Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220759

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Sat Jul 22 2017


High pressure remains off the southeast coast. Multiple upper
level disturbances will be possible through Sunday. An upper
level trough of low pressure will move over the northeastern US
early in the week.



"The hottest time of the year..." is holding true to form. We
have issued a heat advisory for the I-95 corridor from Baltimore
to Fredericksburg east to the Bay. Question may be how much
cloud cover moves into the area. The way I`m playing it is
that there will be a decent amount of sunshine/heating during
the morning, then increasing clouds in the afternoon given
dewpoints in the lower 70s as well as the approaching MCS which
may cap the temp rise in the afternoon. Low to mid 90s air
temperature will be common east of the mountains. However this
is nowhere near daily record values - in 2011 IAD reached 105
(also monthly record) and BWI hit 106. DCA reached 103 in 1926.

The next problem to deal with is potential severe weather this
afternoon/evening. The main players are a) the heat and humidity
leading to large potential temperature values, and b) the system
over Indiana/Illinois. Watches are currently in effect in this
area, and if the storms remain on their current trajectories
these should impact PA through northern VA during prime severe
time. Low level shear is fairly weak but with available CAPE
storms will have the ability to grow tall. HRRR is showing 22Z
west to 02Z east as being the time of greatest potential. Strong
gusty winds will be the primary threat with large hail as a
secondary threat - upper atmosphere is very warm with the -20 C
being at 26.7K feet.



Storms could be ongoing during the evening then another
overnight with lows in the 70s.

Sunday appears to be shaping up to be another severe convective
day. Models progged a stronger upper level disturbance with
significant height falls for summertime standards. Shear is also
on the increase and many ensemble members show moderate CAPE
and some even high CAPE values over 3500 J/kg. Expect clusters
of storms to move across the area some with damaging winds.

A cold front will approach the region Monday before pushing across
the region Monday night. Showers and thunderstorms will develop
along and ahead of this front. Highs will reach the 90s again.



Noticeable change in the weather will occur following the cold
frontal passage on Monday. High pressure will build into the Great
Lakes behind the front Monday night, and translate eastward into the
northeastern United States on Tuesday. This will lead to cooler and
less humid conditions with developing northerly to easterly flow.

The high will then quickly shift offshore by Wednesday, but
lingering easterly flow should still keep the temperatures pleasant
across much of the area. There could be some scattered
showers/thunderstorms south/west nearest to the old frontal boundary
and across the higher terrain.

By the end of the week, the flow will turn around to the southwest
ahead of an approaching frontal system. Temperatures/moisture will
likely spike back up ahead of the front, and along with that the
chances for showers/thunderstorms.

As far as temperatures, highs Tuesday/Wednesday generally in the
80s, and back to near or slightly above 90F for Thursday/Friday.



VFR conditions expected today. Thunderstorms with strong gusty
winds will be possible late this afternoon/early this evening.
Storms will again be possible Sunday.

Predominantly VFR expected Monday night through Wednesday. There may
be some patchy fog/low clouds each morning, but otherwise no
significant aviation weather concerns.



Winds will be below SCA values today through Sunday. Strong
thunderstorms capable of required SMW`s will be possible late
this afternoon/this evening and again Sunday.

Mainly sub-SCA winds expected Monday night through Wednesday,
generally northerly Monday night, turning easterly by Wednesday.


DC...Heat Advisory from noon today to 7 PM EDT this evening for
MD...Heat Advisory from noon today to 7 PM EDT this evening for
VA...Heat Advisory from noon today to 7 PM EDT this evening for


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