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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 121833
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
233 PM 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 --
A faint haze of high level smoke can be observed by satellite and
from the ground this afternoon. It seems that the smoke will be thin
enough that temperatures shouldn`t be impacted much this afternoon.
High pressure positioned along the southeastern coast of the US will
slowly settle off-shore this afternoon and remain in place through
most of this week. The positioning of the high will lead to a
continued south to southwesterly flow that will advect in warm and
moist air into our region. Dry weather with mostly clear skies
should continue through the rest of today. Afternoon temperature
should peak in the mid to upper 80s with a few areas reaching the 90
degree mark down in central VA. Overnight lows will be near to
slightly above normal in the mid to upper 60s to lower 70s. An upper
level jet at 850 will increase late this evening and into early
Monday in the western parts of our region. Possible 50 to 55 knots
aloft may translate to overnight gusts in the 25 to 35 knots range
over our higher elevations but I expect winds to remain below wind
advisory criteria.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...

-- Changed Discussion --
High pressure will remain situated along the eastern seaboard
through the middle parts of this week as weak upper level ridging
remains to the north of our region. A backdoor front is forecast to
drop southward from Canada and stall to the north Monday through the
middle parts of this week. The high to south of our region will lead
to continued advection of warm and moist air into our region. The
warmest weather of September will occur Monday and Tuesday as highs
will peak in the upper 80s to lower 90s with a few areas potentially
breaking daily high temp records. Overnight lows will be near or
above average in the mid to upper 60s to lower 70s to start this
week.

The main question for the Monday through Tuesday period will be
whether showers and thunderstorms will be possible in any parts of
our region. Increasing temperatures and moisture will lead to
increasing instability in our region through the early parts of this
week. Ensembles are suggesting that CAPE values above 2000 will be
likely both Monday and Tuesday with shear values around 25 knots.
Although we be relatively unstable to start this week the threat for
convection will be limited due to the best forcing focused to the
north near the frontal boundary along with increasing heights. High
res guidance and global models do indicate that storms could form
along our higher elevations late Monday evening or a storm to the
north could drop southward into our region. Overall, the confidence
remains low on any widespread thunderstorm threat but a pulse storm
forming off the bay breeze or higher elevations can`t be ruled
especially considering how warm and unstable our region will be this
week.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...

-- Changed Discussion --
By the middle of the week, gradual amplification in the flow will
take shape across the Great Lakes while what remains of Tropical
Storm Nicholas is slated to near the Texas/Louisiana interior
border. A core of the forcing with the approaching trough should
stay north of the Mid-Atlantic while some mid-level vorticity will
peel away from Nicholas and move toward the Appalachian chain. At
the same time, the National Hurricane Center is monitoring a region
of disturbed weather in the vicinity of the Bahamas. There`s a 50
percent chance a tropical depression will form over the western
Atlantic over the next 5 days. With the mentioned upstream trough
approaching the Eastern Seaboard, this system along the Gulf Stream
should stay offshore. Conditions remain somewhat unsettled with the
Mid-Atlantic region confined to the warm sector. The cold front
attendant to the approaching trough will attempt to move through
Wednesday evening before stalling to the north as a stationary
boundary. The belt of westerlies further retreats into eastern
Canada which leaves more summer-like gradients into next weekend. If
the disturbance over the western Atlantic moves closer to the coast,
some uptick in northerly winds are possible inside I-95. Upper
ridging remains largely in charge to finish out the weekend with
summertime heat and humidity a likely fixture. This would be
accompanied by some chance for daily showers and thunderstorms,
albeit with low confidence in coverage and intensity.

For Wednesday, expect high temperatures to rise into the upper 80s
to low 90s, similar to preceding days. Humidity is expected to
increase a tad into Thursday and Friday as moisture from Nicholas
ejects northeastward from the western/central Gulf Coast region. An
increase in cloud cover should lower temperatures back into the mid
to upper 80s for Thursday and Friday. Mid 80s are forecast to remain
commonplace into next weekend given the above average heights in
place. Multi-model ensembles do indicate quite a bit of temperature
spread with upper 70s to low 90s being in that 10th and 90th
percentile range, respectively. Overnight temperatures remain mild
with lows in the mid 60s to low 70s east of the Blue Ridge. Farther
west, low to mid 60s will be more commonplace. These forecasts are
easily 10 to 15 degrees above mid-September climatology.
-- End Changed Discussion --

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...

-- Changed Discussion --
VFR conditions along with winds mainly out of the south to southwest
are expected through Tuesday as high pressure remains off to the
southeast of our region while a front stalls to the north. The main
uncertainty for our terminal forecasts will be whether a pop up
thunderstorm will form and impact one of our terminals.

Mainly VFR conditions can be expected on Wednesday and Thursday
given prevailing southerly winds. With a summer-like air mass in
place, diurnally driven showers and thunderstorms may lead to brief
restrictions at local terminals. Confidence is too low to pinpoint
any further details at this time.
-- End Changed Discussion --

&&

.MARINE...

-- Changed Discussion --
High pressure positioned off the southeast US will lead to periods
of southerly channeling winds. SubSCA conditions expected through
Monday but Small Craft Advisories maybe needed on Tuesday.

Ahead of the approaching cold front, southerly winds will continue
with gusts 15 to 20 knots at times. This supports the potential for
Small Craft Advisories for Wednesday, perhaps into the night. The
advancing front stalls which keeps southerly flow in place into
Thursday. Winds do come down in strength a bit. While confidence is
low, some daily thunderstorm threat exists which may require
convective-based hazard products.
-- End Changed Discussion --

&&

.CLIMATE...

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

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$
SYNOPSIS...DHOFF
NEAR TERM...JMG
SHORT TERM...JMG
LONG TERM...BRO
AVIATION...BRO/JMG
MARINE...BRO/JMG
CLIMATE...