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fxus61 klwx 190800 
afdlwx

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
400 am EDT Fri Jul 19 2019

Synopsis...
high pressure will build over the southeastern United States
through the weekend. A cold front will approach from the Great
Lakes Sunday, then cross the region early next week.

&&

Near term /through tonight/...
dangerously hot and humid weather is expected today. Low-level
temperatures warm to nearly 25 c at 850 hpa over the next 24
hours (near record high for this area), likely resulting in
surface temperatures in the middle 90s to near 100 degrees.
Light westerly flow may help mix out dew points just a touch
this afternoon, but the ambient airmass is so humid that they
should remain near or a touch over 70. This will result in heat
indices of 100-110 for much of the area, the first of 3 days
with expected excessive heat.

It is vitally important to remember heat safety during a
prolonged excessive heat event such as this.

For more information on heat safety, please visit
www.Weather.Gov/safety/heat.

A pop up thunderstorm can't be ruled out due to terrain
circulations between the Allegheny Front and Blue Ridge this
afternoon (bufkit soundings show the least amount of capping
around or just after midday), but strengthening capping and lack
of forcing on a large scale under a building ridge should keep
things in check from a coverage standpoint.

Tonight will not offer much relief with lows in the middle 70s
to lower 80s and very humid (heat indices remaining 80-90).

&&

Short term /Saturday through Sunday night/...
dangerous heat will continue through the weekend.

The heat is expected to peak Saturday, with heat indices
possibly approaching 115 in the I-95 corridor due to ambient air
temperatures in the upper 90s to around 100 and dew points
between 70 and 75.

Again, overnight temperatures and humidity will offer no relief,
with lows in the lower to middle 80s (near all time record warm)
in the major urban centers expected, and just barely below 80
even in outlying areas (dew points will be quite high as well,
mid 70s to lower 80s overnight).

A pop up storm can't be ruled out due to terrain circulations
Saturday, but forcing/coverage look sparse. There's a better
chance by Sunday evening as height falls commence and a front
approaches from the north, intersecting the excessively hot and
humid airmass in place.

&&

Long term /Monday through Thursday/...
on Monday, the ridge which will dominate weather conditions across
much of the Continental U.S. Over the next several days, will start to break
down as a trough dives southward through the Great Lakes. Heights
will start to fall aloft, and a cold front will approach the area
from the north. Compared to 12z guidance, 00z guidance has trended a
touch slower with the progression of the front into our area. This
could result in much of the area warming into the low 90s once again
before the front starts to progress through. Ample instability (1000-
2000 j/kg of mlcape) will build to the south of the front in
response to daytime heating. Winds through the column will pick up
slightly as the trough starts to approach from the northwest, with
around 20-25 kts of shear in place over much of the area. Although
the near moist adiabatic thermal profile should act as a limiting
factor, a few strong wind gusts can't be ruled out with any storms
that form Monday afternoon. The greater threat Monday afternoon will
likely be flash flooding. The front is expected to slow it's forward
progress as it moves into the area Monday afternoon through Monday
night. The combination of a slow moving to nearly stationary
boundary, a near moist adiabatic profile with precipitable water
values in excess of 2 inches, and winds aloft paralleling the
frontal boundary, raises concerns for at least isolated instances of
flash flooding.

Tuesday's weather will be dependent on the southward progression of
the surface front. Although the boundary will be situated to our
south, ample moisture will still be in place at the surface for
approximately 200-300 miles north of the boundary. If the front is
unable to progress well to our south, lingering showers may be
possible with the combination of rich surface moisture in place and
air overrunning the frontal boundary. Even if conditions do stay
dry, it will more than likely be a dreary day by July standards,
with lots of cloud cover and much cooler temperatures compared to
previous days. The highest chances for storms will reside further to
the southeast, where they'll be situated closer to the front.

Drier conditions and slightly below normal temperatures are expected
Wednesday and Thursday as high pressure starts to work in from the
west.

&&

Aviation /08z Friday through Tuesday/...
mainly VFR and very hot and humid through the weekend. Patchy
fog is possible for outlying terminals each night, but low
confidence at this time. West flow at or below 10 kts.

Conditions may deteriorate to sub-VFR Monday afternoon into Monday
night as a cold front moves into the area, bringing chances for
showers and thunderstorms.

&&

Marine...
sub Small Craft Advisory conditions expected through the weekend on light west
flow, and very hot and humid. Thunderstorms may approach by late
Sunday as a front nears.

Sub-Small Craft Advisory level winds are expected on Monday. Thunderstorms will be
possible over the waters Monday and Monday night. Special marine
warnings may be needed for any of the stronger storms that move over
the waters.

&&

Climate...
the record daily warm low temperature for iad for July 18th is
74 degrees, set in 2005 and 1969.

As a reference, here are the warm temperature records for
Friday through this weekend:

Record daily high temperatures
Jul 19 Jul 20 Jul 21
dca 102 (1930) 106 (1930) 104 (1926)
BWI 103 (1930) 102 (1930) 104 (1930)
iad 98 (1977) 101 (1980) 101 (1991)

Record daily warm low temperatures
Jul 19 Jul 20 Jul 21
dca 81 (1930) 82 (2015) 82 (1987)
BWI 80 (1942) 80 (1930) 83 (1930)
iad 77 (2013) 75 (2015) 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 District of Columbia 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 Maryland 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 Virginia area have been kept
at what is now Washington Dulles International Airport (iad) since
1960.

&&

Lwx watches/warnings/advisories...
District of Columbia...excessive heat watch from Saturday morning through Saturday
evening for dcz001.
Excessive heat watch from Sunday morning through Sunday
evening for dcz001.
Excessive heat warning from 11 am this morning to 9 PM EDT
this evening for dcz001.
Maryland...heat advisory from 11 am this morning to 9 PM EDT this evening
for mdz016>018-502.
Excessive heat watch from Saturday morning through Saturday
evening for mdz003>006-011-013-014-016>018-502>508.
Excessive heat watch from Sunday morning through Sunday
evening for mdz003>006-011-013-014-016>018-503>508.
Excessive heat warning from 11 am this morning to 9 PM EDT
this evening for mdz003>006-011-013-014-503>508.
Virginia...heat advisory from 11 am this morning to 9 PM EDT this evening
for vaz025>027-029-030-036>040-050-051-055>057-501-502.
Excessive heat watch from Saturday morning through Saturday
evening for vaz027>031-036>040-050>057-501-502-505-506.
Excessive heat watch from Sunday morning through Sunday
evening for vaz028>031-036>040-050>057-501-502-505-506.
Excessive heat warning from 11 am this morning to 9 PM EDT
this evening for vaz028-031-052>054-505-506.
WV...heat advisory from 11 am this morning to 9 PM EDT this evening
for wvz050-055-502-504.
Excessive heat watch from Saturday morning through Saturday
evening for wvz050>053-055-502-504.
Excessive heat watch from Sunday morning through Sunday
evening for wvz051>053.
Excessive heat warning from 11 am this morning to 9 PM EDT
this evening for wvz051>053.
Marine...none.

&&

$$
Synopsis...dhof
near term...dhof
short term...dhof

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