Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220055

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
855 PM EDT Fri Jul 21 2017

Multiple upper level disturbances will be possible through
Sunday. An upper level trough of low pressure will move over the
northeastern US into the next work week.


A lee trough resides across the Mid-Atlantic region this
evening. A few showers are present across the suburbs of
Washington DC and Baltimore this evening. Elsewhere... isolated
showers can not be ruled out as low-level boundaries and
instability persist overnight however most places will stay
dry. Patchy fog is possible in low lying areas that saw showers
this afternoon including the Shenandoah Valley and central

Another very warm and muggy night is expected tonight.


Global and hi-res models continue to show an MCS forming over
southern Wisconsin late tonight and moving across Chicago and
eastern OH and wrn PA by Sat morning. While this complex is
expected to weaken toward daybreak, redevelopment is expected
during the afternoon across the local area. 0-6km shear
increases somewhat supporting organized convection. CAPE is also
on the increase given hotter temperatures and plenty of
moisture (850 mb dewpoints of 15C). Some severe wx is possible,
but ensemble guidance shows a large spread in CAPE values with
some members showing only weak CAPE.

Sunday appears to be shaping up a potentially more significant
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.

The front could stall just to our south Tuesday, allowing for a
couple of showers or a thunderstorm to develop.

High pressure will build in from the west and northwest Tuesday
night through Thursday. Temperatures will be nearly 10 degrees
cooler than previous days with a comfortable relative humidity.

The next cold front will arrive and push across the region Thursday
night and Friday. Another active pattern of showers and
thunderstorms during the period and could linger into the weekend if
the front stalls across portions of the region.


Sct-bkn clouds tonight. Sct-nmrs t-storms more likely Sat and
especially Sun.

Mvfr to ifr conditions possible with showers and thunderstorms
Monday and Monday night. Vfr conditions expected Tuesday. A shower
cant be ruled out. Winds northwest becoming southwest 5 to 10 knots
Monday and Monday night. Winds north 10 knots Tuesday, becoming
northeast 5 to 10 knots Tuesday night.


Sct-nmrs t-storms Sat and Sun may require SMWs.

No marine hazards expected Monday through Tuesday night. Winds
southwest 5 to 10 knots Monday and Monday night. Winds becoming
northwest 10 knots Tuesday, then northeast 5 to 10 knots Tuesday


Late July is climatologically the warmest time of the year,
just like six months from now is the coldest time. How has the
heat of 2017 compared with heat waves (up to now) in other
years? I chose "consecutive days that reached 90 and above" as
the criteria.

At DCA there have been two times this summer with stretches of
six consecutive days - beginning June 29 and again July 10. In
terms of ranking (going back to 1871) these are #49 and 50.
Currently DCA has exceeded 90 on five consecutive days.

July 16 was 89, otherwise DCA would have exceeded 90 on 12 days
in a row.

For Baltimore there were also six consecutive days beginning
June 29, which puts it in 37th place. Currently BWI has
exceeded 90 on five consecutive days.

July 16 was 89, otherwise BWI would have exceeded 90 on 12 days
in a row.

The all-time record for June-Aug: for Baltimore 25 consecutive
days beginning 7/12/1995. For DC there have been two periods of
21 consecutive days - beginning 7/29/1988 and 7/25/1980.

UPDATED- 0050z 07/22/17




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