749
FXUS61 KLWX 071918
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
318 PM EDT Mon Jul 7 2025

.SYNOPSIS...
The remnants of Chantal will continue to move offshore and away
from the area through the rest of the day. Meanwhile, a cold
front will slowly sag southward through the middle of the week.
Several areas of low pressure moving along this boundary will
bring daily chances for showers and thunderstorms through at
least this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Quieter conditions this afternoon as what is left of Chantal pushes
east into the Delmarva peninsula. This will lead to decreased deep
layer moisture for the remainder of the afternoon and evening. Even
with that said, some convective triggering will likely continue this
afternoon especially over the central and southern Blue Ridge,
Potomac Highlands, and Allegheny Mountains. Surface based CAPE
values continue to hover between 2000 to 3000 j/kg with DCAPE values
hovering between 500-900 j/kg. Effective shear values remain less
than 20 kts with limited steering flow along. There also remains a
sharpened PWAT gradient with values of 1.4 inches over the
Alleghenies and values closer to 2.4" over central and southern MD.

Storm coverage this afternoon will remain isolated to scattered
based upon current radar returns as well as hi-res CAM guidance
(which picks up on the slightly lower PWATS west of the Blue Ridge).
Locally damaging winds and isolated instances of flash flooding will
be the primary concerns with thunderstorms this afternoon given the
high PWATS especially along and east of I-81. With the cloud shield
breaking expect highs in the upper 80s and low 90s. Heat index
values will sit close to 100 degrees east of the Alleghenies with
juiced dewpoints in the low to mid 70s.

Any shower and thunderstorm activity will diminish tonight with the
loss of daytime heating. Skies will remain partly cloudy to mostly
clear with areas of patchy fog late. This is especially true in
areas that do see rain (i.e along and east of I-95 and near the Blue
Ridge). Lows will fall into the upper 60s west of I-81 with low to
mid 70s further east.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
The aforementioned cold front will inch closer to the region on
Tuesday. Ahead of that, a hot and humid summer air mass will
remain in place. This looks to be a classic summer severe
thunderstorm threat across our region. With the approaching
front moving into such an unstable air mass, a pre-frontal
trough develops along the I-81 corridor during the early/mid
afternoon hours. This will act to initiate convection, and there
should be plenty of instability to work with (on the order of
2000-3000 J/kg of MUCAPE). This will be paired with at least
modest deep-layer shear (20-25 knots) as a relatively potent
shortwave slides by to our north. This should support some
semi-organized clusters of thunderstorms, with damaging wind
gusts being the primary threat. Very high PWATs could somewhat
limit that threat, along with somewhat poor mid-level lapse
rates, but still think there will be some wet microbursts that
bring down severe winds. Additionally, if some of these clusters
can become more organized as the atmosphere modifies locally,
could certainly see some damaging wind swaths as well. Very
high precipitable water values (2+ inches) and deep warm cloud
layers will support very heavy rainfall rates at times (perhaps
up to 3"/hr at times). There may be enough flow aloft for
storms to be somewhat progressive, but any sort of merging or
backbuilding on the mesoscale would produce a localized flooding
threat. A Flood Watch may need to be considered on future
shifts.

Before storms arrive, heat index values may reach the upper 90s
and lower 100s. For areas east of the I-95 corridor, where dew
points will be much higher pooled along the Chesapeake Bay, Heat
Advisories were issued for heat indices around 105 degrees.

There`s some uncertainty on where the front ends up Wednesday,
but could bisect the area. Model consensus places the highest
chance of storms across the southern half of the area, but all
locations could see some rain. The main threat will be heavy
rain/localized flooding given the continued moist environment,
but a localized damaging storm can`t be ruled out. Very warm and
humid conditions continue with highs in the upper 80s and lower
90s. Storms will likely follow a diurnal trend again.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Very little change is expected in the persistent pattern which spans
this entire week. Summertime heat, humidity, and daily thunderstorm
chances will be the norm during this period. At the same time, the
forecast frontal analysis generally favors a boundary that meanders
about the region. Such boundaries often get re-positioned by
convective-scale processes which are difficult to forecast this far
out in time. Where this frontal system ultimately sets up each day
will dictate the degree of threats such as severe weather, flash
flooding, and excessive heat. However, until further notice, there
is really no let up in sight.

Looking a bit more closely at the synoptic-scale pattern, above
average heights persist over the southwestern U.S. At the same time,
the northern stream remains amplified, but the core of height falls
largely stay near the international border with Canada. This
ultimately supports the idea that the frontal zone will largely be
difficult to nudge out of the region. The focus for any convection
would be with embedded shortwaves within this broad longwave
troughing regime. Additionally, any upstream complexes that develop
more mesoscale-based phenomena (i.e., mesoscale convective
complexes, outflow boundaries, etc.) may also be triggers. There is
some hint in the global ensembles that a more amplified trough may
approach the area by early next week. Perhaps this finally nudges
the stalled front to the south of the region.

Global ensembles show a rather consistent signal in the temperature
forecast ahead. Daily highs largely sit in the mid to upper 80s,
with overnight temperatures in the upper 60s to low 70s. As usual,
mountain locations can expect cooler readings with highs in the 70s
and lows in the 60s.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
Still hanging onto some low CIGs at MTN as the remnants of
Chantal continue to move up the east coast. Clouds are beginning
to scatter out elsewhere, but there remains a SCT deck around
1500-2500 ft back to DCA. Elsewhere, cloud heights starting to
rise more in the 3000-4000 ft range as we head further into the
afternoon. Additionally, a few isolated showers remain nearby at
MTN/BWI, but will quickly push east over the next hour or so. No
guarantee that there will be any further impacts from these on
those terminals however. Expect improvement thereafter.

Additional isolated to scattered thunderstorms are beginning to
develop over the mountains this afternoon. These will move
towards MRB and CHO first over the next couple of hours
potentially. It`s uncertain if these reach the metro areas, but
IAD will be most at risk, so maintained PROB30 group in the 18z
TAF. Removed it from DCA from the previous TAF, as confidence
has increased that any storms should not make it that far east.

Tonight should be dry with light winds. There isn`t a strong
signal for fog, but can`t rule out some patchy spots.

Thunderstorm coverage will likely be fairly widespread Tuesday
afternoon and evening with heavy rain and gusty winds being
threats. Severe thunderstorms are becoming increasingly likely
for a period during the late afternoon/evening hours. All
terminals could be impacted, and damaging wind gusts in excess
of 50 knots and large hail will both be potential threats as
this line moves through. Tried to give a rough 3 hour window in
the 18z TAF for planning purposes, but the worst impacts will
likely only be felt for an hour or so during that time window.

Patchy fog could again form Tuesday night, especially in areas
where it rained.

With the threat of afternoon/evening thunderstorms each day between
Wednesday and Saturday, likely longer, restrictions will be
possible due to such storms. At this time range, the uncertainty
is quite high in terms of where any possible impacts would
occur. While the current forecast package shows a multitude of
possible wind shifts, when/if these will occur is also
uncertain. This is of course dependent on the location of the
frontal zone and where convective boundaries develop.

&&

.MARINE...
The remnants of Chantal remain to our southeast, but the rain
shield has generally moved off towards the northeast at this
point. No further impacts are anticipated from Chantal, with
partly cloudy skies returning for the afternoon.

Generally sub-SCA winds are expected Tuesday, though some
isolated gusts to 20 kt can`t be ruled out. More widespread
coverage of thunderstorms is expected during the afternoon and
evening hours, which are becoming increasingly more likely to
bring strong winds along with them.

Sub-advisory caliber winds are expected for Wednesday through
Friday. Gradients remain rather weak with wind direction being
dictated by the position of the front and any convective- scale
processes. Given afternoon/evening showers and thunderstorms in
the forecast, hazardous conditions are possible at times over
the waterways. The more robust activity may require Special
Marine Warnings.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Flood Watch until 6 PM EDT this evening for MDZ008.
     Heat Advisory from 1 PM to 7 PM EDT Tuesday for MDZ008-011-013-
     014-016>018-508.
VA...Heat Advisory from 1 PM to 7 PM EDT Tuesday for VAZ057.
WV...None.
MARINE...Flood Watch until 6 PM EDT this evening for ANZ530.
     Heat Advisory from 1 PM to 7 PM EDT Tuesday for ANZ530.

&&

$$

SYNOPSIS...CJL
NEAR TERM...EST
SHORT TERM...ADS/CJL
LONG TERM...BRO
AVIATION...BRO/CJL
MARINE...BRO/CJL