773
FXUS61 KLWX 010807
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
407 AM EDT Tue Jul 1 2025

.SYNOPSIS...
An upper trough and associated cold front will approach from
the northwest today, before moving through the area later
tonight into tomorrow. High pressure will build over the area
later this week into the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
An active weather day is expected today, with potential threats
for both severe thunderstorms and flash flooding.

Earlier thunderstorms have lifted off to the north and east
across eastern PA and NJ, and are in the process of weakening.
Conditions remain dry across the bulk of the forecast area,
although some light showers are present across portions of the
WV Panhandle and western MD. These showers are expected to
weaken over time as they slowly drift off toward the northeast,
resulting in a mix of sun and high clouds through the morning.

As we move toward the afternoon, stronger height falls will
begin to ensue aloft ahead of a positively tilted upper trough
approaching from the Great Lakes/Ohio Valley. These height falls
will encroach upon an uncapped and unstable atmosphere, leading
to the development of numerous showers and thunderstorms this
afternoon. A prefrontal trough may help to focus initial
development of storms, but development should become widespread
as both upper diffluence and low-level convergence increase
across the area ahead of the approaching trough. Both severe
thunderstorms and flash flooding will be possible with these
storms as they move across the area from west to east this
afternoon into this evening. A discussion of individual threats
follows.

Severe thunderstorms: Model soundings show around 1500-3000 J/kg
of MLCAPE later this afternoon (less further west, more further
east), and 20-30 knots of effective bulk shear (more northwest,
less southeast). Thermodynamically speaking, profiles are nearly
saturated in the vertical from the top of the boundary layer to
the top of the troposphere, with PWATs increasing to around 2.2
inches. With such saturated profiles, DCAPE is limited at around
400-600 J/kg. Low-level lapse rates are okay, at around 7-8 deg
C/km, and mid-level lapse rates are very poor at nearly moist
adiabatic. With shear increasing relative to recent days,
storms should be more organized into short line segments and
clusters. While cold pool strength may be limited by the moist
profiles and low DCAPE, increasing winds aloft and very high
levels of moisture should be able to offset that somewhat,
leading to storms capable of producing damaging winds in water
loaded downdrafts. With the deep saturated profiles, large hail
isn`t expected, and low- level shear is too weak to expect
tornadoes. SPC has much of the area outlooked in a Slight Risk
today, driven by damaging wind potential.

Flash flooding: Many of the ingredients are in place for flash
flooding today. On the synoptic scale, increasing upper
diffluence and low-level convergence set the stage for a high
coverage of storms. Moisture levels will be off the charts. PWAT
values are forecast to increase to near or above 2.2 inches
across much of the area, which would break daily records
according the SPC sounding climatology page. Deep saturated
profiles and high freezing levels will also lead to very
efficient precipitation processes. Instability is also
appreciable, as discussed above. The combination of appreciable
instability and highly anomalous PWAT values will make storms
today capable of producing very high instantaneous rainfall
rates. The high coverage of storms will likely lead to multiple
rounds of storms in any one location. Storms could also exhibit
some limited training motion, since a large component of the
wind aloft parallels the orientation of the tightening 850 hPa
front and the pre-frontal trough at the surface. The one
limiting factor today will be fairly quick storm motions, with
flow through the mid- levels increasing to around 30 knots. As a
result of the factors listed above, the environment looks to be
very favorable for flash flooding. A Flood Watch for flash
flooding has been issued for much of the area this afternoon
into this evening. A widespread 1 to 2 inches of rain is
expected within the Watch, with isolated totals of 2-5 inches
possible. The Watch comes to an end at 3z/11 PM, but lighter
showers may linger through the night, with the surface front
trailing off to the west.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
The aforementioned cold front will make slow, but steady
progress toward the southeast during the day Wednesday, before
eventually clearing the area Wednesday night. Showers will
linger along and southeast of the front Wednesday morning,
primarily impacting locations south and east of DC. Drier air
aloft will gradually filter into the area from northwest to
southeast over the course of the, leading to breaks of sunshine
developing by afternoon, especially to the north and west of DC.
With ample moisture still in place at the surface, some
instability will remain. As a result, a stray shower or storm
can`t be ruled out Wednesday afternoon, but most locations
should remain dry. High temperatures on Wednesday will be in the
low to mid 80s for most.

Dry conditions are expected Wednesday through Thursday as
slightly drier air starts to filter in at the surface. The
slightly lower dewpoints will enable temperatures to drop back
into the 60s Wednesday night, before climbing back up into the
mid to upper 80s on Thursday beneath mostly sunny skies.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Dry conditions continue for the 4th of July and into this coming
weekend as a ridge of high pressure moves overhead. The forecast
for the 4th looks very pleasant, as we remain in the post-frontal
air mass with low humidity. Temperatures will rise into the upper
80s to low 90s, but heat indices won`t be much different thanks to
the lower humidity.

This ridge remains overhead through at least Sunday, but humidity
will gradually build as the Bermuda High becomes more established
offshore. This will result in warmer temperatures each day, and heat
indices approaching the upper 90s to near 100 by Sunday afternoon.
Additionally, the ridge may begin to break down Sunday afternoon,
which could bring the potential for a few thunderstorms to develop
across our western areas. That chance is only around 15 to 20
percent at this time however.

The high sliding to the south and east of the area Sunday will allow
for a cold front to approach from the Ohio River Valley and Great
Lakes region. This front will bring renewed chances for spotty
showers and thunderstorms mainly west of the Blue Ridge for the end
of the weekend into the start of next week. Highs Sunday and Monday
will push into the upper 80s and low 90s on southwesterly return
flow.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Prevailing VFR conditions are expected at the terminals through
the morning. Numerous showers and thunderstorms are expected to
develop across the area this afternoon and continue into this
evening. Multiple rounds of thunderstorm may be possible at each
site, and TEMPO groups currently highlight a four hour window
with the highest threat for storms at each site. Outside of
thunderstorms, light south to southwest winds are expected.
While showers may linger overnight, thunderstorm activity is
expected to wind down this evening. Ceilings may potentially
drop to MVFR or potentially even IFR for a time tonight.

Improvement back to VFR conditions is expected during the day
tomorrow. Although a stray afternoon thunderstorm can`t be ruled
out, most locations should remain dry. VFR conditions and mostly
sunny skies are expected on Thursday. Winds will be light out of
the northwest both tomorrow and Thursday.

VFR conditions are most likely for Wednesday through Saturday with
high pressure nearby.

&&

.MARINE...
Low-end SCA conditions may linger across the Middle Bay through
much of the day. Otherwise, gusts of around 10-15 knots are
expected with winds out of the south to southwest. Numerous
thunderstorms will impact the waters this afternoon into this
evening, likely leading to the issuance of SMWs.

A cold front will move over the waters later tonight into
tomorrow morning, causing winds to become light out of the
northwest by tomorrow afternoon. Light northwesterly winds will
continue through Thursday.

Sub-SCA level winds are expected through Saturday as high
pressure builds over the region. A dry cold front will pass
through the area Friday into the start of the holiday weekend.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch from 2 PM EDT this afternoon through this evening
     for DCZ001.
MD...Small Craft Advisory until 6 AM EDT early this morning for
     MDZ008.
     Flood Watch from 2 PM EDT this afternoon through this evening
     for MDZ003>006-008-011-013-014-503>508.
VA...Flood Watch from 2 PM EDT this afternoon through this evening
     for VAZ026>031-038>040-051-053-054-501-502-505>507-526-
     527.
WV...Flood Watch from 2 PM EDT this afternoon through this evening
     for WVZ050>053-055.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
     ANZ530>534-536>543.
     Flood Watch from 2 PM EDT this afternoon through this evening
     for ANZ530.

&&

$$

SYNOPSIS...KJP
NEAR TERM...KJP
SHORT TERM...KJP
LONG TERM...CJL
AVIATION...CJL/KJP
MARINE...CJL/KJP