556
FXUS61 KLWX 120758
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
358 AM EDT Sat Sep 12 2026

.WHAT HAS CHANGED...
The threat for locally heavy rainfall continues to appear in all
high-resolution guidance. The scatter about the possible
outcomes remains on the high side. Thus, the issuance of any
Flood Watches will be held off until the next shift can view 12Z
models. The forecast has trended a bit drier for Sunday given
some downsloping component to the flow. Looking out to Monday
night, strong Canadian high pressure could easily yield colder
overnight temperatures than shown. Recent guidance has been slow
to show the rapid drying of the air mass.

&&

.KEY MESSAGES...
- 1) Widespread convection expected through tonight, while
  turning cooler and drier into early next week.

- 2) Seasonably warm and dry ahead of a mid-week cold front.

&&

.DISCUSSION...
KEY MESSAGE 1...Widespread convection expected through tonight,
while turning cooler and drier into early next week.

The current setup features a stalled surface boundary sitting
just south of the Virginia-North Carolina border. This is
bounded by a modest area of high pressure stretching across much
of New England into the Mid-Atlantic states. At the same time, a
broad upper trough currently swirling across the Mid-South. As
this trough axis pushes off toward the east, models show a low
level response of enhanced moisture/theta-e advection. With
surface to 850-mb winds shifting to mainly south to
southeasterly, precipitable water values will further rise in
time. Increasing isentropic lift atop the poleward advancing
boundary should set the stages for a more active day of
convection.

At the moment, fairly tranquil weather remains amidst a
thickening area of low clouds. Over the last hour, there has
been a notable moistening of the boundary layer with stratus
expanding from the central Virginia Piedmont up across the
Shenandoah Valley. This should eventually yield a fairly
extensive stratus deck across the area this morning.
Temperatures largely sit in the mid 60s to low 70s, with dew
points in the 60s. Given increasing moisture advection, widely
scattered showers are expected to pop through the morning hours.
With upstream forcing from the trough still off to the west,
any activity should stay fairly disorganized in nature.
However, storm-scale organization should improve in time
heading into the late afternoon to evening/overnight period.

The 00Z high-resolution model suite shows two possible areas of
more widespread convective development. (1) As depicted in the
00Z HREF 40-dBZ paintball plots, the more pronounced activity
forms across West Virginia up into western Pennsylvania, mainly
in the 4 to 8 PM timeframe. As these cells encroach on the
Allegheny Front, the slow moving nature of such storm elements
coupled with saturated soils (per satellite) would afford a non-
zero flash flood risk. (2) Additionally, the warm conveyor belt
along the I-95 corridor will likely be an additional focus area
for storm genesis. This may occur more into the evening hours as
this activity is driven by instablity along/south of the warm
front. How this convection interacts with development coming off
the Alleghenies will determine the risk of flash flood
potential along the I-95 corridor. High-resolution model
depictions of this evolution feature quite a bit of spread, but
the signal bears watching. Flood Watches may be needed at some
point during subsequent shifts.

Depending on instability and storm evolution, the mentioned
convective complexes could fester into tonight. A preponderance
of solutions favor shifting this activity into northeastern
Maryland by around 3-5 AM (early Sunday). Patchy fog could
materialize in the wake, particularly for areas seeing some of
the heavier rainfall.

For Sunday into Monday, multiple temperature swings are
expected. After clouds/rain keep today`s forecast in the 70s to
low 80s, some uptick is expected on Sunday. Ahead of the
approaching cold front, some weak downslope component to the
wind fields should steer highs well into the 80s. As this front
crosses during the diurnal minimum in heating (i.e., overnight
Sunday/early Monday), storm chances will be rather limited. Will
maintain showers and a few rumbles of thunder along the
Alleghenies, with mainly dry conditions downstream. Monday`s
forecast features prevailing northwesterlies with afternoon
gusts up to 15 to 20 mph. High temperatures should range from
the mid 70s to low 80s, while being locally cooler in the
mountains. This also comes with falling humidity and cool
temperatures on Monday night. Robust surface high pressure
crossing the northeastern U.S. will support widespread 50s
overnight. Even some upper 40s are possible in spots that can
fully decouple and remain cloud-free.


KEY MESSAGE 2...Seasonably warm and dry ahead of a mid-week cold
front.

H5 ridging builds Mon through Wed over the SE-US. This will bring a
drier and less humid air mass, though temps will increase through
the week. Mon night looks like coldest of the fall, with 50s
areawide. Colder valleys likely fall into 40s. Ridging weakens as sw
trofs and associated sfc cold front move through midweek. Some
spread on exactly what day this happens, but overall consensus
around Thu. This could bring showers and thunderstorms, but
probability of svr wx remains low.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
At this point, MVFR ceilings have been slower to emerge than
expected with only KCHO seeing such conditions. However, current
hourly trends over the area do show low-level moistening
underway as wind fields in this layer turn more south to
southeasterly. Although some breaks are possible, most terminals
can expect MVFR conditions to persist through the day. This also
comes with increasing shower coverage, particularly during the
evening to early overnight period. It remains to be seen whether
this is accompanied by a risk of thunderstorms. Will maintain a
mention of PROB30 thunderstorms at KCHO for the 6 to 8 PM
window, but will await additional guidance to expand this threat
northward. Locally heavier rainfall this evening into the night
could lower conditions to IFR at times. Once showers exit into
northeastern Maryland, a mixture of MVFR to IFR ceilings are
expected for all sites.

Despite starting off with restrictions on Sunday morning, expect
improvements through the day with numerous breaks in the clouds.
VFR conditions are likely for the remainder of Sunday into
Monday. Northwesterly winds increase on Monday behind a strong
cold front with afternoon gusts possibly reaching 20 knots or
so.

VFR conditions Tue and Wed with light S`ly winds.

&&

.MARINE...
Quiet conditions are noted over the marine waters early this
morning with southeasterly gusts up to 5 to 10 knots. As a
stalled front to the south returns northward as a warm front,
there will be an uptick in southeasterly flow across the
waterways. A few high-resolution models indicate southeasterly
gusts to around 20 knots by late this morning through around
sundown, especially for the more southern waters given
channeling effects. Small Craft Advisories may be added for this
threat. Additionally, showers increase in coverage toward the
evening to early overnight hours. The most likely area to see
thunderstorms would be south of U.S. 50. It remains to be seen
how far north instability can reach.

Sub-advisory winds are expected for Sunday before a stronger
surge of northwesterlies ensue behind a cold front on Monday.
Widespread advisory-caliber wind gusts are likely which will
necessitate Small Craft Advisories.

Winds light out of the S Tue into Wed. No SCAs expected.

&&

.TIDES/COASTAL FLOODING...
Strengthening onshore flow today will bring tide levels up
across the area. Some locations could reach Action Stage by
tonight to early Sunday high tides. Annapolis could near Minor
during the higher of the two astronomical high tides. A cold
front moves through early Monday, which should bring an end to
any coastal flooding potential.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

DISCUSSION...BRO/CPB
AVIATION...BRO/CPB
MARINE...BRO/CPB
TIDES/COASTAL FLOODING...LWX

NWS LWX Office Area Forecast Discussion