-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 051338
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
938 AM EDT Sun Sep 5 2021

.SYNOPSIS...
A cold front will cross the region from the northwest today
into tonight. 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 MONDAY/...
-- Changed Discussion --
Latest analysis depicts high pressure slipping eastward out to
sea and a cold front stretching from southern Ontario and lower
Michigan southwestward towards the Red River. Aloft, a closed
low is located over northern Ontario with a shortwave dropping
southeastward across the Great Lakes and north/central Plains.
Satellite and radar depict a stream of moisture extending east-
northeastward ahead of the front, with clouds and showers
overspreading our region. Much of the activity remains light in
nature, although some modest enhancement is noted upstream back
over West Virginia.

For today, clouds will be the main story, keeping temps mostly
in the 70s as they will dominate through the day thanks to warm
advection/isentropic lift over the relatively cool/dry air mass
in place. The lack of sunshine and strong Gulf feed combined
with most dynamics with the upper level system staying to our
north means that the risk of thunder today and tonight is near
zero, but showers should become increasingly common, with
greatest coverage likely tonight. That said, rainfall amounts
look light, with generally less than a quarter of an inch
expected, so no flood concerns at all.

The front looks to clear the region early Monday, and while a
few clouds and showers may linger early, especially southeast of
I-95, the balance of Labor Day should turn out mostly sunny. The
air mass behind the front is more Pacific than Canadian, so
expect highs to rebound into the mid 80s once the sun comes out.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
Pacific high pressure will dominate Monday night through Tuesday
night. Skies will be mostly clear with temperatures near to
slightly above normal, and relatively low humidity. Clouds
increase later Tuesday night ahead of the next shortwave and
cold front, but not expecting any precip before Wednesday.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
An upper level trough over the the upper plains and Great Lakes
region is forecast to shift eastward to the north of our region
over PA and the NE US on Wednesday. A surface low is expected
form along the eastern side of the trough up in Canada. A front
associated with the SFC low is forecast to drop down through our
region Wednesday into Thursday morning. The frontal passage
will bring showers to the region with an isolated threat for
thunderstorms. Ahead of the frontal passage, a general south to
southwesterly flow will continue to advect in warm and moist air
into the region with afternoon temperatures expected to trend
up into the mid to upper 80s. The threat for strong to severe
thunderstorms remains low at this time as the main forcing
mechanism will be located further north over PA underneath the
upper trough axis. We do experience some diabatic heating ahead
of the front but increasing cloud cover will likely limit how
warm we will be able reach ahead of the front. There remains
some uncertainty on the timing of the frontal passage along with
the location of the upper trough to the north. If the upper
trough sinks further south and the front continue to trends
slower, there could be increased forcing and instability. At
this time it looks like instability will remain low with SFC-6KM
shear above 40 knots. An upper jet may provide some lift over
our region but it seems like it forms after the front passes
through our region and winds become more northwesterly limiting
the available moisture and instability. Overall the trend has
been further north with the upper trough axis and a less threat
for strong to severe weather.

Behind the frontal passage late Wed through Thurs morning, high
pressure will settle over our region Thursday afternoon through
the early parts of next weekend. Winds will become light and
out of the northwest which should mean the return of cooler and
dry conditions for the second half of this week. Afternoon
temperatures should hover in the low to mid 80s with overnight
lows in the 50s and lower 60s.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Brief intervals of sub-VFR are possible later today into tonight
as showers move across the region ahead of a weak cold front. In
addition, patchy low clouds and fog may develop late tonight
after rain showers end and partial clearing ensues. VFR should
then predominate by late morning Monday thru Tuesday night under
high pressure, though can`t rule out a little patchy fog late
Monday night or early Tuesday.

A cold front will pass through all terminals on Wednesday
bringing sporadic showers along with a slight chance for
thunderstorms. The coverage of showers should be low enough that
aviation restrictions should be minimal and VFR conditions are
mainly expected at this time. Winds will begin out of the south
on Wednesday and then become northerly toward the end of this
week. VFR conditions should be predominate Thursday through
early this upcoming weekend.

&&

.MARINE...
Southerly channeling ahead of a cold front will result in
marginal SCA conditions on much of the tidal waters today,
especially this morning, which will gradually wind down later
today and tonight as the front moves through the area. We could
briefly see some SCA gusts behind the front on Monday, but
confidence on this is not high. Light winds will prevail Tuesday
under high pressure.

A southerly channeling flow ahead of a frontal passage may
require Small Craft Advisories on Wednesday. High pressure
builds over our waters toward the end of this week with subSCA
conditions expected.

&&

.TIDES/COASTAL FLOODING...
Southerly flow will allow anomalies to remain high through
today, with highest ones near heavy fresh water inflows such as
the tidal Potomac. As winds turn westerly behind a weak cold
front later tomorrow, anomalies likely drop a bit, and this will
also be assisted by a slow diminishment of freshwater inflow.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until noon EDT today for ANZ531>533-
     539>541.
     Small Craft Advisory until 6 AM EDT Monday for ANZ534-543.
     Small Craft Advisory until 6 PM EDT this evening for ANZ537.

&&

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