Severe Thunderstorm Warning 342, NWS Baltimore/Washington

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
304 PM EDT Sat Jul 6 2019

.SYNOPSIS...
A weak cold front will approach from the northwest this weekend
before settling to our south early next week. High pressure
will then build north of the area into the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Hot and humid air mass remains in place, with heat indices into
the low 100s in many places. This combination is fueling
scattered showers and thunderstorms, but with minimal shear, the
main severe mode should be pulse through the afternoon. A linear
system is expected to evolve in Pennsylvania this afternoon and
drop southward toward our area this evening, but odds favor the
storms beginning to weaken when they arrive in the metro. That
said, this potential line is the main source of any organized
severe threat. With high PW's and relatively slow storm motion,
any back-building or training could result in a flash flood
risk, but right now it appears a bit too isolated to warrant a
watch, so have held off for now. After dark, most convection
should start to wane as we lose our main forcing mechanism, and
patchy fog/low clouds may develop as they did last night. Lows
in the muggy 70s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Cold front will slide southward into the region late Sunday and
cross the metro by early Monday. An upper level disturbance will
also cross the region during this time. These two factors,
combined with very high PW's in excess of 2 inches, may result
in heavy rain with any storms. The main factor against flooding
is CAPE, because clouds may keep instability more limited on
Sunday than today, but its possible we need a flash flood watch
for Sunday. With minimal CAPE and shear, severe risk should be
lower than today. Highs will be in the upper 80s in general,
while lows will slip into the 60s outside the cities.

Front crosses the metro early Monday morning and clears the rest
of the forecast area by later in the afternoon. This will result
in a chance of showers and storms in central VA/Shenandoah
Valley on Monday, with a lower risk further north where drier
and more stable air will be building in. Temps and humidity
will both decline somewhat behind the front, with highs in the
80s. Lows at night will also drop into the 60s in most areas.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Tuesday and Wednesday look dry, with high temperatures near, to
slightly below, average thanks to surface high pressure
building in from the north. High temperatures on both days will
be in the mid to upper 80s.

High pressure pushes offshore by Thursday ahead of an
approaching mid-upper trough and associated surface low. As a
result, Thursday will be slightly warmer, and noticeably more
humid. The cold front associated with the aforementioned area of
low pressure, sliding across the northeast, will slide through
the region on Thursday. As a result, showers and thunderstorms
are expected. Given the warm and humid air mass and at least
modest shear, owing to the close proximity of the mid-upper
trough, some storms could produce gusty winds and maybe even
some hail. A little too far out to say for sure, but can't rule
it out.

High pressure builds in on Friday behind the front, with high
temperatures expected to be near, to slightly below, average. No
precipitation is expected Friday at this time.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Main concern thru this evening is scattered thunderstorms, which
may briefly produce sub-VFR conditions in heavy rain and gusty
winds. Storms die out overnight, but will need to watch for
reduced visibility and cigs due to patchy fog and low clouds.
Biggest concern will be MRB/CHO, but can't rule out it impacting
a larger terminal as well, as we saw with the low cigs at DCA
this morning. After sunrise Sunday, concern will again become
scattered to numerous showers and thunderstorms. Convective risk
begins to dwindle on Monday, with only isolated risk in the
north (Perhaps no risk at all BWI/MTN).

VFR conditions expected Tuesday and Wednesday, as high pressure
keeps things dry. Not expecting any wind issues either, with
light winds expected both days.

&&

.MARINE...
Southerly channeling combined with scattered thunderstorms have
prompted the issuance of a small craft advisory through this
evening. Winds will be marginal except in thunderstorms, and
Special Marine Warnings may still be necessary. Storms should
die out overnight, but likely redevelop on Sunday, with similar
hazards. Storm risk declines significantly Monday behind a cold
front, but cold advection behind the front may result in SCA
gusts.

Winds remain below SCA criteria for at least Tuesday and
Wednesday, as high pressure builds over the region.

&&

.TIDES/COASTAL FLOODING...
Southerly flow has resulted in elevated anomalies. As the winds
start to shift northerly early next week, anomalies should
decline, but until then, sensitive sites likely reach action
stage, and could hit minor flood stage. Will continue to
monitor.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.

&&

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

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