886
FXUS61 KLWX 171937
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
337 PM EDT Thu Sep 17 2026
.WHAT HAS CHANGED...
The initial round of convection is moving through a bit faster
than originally predicted, resulting in some uncertainty whether
there is another round of showers this evening closer to the
cold front. While considerable uncertainty still exists in the
pattern next week, WPC collaborated to significantly lower high
temperatures next Tuesday through Thursday given a surface cold
air damming pattern.
&&
.KEY MESSAGES...
- 1) Shower and thunderstorm chances shift southward with a cold
front through Friday, which will be followed by cooler
temperatures.
- 2) Showers and thunderstorms return at times Sunday into next
week, with temperatures likely falling below normal.
&&
.DISCUSSION...
KEY MESSAGE 1...Shower and thunderstorm chances shift southward
with a cold front through Friday, which will be followed by
cooler temperatures.
Height falls amidst a humid airmass resulted in showers and
thunderstorms expanding in coverage from northwest to southeast
over the past several hours. Poor mid level lapse rates and weak
shear have prevented the convection from becoming too
deep/strong. The weak shear and sufficient (but generally modest)
DCAPE has allow the storms to become outflow dominant, with
some observed gusts of 30-40 mph. At this point the probability
of severe thunderstorms is low. Instability decreases east of
the I-95 corridor, and so far, convection has been weakening as
it approaches this threshold. The main question now is whether
there is another round of showers later this afternoon and
evening closer to the approach cold front. This would likely
originate from the activity in the upper Ohio Valley to northern
Pennsylvania. Given the diurnal timing and an airmass which has
already been cooled from the previous convection and lingering
clouds, thunder appears less likely with this round.
While the cold front drops in later tonight, guidance indicates
some patchy fog could develop before the wind shift occurs. This
would most likely occur along rivers and low lying areas,
although low clouds may move into the Allegheny and Potomac
Highlands which could also reduce visibility.
While the wind shift portion of the cold front likely pushes
south of the area Friday morning, the moisture gradient may hang
back across central Virginia up to the Potomac Highlands. As a
shortwave trough swings through during the afternoon, some
additional showers and thunderstorms may develop in these areas.
Temperatures will fall back into the lower to mid 80s with
northerly gusts up to 20 mph at times. There may also be a fair
amount of stratocumulus at times as well. A cooler night lies
ahead as high pressure crosses southern Quebec into New England.
Friday night`s lows should be in the upper 50s to mid 60s.
High pressure to the northeast on Saturday should provide enough
dry air to keep rain at bay. One exception may be along the
Allegheny Front due to convergence in an inverted surface
trough. Warm advection aloft and mid level perturbations will
likely provide cloud cover areawide. Temperatures will be
closer to climatology, ranging from the mid 70s to lower 80s.
Low pressure moving into the Ohio Valley may increase rain
chances Saturday night.
KEY MESSAGE 2...Showers and thunderstorms return at times Sunday
into next week, with temperatures likely falling below normal.
A cold front drops through the forecast area on Sunday before
stalling to the south, bringing daily chances for showers and
thunderstorms. In addition to daily precipitation, a cooler airmass
builds overhead in the wake of the cold front, yielding cooling
temperatures each day. On Sunday, high temperatures will be in the
low 80s for most (70s mtns) with overnight lows in the 60s. By
midweek, high temperatures will top out in the upper 50s to 60s with
overnight lows in the 50s. These temperatures remain somewhat
uncertain with large model spread, but the forecast favors the
cooler side of guidance given a cold air damming surface
pattern. Overall, nearby disturbances bring unsettled weather
to the region beginning Sunday and persisting through midweek.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
A line of showers & storms has been causing brief periods of MVFR
and IFR conditions at most terminals as it tracks southeast through
the afternoon. Some of these storms could bring 20-30 knot gusts as
it tracks across central VA. As a few lingering showers across
southwestern PA cross into the area later this evening, a few more
scattered rain showers could be in the vicinity of terminals
between 00Z-04Z. Thunder chances appear more reduced should this
activity materialize.
Otherwise, VFR conditions are anticipated across terminals through
most of tomorrow. Patchy mountain valley fog could briefly bring
VSBYs down at KMRB and KCHO to MVFR early Friday morning before
returning to VFR through most of the day. Winds shift northerly
Friday morning and conditions remain largely unchanged throughout
the day Saturday. Beginning Sunday, more showers and thunderstorms
could intermittently impact terminals as a trough moves through the
region with southerly winds potentially gusting to 20 kt.
Winds shift to north/northeasterly on Monday in the wake of the
front, gusting 10 to 15 knots in the afternoon. Showers and
thunderstorms are possible each day, with restrictions expected
during heaviest precipitation.
&&
.MARINE...
A line of showers and thunderstorms formed a bit earlier than
previously forecast. While these have been weakening as they
approach the waters due to weaker instability, some gusty
outflows have been bringing wind shifts to the north. Southerly
flow does seem established along the bay, which could enhance
further into the evening. A Small Craft Advisory remains in
effect for the wider waters until 11 PM.
Winds shift to northerly on Friday morning behind the cold
front. Some northerly channeling effects are possible on Friday
morning into the afternoon due to the frontal surge. Small Craft
Advisories may be needed for such an evolution, although current
guidance does not offer enough confidence in more than
occasional marginal gusts. A second surge could also occur
Friday evening. As high pressure passes by to the north, winds
shift from northeasterly to east- southeasterly on Saturday.
This could bring a few gusts to near 20 knots which could
approach advisory levels, especially by Saturday night.
Small Craft Advisory conditions are possible on Sunday as
south/southwest winds gust up to 20 knots across the waters. Winds
diminish overnight before shifting to north/northeasterly on Monday
with SCA criteria wind gusts possible. Additionally, showers and
thunderstorms each day may lead to SMWs.
&&
.TIDES/COASTAL FLOODING...
With winds remaining out of the south to southeasterly direction,
this flow regime has kept tidal anomalies around 0.50 to 0.75
feet. This has been enough to push a few of the more sensitive
locations into the Action stage. Until a cold front moves
through early Friday, water levels will remain somewhat
elevated. Although no tidal site is shown to experience any
coastal flooding, it will need to be monitored. This is
particularly the case at Annapolis, especially during the higher
of the two astronomical high tides tonight. Expect anomalies to
drop on Friday into Saturday behind the mentioned cold front,
though anomalies may increase again due to southerly flow
Saturday night into Sunday.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for
ANZ532>534-543.
&&
$$
DISCUSSION...ADS/AVS
AVIATION...ADS/AVS/SRT
MARINE...ADS/AVS