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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 091849
AFDLWX

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

.SYNOPSIS...
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A cold front will continue to progress off toward our south and east
this afternoon as an upper level trough lingers overhead. The upper
trough will progress off to our east tomorrow, enabling high
pressure to move into the area. 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.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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As of 2 PM, a cold front is situated well off to our south and
east, extending from the Virginia Tidewater southwestward into
North Carolina. While much of the precipitation (some
anafrontal) has cleared the area, ample mid-high level cloud
cover remains to the east of the Blue Ridge. Although some
breaks in the clouds can`t be ruled out later this afternoon,
skies will likely stay mostly cloudy for locations east of the
Blue Ridge for the remainder of the afternoon. More widespread
breaks in the cloud cover have developed to the west of the Blue
Ridge. Surface heating combined with cooling aloft as the mid-
upper level trough axis approaches from the west is acting to
create some limited surface based instability across these
areas. Developing cumulus is evident on visible satellite
imagery over northwestern portions of the forecast area, with
even a few showers around. A more organized line of showers and
thunderstorms is located along a reinforcing cold front just to
the north and west of our forecast area across southwestern PA
and north central WV. This line of showers and storms will work
into northwestern portions of the forecast area over the next
few hours. A few isolated showers and storms may be possible as
well in advance of the line. Current SPC mesoanalysis shows
around 500-1000 J/kg of MLCAPE located just to our west at the
moment, and most model guidance has comparable levels of
instability translating into western MD and the WV Panhandle
over the next few hours. Flow isn`t overly impressive in the
instability bearing layer (around 30 knots of shear), but winds
increase rapidly just above the EL. Low-level lapse rates are
very steep, and temperatures are relatively cool both at the
surface and aloft. As a result, both gusty winds and small hail
may be possible with these storms. Storms aren`t expected to
reach severe levels. Activity should rapidly weaken with loss of
daytime heating this evening, and skies will clear out for all
overnight. Light winds will continue out of the northwest
overnight. Low temperatures will range from the upper 40s in the
mountains to the lower 60s in the urban areas and along the
bay.
-- End Changed Discussion --


&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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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.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
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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.
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&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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Prevailing VFR conditions are expected through Saturday. A stray
shower or thunderstorm can`t be ruled out later this afternoon
into this evening, especially at MRB. Fog may also be possible
at MRB tomorrow night.

Winds will be out of the north to northwest today into tomorrow,
with gusts to around 15-20 knots possible tomorrow afternoon.
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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Sub-SCA level winds in northerly flow are expected through the rest
of the day. 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.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies should start to drop as winds turn northwesterly
and start to increase in magnitude later tonight into tomorrow.
Despite the decreasing anomalies, the more sensitive sites will
still likely reach action stage during many of the upcoming
tidal cycles.

&&

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

&&

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