850
FXUS61 KLWX 130759
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
Issued by National Weather Service State College PA
359 AM EDT Fri Jun 13 2025

.SYNOPSIS...
A backdoor cold front will slowly approach the area through this
afternoon before moving into the area tonight. The backdoor
boundary will stall out overhead for Saturday through early next
week before returning north as a warm front later Tuesday. High
pressure over the Atlantic will bring hotter conditions for the
middle portion of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A confluent zone from the northern stream of the jet will
cause a cold front to push south into our area today while an
upper-level low approaches from the west. Ahead of the cold
front, a low-level southerly flow will continue to advect in
more moisture (Blended TPW satellite shows PWATS around 2" over
North Carolina).

There are some high and mid-level clouds, but there will be some
sunshine and that will be enough for another very warm afternoon
with highs well into the 80s for most areas. The heat and
increasing moisture will cause moderate amounts of CAPE to
develop. The morning should be dry for most areas, but showers
and thunderstorms are likely to increase in coverage during the
afternoon through the evening hours. The most coverage is
expected this evening when a weak shortwave/jetmax well ahead
of the upper-level low passes through our area. There continues
to be some reflection at the surface, with most guidance showing
surface low pressure developing overhead. All the ingredients
are there for heavy rainfall and a flash flood threat (moderate
CAPE, increasing moisture, warm rain processes, and surface
convergence). However, there is still divergence among the CAMs
as to exactly where the heaviest rain will be.

We did decide to go with a Flood Watch for the Washington DC
Metro area into the Virginia Piedmont/central Virginia and
southern MD. This is where most guidance shows the best overlap
of low-level convergence, higher instability, and anomalously
high moisture moving into the area. There is even a hint of
training convection with the shear vector nearly parallel to the
convergence associated with the developing surface low.

Elsewhere, heavy rain and flash flooding is possible, but
confidence is too low for a watch at this time since storms may
be a little more progressive (steep low-level lapse rates and
some mid-level dry air causing a stronger cold pool). The Flood
Watch is in effect from 6 PM through 2 AM. Some convection may
develop this afternoon, but even for the DC metro into central
VA the cold pool may be more dominant during this time. The
deeper moisture arrives this evening when low-level convergence
is stronger with that system passing through during this time.

Convection will wane overnight, but showers are possible along
with low clouds and areas of fog/drizzle. Some fog may be
locally dense. Lows tonight will be in the 60s and 70s for most
areas.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
The backdoor boundary will shift to the southwest Saturday
behind the departing disturbance from Friday night. The upper-
level low will continue to build closer to the area, and plenty
of moisture will hang around. There will likely be a lull in the
activity Saturday morning (a few showers and some drizzle/fog),
but another round of heavier showers and thunderstorms is
expected to develop Saturday afternoon into Saturday evening.
There is still some uncertainty as to exactly where this will
setup, but latest guidance continues to suggest areas south and
west of the Potomac River (near and ahead of the boundary) as
the areas most likely to get the strongest convection. All the
ingredients are there for a flash flood threat. Will continue to
monitor, because the position of the front will be vitally
important as to exactly where the strongest convection will be.
For areas to the northeast of the boundary (most likely north
and east of the Potomac River). A few showers and a thunderstorm
are still possible (MUCAPE is still progged to be well north
and east of the surface boundary), especially late in the day
into the evening as stronger convection upstream propagates into
the area.

The upper-level low will shear apart as it moves into the area
Sunday, but latest guidance shows the boundary pushing a little
farther south and west. This is most likely in response to
subsidence associated with a departing jetmax in the northern
stream, causing high pressure to strengthen off the New England
Coast. Even so, subtropical moisture overrunning marine air
(note that low-level flow has veered to the south ahead of the
upper-level low) will cause more showers and perhaps a
thunderstorm. The threat for heavy rain is most likely across
central Virginia into the Allegheny Highlands, but that can
change if the location of the front is off. Will continue to
monitor.


&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
The backdoor boundary will remain stalled out nearby for Monday,
with cool marine air remaining in place for most areas. The
boundary will dissipate and move north Tuesday and high pressure
over the Atlantic will likely control the weather pattern for
the middle of next week with a return of hotter and humid
conditions. Unsettled conditions will likely persist during this
time with chances for showers and thunderstorms. Perhaps the
best chance for stronger storms will be Thursday as a cold front
approaches from the west.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected for most of the day. Showers and
thunderstorms will increase in coverage later this afternoon
through this evening. A few stronger storms are possible with
gusty winds and brief IFR conditions. The best chance for
stronger storms is between 22Z and 04Z. Left Prob30 for
convection in the TAFS at this time due to some uncertainty as
to exactly when the storms will develop.

Low clouds and areas of fog/drizzle are likely to develop late
tonight behind a backdoor boundary that moves into the area.
There is still some uncertainty as to exactly where the boundary
will set up, but latest indications are that most areas will end
up in the marine air for Saturday through Monday. This means
that low clouds and subVFR conditions are likely most of the
time with IFR/subIFR conditions possible, especially at night
into the morning hours each day. Unsettled conditions will
continue with the likelihood for showers and perhaps a few
storms. The best chance for storms will be around KCHO, KMRB and
KIAD Saturday afternoon and evening and KCHO for Sunday
afternoon and evening. However, storms are possible everywhere.

More low clouds and fog will likely hang around through Tuesday
morning, but cigs/vsbys should improve as the backdoor boundary
dissipates and moves northward.

&&

.MARINE...
A southerly flow will increase today into this evening, but
winds should remain below SCA criteria (close over the open
waters of the Bay). Thunderstorm coverage will increase later
this afternoon and especially this evening. Gusty winds
associated with storms may warrant Special Marine Warnings.

A backdoor boundary will move into the area tonight and
eventually stall off to the south and west for later Saturday
through Monday night. An easterly flow will bring low clouds and
areas of fog, and the likelihood for showers and perhaps a
thunderstorm will persist. Winds should be below SCA criteria
for most areas). The boundary will dissipate Tuesday and a
southerly flow will develop for the middle portion of next week.


&&

.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. An easterly flow may elevated water levels for
Sunday into early next week as well.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Flood Watch from this evening through late tonight for DCZ001.
MD...Flood Watch from this evening through late tonight for MDZ013-
     016-017-504.
VA...Flood Watch from this evening through late tonight for
     VAZ037>039-050-051-053>057-502-527.
WV...None.
MARINE...None.

&&

$$

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