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000
FXUS61 KLWX 061851
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
251 PM EDT Mon Sep 6 2021

.SYNOPSIS...
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Behind this morning`s cold front, high pressure will build in
and remain over the area into Tuesday. A cold front will
progress through the area during the middle of the week with
high pressure building in by late in the work week and into the
weekend.
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&&

.NEAR TERM /THROUGH TUESDAY/...
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As of early this afternoon, the frontal boundary which moved through
this morning has advanced off the Delmarva Peninsula. General west
to northwesterly winds have ensued in the wake which has ushered
in a decidedly drier air mass. Dew point temperatures are currently
running in the 50s accompanied by occasional wind gusts up to
around 20 mph. GOES-16 visible imagery shows nearly cloud-free
skies, although some mid-level cumulus are starting to move down
from the Mason-Dixon Line. Seasonable temperatures are being observed
around the region given substantial sunshine and some local downsloping
effects. Current temperatures are sitting in the low 80s with
readings likely rising by a couple more degrees this afternoon.
High pressure continues to build in from the west which will lead
to a cooler night ahead. Decent radiational cooling should take
place as winds lighten and skies remain mostly clear. While low 60s
will be commonplace inside I-95, mid/upper 50s can be expected
elsewhere. Some patchy fog may develop in this environment, mainly
along I-81 and back into the Alleghenies.

With high pressure gradually shifting offshore on Tuesday, return
flow ensues bringing humidity levels back up a bit. Sunshine
will remain plentiful as a shortwave ridge tracks overhead. The
steady warm advection through the day will bolster temperatures
back into the mid 80s which is about 3 to 5 degrees above early
September normals.
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&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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A much milder night will be on tap for the region with the
persistence of south to southwesterly flow. Mid to upper 60s are
likely for most spots east of the Blue Ridge and Catoctin with near
70 degree readings in the warmer DC and Baltimore city centers.

Wednesday ultimately brings the best convective chances to the
region as a strengthening upper trough approaches from the west.
Currently near the Alberta/Saskatchewan border, this system will
dive southeastward during the next couple of days toward the
Mid-Atlantic region. The core of lower heights remains over the
Great Lakes with thhis mentioned feature sweeping through
underneath by late Wednesday. The lack of collocation of the
forcing from the trough and diurnally forced instability leaves
some uncertainty around convective coverage and intensity.
However, the 12Z NAM nest and a couple global solutions show a
lee trough forming during the afternoon hours. Vertical motions
associated with this or any mesoscale boundary may prove
instrumental to some shower/thunderstorm activity. Surface
conditions will be more ripe for instability based on
temperatures in the mid/upper 80s and dew points in the upper
60s. Will continue to monitor the convective threats in the
upcoming forecast cycles.

As the height falls track through late Wednesday into the overnight,
a band of showers are forecast to progress eastward ahead of a cold
front. Much of this activity should wind down before daybreak the
following day. Temperatures cool in the wake of this boundary with
overnight readings in the lows 50s along the Allegheny Front.
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&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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The aforementioned cold front will continue moving through the
eastern part of the CWA Thursday morning. Therefore, have continued
to maintain a slight chance for showers early on Thursday mainly
southeast of I-95. High pressure will then build in through the end
of the week. The next front/disturbance arrives later next weekend,
but confidence is low rain making it this far south at this time.

Temperatures Thursday into Friday will be slightly below average.
Given the dry airmass associated with the region of Canadian high
pressure, temperatures Thursday night could be the coldest across
the region since June. Currently have widespread 50s west of I-95
except for in the mountains where temps could fall into 40s, with
60s expected near the metros/bay. The colder elevated valleys of
Garrett, Grant, Pendleton, and Highland counties could make a run
into the lower 30s, resulting in patchy frost Thursday night.
Similar conditions, though a degree or two milder, are possible
Friday night.

Temperatures moderate a few degrees over the weekend as heights rise
and high pressure moves offshore.
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&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
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VFR conditions are expected through at least the first half of
Wednesday. Dry conditions will occur during that period of time
with west-northwesterly winds shifting to southerly on Tuesday.
Any patchy fog formation should occur well west of the area
terminals. For Wednesday afternoon and into the night, showers
and thunderstorms are possible as a cold front approaches from
the west. This may lead to some restrictions with confidence low
in exact timing and placement.

Aside from a few morning showers that could result in MFVR condtions
at the terminals along I-95 Thursday morning, VFR condtions should
dominate Thursday afternoon into Friday. The winds behind the front
Thursday into Friday will generally be northwest up to 10 knots.
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&&

.MARINE...
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Occasional SCA caliber winds are being observed in the post-
frontal west-northwesterly flow, but such breezes should quickly
diminish in the next couple of hours. By Tuesday, winds shift to
southerly which leads to some channeling of the winds by the
evening hours and into the overnight. As such, a Small Craft
Advisory has been issued for much of the Chesapeake Bay as well
as lower portions of the tidal Potomac. On Wednesday
afternoon/evening, scattered showers and thunderstorms may lead
to periods of hazardous conditions over the marine waters.

There could be a period of SCA winds early Thursday behind the cold
front as northerly channeling sets up over the Chesapeake Bay. SCA
conditions are not likely to later Thursday into Friday as high
pressure builds.
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&&

.TIDES/COASTAL FLOODING...
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Winds have shifted offshore this afternoon, allowing tidal anomalies
to drop drastically since this morning. This will be short-lived,
however, with southerly flow resuming with rising anomalies by
Tuesday night. This might result in minor flooding at sensitive
sites by Wednesday morning.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 8 PM Tuesday to 6 AM EDT Wednesday
     for ANZ531>534-538>541-543.
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&&

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