TM () > WX — Sunday, July 21, 2019
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Excessive Heat Warning
Hazardous Weather Outlook

Today: Isolated showers and thunderstorms after 3pm. Mostly sunny and hot, with a high near 100°. Heat index values as high as 109. West wind 5 to 8 mph. Chance of precipitation is 20%.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 80°. West wind 3 to 8 mph. Chance of precipitation is 40%.

Monday: A chance of showers and thunderstorms, then showers and possibly a thunderstorm after 1pm. Some of the storms could produce heavy rain. High near 91°. Light and variable wind becoming southwest 5 to 8 mph in the morning. Chance of precipitation is 80%. New rainfall amounts between a quarter and half of an inch possible.

Monday Night: Showers and thunderstorms likely before 1am, then showers likely and possibly a thunderstorm after 1am. Some of the storms could produce heavy rain. Cloudy, with a low around 70°. West wind 3 to 7 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Tuesday: Showers likely and possibly a thunderstorm before 1pm, then a chance of showers. Mostly cloudy, with a high near 82°. Northwest wind 7 to 9 mph. Chance of precipitation is 60%.

Tuesday Night: A chance of showers, mainly before 7pm. Mostly cloudy, with a low around 67°. Chance of precipitation is 30%.

Wednesday: Mostly sunny, with a high near 84°.

Wednesday Night: Mostly clear, with a low around 66°.

Thursday: Sunny, with a high near 86°.

Thursday Night: Mostly clear, with a low around 67°.

Friday: Sunny, with a high near 88°.

Friday Night: Mostly clear, with a low around 69°.

Saturday: Sunny, with a high near 89°.

Baltimore/Washington Forecast Office

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000
FXUS61 KLWX 210742
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
342 AM EDT Sun Jul 21 2019

.SYNOPSIS...
High pressure will remain over the southeastern United States
through this afternoon. A cold front will approach from the
Great Lakes tonight through Monday before passing through our
area Monday night into Tuesday. High pressure will return for
Wednesday into next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
The upper-level high will remain overhead through this afternoon
while surface high pressure remains draped across the southeast
CONUS into the Atlantic. More very hot and humid conditions are
expected. Low level temps are progged to be very close to
Saturday`s, if not perhaps in a degree C warmer when compared to
Saturday. Therefore, max temps will be very similar to Saturday
with highs well into the 90s for most areas with locations
around the Washington and Baltimore Metro areas close to 100
degrees. Dewpoints will remain in the 70s for many locations.
This will cause heat indices to top off around 100 to 115
degrees, with the highest values near and east of Interstate 95.
An Excessive Heat Warning remains in effect for areas around and
east of Interstate 95 as well as central Maryland, northern
Virginia, and the eastern Panhandle of West Virginia. A Heat
Advisory is in effect for the Shenandoah Valley and portions of
the valleys in the Potomac Highlands.

The upper-level ridge should break down just a bit later this
afternoon and tonight as a cold front drops through the Midwest
and the upper-level trough begins to dig through the northern
Plains. As the ridge breaks down a little, this will cause a
southwest flow to develop at the mid-levels, and this southwest
flow will usher in some more moisture into the area. This
combined with a weakening capping inversion from height falls
may be enough to trigger some showers and thunderstorms during
the afternoon and evening hours. Latest thinking is that
coverage will be isolated to scattered since there will not be a
strong lifting mechanism, but with this type of heat and
humidity any storms that do develop may become severe.

The cold front will continue to drop south approaching the Ohio
overnight, and height falls will continue as a result.
Therefore, showers and thunderstorms are possible during the
overnight hours as well, and some storms may be strong to
perhaps even severe. Confidence is lower for this to occur
because it will depend on how much the atmosphere gets worked
over from convection earlier (during this afternoon and
evening). If convection is not realized or sparse this afternoon
and evening, then confidence for convection overnight will be
higher.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The cold front will pass through the Ohio Valley Monday and into
our area Monday night. Lower heights and a southwest flow aloft
combined with forcing from the approaching front and a pressure
trough overhead will be enough to trigger showers and
thunderstorms, especially during the afternoon and evening
hours. Increased shear profiles along with the high instability
suggests that storms will have the chance to be severe. A
southwest flow aloft combined with a low-level southwest flow
will cause storms to have the potential to train over the same
areas, or at least have multiple rounds of convection.
Therefore, flash flooding is a concern as well. Exactly where
remain uncertain at this time, but assessment this morning
suggests eastern WV, northern VA, northern and central MD as
well as the metro areas would have the best chance. These areas
will likely have high amounts of instability, but still be close
enough to the approaching cold front and the associated upper-
level trough.

Monday will not be as hot as recent days due to more cloud
cover and more coverage of showers and thunderstorms, but max
temps in the 80s and 90s with high humidity will still make it
feel quite hot with heat indices around 100 degrees for
locations near and east of Interstate 95. The upper-level trough
and the cold front will pass through the area Monday night.
Timing is still a bit uncertain among guidance, but more showers
and thunderstorms are possible Monday night and some may contain
heavy rainfall.

The cold front will move off to the east Tuesday, but the
upper-level trough lagging behind will be slower to pass
through. Therefore, unsettled conditions are possible Tuesday
but confidence remains low due to uncertainty in guidance with
the exact timing. However, it will be noticeably cooler and less
humid than recent days.

The upper-level trough may hang around Tuesday night as well,
but most guidance suggests that the building surface should
provide enough dry air advection for drier conditions Tuesday
night. Tuesday night will be much less humid and cooler compared
to recent nights.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Tranquil weather is in store for much of the long term portion of
the forecast. High pressure over the central U.S. on Wednesday
will track eastward, settling overhead Thursday into Friday,
before shifting offshore on Saturday. As a result, dry
conditions and slowly moderating temperatures can be expected.
Below normal temperatures for late July will be advertised
Wednesday through Friday, with the Potomac and Virginia
Highlands likely holding only in the 70s during the day on
Wednesday while lower 80s will be realized elsewhere. Overnight
lows in the upper 50s to middle 60s Wednesday night will trend
into the 60s to near 70 degrees by Friday night.

As the high shifts offshore Saturday, return flow will yield
increasing humidity levels and near normal temperatures, but
forecasted middle 60s dewpoints will fall short of the oppressive
dewpoints in the 70s that currently engulf the region. The next
shot of precipitation likely holds off until Saturday
afternoon as moisture increases and weak shortwave energy
approaches to our west. That being said, will only be
introducing slight chance POPs west of the Blue Ridge at this
time, with a majority of the CWA likely favoring the dry side of
things.


&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
Patchy fog may impact the terminals this morning, but vsbys
should hold at MVFR or above. Isolated to scattered showers and
thunderstorms are expected later this afternoon and tonight.
With the intense heat and humidity in place, some storms may be
strong with gusty winds and brief subVFR conditions.

A cold front will bring a better chance for showers and
thunderstorms Monday afternoon into Monday night. Severe storms
are possible along with IFR/subIFR conditions in convection.
Drier air will gradually move in for Tuesday and Tuesday night,
but timing of the dry air remains somewhat uncertain. Therefore,
showers and subVFR conditions are possible Tuesday.

High pressure building in from the west will yield light
northerly winds and dry conditions Wednesday through Thursday,
as VFR conditions dominate over the terminals.

&&

.MARINE...
Winds should remain below SCA criteria for most of the time
tonight. However, it will be close at times early this morning
across the middle portion of the Bay, and again tonight through
Monday across the middle portion of the Bay and lower Tidal
Potomac River. Isolated to scattered thunderstorms are expected
later this afternoon through tonight, and some of those storms
may contain damaging winds. There is a better chance for
showers and thunderstorms Monday and Monday night (especially
during the afternoon hours and Monday night). Some of these
storms may be severe with damaging winds.

A Small Craft Advisory may be needed for portions of the waters
Monday night as a cold front moves into the area. The cold front
will move off to the south later Tuesday through Tuesday night
and an SCA may be needed for portions of the waters during this
time.

Light winds and sub SCA conditions expected as high pressure over
the central U.S. builds eastward toward the waters through
Thursday.

&&

.CLIMATE...
Here are the warm temperature records for today, July 21st:

Record Daily High Temperatures
Jul 21
DCA 104 (1926)
BWI 104 (1930)
IAD 101 (1991)

Record Daily Warm Low Temperatures
Jul 21
DCA 82 (1987)
BWI 83 (1930)
IAD 77 (1987)

Highest July Temperatures
Highest Max Warmest Low
DCA 106 (7/20/1930) 84 (7/24/2011, 7/23/2011, 7/16/1983)
BWI 107 (7/10/1936) 83 (7/21/1930)
IAD 105 (7/22/2011) 78 (7/24/2010, 7/8/2010)

All-time Highest Temperatures
Highest Max Warmest Low
DCA 106 (7/20/1930, 8/6/1918) 84 (7/24/2011, 7/23/2011, 7/16/1983)
BWI 107 (7/10/1936) 83 (8/5/1930, 7/21/1930, 6/6/1925)
IAD 105 (7/22/2011) 79 (8/8/2007)

Longest stretches of consecutive days with high temperatures at or
over 100 degrees at IAD:
2 (7/7-8/2012, 7/21-22/2011, 7/6-7/2010, 8/16-17/1997, 7/16-17/1988
and 7/20-21/1980)

Longest stretch of consecutive days with low temperatures at or over
80 degrees at DCA:
5 (7/16-20/2013)

Longest stretch of consecutive days with low temperatures at or over
80 degrees at BWI:
4 (8/8-11/1900)

Temperature records for the Washington DC area have been kept at
what is now Ronald Reagan Washington National Airport (DCA) since
1941. Additional temperature records observed downtown extend the
period of record back to 1872.

Temperature records for the Baltimore MD area have been kept at what
is now Baltimore-Washington International Thurgood Marshall Airport
(BWI) since 1950. Additional temperature records observed downtown
extend the period of record back to 1872.

Temperature records for the Sterling/Dulles VA area have been kept
at what is now Washington Dulles International Airport (IAD) since
1960.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Excessive Heat Warning from 11 AM this morning to 9 PM EDT
this evening for DCZ001.
MD...Heat Advisory from 11 AM this morning to 9 PM EDT this evening
for MDZ502.
Excessive Heat Warning from 11 AM this morning to 9 PM EDT
VA...Heat Advisory from 11 AM this morning to 9 PM EDT this evening
Excessive Heat Warning from 11 AM this morning to 9 PM EDT
WV...Heat Advisory from 11 AM this morning to 9 PM EDT this evening
for WVZ050-051-055-502-504.
Excessive Heat Warning from 11 AM this morning to 9 PM EDT
this evening for WVZ052-053.
MARINE...None.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...BKF
AVIATION...BJL/BKF
MARINE...BJL/BKF
CLIMATE...DHOF

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