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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 121415
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1015 AM EDT Sun Sep 12 2021

.SYNOPSIS...
High pressure will remain anchored offshore through much of the
week. A backdoor cold front will approach from Pennsylvania Monday
night, then retreat northward as a warm front Tuesday. Low pressure
may develop near the Carolina coast Thursday into Friday as a
weakening cold front approaches from the Great Lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...

-- Changed Discussion --
High level smoke is being observed this morning and is expected
to increase through this afternoon. I have increased cloud grids
to 40% to show the high level smoke layer. Depending on the
thickness of the smoke layer, high temperature could be stunted.
Weather offices up stream observed a 2 to 5 degree reduction in
high temps as compared to model/forecast values due to the
smoke layer.


.Previous DiscussionMid-upper level ridge will build over the
area today with ridge axis expected overhead by day`s end.
Meanwhile, sfc high pressure will remain offshore through the
middle of the week and maintain a very warm/hot and increasingly
humid air mass. Mostly clear, except hazy skies, are expected
today due to moderately dense smoke arriving from western fires
per latest HRRR Vertically Integrated Smoke output. Highs today
will be in the upper 80s to near 90. Lows tonight around 70.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Hotter and more humid on Monday as ridge axis remains overhead.
A weak cold front moving through southern NY and northern PA is
expected to trigger sct-nmrs convection across PA Mon evening
which could make it into northeast MD overnight Monday. Kept
20% PoP for areas generally north of I-70.

By Tue afternoon, 925/850 mb dewpoints increase further as ridge
axis shifts offshore resulting in strong instability. Isold
afternoon t-storms may develop west of the Blue Ridge due to
orographic lift and across northern MD due to potential remnant
outflows from overnight convection Monday night.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Details in the medium range period remain mired in uncertainty. What
we do know (or at least have high confidence of) is large scale
ridging over the eastern United States with Bermuda high pressure
anchored offshore at the surface. This will result in a continuation
of above normal temperatures, albeit with a slight cooling trend.

A weakening cold front is progged to slowly approach from the Great
Lakes during the second half of the week. Meanwhile, low pressure
may develop off the Carolina coast. The strength and timing of the
cold front as well as the strength and track of low pressure off the
coast are where the uncertainty stems from. Most ensemble clustering
keeps the low to our east, with a more muted influx of tropical
moisture interacting with the incoming weak front in a sloppy sense
by week`s end. This would result in periods of scattered showers or
thunderstorms rather than an all out washout, though the latter
scenario can`t be entirely ruled out at some point. Subsequent
forecast cycles will refine potential timing and placement of any
more focused precipitation potential late this week into the
upcoming weekend.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Fair weather today and Mon. Slight chance of t-storms Tue
afternoon west of the Blue Ridge and across northern MD may
affect KMRB, KBWI, and KMTN.

Shower and thunderstorm potential may increase later this week as a
weakening cold front approaches and low pressure develops
offshore.

&&

.MARINE...
Gusty srly winds through today will begin to diminish late
tonight into Monday morning. SCAs remain in effect today through
12Z Monday. Winds relax Monday into Tuesday.

The chance for showers and thunderstorms looks relatively low
Wednesday, though it may increase Thursday into Friday as a
weakening cold front approaches from the Great Lakes and low
pressure develops off the Carolina coast. Southerly channeling will
likely result in gusts of 20 to 25 knots Wednesday evening and
night. The wind forecast becomes uncertain Thursday into Friday and
depends on the strength of an approaching cold front and the track
of low pressure developing offshore.

&&

.CLIMATE...

-- Changed Discussion --
Unseasonably warm weather this week may result in some record
warm temperatures, though at this time we think the probability
is below 50 percent. As a reminder, low temperature records are
for the period 1 AM EDT to 1 AM EDT (midnight EST to midnight
EST).

Record high maximum temperatures
SITE   Sun 9/12    Mon 9/13    Tue 9/14    Wed 9/15    Thu 9/16
DCA   98 in 2019  94 in 1925  95 in 2016  97 in 1930  96 in 1991
BWI   97 in 2019  97 in 1952  94 in 1931  97 in 1927  98 in 1991
IAD   95 in 2019  94 in 1974  95 in 1998  95 in 1998  97 in 1991

Record high minimum temperatures
SITE   Sun 9/12    Mon 9/13    Tue 9/14    Wed 9/15    Thu 9/16
DCA   75 in 1983  74 in 2008  75 in 2008  75 in 2005  75 in 2005
BWI   75 in 1931  74 in 1915  74 in 1915  74 in 1915  73 in 2005
IAD   71 in 1963  71 in 2018  72 in 2018  71 in 2005  69 in 2005
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ532-533-537-
     539>541.
     Small Craft Advisory until 2 AM EDT Monday for ANZ530-531-538.
     Small Craft Advisory from 2 AM to 6 AM EDT Monday for ANZ542.
     Small Craft Advisory until 8 AM EDT Monday for ANZ534-543.
-- End Changed Discussion --

&&

$$
SYNOPSIS...DHOF
NEAR TERM...LFR/JMG
SHORT TERM...LFR
LONG TERM...DHOF
AVIATION...LFR/DHOF
MARINE...LFR/DHOF
CLIMATE...