Arlington, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

162
FXUS61 KLWX 171250
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
850 AM EDT Fri Jul 17 2026

.WHAT HAS CHANGED...
Current AQI values are teetering between Code Red and Code
Purple. Will be in touch with partners at state environmental
departments to see if any alert level changes are needed. Either
way, air quality is poor and avoiding prolonged time or
strenuous activity outdoors is advised.

&&

.KEY MESSAGES...
- 1) Poor air quality due to smoke can be expected today along
  with a few showers and thunderstorms in the Allegheny
  Highlands and central Shenandoah Valley.

- 2) A strong cold front brings the threat of severe weather
  Saturday, possibly lingering into Sunday to the south.

- 3) Brief high pressure Monday before another strong front
  crosses midweek.

&&

.DISCUSSION...
KEY MESSAGE 1...Poor air quality due to smoke can be expected
today along with a few showers and thunderstorms in the
Allegheny Highlands and central Shenandoah Valley.

A weak cold front has drifted south through the area this
morning, with thicker near-surface smoke originating from
Canadian wildfires advecting southward in its wake. Regional
observations show visibilities as low as 1-2 SM, and computer
models suggest similar values could persist through much of the
day, especially in the northern portions of the area. Air
quality will be poor as a result through the day and possibly
through tonight. Visit airnow.gov for the latest air quality
forecasts from the subject matter experts at state environmental
agencies.

The front will stall roughly from Pendleton County toward the SE
Virginia tidewater by this afternoon. A few showers and
thunderstorms may try to pop up this afternoon across the
Allegheny Highlands and central Shenandoah Valley aided by
instability near/south of the stalled front and orographic lift.
While models indicate high temperatures in the upper 80s to mid
90s, locations that have thicker smoke may remain in the mid
80s. Humidity will be a touch lower behind the front however.

The front will begin to push back northward tonight in response
to low pressure moving through the Great Lakes. While the low
levels will likely be stable, elevated instability will advect
northward with the front, especially closer to the Chesapeake
Bay. The main question is whether there is a strong enough
trigger aloft to produce convection. Most guidance has isolated
to scattered coverage, if anything at all. Should a storm tap
into the instability, there is enough shear to result in a
stronger storm, although most of that potential holds off until
after sunrise Saturday.


KEY MESSAGE 2...A strong cold front brings the threat of severe
weather Saturday, possibly lingering into Sunday to the south.

An unseasonably strong upper trough and embedded shortwave/jet
streak will pivot near and north of the area Saturday. Strong
height falls associated with this trough, coupled with high
low-level moisture content and modest mid-level lapse rates will
likely result in strong instability, perhaps even if cloud
breaks are muted by early day precip. The other question mark is
whether smoke could have any lingering effects, though the shift
in wind direction should lead to noticeable improvements in that
regard. The strong deep layer flow will lead to effective shear
magnitudes of 30-40 kts, helping to organize storms that
develop in the vicinity of a pre-frontal surface trough in the
wake of any morning activity. Low-level flow will be a bit
weaker during the day, so although transient supercell
structures are possible, the main risk should be damaging wind
gusts and perhaps large hail as opposed to tornadoes. This could
change if the effective warm front lingers overhead or
mesoscale boundaries back the low level flow.

Depending on storm coverage, temps could reach well into the 90s
Saturday, especially along the I-95 corridor. With high
humidity, heat indices may reach 100-105 east of the Blue Ridge.

Heading into Saturday evening, low-level flow increases again
ahead of the approaching synoptic cold front associated with
the aforementioned upper trough. This sends PWATs hurdling to
over 2.2" and keeps CAPE elevated well into the evening. The
expectation is for a strongly forced line of storms to develop
in the unstable airmass from the eastern Great Lakes into the
upper Ohio Valley (i.e. western NY/PA into OH/WV). This line of
storms may be slow to weaken as it treks into the area from the
northwest through the evening, especially if there is moderate
to strong instability left (depends on earlier activity). The
main threat at this point would appear to be gusty to damaging
winds and heavy rain due to multiple rounds of storms. High
instantaneous/sub-hourly rain rates would be plausible in this
setup. If any discrete activity develops in the evening ahead of
the line as the LLJ increases, there may be a risk for large
hail as well as a couple tornadoes, particularly in areas for
surface flow is backed. With that said, much of the 00Z guidance
shows this upstream convection weakening as it reaches the CWA
during the evening.

Activity should wane during the overnight hours Saturday as the
front and associated convection drop south and the atmosphere
gradually stabilizes. The front will probably end up near or
south of I-64 Sunday, with any remaining severe threat being
near and south of the effective frontal boundary. Expect cooler
temperatures in the wake of the front.


KEY MESSAGE 3...Brief high pressure Monday before another strong
front crosses midweek.

The front continues to sag south and east of the area Monday as high
pressure briefly builds in. Most of the area will remain dry with a
leftover shower or thunderstorm, mainly south of I-64 where the
front looks to reside. Temperatures will cool back to more
seasonable levels with highs in the 80s (70s mountains).

Beyond Monday, uncertainty remains in regards to the timing of
a strong upper level trough and it`s associated cold frontal
boundary. Some of the guidance has a leading shortwave trough
crossing the area Tuesday with the cold front to follow Tuesday
night into Wednesday. Depending on how this is timed with the
diurnal cycle, as well as any impacts from the lingering frontal
zone offshore (which could cause some sinking motion to its
west locally), additional strong to severe storms are possible
mid next week.

A secondary cold front will follow Wednesday into Thursday before
broad high pressure over the upper Midwest expands into the region.
This series of fronts will flip the airmass over to more seasonable
norms if not below normal temperatures and lower humidity for the
end of next week.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
A weak front has pushed south through the area this morning,
with thick smoke from Canadian wildfires moving across the
region in its wake. MVFR to intermittent IFR conditions are
expected through today in smoke, although CHO may have
relatively higher visibility overall. Given that modeling of
visibility in smoke is far from perfect, the TAFs represent a
combination of what has been happening upstream with anticipated
changes due to daytime mixing and wind shifts as the front
lifts back north tonight. While a shower or storm could approach
CHO this afternoon or evening, and across the rest of the area
late tonight, the probability is currently too low to include in
the TAF. Light north winds will shift southerly tonight as the
front lifts north.

Smoke should disperse by Saturday, but multiple rounds of
showers and thunderstorms are possible between Saturday morning
and Saturday evening. Some of these could be strong to severe.

Thunderstorms are possible Sunday near CHO depending on how far
south the front makes it. Prevailing VFR conditions are expected Monday
with additional sub-VFR reductions Tuesday and Wednesday pending
thunderstorm development.

&&

.MARINE...
Lowered visibility in smoke can be anticipated through Friday.
Winds flip to southerly tonight as the front lifts back north.
Advisories may be needed for portions of the waters starting
tonight, but are more likely Saturday into Saturday evening.
Strong storms are possible Saturday into Saturday evening as
well, which may prompt Special Marine Warnings.

Leftover storms on Sunday would probably be limited to areas around
southern MD, but there is uncertainty in just how far south the
front gets. Otherwise winds become northerly in the front`s
wake.

Expect sub-SCA level conditions Monday before SCA level channeling
returns Tuesday as the gradient tightens ahead of an associated upper
level trough/cold frontal boundary.

&&

.TIDES/COASTAL FLOODING...
Increasing southerly flow on Saturday and again on Tuesday could
lead to water levels approaching minor flood stage, especially
at Annapolis.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...Air Quality Alert until midnight EDT tonight for VAZ025>027-
     029-030-036>040-050-051-055>057-501>504-507-508.
WV...Air Quality Alert until midnight EDT tonight for WVZ050-055-
     501>506.
MARINE...None.

&&

$$

DISCUSSION...ADS/DHOF/EST
AVIATION...ADS/DHOF/EST
MARINE...ADS/DHOF/EST
TIDES/COASTAL FLOODING...ADS