Arlington, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

176
FXUS61 KLWX 171941
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
341 PM EDT Mon Aug 17 2026

.WHAT HAS CHANGED...
Updated rain chances and aviation forecasts this
afternoon/evening based on observations and latest computer
models. A few showers and thunderstorms may develop near central
Virginia on Tuesday. Rain chances have increased slightly this
weekend.

&&

.KEY MESSAGES...
- 1) Scattered showers and thunderstorms remain possible until a
  cold front crosses tonight, with a chance possibly persisting
  into Tuesday.

- 2) Thunderstorm chances return Wednesday night into Thursday,
  and continue into next weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...Scattered showers and thunderstorms remain
possible until a cold front crosses tonight, with a chance
possibly persisting into Tuesday.

A couple of perturbations are approaching the area this
afternoon while a surface cold front moves southward from the
Great Lakes. Despite west to northwest winds, dew points remain
in the upper 60s to mid 70s with precipitable water values near
2 inches. Scattered showers and a few thunderstorms have already
developed across the northern part of the CWA and across PA in
this environment. This convection will gradually drift east and
southeast with time through the evening. Steepened low-level
lapse rates with lingering low- level moisture could result in a
few gusty thunderstorms (generally 35-50 mph), along with some
downpours and lightning. Heating and instability will be a bit
more pronounced across central VA to southern MD, so these areas
would probably stand the highest chance at seeing anything at or
near severe thresholds (which is 58 mph). DCAPE will be very
marginal (400-600 J/kg) due to lingering mid- level moisture and
meager lapse rates aloft, but a bit higher to the south
(especially Fredericksburg to southern MD). Typically, values
of at least 600-800 J/kg are needed to accelerate downdraft
winds to severe levels. However, storms may not reach this area
until near or after sunset, so the net effect may be strong to
perhaps near severe storms.

The low-level synoptic cold front will cross the region
tonight. Therefore, a few additional showers are possible, but
the threat for thunderstorms should start diminishing after
midnight. Areas which clear out tonight could have patchy fog.
Most guidance favors the western river valleys at this time.

While the surface front will likely be south of the area
Tuesday, it will be losing its definition, and some low and mid
level moisture may linger, especially across the southern half
of the area. With daytime heating, this will result in some weak
instability. Some models have scattered showers and storms
developing off the terrain and moving eastward during the
afternoon across the southern quarter to half of the forecast
area (mostly south of I-66 if not I-64). The weak instability
will limit the strength of this activity despite shear which
could approach 30 kt. Temperatures and dew points will be a
touch lower today, but still seasonable with highs in the mid to
upper 80s.


KEY MESSAGE 2...Thunderstorm chances return Wednesday night into
Thursday, and continue into next weekend.

High pressure building from the Ohio Valley will keep dry
conditions Tuesday night into Wednesday. Temperatures may tick
back up closer to 90. The next cold front will approach from
the northwest Wednesday night, but the timing for rain chances
has generally been pushed to the second half of the night, which
would reduce the threat for thunderstorms. Where this cold
front ends up by Thursday afternoon will have an effect on the
coverage and strength of showers and thunderstorms. While
everyone could see some rain, there is uncertainty with the
amount of instability and how much it would overlap with shear.
AI/ML guidance has been consistent the past several days
showing the greatest risk for any stronger thunderstorms being
across the southern or southeastern portion of the forecast
area.

It`s possible the front will stall or only move just south of
the area, which will play a role in precipitation chances
Friday. It will be far enough south to bring a cool down, with
highs in the 70s and 80s by Friday.

A deepening trough of low pressure approaching from the Great
Lakes (possibly even a closed low) may result in one or more
areas of low pressure developing along the front between Friday
and this weekend. Thus chances of rain have been trending
upward, even if we are north of the low track. Expect
temperatures slightly below normal given the clouds and
potential rain.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
A cold front approaches from the northwest through tonight.
Scattered showers and thunderstorms have been developing north
and west of MRB and will drift south and east with time through
this evening. Given relatively good agreement on the timing and
placement in the latest models, decided to convert to VCTS for a
few hours from late afternoon through early evening. TEMPOs may
eventually be needed. Kept PROB30 at CHO given more uncertainty
in the development of storms in this area. NW flow 7-12 kts is
expected, perhaps becoming briefly a bit more W this evening
before shifting to N by daybreak Tue. IFR CIGs/fog possible
especially near MRB/CHO after 06Z tonight, but given the amount
of uncertainty, kept visibility at MVFR for now.

VFR with return to S flow Wednesday, then potential showers and
thunderstorms re-enter the forecast at times Thursday through
Saturday. Winds shift back to the NW or N Thursday in the wake
of a cold front.

&&

.MARINE...
Generally light winds are expected through the upcoming week.
NW winds today briefly shift to W this evening, then N Tuesday
before returning to S Wednesday. A few enhancements are possible
along the bay during any of these wind shifts due to channeling,
but prospects of advisory conditions are marginal at best.

A few thunderstorms are possible and may prompt a couple
Special Marine Warnings this afternoon and evening. A cold front
may bring additional thunderstorms Thursday into Friday.

Coastal low pressure may develop at some point between Friday
and Saturday, but it`s uncertain if it will be strong enough to
increase the winds much.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

DISCUSSION...ADS/DHOF
AVIATION...ADS/DHOF
MARINE...ADS/DHOF