

High pressure will build offshore for Wednesday and Wednesday
night...allowing for unusually warm conditions to return. Max
temps Wednesday will once again be well into the 60s and 70s.


Dry conditions expected for Thursday with southerly
flow over our region and high temperatures in the 60s and low
70s. A frontal boundary will be approaching the region from
the north allowing for some showers Thursday afternoon into
Thursday night. Warm air advection continues Friday into Friday
night with an increase in PoPs as cold front approaches from the

Deep low moves across the Great Lakes and a cold front moves
across the Mid-Atlantic on Saturday... showers and
thunderstorms likely. Dry conditions return Sunday into Monday
as high pressure builds behind the front... high temperatures
will be in the 50s and 60s, and in the 40s and 50s at higher


Predominantly VFR conditions expected through Tuesday.
Winds light out of the northeast tonight will turn southeasterly
for Tuesday, generally less than 10 knots. Will see an increase
in high clouds overnight that will persist through Tuesday. A
strato-cumulus deck will also likely develop on Tuesday, but
generally expected to remain at or above VFR.

An upper-level disturbance will pass through the terminals
Tuesday night into Wednesday. A couple showers cannot be ruled
out...but most areas will be dry. A light south to southwest
flow is expected during this time. Areas of fog are possible
Tuesday night and again Wednesday night.

Dry/VFR conditions expected for Thursday before a front
approaches the area on Thursday night... showers possible into
Saturday, when a strong cold front moves across the Mid-
Atlantic. Sub-VFR conditions possible Thursday night into
Saturday at moments. Gusty winds expected Friday night into
Saturday, reaching up to 20 kt.


Winds have turned to the northeast this evening and will
continue through the overnight. A weak pressure surge is
expected over the waters this evening, and gusts may approach
SCA criteria, but should generally stay below.

High pressure will build over the Atlantic for Tuesday and
Wednesday. Southeast winds Tuesday will turn to the south or
southwest Tuesday night through Wednesday night. Wind speeds
should remain below SCA criteria.

Dry conditions expected for Thursday before a front approaches
the area on Thursday night... showers possible into Saturday,
when a strong cold front moves across the Mid-Atlantic. Gusty
winds expected Friday night into Saturday, reaching up to 20 kt,
therefore small craft advisory possible.


Unseasonably warm temperatures are expected during the second
half of the week. Below are record daily high maximum and high
minimum temperature values for the 22nd through 24th (Wednesday
through Friday).

February 22nd
DCA    77 (1874)    60 (1874)
BWI    74 (1874)    51 (1874)
IAD    71 (1991)    52 (1981)

February 23rd
DCA    78 (1874)    51 (1922)
BWI    78 (1874)    52 (1874)
IAD    73 (1985)    51 (1975)

February 24th
DCA    78 (1985)    52 (1975)
BWI    79 (1985)    55 (1985)
IAD    79 (1985)    53 (1985)




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