467
FXUS61 KLWX 121546
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1146 AM EDT Sat Sep 12 2026

.WHAT HAS CHANGED...
There may be a focus for heavy rain over western Maryland late
this afternoon and evening, but uncertainty lingers in placement
and magnitude elsewhere. Expanded the Small Craft Advisory to
include the middle tidal Potomac River, to North Beach MD on the
Chesapeake Bay and into the tidal Patuxent River given a
favorable wind direction.

&&

.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. With upstream forcing from the
trough still off to the west, any activity should stay fairly
disorganized in nature for most of the day. However, storm-
scale organization should improve in time heading into the late
afternoon to evening/overnight period.

The 12Z high-resolution model suite shows two possible areas of
more widespread convective development. (1) As depicted in the
12Z HREF 40-dBZ paintball plots, the more pronounced activity
forms across West Virginia up into western Pennsylvania, mainly
in the 4 to 10 PM timeframe. As these cells encroach on the
Allegheny Front, the slow-moving nature of such storm elements
coupled with saturated soils (per satellite) could afford a
flash flood risk in the vicinity of western MD into the
overnight hours. (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 instability 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, especially given the notably more
aggressive 12Z NAM12.

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 /15Z SATURDAY THROUGH WEDNESDAY/...
Have throttled back prevailing MVFR CIGs to TEMPOs through 18Z
for the metros. Increasing shower coverage likely holds off
until the evening to 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, 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...
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 have been added for
this threat, and may need to be expanded/extended into the
evening. 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
tonight/early Sunday. Annapolis could near Minor. 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...Small Craft Advisory until 9 PM EDT this evening for ANZ533-
     534-536-537-542-543.

&&

$$

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

NWS LWX Office Area Forecast Discussion