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000
FXUS61 KLWX 100115
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
915 PM EDT Thu Sep 9 2021

.SYNOPSIS...
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An upper-level trough will pass through the region tonight and
high pressure will build overhead for Friday. High pressure
will remain overhead through the first half of the weekend,
before moving offshore for the second half of the weekend into
early next week.
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&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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An upper-level trough overhead this evening will begin to slide
to the east overnight. A cold front associated with the upper-
level trough (currently located over southern MD late this
evening) will also move off to our southeast overnight.

Subsidence will continue to increase behind the departing trough
and cold front, and this will result in high pressure that
builds to our west over the Ohio Valley. A northwest flow behind
the departing cold front and ahead of the high will usher in
noticeably cooler and drier conditions overnight. Min temps
will range from the 40s and lower 50s in the Potomac Highlands
to the upper 50s and lower 60s near downtown Washington and
Baltimore.

Any leftover shower late this evening over the Virginia Piedmont
and southern MD will clear out overnight as the drier air moves
in.
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&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
The mid-upper level trough axis will shift off to our east tomorrow,
enabling high pressure to start to build in from the Ohio Valley.
Winds will be northwesterly in advance of the approaching high, and
could gust to around 20 mph through much of the day. Skies will be
sunny, with just a few fair weather cumulus possible by late
afternoon into the evening. Highs tomorrow will be in the mid-upper
70s for most, with 60s in the mountains.

High pressure will become centered overhead tomorrow night. With
clear skies and calm winds, conditions will be ideal for radiational
cooling. Temperatures will bottom out in the upper 40s to lower 50s
in most spots, with lower 60s in downtown DC and Baltimore, and some
upper 30s to lower 40s even possible in the coldest mountain
valleys. Areas of fog will also be possible, especially in sheltered
river valleys to the west of the Blue Ridge.

High pressure will begin to shift offshore during the day
Saturday. As light southerly flow develops, slightly warmer air
will start to work into the area. Sunny skies are expected
again, with highs in the upper 70s and lower 80s for most. Skies
will stay clear Saturday night, but temperatures will be much
warmer than Friday night with light southerly winds in place.
Low temperatures will range from the 50s to middle 60s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Weak general ridging will remain in place over our region Sunday
through Wednesday.  Bermuda high pressure is forecast to be in place
over SE US and mid-Atlantic Sunday and Monday and will lead to the
formation of a south to southwesterly flow. The southerly flow will
lead to increased advection of warm and moist air and will begin the
warming trend that will continue through most of next week.
Afternoon temperatures will hover in the mid to upper 80s on Sunday
but dewpoints will still remain relatively low which will limit
instability. On Monday, afternoon highs will rise up into 90s with
dewpoints in the mid 60s. This combination will lead to CAPE rising
up above 1000 with the possibility of values above 2000. There will
be lack of good forcing on Monday but a few showers/thunderstorms
could be possible along the bay breeze.

Moisture and temperatures will remain elevated Tuesday through
Wednesday with highs in the upper 80s. Instability will remain high
as CAPE will likely be above 2000 and decent mid level lapse rates
will be possible. Some models hint that a shortwave could clip part
of our region which may provide enough forcing to produce some
showers and thunderstorms. There remains a lot of uncertainty on the
threat level for thunderstorm development next week.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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Prevailing VFR conditions are expected through Saturday. Fog
may also be possible at MRB tomorrow night.

Northwest winds are expected tonight, a brief period of gusts
around 20 knots are possible this evening with a pressure surge
behind the front, but the nocturnal inversion should cause
winds to remain lighter overnight. Winds will quickly increase
after sunrise Friday morning with gusts around 20 to 25 knots
possible, before gradually diminishing throughout the mid and
later afternoon into the early evening. Winds will go light
tomorrow night as high pressure moves overhead, before turning
around to light out of the south on Saturday.

High pressure will remain in place Sunday through Tuesday with winds
generally out of the south. Warm and humid conditions may combine
with a sea breeze to produce some showers and thunderstorms that
could impact some terminals mainly along and east of the I-95
corridor.
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&&

.MARINE...
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Winds will pick up in north to northwesterly flow tonight, and
SCA level winds are expected over the waters later tonight
through the day tomorrow. Winds will slacken tomorrow night as
high pressure builds overhead. Winds will become light out of
the south on Saturday as high pressure moves offshore.

High pressure over the waters will lead to sub-SCA conditions
Sunday and Monday.
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&&

.TIDES/COASTAL FLOODING...
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Tidal anomalies will continue to drop overnight due to a
northwest flow.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ530>534-536-
     537-539>541-543.
     Small Craft Advisory from 6 AM to 6 PM EDT Friday for ANZ535-
     538-542.
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&&

$$
SYNOPSIS...KJP
NEAR TERM...BJL/KJP
SHORT TERM...KJP
LONG TERM...JMG
AVIATION...BJL/KJP/JMG
MARINE...BJL/KJP/JMG
TIDES/COASTAL FLOODING...BJL/KJP