Deale, Maryland Weather Forecast Discussion

155
FXUS61 KLWX 230000
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
800 PM EDT Mon Sep 22 2025
.SYNOPSIS...
High pressure will weaken into the night while a warm front
remains north of the region. An area of low pressure and its
associated cold front will eject out of the Central Plains and
Upper Midwest toward the Ohio Valley Tuesday into Wednesday.
The front will be slow to cross the area with a series of low
pressure systems traversing the boundary through at least
Friday. High pressure gradually builds in from the west by later
in the weekend.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
High pressure currently (as of 00Z/8PM EDT) extends from just
offshore of the Carolinas up along the Eastern Seaboard into the
Canadian Maritimes.
Earlier shower and thunderstorm activity just to the east of the
Appalachians has largely diminished, though additional activity
was developing over the mountains in weakly convergent upslope
flow beneath subtle height falls aloft and moisture advection.
Further to the west over the Ohio Valley, a semi organized line
of storms has developed. This line will outpace better forcing
and run out of instability with the loss of daytime heating, but
a few lightning strikes, downpours, and 30-40 mph wind gusts are
possible in the vicinity of western Maryland around or shortly
after midnight tonight. Otherwise, the forecast looks dry
especially east of I-81. Patchy fog may develop overnight in two
regimes: (1) radiative fog near where it rained earlier and
where the sky is clear and winds go calm near/west of I-81, and
(2) perhaps in light onshore advection fog near southern MD
(there is lower certainty in the second area).
Regarding temperatures, tonight`s forecast calls for lows in
the upper 50s to low 60s. With ample low-level moisture and
light winds.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
The coverage of showers and thunderstorms will increase within
this summer-like pattern. A complex upper pattern sets up with
multiple players involved in this evolution. The key features to
note are an evolving closed low across the Great Lakes and a
positively-tilted trough over the central U.S. As the latter
system slides eastward, ample perturbations in the low-amplitude
flow approach the eastern U.S. By mid-week, this pair of systems
gradually becomes adjoined while trekking through the Upper
Midwest into the Missouri Valley.
At the surface, any associated frontal features will remain west
of the local area through at least mid-week. However, it does
appear a lee trough forms each day which should act as an
impetus toward convective development. On Tuesday, with high
temperatures warming into the mid 80s and dew points hitting the
mid/upper 60s, surface-based instability (CAPE) values rise to
around 1,500 to 2,000 J/kg. Given deep-layer shear vectors of 20
to 30 knots, some storms could become fairly organized and
capable of damaging wind gusts. The 12Z high-resolution model
suite is supportive of this as shown by the cluster of 40 dBZ
paintballs. As such, the Storm Prediction Center has upgraded
to a Marginal risk from I-81 eastward. The potential for any
severe storms should wane with the loss of daytime heating.
Overnight lows fall back into the upper 50s to mid 60s which may
come with some patchy fog across areas hit by earlier rainfall.
Similar to Tuesday`s forecast, expect a decent coverage of
showers and thunderstorms on Wednesday. The eastward extent of
the approaching longwave trough nears the region which should
yield ample forcing for ascent. A lee trough also appears
present while the parent frontal waves sit back over the Ohio
Valley. Forecast temperatures are slightly cooler than the
preceding day, but it will remain plenty humid. While the NAM
nest can often produce robust solutions, its 60-hour forecast
(Wednesday early evening) certainly supports another active day.
Nights become milder in time with lows rising into the
mid/upper 60s along and east of I-95.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
A surface low pressure system tracking from the Great Lakes Region
towards New England Thursday and Friday will push the associated
cold front towards and across the forecast area at the end of the
week. Daily shower and thunderstorm chances are expected with
recent dry conditions yielding primarily beneficial rainfall.
The greatest chances for rainfall will be Thursday and Friday as
the front approaches and moves through the region, but
precipitation chances linger on Saturday as the front remains
nearby offshore.
In the wake of the cold front, surface high pressure builds over the
Mid-Atlantic from the central CONUS. Conditions generally dry out
overnight Saturday into Sunday. The exception will be a slight
chance of showers Sunday afternoon due to lingering moisture.
Coverage is expected to be isolated in nature with most areas
remaining dry. Conditions continue drying into next week as high
pressure builds to the north.
High temperatures will be in the 70s to low 80s for most each day
with higher elevations staying in the 60s. Overnight lows will be in
the 50s to 60s each night.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Expect VFR conditions through tonight across most of the TAF
sites with a light S/SE wind. Some fog may develop near KMRB
toward daybreak, but given that most observed shower activity
diminished prior to reaching the terminal this potential is of
low certainty at this time.
Winds remain southerly into Tuesday, but with better
thunderstorm chances. Have introduced a PROB30 group for KDCA,
KIAD, and KBWI, which may include other terminals as they move
into this time range. Some restrictions are possible as this
convection rolls through during the late afternoon into
portions of the evening. Additional rounds of convection may
affect the area again on Wednesday, but details of coverage and
timing are more uncertain.
Shower and thunderstorm chances across the terminals Thursday and
Friday may lead to sub-VFR conditions. Southwest winds on Thursday
shift to northwest on Friday, blowing 5 to 10 knots each
afternoon.
&&
.MARINE...
Some southerly channeling effects have led to occasional 15-20
knot gusts over the main channel of the Chesapeake Bay from
Pooles Island to Drum Point MD and over the tidal Patapsco River
as of early this evening. Channeling effects increase a bit by
late evening through just after midnight, then again late just
prior to daybreak. For this reason, have hoisted a targeted SCA.
Convective chances increase on Tuesday and Wednesday as an upper
trough slowly approaches from the central U.S. to Great Lakes
region. Those with marine interests can expect the potential for
gusty showers and frequent lightning, particularly during the
late afternoon to evening hours. Special Marine Warnings may
accompany any of the stronger thunderstorms. Outside of
convection, background southerly winds should top out below
advisory criteria through mid-week.
Southwest winds on Thursday shift to northwest on Friday, with Small
Craft Advisory criteria winds possible Thursday evening. Otherwise,
winds remain below SCA criteria. Showers and thunderstorms are
possible both days over the waters.
&&
.TIDES/COASTAL FLOODING...
Anomalies are forecast to remain slightly elevated through
Thursday, so additional near minor flooding is possible at
sensitive locations. This is most likely with the higher daily
tide cycle in the afternoon and evening, with the strongest
onshore flow and highest anomalies possible on Thursday.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Tuesday for ANZ531>533-538.
&&
$$
SYNOPSIS...BRO/DHOF
NEAR TERM...BRO/DHOF
SHORT TERM...BRO/DHOF
LONG TERM...AVS
AVIATION...AVS/BRO/DHOF
MARINE...AVS/BRO/DHOF
TIDES/COASTAL FLOODING...LWX

NWS lwx Office Area Forecast Discussion