Potomac, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

001
FXUS61 KLWX 130111
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
Issued by National Weather Service State College PA
911 PM EDT Thu Jun 12 2025

.SYNOPSIS...
High pressure will shift offshore tonight. A cold front will
slowly approach the area from the north on Friday through
Saturday before stalling out nearby through the middle of next
week. Daily chances for showers and thunderstorms will be the
result.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Mid to high level clouds approaching from the west will continue
spreading eastward tonight ahead of an upper level cutoff low.
It will remain dry, though the southerly flow will continue
overnight increasing Tds by daybreak. This will in part result
in temps several degrees warmer than the past several nights. Lows
will drop into the mid/upper 60s to mid 70s (upper 50s to lower
60s in the high elevation valleys).

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
The subtropical ridge will continue to build over Florida into
the Atlantic and surface high pressure will strengthen over the
Atlantic as a result. At the same time, the area of upper-level
low pressure across the central/southern Plains today will
shift east from the Plains into the Midwest/Tennessee Valley for
Friday. Additionally, an area of low pressure well of to the
north in Canada will continue to drag a slow-moving backdoor cold
front towards the region from the north on Friday as high
pressure builds north of the Great Lakes. The greatest bit of
uncertainty lies with exactly how far south that boundary is
going to drop into our region. This will likely be a focal point
for convection during the afternoon/evening hours on Friday.

Given that the shortwave is still off to the west, and there
isn`t a lot of shear to work with, storms that fire early
tomorrow afternoon are going to be slow-moving with little
forcing/steering. They will also be developing in an air mass
with temperatures in the mid to upper 80s and dew points
approaching the low 70s, yielding CAPE values in the
neighborhood of 1250 to 1500 J/kg. Pair that with a somewhat
skinny CAPE profile and PWATs in the 2" range, and you start to
worry about a decent flooding setup across the region. One thing
that is even a bit more concerning is that once the backdoor
front starts dropping southward, the southerly flow south of
the front starts to help to squeeze some even higher PWATS out
in some of the guidance (around 2.2" or so). Consideration for a
flood watch was given, but opted to hold off for now to try to
better pinpoint where the highest QPF totals will occur, which
will largely vary depending on the frontal placement.
Additionally, the lapse rates in the low-levels are decent, and
there is a bit of dry mid-level air in model soundings. This
could help to accelerate some downdrafts and bring some gusty
winds along with some of the stronger storms. This could cause
storms to be a bit more cold pool dominant, thus maybe not
resulting in as much training. This is one level of uncertainty
as well, which was another reason to hold off for now. At any
rate, tomorrow`s thunderstorms are likely to bring some very
heavy rainfall rates, so any given location picking up a quick
inch or two in a short time span is not out of the question.
Picking where that will occur exactly is just something that is
going to occur a little closer in time as we see all of the
pieces coming together later this evening into the overnight
hours.

Convection should wane overnight Friday/early Saturday morning,
but plenty of moisture will remain in place and this may result
in low clouds/areas of fog.

The upper-level low will continue to approach Saturday through
Saturday night while a backdoor boundary approaches from the
northeast. Plenty of moisture will remain in place for more
showers and thunderstorms to develop (mainly during the
afternoon and evening). PWATs look to remain high on Saturday,
which when combined with an unstable atmosphere suggests that
storms may contain heavy rainfall that leads to flooding once
again. There is still some uncertainty as to exactly where the
backdoor boundary sets up on Saturday as well, and consequently
where the best lift and instability will be for the stronger
storms to develop. Additionally, convection on Friday could even
help to drive headline decisions on Saturday, if necessary,
depending on which places get the most rain Friday. The CAMs are
just coming into range with this, and are all depicting a
somewhat similar scenario, being a strong MCS rolling through
during the afternoon/evening. This could come with an isolated
damaging wind threat, but especially heavy rain and lightning.
The main puzzle piece left is figuring out where the worst of
that occurs, and that is still a bit uncertain, as mentioned
previously. Recent guidance does still show that the best low-
level convergence may set up near and to the south and west of
the Potomac River. So perhaps this area could be the focal
point, though I wouldn`t count on that still a couple of days
out. The position of that backdoor front is going to be the
driving factor. The strongest storms will be most likely
near/south of the front of course.

Convection should wane in coverage overnight Saturday, but a
few showers along with low clouds and areas of fog will likely
persist.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
The backdoor boundary will likely stall out near the area Sunday
through Monday while the upper-level passes through the area.
This will likely cause more showers and thunderstorms, and there
is a threat for heavy during this time. Exact details remain
uncertain, but the heaviest rain will most likely set up near
and to the south/west of the backdoor boundary.

The upper-level low will move off to the east for Tuesday and
Wednesday, but a nearly zonal flow aloft will persist along
with additional weak disturbances passing through the area. This
means more unsettled conditions will persist with chances for
showers and thunderstorms (especially during the afternoon and
evening hours each day).

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected through tonight along with light
winds. Showers and thunderstorms becoming increasingly likely
Friday afternoon and evening. Have introduced TSRA into the 18z
TAF updates towards the end of the period, along with PROB30
groups for a couple hours prior. This is due to potential storms
firing earlier than anticipated.

Low clouds and fog are likely overnight Friday, especially in
areas that receive rainfall, with IFR conditions possible.

An unsettled pattern with the likelihood for showers and
scattered thunderstorms will persist for Saturday through
Monday. Low clouds and areas of fog are possible during this
time, especially during the nighttime and morning hours each
day, resulting in subVFR and possible IFR conditions.

&&

.MARINE...
Weak high pressure will move offshore tonight. Winds will
remain light, but turning southerly this afternoon into tonight.
Southerly channeling will cause wind gusts to approach SCA
criteria over the open waters, but confidence is too low for a
headline at this time.

A southerly flow will usher in plenty of moisture Friday, and
this will increase the chances for thunderstorms. Some stronger
storms with gusty winds are possible during the afternoon and
evening hours. A backdoor boundary will approach the waters
Saturday and stall out nearby for early next week. More showers
are likely with possible thunderstorms during this time.

&&

.TIDES/COASTAL FLOODING...
The more sensitive tidal sites could continue to hit action
stage during the higher of the 2 high tide cycles the next
couple of days. But overall, anomalies will slowly drop.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Air Quality Alert until midnight EDT tonight for DCZ001.
MD...Air Quality Alert until midnight EDT tonight for MDZ008-011-
     013-014-504-506-508.
VA...Air Quality Alert until midnight EDT tonight for VAZ053-054-
     505-506-526-527.
WV...None.
MARINE...Air Quality Alert until midnight EDT tonight for ANZ530.

&&

$$

SYNOPSIS...BJL
NEAR TERM...CJL/CPB
SHORT TERM...CJL/CPB
LONG TERM...BJL/CJL
AVIATION...BJL/CJL/CPB
MARINE...BJL/CJL/CPB
TIDES/COASTAL FLOODING...LWX