662
FXUS61 KLWX 300100
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
900 PM EDT Tue Jul 29 2025

.SYNOPSIS...
High pressure remains nearby through Wednesday. A cold front slowly
moves across the Mid-Atlantic Thursday into Friday. Strong high
pressure builds into the area over the weekend, bringing well below
normal temperatures and humidity.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Convection across the Allegheny Front and into the adjacent
mountain valleys proved to be longer lasting than anticipated.
After dumping locally heavy rainfall earlier this afternoon,
cloud tops continue to warm with the loss of daytime heating. As
of 845 PM this evening, some residual weakening showers continue
to drop southeastward to near the I-64/I-81 interchange.
Otherwise, some anvil cirrus continue to advance eastward in
response to the 20 to 30 knot jet-level winds. Expect any
decaying showers to eventually clear out within the next couple
of hours. This yields a dry forecast ahead into the overnight
hours.

Compared to 24 hours ago, the atmosphere has moistened considerably
as noted by the IAD sounding (up from 1.23 inches to 1.90 inches).
With that in mind, patchy fog is possible, particularly west of
the Blue Ridge. Very warm and muggy conditions as lows settle
in the low to mid 70s.

The surface high drifts offshore Wednesday and the frontal
boundary over the OH valley slowly meanders south/east toward
the Central Appalachians. Expect most of the area to remain dry
through early Wednesday afternoon. Scattered showers and a few
thunderstorms are possible in the Alleghenies and northern
Shenandoah Valley in the later afternoon to evening hours.
Expect another day of hot and humid conditions. Highs are
forecast to reach the mid to upper 90s once again, and heat
indices in the low 100s across the area. This will warrant a
Heat Advisory west of the Blue Ridge for the I-81 corridor and
eastern valleys of the Allegheny Front.

For areas east of the Blue Ridge, a number of the statistical
guidance show a 1 to 3 degree uptick in dew points.
Consequently, this pushes heat indices to around 105 degrees or
slightly above. As such, Heat Advisories have been extended
eastward across U.S. 15 into the D.C./Baltimore metros and down
so southern Maryland. Like to the west, such advisories run from
11 AM until 8 PM on Wednesday.

A few showers could linger Wednesday evening along the MD/PA
border, otherwise is will be dry.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
As the surface high dissipates/moves well offshore, the front over
the OH Valley will slide down into our area Thursday morning. The
synoptic pattern over our region will become more dynamic Thursday
with the collapse of a strong mid-level ridge over the Southeast
states. A broad trough over the Great Lakes slides southward toward
the northern Mid-Atlantic, with a potent shortwave trough forecast
to move over our area Thursday afternoon. As that occurs, a surface
low could develop along the surface frontal zone, then track east
toward the Delmarva Thursday evening.

Deep tropical moisture is going to be in place over the region, with
dew points in the low to mid 70s and PWATs well over 2". There is
increasing confidence for widespread showers and thunderstorms
developing Thursday afternoon to evening. There will be sufficient
instability to sustain storms through the day, though the severe
threat looks limited due to high freezing levels and weak mid-level
lapse rates. Abundant cloud cover could also work against a more
widespread severe threat. However, that is something to continue
monitoring in the days ahead.

The bigger threat for Thursday is likely going to be from flash
flooding. Thunderstorms will be capable of producing torrential
downpours due to high PWATs and efficient warm cloud processes.
Model soundings indicate mean storm motion is going to be slow, at
or less than 10 knots. This is a scenario where slow-moving and/or
training thunderstorms are possible. Rainfall rates of 1-2" in 30
minutes is possible, and some areas could receive several inches of
rain in a 1-2 hour period. While the exact details are still unclear
(as is always the case two days out for a convective event), the
potential is there for impactful flash flooding.

One final day of hot and humid conditions. Highs are forecast to be
in the low 90s, with peak heat indices between 95-105. The front
will be slow to move through the area, so some showers linger into
Thursday night.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Precipitation lingers on Friday as the a cold front remains nearby
to the south. Friday will be the coolest day of the long term period
due to cloudy skies and a post frontal airmass. Highs will be in the
70s for most with only metro locations staying in the 80s. Those at
higher elevations will top out in the upper 60s. Conditions dry out
overnight Friday through the weekend as surface high pressure builds
in from the Great Lakes region. Decreased cloud cover and high
temperatures in the 70s to low 80s can be expected both Saturday
through Monday.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
High pressure over the area slides offshore on Wednesday, with VFR
conditions prevailing at all the terminals. There could be a bit of
patchy ground fog at MRB and CHO tonight. Also, could see a few
thunderstorms in vicinity of MRB Wednesday afternoon.

A cold front sags south into the area on Thursday, bringing
widespread showers and thunderstorms. There are likely going to be
periods of sub-VFR conditions at all terminals, with gusty winds and
torrential downpours possible. As the front stalls over the area,
there could be low stratus Thursday night.

Precipitation lingers across the terminals on Friday as a cold front
remains nearby. Sub-VFR conditions are possible at times. VFR
conditions return Saturday as conditions dry out. Northerly winds on
Friday shift to northeasterly on Saturday, gusting up to 15 knots
each afternoon.

&&

.MARINE...
Favorable marine conditions look to persist most of the time through
Wednesday night as high pressure dominates across the region.
Southerly channeling tonight could bring winds close to SCA
conditions for a few hours over the Chesapeake Bay. Winds look to be
light for Thursday as a cold front slowly sags south over the
waters. Numerous thunderstorms are likely to move across the area,
and these will pose a threat to mariners from gusty winds and
lightning strikes.

Small Craft Advisories are likely on Friday as northerly winds gust
15 to 20 knots over the waters. Northerly winds shift to
northeasterly on Saturday, with Small Craft Advisories likely
needing to be extended in the southern portions of the waters.

&&

.TIDES/COASTAL FLOODING...
Tide anomalies are forecast to rise again over the next several
days as wind direction gradually becomes southerly. No areas
are forecast to hit minor flood at this time, but sensitive
tidal locations may reach Action Stage during the high tide
cycles through mid-week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Heat Advisory from 11 AM to 8 PM EDT Wednesday for DCZ001.
MD...Heat Advisory from 11 AM to 8 PM EDT Wednesday for MDZ003>006-
     008-011-013-014-016>018-502>508.
VA...Heat Advisory from 11 AM to 8 PM EDT Wednesday for VAZ026>031-
     053>057-505-506-526-527.
WV...Heat Advisory from 11 AM to 8 PM EDT Wednesday for WVZ050>053-
     055-502-504.
MARINE...Heat Advisory from 11 AM to 8 PM EDT Wednesday for ANZ530.

&&

$$

SYNOPSIS...KRR
NEAR TERM...BRO/KRR
SHORT TERM...KRR
LONG TERM...AVS
AVIATION...AVS/KRR
MARINE...AVS/KRR
TIDES/COASTAL FLOODING...LWX