-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 050124 AAA
AFDLWX

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
924 PM EDT Sat Sep 4 2021

.SYNOPSIS...
High pressure will move offshore today while a cold front
approaches from the northwest on Sunday into Sunday night. High
pressure will return later Monday into Tuesday. Another cold
front will progress through the area during the middle of the
week with high pressure building in by late in the work week.

&&

.NEAR TERM /THROUGH SUNDAY/...

-- Changed Discussion --
Increasing mid-high level clouds tonight in advance of a cdfnt
moving through the Great Lks. Showers are expected to arrive
into western MD after 09Z and affect northern areas and areas
west of the Blue Ridge. Rainfall amounts will be light under a
tenth of an inch.

Previous afd...

Expect high clouds to increase in coverage later tonight and
into the overnight hours given warm advection from the Great
Lakes trough. The mostly cloudy conditions will moderate
temperatures some as lows remain in the 60s with upper 50s over
the mountain ridgetops.

The mentioned system over the Great Lakes is expected to track
toward New England through the remainder of the Labor Day
weekend. The core of the height falls remain well to the north
of the region with a loosely defined cold front tracking through
overnight. The latest suite of 12Z high-resolution models depict
minimal instability, likely 200 to 400 J/kg at best. While some
moisture return is expected with the prevailing southerly flow,
dewpoints may only reach the low/mid 60s. Conditions on Sunday
will be mostly cloudy with some chance for light showers by the
afternoon. The best chance for any rumble of thunder would be
west of I-81 where lift may be augmented by the terrain. Highs
should top out in the upper 70s to low 80s which is a few
degrees below climatology.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Some residual showers may linger into the night as the cold
front drifts through. By Monday morning, the frontal boundary
should be east of I-95 before moving offshore. As the system
moves off the coast, the flow aloft remains westerly as the Mid-
Atlantic sits on the southern edge of the exiting upper trough.
Downsloping flow in this regime should crank temperatures up a
tad with mid 80s being attainable from I-95 southward. Sunny
conditions can be expected with dry weather throughout.
Nighttime lows will cool off by around 4 to 8 degrees relative
to the previous night as high pressure settles in. Areas along
the Alleghenies are forecast to see temperatures down into the
low/mid 50s with low 60s inside the I-95 corridor.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
igh pressure will maintain dry conditions with temperatures in the
low to mid 80s aside from the higher terrain on Tuesday.

Models are in agreement with a cold front passage sometime on
Wednesday, however differences exist on the location of the parent
upper level trough and therefore when the cold front will pass over
the region. This has implications on the potential for strong to
severe thunderstorms. A slower frontal passage will result in warmer
temperatures and lead to more instability. Given the ample shear
(near 40 knots) in place Wednesday and favorable dynamics (though
better offset to the north), an increase in instability could result
in thunderstorms that could become organized resulting in at least
an isolated strong to severe wind gust. Given the progressive nature
of the front, do think the flash flood threat is low.

The winds will turn northwesterly behind the front and a region of
Canadian high pressure will move in through the end of the week.
This will bring high temperaturesback into the 70s for most (60s in
the mountains). Given the dry airmass, do think some of the cooler
elevated valley locations of Garrett, Grant, Highland, and Pendleton
counties could see patchy frost Thursday and Friday night.

There is an area being monitored for tropical development in the
Gulf of Mexico (see hurricanes.gov for the latest). The remnants of
this disturbance could move northeast into the southeast US late
next week, and most guidance keeps it south of the FA due to the
frontal passage and high pressure overhead.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
VFR conditions are expected a majority of the period through
Monday. Some light showers are possible on Sunday, but any
restrictions should be brief in nature. At this point,
instability appears to be too meager to support any thunderstorm
chances. Winds remain south to southwesterly through Sunday
before turning northwesterly by Monday morning behind the cold
front.

High pressure will promote VFR conditions into Tuesday. There could
be a period of sub VFR conditions Wednesday in any showers or
thunderstorms.

&&

.MARINE...
A Small Craft Advisory will be in effect late tonight through
much of Sunday across a vast majority of the Chesapeake Bay and
lower portions of the tidal Potomac. This is in response to
southerly channeling of the wind fields. Eventually this
subsides late Sunday night into Monday morning as winds shift to
west and northwesterly. Post-frontal northwesterlies may
approach SCA levels on Monday, but weak thermal gradients over
the waters may mitigate some of this potential.

SCA conditions are not expected Tuesday. Northwest winds could
approach SCA criteria behind the cold front Wednesday night into
Thursday.

&&

.TIDES/COASTAL FLOODING...
Anomalies will remain elevated due to continued fresh water
influx from streams and river basins into the Chesapeake Bay and
Potomac watershed. Southerly winds this weekend will allow elevated
anomalies down in the southern bay to return northward. Action
and Minor flooding will be possible, especially along the
Annapolis coast and northward.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 1 AM to 6 PM EDT Sunday for
     ANZ531>533-539>541.
     Small Craft Advisory from 1 AM Sunday to 4 AM EDT Monday for
     ANZ534-537-543.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...BRO
LONG TERM...CPB
AVIATION...LFR/CPB
MARINE...LFR/CPB
TIDES/COASTAL FLOODING...LWX