Potomac, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

940
FXUS61 KLWX 141850
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
250 PM EDT Wed May 14 2025

.SYNOPSIS...
An upper low will slowly drift northeastward toward the area
today, before shearing out into an open wave and lifting to our
northeast on Thursday. An area of low pressure will track
toward the Upper Midwest and Western Great Lakes by Friday,
before tracking eastward across Quebec and Ontario this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
The once cutoff upper low that has been impacting our region in
recent days has now become a bit more diffuse/elongated, as
evident in latest GOES water vapor imagery. The axis of this
upper-low remains to our west, but is finally starting to get
moving towards the eastern seaboard.


Looking at current visible satellite imagery, a clearing trend
can be seen across most areas, aside from central/northeast MD.
Outside of those areas, instability is growing across,
especially across central VA into southern MD. A vort max
embedded within the aforementioned upper-low will traverse the
region this afternoon/evening. This feature is what is currently
setting off some potent convection across south-central VA.

This activity will gradually spread northeastward through the
remainder of the afternoon and evening, becoming much more
widespread. Shear will be marginal, around 20-30 kt, but this
could support a few stronger storms, primarily in central VA and
into the VA Piedmont. Lowering freezing levels suggest a hail
threat, but the marginal shear combined with moist profiles will
likely limit the threat for severe winds and hail. Would expect
to see a few stronger storms perhaps put out about 40 mph and
perhaps some smaller hail. The 12z guidance came in with a
similar tune to the overnight guidance in terms of the coverage
of any potential severe coverage, keeping it mostly over
southern/southeastern VA.

Looking at the heavy rainfall threat this afternoon, this is
where we may see a bigger impact, primarily if areas that were
hit yesterday manage to get hit again today. Many of the small
streams remain at least somewhat elevated, and any additional
rainfall could lead to rapid water level increases. There are
certainly some limiting factors compared to yesterday (lower
PWATS, lower PPP, weaker convergence, etc.). However, storms
today are still capable of producing a quick 1-3 inches in an
hour. Should this occur in an area that was impacted yesterday
with significant flooding, this would certainly cause some
issues. In conjunction with WPC issuing their slight risk of
excessive rainfall today, a Flood Watch was issued for areas
generally south of US-29 and along/west of the Blue Ridge
through 10 PM this evening.

Remnant showers will gradually lift to the northeast tonight
with low clouds and fog possible again. Lows will be in the mid
50s to mid 60s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The weakening trough axis and possible weak surface low will be
near the Chesapeake Bay Thursday morning. This means any
remaining showers northeast of the Potomac should pivot away
during the morning hours. More breaks of sun are likely by the
middle of the morning on Thursday. However, northeast MD could
see clouds and a few shower linger even into the early portions
of the afternoon. For those that do break out on Thursday, high
temperatures are expected to rise toward 80. Not a lot of
confidence in the precipitation forecast thereafter. Advection
of a high theta-e airmass will be approaching from the west.
Other than possible terrain lift, forcing is otherwise nebulous
through the day, especially with mid-level heights rising in the
wake of the trough passage. However, CAMs suggest some storms
may develop over the central Appalachians at a minimum. Given
steepening lapse rates (in both the mid and lower levels) and
increasing shear, some storms could be severe. However, again
referring to those rising heights, still lots of questions
about the coverage, and also the strength should anything get
going. SPC has added a Marginal Risk for severe for now.

The uncertainty theme continues Thursday night through Friday
night as possible upstream convection moves toward the area. The
airmass will be characterized by steep lapse rates and strong
shear, so storms may be able to maintain themselves. Depending
on how the airmass is modified by upstream convection, Friday
in particular could have a high end CAPE/shear parameter space
across the area. However, the atmosphere may remain capped with
little to no storm development. Hopefully this becomes clearer
with time. What`s more certain is that it will turn hot and
humid Friday, with highs well into the 80s and dew points in the
mid 60s to lower 70s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
An area of surface low pressure will track northeast across the
Great Lakes towards Quebec Saturday and Sunday with the associated
cold fronts pushing through the forecast area on Saturday. Showers
and thunderstorms are expected ahead of the frontal passage Saturday
afternoon. High temperatures will be in the upper 70s to upper 80s
for most with those at higher elevations staying in the upper 60s to
lower 70s. Overnight low temperatures will be in the 50s to mid 60s
across the area.

Conditions dry out overnight into Sunday as high pressure builds in
from the northwest. In the wake of the cold front, temperatures will
be noticeably cooler with high temperatures in the 60s to 70s for
most. Those in the southernmost portions of the area may reach the
low 80s. Dry conditions continue on Monday with high highs in the
60s and 70s across the forecast area.

Precipitation chances return Tuesday evening as another low pressure
system tracks from the central CONUS towards the Great Lakes. The
associated warm front lifts north towards the forecast area on
Tuesday, bringing a chance for showers and thunderstorms Tuesday
night.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Low clouds continue across central/northeast MD this afternoon,
with IFR conditions continuing at BWI/MTN. Elsewhere, generally
seeing MVFR CIGs area-wide, as there wasn`t quite as much
improvement as initially expected today.

Showers and thunderstorms will form during the afternoon,
generally progressing southwest to northeast. Thunderstorms are
most likely at CHO, but may be more scattered once they reach
the metro terminals (thus PROB30 groups remain at this time).
Showers may linger at BWI/MTN into the night. Otherwise, expect
a return to IFR to perhaps LIFR ceilings. Light E to S winds are
expected through the TAF period. Additionally, could see some
patchy dense fog develop overnight. CHO, MRB and IAD seem the
most likely candidates for that.

Conditions improve to VFR on Thursday morning, at least for
everyone except BWI and MTN. The highest chance for an
afternoon/evening thunderstorm appears to be at CHO on Thursday,
but this is highly uncertain. By the afternoon, even BWI and MTN
should try to clear out. Have added some PROB30 groups in
tomorrow afternoon for thunderstorms at BWI, DCA, and IAD. This
is a very low threat at this time, again with highest chances at
CHO, but thought it was worthy of mentioning.

Sub-VFR conditions (ceilings or fog) may return to mainly
MRB/BWI/MTN Thursday night. There is also potential for one or
more rounds of showers and thunderstorms late Thursday night
through Friday night, but details remain very uncertain at this
time.

Sub-VFR conditions are possible on Saturday during showers and
thunderstorms. Southwest winds in Saturday morning shift to westerly
in the afternoon, gusting 15 to 20 knots. Winds shift to
northwesterly Sunday afternoon, gusting 15 to 20 knots.

&&

.MARINE...
Strong thunderstorms could approach from the south later this
afternoon into the evening, which could warrant Special Marine
Warnings. Otherwise, winds remain light, with no marine hazards
in effect at this time.

South to southwest winds should remain sub-SCA Thursday night through
Friday night. The main concern will come from thunderstorms,
although the timing, coverage, and strength of any storms is
very uncertain at this time. Storms aren`t likely to reach the
waters Thursday, but there is still a chance.

Southwest winds shift to westerly on Saturday afternoon with showers
and thunderstorms possible across the waters. Winds are expected to
near, but remain below SCA criteria both days.

&&

.TIDES/COASTAL FLOODING...
General improvement is expected for most in the coming days as
tidal anomalies continue to fall. However, generally light
southerly flow will continue to bring the more sensitive tidal
sites near/into action stage.

Lastly, and most importantly, Georgetown will likely have some
freshwater related flooding by Thursday, and a Coastal Flood
Watch remains in effect for this threat. Current forecast brings
Georgetown to Moderate for much of the day on Thursday as a
result of the freshwater influence flowing down from the west.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Watch from Thursday morning through Friday
     afternoon for DCZ001.
MD...Flood Watch until 10 PM EDT this evening for MDZ501-502-509-
     510.
VA...Flood Watch until 10 PM EDT this evening for VAZ025>030-
     036>040-050-051-056-503-504-507-508.
WV...Flood Watch until 10 PM EDT this evening for WVZ050-051-055-
     501>506.
MARINE...None.

&&

$$

SYNOPSIS...ADS
NEAR TERM...ADS/CJL
SHORT TERM...ADS/CJL
LONG TERM...AVS
AVIATION...ADS/AVS/CJL
MARINE...ADS/AVS/CJL
TIDES/COASTAL FLOODING...CJL