Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211919

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
219 PM EST Tue Feb 21 2017

High pressure will move off the east coast tonight. A weak
disturbance will cross the area late tonight into Wednesday.
High pressure will be located off the southeast coast of the
United States late in the week. A cold front will pass through
the area this weekend.


High pressure will continue to move off the New England coast
this afternoon. An onshore flow has allowed for cooler
conditions compared to recent days...but still above climo.
Climatologically highs should be in the upper 40s. We are still
expecting highs this afternoon to be in the upper
50s...possibly lower 60s in the central Shenandoah Valley.

A broken deck of high clouds will continue to move over the
area as moisture sneaks in ahead of an upper-level disturbance.
Partly to mostly cloudy skies are expected.

A cutoff low in the southern stream of the jet will track
through the Gulf Coast States tonight while an upper-level
disturbance in the northern stream move into our area. The
southern stream system should remain well off to our
south...but there may be just enough moisture that makes it into
our area for a few showers as the northern stream passes
through. The best chance for showers will be overnight into
Wednesday morning across central Virginia perhaps into southern
Maryland. With less moisture farther north...the forecast
remains dry for these areas although a few sprinkles cannot be
ruled out.

The upper-level disturbance will move off to the east by
Wednesday and subsidence behind this system should allow for
some sunshine. A southerly flow around high pressure over the
Atlantic along with the sunshine will cause more unusually warm
conditions. Leaned toward the higher guidance or even above
based on temperatures aloft and mixing potential...but did tweak
temps down a few degrees across central Virginia where cloud
cover may hang on a bit longer. Max temps will be in the upper
60s to 70 degrees across most areas...but much cooler (50`s)
along the shore of the Bay and along the ridge tops of the
Potomac Highlands.


High pressure will remain over the Atlantic Wednesday night
through Thursday night while upper-level ridging builds
overhead. A southerly flow along with sunshine will result in
unusually warm condtions for this time of year. Max temps
Thursday are expected to be well into the 70s for most
areas...but cooler (50s-60s) along the shore of the Bay and in
the ridges. Near record warmth is possible during this time. See
the climo section below.

Very mild conditions are expected for both Wednesday night and
Thursday night...but with increased moisture there will likely
be areas of fog. Some fog may be locally dense.

A couple popup showers are possible Thursday afternoon due to
limited instability from daytime heating. However...coverage
will be widely scattered or isolated and much of the time should
be dry.


Dry conditions expected for Friday with southerly
flow over our region and high temperatures in the 60s and 70s.
Deep  low pressure moves across the Great Lakes and its
associated cold front moves across the Mid-Atlantic on
Saturday... showers and thunderstorms likely. Dry conditions
return Sunday as high pressure builds behind the front.
Shortwave trough could bring showers over our CWA on Sunday
night, followed by dry conditions on Monday. Frontal boundary
could increase PoPs again for Tuesday.


VFR conditions expected through this evening. Patchy fog is
possible overnight...but coverage should be limited due to mid
and high clouds along with low-level dry air still in place. A
few showers are possible late tonight into Wednesday...mainly
across KCHO.

High pressure will build to our south and east for later
Wednesday through Thursday night. Areas of fog are possible
Wednesday night into Thursday and again Thursday night into
Friday. Fog may be locally dense with IFR/subIFR conditions

Dry/VFR conditions expected for later Friday before a cold
front approaches the area on Saturday... with showers and
thunderstorms possible into Saturday. Sub-VFR conditions
possible Friday night into Saturday at moments. Gusty winds
expected Friday night into Sunday, reaching up to 20 kt.


High pressure will remain off the coast through Thursday night.
A southerly flow is expected during this time...but wind speeds
should remain below SCA criteria.

Dry conditions expected for Friday before a cold front
moves across the Mid-Atlantic on Saturday. Showers and thunderstorms
possible. Gusty winds expected Friday night into Sunday, with
SCA conditions likely.


Did a check to see how warm it has been both for meteorological
winter and since Feb 1 at the three major airports in terms of
ranking (average temp): The statistics below are from February
1st through February 20th.

        Since Dec 1      Since Feb 1
DCA     5th warmest      2nd warmest
BWI     14th warmest     13th warmest
IAD     2nd warmest      2nd warmest

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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