Frederick, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

460
FXUS61 KLWX 130135
AFDLWX

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

.WHAT HAS CHANGED...
Showers and thunderstorms continue to develop and expand in
coverage near and west of the Appalachians as well as over
the Virginia Piedmont.

&&

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

- 2) Seasonably warm & dry conditions anticipated early next
  week ahead of a 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 surface boundary located near the
Virginia-North Carolina border this evening. This boundary will
lift northward as a warm front overnight. At the same time, a
shortwave trough is swinging into the upper Ohio Valley. As this
trough axis pushes off toward the east, models continue to 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
warm front should set the stage for convection through tonight.

Current radar imagery shows two areas of ongoing showers and
storms. The first is located near and west of the Allegheny
Front. This area of showers and storms is expected to continue
to gradually progress toward the north and east through the
night, following a zone of large scale ascent associated with
the aforementioned shortwave trough. A second area of showers
and a few thunderstorms is ongoing across much of the Virginia
Piedmont. This activity is associated with warm/moist advection
to the north of the front, and is expected to gradually, Havre
de Grace, and Annapolis lift northward through the night.
Embedded areas of higher rainfall rates have occurred with some
of the showers and storms in what is a high PWAT environment. A
Flood Watch remains in effect for extreme Western Allegany and
Garrett Counties through 2 AM. Current radar trends suggest that
the flood threat there may have peaked, but a few of the recent
runs of the HRRR try to build heavier rain back in from the
west next over the next few hours. For that reason, we`ll keep
the Watch going. Further east, an isolated instance or two of
flooding can`t be ruled out overnight, but confidence is too low
for a Watch. The back edge of the precipitation should clear
the area by mid-morning tomorrow.

For Sunday into Monday, multiple temperature swings are
expected. Ahead of the approaching cold front, some weak
downslope component to the wind fields should steer highs well
into the 80s on Sunday. 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
lower (but not quite zero) probabilities further east across the
piedmont. Monday`s forecast features prevailing northwesterlies
with afternoon gusts up to 15 to 25 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 likely in spots that can
fully decouple and remain cloud-free.


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

High pressure will continue to build on Tuesday as mid-level dry air
moves in from the Great Lakes. Expect seasonable and dry
conditions to persist during this time as highs reach into the
lower 80s with dewpoints potentially dipping into the upper 40s
on Tuesday morning.

Strong upper-level ridging builds toward the area Tuesday into
Wednesday, then begins to break down by late in the week as a
retrograding low tracks south into the Florida Peninsula from
the Atlantic. Humidity likely begins to increase again on
Wednesday as any lingering dry air is driven east out of the
region. Meanwhile, a trough will begin to develop over the
Northern Plains with a stemming cold front tracking east through
the Mid-Atlantic sometime in the mid-to-late week period.
Updated model guidance has delayed the arrival of this front
potentially to Thursday & into Friday, with showers &
potentially a few thunderstorms accompanying the front. However,
significant uncertainty remains in the time of arrival here as
models continue to grasp this synoptic setup. Regardless,
severe probabilities continue to look low as we begin to
transition out of the summertime thunderstorm season.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
Showers and a few embedded thunderstorms continue to move into
the area this evening. PROB30 groups for thunder have been
introduced at many of the TAF sites. 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 25 knots.

Prevailing VFR conditions are expected to continue at terminals
Tuesday through Thursday. A few showers forming ahead of a cold
front on Thursday evening could bring temporary reductions.
Winds generally flow between 5-10 knots southerly to southeasterly.

&&

.MARINE...
Earlier SCAs have been allowed to expire. Showers increase in
coverage overnight. 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 likely remain below SCA thresholds Tuesday through Thursday,
shifting NE Tuesday to SE Wednesday, then S by Thursday.

&&

.TIDES/COASTAL FLOODING...
Strengthening onshore flow will bring tide levels up across the
area through tonight. Coastal Flood Advisories have been issued
for Alexandria and Havre de Grace for the current tide cycle. A
cold front moves through by early Monday which should bring an
end to any coastal flooding potential.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Flood Watch until 2 AM EDT Sunday for MDZ501-509-510.
VA...None.
WV...None.
MARINE...None.

&&

$$

DISCUSSION...BRO/DHOF/KJP/SRT
AVIATION...BRO/DHOF/KJP/SRT
MARINE...BRO/DHOF/KJP/SRT