583
FXUS61 KLWX 260136
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
936 PM EDT Fri Apr 25 2025

.SYNOPSIS...
As low pressure approaches from the Midwest, a warm front will
lift north tonight, followed by a cold front crossing on Saturday.
Canadian high pressure will settle in on Sunday into Monday.
Another frontal system will affect the region during the middle
to latter half of next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Current radar imagery shows numerous showers and a few embedded
thunderstorms ongoing, primarily to the west of the Blue Ridge.
This activity is occurring within a zone of weak synoptic scale
ascent downstream of a low-amplitude mid-upper level trough
over the Ohio Valley. Those showers and storms will continue to
spread northeastward through the rest of the night. Most
locations will experience on and off showers through much of the
night, with a few embedded lightning strikes possible. A few
brief heavier downpours may also be possible, given a very deep
layer with near saturation, weak instability, and PWAT values
nearing 1.5 inches evident on the 00z IAD sounding. Overall, a
general quarter to half inch of rain is expected across much of
the area, which should be beneficial given ongoing drought
conditions. Temperatures will remain mild overnight with lows
in 60s (mid- upper 50s mountains).

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The surface low will be moving into the St. Lawrence Valley by
Saturday morning. A cold front will trail southwestward along
the Appalachian Mountains. Aloft, a compact shortwave/closed low
will be moving through the Great Lakes, while a more subtle
shortwave accompanies the surface front. Scattered showers will
likely be occurring along and ahead of the front as it moves
eastward during the morning. The extent of these showers and low
cloud cover could play a role in destabilization ahead of the
cold front. However, most guidance does have some instability
available along and east of I-95 during the afternoon. Wind
fields aren`t terribly strong, but around 30 kt of deep shear
may aid in storm organization for anything that develops. The
main threat with any stronger storms will be gusty winds, with
CAMs focusing on southern Maryland for the greatest potential of
these stronger storms. Highs should make it back into the 70s
for most, with 80s most likely in central Virginia and southern
Maryland where some thinning of clouds may occur.

Showers and storms will depart to the southeast during the
evening. The most potent part of the northern trough will remain
north of the area, so any light lingering upslope precipitation
in the Alleghenies should wind down before colder temperatures
arrive. Lows will be in the 40s, with 30s in the higher
elevations.

The other aspect of this cold front will be the gusty westerly
winds in its wake. Despite the setting sun, winds may increase
into Saturday evening due to cold advection and strong pressure
rises. Most gusts will be 20-35 mph but higher on the ridge
tops. While winds may decrease the second half of the night,
especially in sheltered areas, expect them to increase again
after sunrise Sunday. While cooler, highs in the mid 60s to
lower 70s on Sunday will be near to a few degrees below normal.

Winds rapidly diminish Sunday evening as high pressure builds in
from the northwest, and skies should be clear. This will provide
favorable radiational cooling conditions with temperatures
falling into the upper 30s to mid 40s (warmer in urban and
bayshore areas). Dew points have been trended downward however,
which could present an opportunity for frost, in particular
across the Shenandoah valley, but potentially in colder spots
across northern Maryland as well. Growing season for the far
western zones starts May 1.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Surface high atop the area Monday quickly slides offshore of the
Carolinas Monday night as a strong upper trough approaches from the
west. The main upper trough is forecast to slide across the Great
Lakes into Ontario, though its trailing cold front moves south into
the OH Valley Tuesday, then across the Mid-Atlantic Wednesday. There
could be a chance for strong to severe thunderstorms as the front
moves through the Potomac Highlands on Tuesday, then possibly along
and south of US-50 on Wednesday. Temperatures each day are forecast
to be well above normal, in the mid to upper 80s on Tuesday and
upper 70s to mid 80s on Wednesday.

Taking a closer look, Tuesday looks to start dry as sharp mid-level
ridging and residual surface air cap convection during the first
half of the day. As the mid-level ridge moves east some slight
height falls Tuesday evening accompanied by modest instability ahead
of the front could support some strong to severe thunderstorms in
the Potomac Highlands. Shear looks to be marginal at 30-35 knots in
mostly zonal flow aloft, but enough to support some organized
convection. East of the Alleghenies storms could struggle with the
loss of daytime heating and increasing stability/capping.

The front moves south into our area Tuesday night into Wednesday
morning where it flattens out and slows down around US-50. However,
the exact location of the frontal surface will be key in whether
severe storms are possible Wednesday afternoon/evening. Abundant
cloud cover in stable northwest winds to the north of the boundary
likely prevent any storms from developing. To the south of the
boundary, ample instability and moisture with slightly better deep-
layer shear profiles (35-40 kt) could support more robust
convection. Based on the current 12Z guidance this puts portions of
Central VA and far southern MD with the better chances for some
strong to severe storms. Something to keep watching in the days
ahead.

A reinforcing trough pushes the nearly stalled cold front south of
our area Wednesday night. Still, shower and thunderstorm chances
will remain in the forecast through the end of the week due to
another area of low pressure approaching from the Mid-South on
Thursday. Its associated cold front moves across the Mid-Atlantic on
Friday. Highs remain in the 70s to low 80s each day.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
Cloud bases continue to lower as a system approaches from the
west. A more substantial increase in shower coverage is
expected later this evening, which will likely bring some
periods of MVFR conditions to the area TAF sites. While a few
thunderstorms may affect the metro areas this evening, still
think the chance is too low to include in the TAFs. There may be
a relative lull in shower chances late tonight into Saturday
morning.

Ceiling forecasts are rather uncertain tonight, perhaps
contingent on the placement of the advancing surface warm front.
In fact, there could be a tight gradient between areas that are
VFR compared to IFR. For now, limited IFR conditions to MTN,
with MVFR at MRB/IAD/DCA/BWI. Lower ceilings will gradually
lift by midday or early afternoon Saturday. After further
evaluation, LLWS in previous TAFs appeared unlikely, so removed
it from the TAFs.

A cold front will work across the area Saturday. Potentially
light showers during the morning may take an increasingly
convective nature by midday, especially moving southeast from
BWI/DCA. With coverage of thunder uncertain, have included
PROB30 for thunder for the metro TAFs and heavier convective
showers at MRB/CHO. Activity should be southeast of the TAF
sites by 22 or 23Z.

In the wake of the front, winds shift to the west and northwest.
A surge of gusts 25-35 kt may occur during the evening, with
renewal of 20-30 kt gusts after sunrise Sunday. VFR conditions
prevail however, and winds will rapidly diminish Sunday evening.

VFR conditions continue through the start of next week. Showers and
thunderstorms return to the forecast for Tuesday evening, though
coverage looks to be low at the terminals at this time. Still,
something to watch as a storm or two could be strong (again chances
are low at this time). Southerly winds will increase Tuesday into
Tuesday night and possibly gust to around 20 knots.

&&

.MARINE...
South to southeasterly winds continue to produce spotty
advisory level conditions this evening. The intermittent and
spotty nature of the gusts could continue through the night.
Because of this potential, Small Craft Advisories are in place
across all waters through early evening, continuing everywhere
outside the upper tidal Potomac into tonight.

Showers and isolated thunderstorms move through tonight. As a
cold front approaches Saturday afternoon, some stronger
thunderstorms may develop which require Special Marine Warnings
for gusty winds. Behind the cold front, an increasingly gusty
west to northwest wind overspreads the waters. This will bring
gusts to around 25 to 30 knots, which may include occasional
gale force winds at times. The most likely time for this will be
in the post frontal surge, but some potential may linger along
the bay until Sunday morning. Due to uncertainties in mixing
depth, have only issued Small Craft Advisories at this time, but
upgrades may eventually be warranted. Small Craft Advisories
will likely be needed into Sunday afternoon. Winds drop off
pretty quickly Sunday evening given the influence from Canadian
high pressure.

Marine conditions look to be favorable Monday as high pressure over
the area moves offshore of the Carolinas. As that happens southerly
winds increase Tuesday morning into Tuesday night, with SCA
conditions possible over most of the waters.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies currently range from 0.25 to 0.50 feet this
afternoon. There will be some uptick in water levels ahead of a
cold front that tracks through Saturday afternoon. The current
forecast brings Annapolis and Baltimore into Action stage, but
all others remain below. Behind the front, a west to
northwesterly wind will quickly lower anomalies across the area.
No tidal flooding is expected on Sunday into Monday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 6 AM EDT Sunday for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ530>534-
     536>543.
     Small Craft Advisory from 11 AM Saturday to 6 AM EDT Sunday
     for ANZ535.

&&

$$

SYNOPSIS...ADS
NEAR TERM...KJP
SHORT TERM...ADS
LONG TERM...KRR
AVIATION...ADS/KRR
MARINE...ADS/KRR
TIDES/COASTAL FLOODING...BRO