Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201930

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
230 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.


Upper-level ridge will build overhead through tonight while
surface high pressure builds into New England. The surface ridge
axis associated with the high will build over our area during
this time. An easterly flow around the high will usher in cooler
air compared to recent night. In fact...some areas may decouple
overnight and radiational cooling may lead to chilly
conditions...especially over northern Maryland. Min temps will
range from the lower 30s in northern Maryland to the upper 30s
and lower 40s in central Virginia.

High clouds will gradually increase as they rotate around the
periphery of the upper-level ridge. A broken deck of lower
clouds are possible overnight across the Shenandoah Valley into
the Potomac Highlands due to light overrunning of the cooler air
in place. precipitation is expected.

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


VFR conditions expected most of the time through Tuesday.
Northerly winds may gust around 15 knots this afternoon...but
winds will turn to the northeast and diminish tonight.
Southeasterly winds are expected for Tuesday around 10 knots. A
bkn cu deck may lead to a period of MVFR cigs later Tuesday
morning into Tuesday afternoon...especially across the western

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 will turn to the northeast this afternoon into tonight. A
weak pressure surge is expected over the waters this evening.
Gusts may approach 20 knots...but confidence is low for a
headline at this time since the pressure surge will be weak.

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.


Record high minimums were set yesterday at IAD and BWI. See
RERs for more details. More record high mins are likely later
this week.




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