848
FXUS61 KLWX 182003
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
403 PM EDT Fri Jul 18 2025

.SYNOPSIS...
A stationary front over the area today will return northward as a
warm front tomorrow. A cold front will move through Sunday night.
High pressure will build to our north early next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Current surface analysis shows a stationary front extending
west-northwestward from just north of Richmond toward
Charlottesville, Staunton, and Harrisonburg, and then eventually
into central West Virginia. Storms are in the process of
developing in the vicinity of and south of this boundary, but
activity has struggle to develop north of roughly Harrisonburg,
as earlier cloud cover/shower activity has limited daytime
surface heating. Model guidance has struggled mightily with the
evolution of storms thus far today, and there is a growing
amount of skepticism regarding whether stronger storms will make
it into the far northern reaches of the Flood Watch that is in
effect. Based on the current evolution of the cumulus field, it
appears as though the greatest threat for stronger storms and
resultant risk for flash flooding will be from the
Harrisonburg/Staunton/Waynesboro/Charlottesville vicinity
eastward toward Fredericksburg. While confidence isn`t quite
there to cancel the Watch further north, confidence in flooding
occurring north of those locations is decreasing. Any stronger
storms today will still be capable of producing very heavy
rainfall, given high PWAT values, deep saturated profiles and
ample instability. The background environment isn`t overly
favorable for damaging winds with low DCAPE values (300-600
J/kg) and subpar low-level lapse rates (around 7 C/km), but a
few instances of damaging winds may still be possible,
especially if storms start to exhibit weak supercellular
characteristics (as some of the storms near Roanoke have started
to do).

Further north toward the DC/Baltimore Metros, most of the
precipitation is expected to occur as showers, but a few
thunderstorms may try to drift northeastward toward the DC Metro
late this evening. The threat for flash flooding looks to be
low in the DC Metro, but not zero, with any potential chance
coming if storms approach from the southwest during the late
evening hours. Any activity will wind down by around or shortly
after midnight, with dry conditions expected during the second
half of the night. Low clouds may try to develop later tonight,
and fog may form in locations that don`t get the low clouds.
Overnight lows are expected to be in the upper 60s and lower
70s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
The stationary boundary located over the area today will make
slight northward progress as a warm front tomorrow. Flow aloft
will remain primarily zonal. A weak convectively generated
disturbance may approach from the west during peak heating. The
combination of daytime heating and weak ascent associated with
this feature will result in another round of showers and
thunderstorms tomorrow afternoon into tomorrow evening.
Currently it appears as though the highest coverage of these
storms (much like today) will be in the Central Shenandoah
Valley and Central Virginia. However, a brief afternoon or
evening thunderstorm may be possible anywhere in the forecast
area. Storms may be capable of producing isolated to scattered
instances of flooding, as well as a damaging wind gust or two.
High temperatures will be in the mid-upper 80s for most, with
dewpoints holding in the 70s.

Upper troughing will start to dig to our north across Northern
New England on Sunday, while low pressure tracks through the
Canadian Maritimes. This will cause a cold front to drop
southward across NY, New England and PA over the course of the
day. Storms may try to form along a pre-frontal trough Sunday
afternoon. Some of these storms may be strong to severe. SPC
currently has the entire area outlooked in a Marginal Risk for
severe thunderstorms.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Characterized by 500-mb height anomalies running around 1.5 to 2
standard deviations below average, a formidable upper trough is
forecast to continue tracking eastward across the Canadian
Maritimes. This pattern shift allows for a broad dome of Canadian
high pressure that settles over Quebec into New England through mid-
week. On Monday, a steady northerly component to the surface winds
will sufficiently lower dew points over the area. This ultimately
results in a multi-day reprieve from the 2 to 3 weeks of continued
heat and humidity. Although the current forecast package shows dew
points in the upper 50s to mid 60s, plenty of solutions carry
readings into the mid 50s. This is accompanied by daily high
temperatures in the low/mid 80s (upper 60s to 70s in the mountains).
Widespread overnight lows will be in the 60s, with some upper 50s
along the mountain ridges. Any shower chances through Tuesday are
tied to the Potomac Highlands into the central Shenandoah Valley.
Some perturbations circulating clockwise around a ridge across the
Lower Mississippi Valley could invigorate some localized lift.

By Wednesday, some return flow picks up as the surface anticyclone
exits the New England coast. The global ensemble consensus shows
this scenario unfolding which helps increase dew points across the
Mid-Atlantic region. At the same time, a broad upper ridge initially
over the south-central U.S. will expand both north and east in time.
Its influence on the local area is expected to come with rising
daily temperatures, especially by Thursday and Friday. A return of
temperatures in the low/mid 90s is looking more likely, but ensemble
spread does increase as noted by sizeable box-and-whisker plots.
While thunderstorms do not come back immediately, expect a better
chance for such storms by late in the week. This is in response to
some northern stream amplification noted in a number of models.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
The main concern through the rest of the day will be thunderstorm
potential, with otherwise prevailing VFR conditions. The best chance
for storms looks to be around CHO, which is located in the vicinity
of a stationary front. Further north and east, conditions are a bit
more stable, so chances for thunderstorms appear to be lower, albeit
non-zero. At the moment, light rain is moving eastward from the
vicinity of MRB toward the DC/Baltimore metros. This activity is
expected to continue on as just showers. Any potential thunderstorms
would likely develop off to the southwest in more unstable air and
move northeastward toward the Metro terminals later this evening. As
a result, the PROB30s for DCA and IAD have been pushed back a couple
hours. The PROB30 has been removed at BWI, where confidence is
increasing that storms will remain off to their south and west.

Any thunderstorms should wind down during the first half of the
night, but low clouds may move in later during the night. IFR
ceilings appear possible for a time later tonight into early
tomorrow morning, but gradual improvement back to VFR ceilings
is expected over the course of the morning tomorrow.
Thunderstorms will form again tomorrow afternoon, with most of
the activity focused over central VA. Confidence is currently
too low to introduce PROB30s in the DC/Baltimore Metro
terminals, but at least a PROB30, if not a TEMPO will eventually
be needed for CHO. Additional thunderstorms may be possible on
Sunday afternoon.

With precipitation chances looking pretty low on Monday through
Wednesday, expect VFR conditions at all terminals. The shift in the
pattern ushers in a northerly wind on Monday before turning more
east-southeasterly by Tuesday. Once Canadian high pressure exits the
New England coast on Wednesday, a return southerly flow is
expected.

&&

.MARINE...
Light and variable winds are expected over the waters this
afternoon. An SMW for thunderstorms may be needed later this
evening, particularly over the middle to lower Tidal Potomac. Light
south to southeasterly winds are expected tomorrow, and then light
westerly winds on Sunday. Winds will shift to out of the north
behind a cold front Sunday night, and potentially could near low-end
SCA levels during that time. SMWs may potentially be needed for
thunderstorms during the afternoon and evening hours both days this
weekend.

Winds across the marine waters should stay below advisory levels
through Tuesday. A northerly wind may gust around 10 to 15 knots on
Monday before shifting to east to northeasterly on Tuesday. There is
no threat for thunderstorms as Canadian high pressure builds to the
north.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Flood Watch until midnight EDT tonight for MDZ016-501-509-510.
VA...Flood Watch until midnight EDT tonight for VAZ025>031-036>040-
     050-051-055>057-501>504-507-508-526-527.
WV...Flood Watch until midnight EDT tonight for WVZ050-055-501>506.
MARINE...None.

&&

$$

SYNOPSIS...KJP
NEAR TERM...KJP
SHORT TERM...KJP
LONG TERM...BRO
AVIATION...BRO/KJP
MARINE...BRO/KJP