Severe Thunderstorm Warning 182, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
241 PM EDT Sun Jul 5 2020

.SYNOPSIS...
Surface high pressure continues to build over the Atlantic
through Tuesday. Meanwhile, upper-level ridging builds in across
the area as well. Cutoff low pressure will develop to the south
for Wednesday and it may impact the area late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Current temperatures are not quite as warm as had been expected
for much of the area, but still in the upper 80s to low 90s.
Expect to add a degree or two to that for the highs today. Dew
points are in the low to mid 70s for most of the area, keeping
heat indices generally in the mid-upper 90s and even near 100
in a few spots. As a result of this very warm and humid airmass,
starting to see several thunderstorms pop up across the area.
The environment is characterized by 2500-3500 J/kg of MLCAPE,
upwards of 1300 J/kg of DCAPE, but very little in terms of
shear overall, with only 20-25 knots over northeast MD,
decreasing further south and west. Coverage of storms has been
best over central VA thus far, coming off of the higher terrain.
However, we are beginning to see storms fire off of the
river/bay breezes in central and northeast MD. Storms are
expected to continue into this evening. SPC has put much of the
area under a marginal risk for severe weather this afternoon.
Given the DCAPE present across the region, any storm that really
gets going is bringing down some wind. The lack of shear should
allow for a more pulse-type storm environment, rather than
longer lived multicells. However, in a similar environment
yesterday, there was one storm that proved that theory wrong, so
can't rule out an isolated more organized cell somewhere. Storms
have generally been slow-moving thus far, but flooding isn't
expected to be much of an issue given the lack of any well
defined surface boundaries, and the presence of mid-level dry
air, which should facilitate strong cold pool production and
resultant propagation of storms.

Storms should quickly die off this evening as we lose daytime
heating. Areas of patchy fog may be possible, especially to the
west of the Blue Ridge, where winds are more likely to go calm
within sheltered valleys. Lows tonight will range from the mid
60s in the mountains to the mid-upper 70s in the urban areas.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
With surface high pressure remaining in place over the
Atlantic, and upper-level ridging building in overhead, expect
much of the same on Monday and Tuesday. High temperatures will
reach into the low-mid 90s, with continued high humidity leading
to heat indices in the mid-upper 90s each afternoon. In fact,
lows Monday and Tuesday night only get down into the low 70s for
most areas (upper 60s in higher terrain and mid 70s in
DC/Baltimore).

On Monday, things get a little more interesting. A weak upper-
level shortwave will pass overhead in this very unstable
environment. While weak, this shortwave will provide a little
bit more shear than we have had in recent days. Given the
combination of 20-25 knots of deep layer shear and high
instability (2000 J/kg or so), should see some more intense and
organized multicell clusters. For that reason SPC has place much
of the forecast area under a marginal risk for severe weather on
Monday. Damaging winds would be the primary risk with any
storms, but some hail cannot be ruled out as well.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A warm and potentially fairly stormy pattern exists through the long
term. To start, on Wednesday a weak upper low be near or just south
of the region. This low lingers Thursday. The location of this low
will help dictate how stormy the weather is, with a closer locale
likely resulting in more afternoon thunderstorms and slightly cooler
temperatures. Friday and Saturday, uncertainty grows, with some
guidance kicking the upper low east ahead of a stronger trough
approaching from the west, while others keep the low around. This
will significantly affect the forecast, but uncertainty is high.
Bottom line, however, is that slightly warmer than normal
temperatures are likely, but the extent of thunderstorms is a more
uncertain.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Generally expecting VFR at all terminals through Tuesday.
However, there will be a chance for afternoon showers and storms
each day, given the hot and humid air mass we are stuck in. This
threat will generally end once the sun sets each evening.

Most of the activity thus far this afternoon has been near CHO,
but will continue to keep TSRA in DCA/BWI between 20-22z, with
greatest confidence in a storm hitting one of the terminals.
VCTS remains for IAD and MTN as well, but think they may just
get by without a direct hit this afternoon. Will continue to
monitor radar and update as needed.

Main concern Wednesday and Thursday will be potential for early
morning fog and afternoon thunderstorms. Both of these concerns are
most likely to affect CHO and MRB.

&&

.MARINE...
Light southerly winds (below SCA) are expected over the waters
through Tuesday. Isolated to scattered showers and thunderstorms
are expected each afternoon today through Tuesday. Special
Marine Warnings may be needed for any stronger storms that form.

Mainly light winds on the waters Wednesday and Thursday, with the
primary hazard being potential for afternoon thunderstorms both
days.

&&

.TIDES/COASTAL FLOODING...
Southerly flow continues over the next several days, which will
help to keep anomalies generally elevated. Could see minor
coastal flooding in many of the same spots this evening/tonight
yet again. For now though, am holding off, as subtle shifts in
the wind speed/direction could lead to quick drops in the
anomalies, which could quickly bump the forecast back down. So,
will hold off on any advisories at this time.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

SYNOPSIS...CJL
NEAR TERM...CJL
SHORT TERM...CJL
LONG TERM...RCM
AVIATION...RCM/CJL
MARINE...RCM/CJL
TIDES/COASTAL FLOODING...CJL

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