859
FXUS61 KLWX 191425
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1025 AM EDT Sat Apr 19 2025

.SYNOPSIS...
A cold front will move through the area tonight. High pressure will
build to our north Sunday, before progressing offshore Monday. Low
pressure will track into the Great Lakes on Monday, with a trailing
cold front moving through Monday night into Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Current radar imagery shows convection progressing across the
central plains towards the Ohio River Valley. The 12Z CAMs
continue showing the majority of convection staying to our north
in PA. However, the 12Z HRRR and 12Z Namnest indicate
supercells tracking through Garrett and Allegany Counties in MD
later this evening. For this reason, SPC has shifted the
marginal severe risk further east to accommodate this threat.
The 12Z KIAD sounding shows a notable cap at around 700mb, with
convection unlikely outside of the NW portions of the forecast
area. No changes were made to the forecast with the previous
forecast discussion below.

Current water vapor imagery shows a large, positively tilted
trough, which extends northeastward from the Four Corners
region across the Central Rockies, Northern Plains, and
eventually toward Hudson Bay. Downstream of this trough, a
strong upper ridge is in place across the Southeast, with an
associated ridge axis extending northward into the Mid-Atlantic.
At the surface, a cold front (becoming stationary with southward
extent), resides just downstream of the trough, extending from
southwest to northeast from the Southern Plains through the
Mid-Mississippi Valley, and into the Great Lakes.

Over the course of the day, the northern half of the
aforementioned trough will become progressive, tracking across
the northern Great Lakes and eventually reaching Northern New
England by late tonight. Meanwhile, the southern end of the
trough will lag behind and close off into an upper low over the
Southern High Plains. At the surface, the northern half of the
cold front will start to make more rapid southeastward progress,
eventually reaching the local area overnight tonight.

Current radar imagery shows lots of convection ongoing in the
vicinity of the front from Oklahoma northeastward into Illinois.
It`s expected that the remnants of any ongoing storms should
pass off to our north across PA later this morning. Locally,
much of the day should feature high clouds and dry conditions,
as the 00z IAD sounding and forecast soundings both show a
prominent cap around 700 mb, associated with a remnant elevated
mixed layer. This cap should help to prevent the development of
storms, despite what will be a very warm day, with temperatures
expected to reach well into the 80s.

There are some hints that mid-level capping may start to erode
across far northwestern portions of the forecast area later
this afternoon into this evening. As a result, a storm can`t be
ruled out along the MD/PA border from the Catoctins westward,
with Garrett and Allegany counties having the greatest chance.
If storms were to occur, they`d likely form upstream over the
Ohio Valley along the cold front, and then track east-
northeastward into the area. While the overall chance for a
storm in those areas appears to be very low, any storms that do
occur could produce very strong winds, given 60-70 knots of flow
present at 700 hPa and deep, well-mixed boundary layers with
steep low-level lapse rates.

The frontal boundary will drop southward into our area tonight,
causing winds to shift to out of the north during the second
half of the night. Other than a stray shower or storm in far
northwestern portions of the forecast area, dry conditions are
expected overnight. Lows should be in the 60s for most, with 50s
in the mountains and across northern MD.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
High pressure will build to our north tomorrow, causing winds to
shift from northerly to easterly over the course of the day. The
aforementioned frontal boundary should clear the bulk of the
area, but may get caught up across southwestern portions of the
forecast area. Daytime heating and residual low-level
moisture/convergence in the vicinity of the boundary may be
enough for some showers and thunderstorms to form tomorrow
afternoon across southwestern portions of the forecast area
(Central Shenandoah Valley and southern Potomac Highlands,
roughly south of US-48 and west of the Blue Ridge). While
instability looks to be limited, some small hail can`t be ruled
out with any that thunderstorms that form, given weak low-level
shear, ample shear in the mid-levels, minimal CAPE below the
freezing level, and low freezing levels. Elsewhere, conditions
should remain dry with mostly cloudy skies. High temperatures
tomorrow will range from the upper 60s in northeast MD to near
80 in the Central Shenandoah Valley.

An upper trough will lift northeastward from the Mid-Mississippi
Valley toward the Great Lakes on Monday. Much of the day should
remain dry, but a shower can`t be ruled out during the late
afternoon or overnight hours as the system`s cold front moves
through.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
By Tuesday, the aforementioned cold front will continue to
slowly settle toward the south as low pressure tracks through
the St. Lawrence and upper troughing lifts off to our north and
east. Weak zonal flow will move in aloft, which will likely
cause the front to slow its southward progress. Guidance differs
with respect to the positioning of the front on Tuesday, with
some models having it clear the entire area prior to daybreak,
and some others stalling the front from central Virginia to
southern Maryland. Depending on the positioning of the front, a
shower could be possible, especially to the south of I-66, but
most solutions point toward dry conditions locally. High
temperatures are expected to be in the upper 70s and lower 80s
for most.

Weak high pressure at the surface and zonal flow aloft should
lead to mostly sunny skies on both Wednesday and Thursday.
Temperatures will continue to run above normal, with highs in
the upper 70s/lower 80s, and lows in the 50s.

Spread in guidance begins to increase by Friday, but there are
some signs that by then we may begin to see an uptick in low-
level moisture as high pressure shifts offshore and return flow
starts to develop. Some solutions also have a shortwave
disturbance tracking to our northwest across the Great Lakes.
This increase in low-level moisture and large scale forcing for
ascent could potentially lead to a chance for showers or
thunderstorms.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions and southwesterly winds are expected today. Winds may
gust to around 25-30 knots this afternoon. A weak cold frontal
boundary will move through the area tonight, with winds turning
north to northwesterly during the second half of the night behind
the front. While no precipitation is anticipated with this front,
some brief MVFR ceilings may be possible later tonight into early
tomorrow morning while the front is in the vicinity. VFR conditions
are expected for much of the day Sunday. Winds will be northerly
around daybreak, and gradually shift around to out of the east over
the course of the day. MVFR ceilings may be possible within onshore
flow Sunday night, and potentially even into the day Monday as winds
turn southeasterly.

Prevailing VFR conditions are forecast for both Tuesday and
Wednesday, although a brief shower can`t be ruled out on Tuesday.
Winds will be out of the west on Tuesday, and then light and
variable on Wednesday.

&&

.MARINE...
Low-end SCA conditions are ongoing in channeled southerly flow early
this morning. SCA conditions are expected to continue through the
day today as winds gradually turn southwesterly. A cold front will
move over the waters later tonight, with winds abruptly turning
north to northwesterly behind the front. Low-end SCA conditions may
be possible for a few hours in the front late tonight. Winds will
decrease to sub-SCA levels on Sunday and gradually shift from
northerly to easterly over the course of the day. Winds will turn
southeasterly and then eventually southerly on Monday. Winds may
near low-end SCA levels in channeled southerly flow Monday afternoon
into Monday evening.

Sub-SCA level winds are expected on both Tuesday and Wednesday.
Winds will be out of the west on Tuesday, and then light and
variable on Wednesday.

&&

.TIDES/COASTAL FLOODING...
Tidal levels are expected to increase a bit today within
southwesterly flow. Annapolis and Havre de Grace may potentially
reach Action stage with the tide cycle this afternoon, but no
flooding is anticipated. Tidal anomalies will rapidly decrease later
tonight as wind turn northerly behind a cold front, with no tidal
flooding concerns evident over the next several days.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until midnight EDT tonight for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.

&&

$$

SYNOPSIS...KJP
NEAR TERM...AVS/KJP
SHORT TERM...KJP
LONG TERM...KJP
AVIATION...KJP
MARINE...KJP
TIDES/COASTAL FLOODING...KJP