Arlington, Virginia 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

399
FXUS61 KLWX 191429
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1029 AM EDT Wed Aug 19 2026

.WHAT HAS CHANGED...
We continue to monitor the severe weather threat on Thursday for
those along and east of I-95. No significant changes were made
to the forecast.

&&

.KEY MESSAGES...
- 1) Departing high pressure gives way to a cold front and
  increasing shower and thunderstorm chances by Thursday.

- 2) Chances for showers and thunderstorms continue through at
  least Saturday, before cooler and drier air moves in early
  next week.

&&

.DISCUSSION...
KEY MESSAGE 1...Departing high pressure gives way to a cold
front and increasing shower and thunderstorm chances by
Thursday.

High pressure moving overhead will maintain dry conditions with
partly to mostly sunny skies today. The high will move offshore
tonight as a cold front approaches from the Great Lakes. Clouds
will increase this evening, with shower chances ticking up near
and west of I-81 after midnight. Shower activity is possible
across much of the area by daybreak Thursday, depending on the
evolution of showers and storms over the OH Valley today.

Latest guidance is a bit slower and further west/northwest with
the position of a cold front on Thursday. SLP progs hint at two
subtle warm front type features that will lift northeast during
the day on Thursday ahead of a pair of weak surface lows (one
near PA/NJ, and the other near central VA). Where this front
ends up just prior to peak heating will be crucial in
determining the severe weather threat locally on Thursday.

Forecast soundings show strong mid-level capping west of the
front Thursday afternoon, with no capping and notably stronger
CAPE approaching or exceeding 2000 J/kg east of it. The
consensus is for this front to be more or less over I-95
Thursday afternoon during peak heating, though there is some
variance anywhere from near the Blue Ridge to the Chesapeake
Bay. Mid-level lapse rates start the day unimpressive, around 5
C/km likely due to saturation aloft associated with a weak wave
of showers, but steepen slightly closer to 6 C/km by afternoon
due to some cooling aloft.

The extent of any clouds and showers cast some uncertainty on
the extent of heating and instability later in the day. The
background environment is favorable for strong to severe
updrafts and even supercells. An 80-90+ kt upper jet will pivot
over the area, with its right entrance ascent positioned over
the surface frontal zone in the afternoon. Mid-level heights
stay relatively steady, but PVA (strongest north) will be
prevalent ahead of the aforementioned mid/upper wave and jet.

Flow will increase through the column, with 25-40 kts in the
2-5 km AGL layer and effective deep layer bulk shear around 40
kts. SRH also increases to 100-200 m2/s2. Initial discrete cells
in this environment may quickly grow upscale into a line
capable of surges of strong to severe straight-line wind and a
few embedded spin ups. Some hail can`t be ruled out in the
strongest storms due to cooling temps aloft. Finally, although
Corfidi vectors are not too low (10-15 kts), on the mesoscale
some backbuilding or training potential may exist on the tail
(southwest) end of any developing line heading into the evening.

Again, the highest potential will be along and east of the front
which currently appears to be near I-95 during the afternoon
into the early evening hours.

Although somewhat conditional based on (1) the placement of the
front, and (2) the degree of instability, Thursday`s severe
weather and excessive rainfall risk bears monitoring. For now,
given the uncertainties listed above, the risk is more in the
Marginal (level 1 out of 5) bin for severe weather (i.e. any
damaging winds, large hail, tornadoes), but with a conditionally
much higher ceiling than most typical late summer days. The
excessive rainfall/flood risk may be even more conditional due
to uncertain mesoscale factors and lingering drought.


KEY MESSAGE 2...Chances for showers and thunderstorms continue
through at least Saturday, before cooler and drier air moves in
early next week.

The longwave pattern across the CONUS will amplify moving into the
weekend, with a shortwave disturbance and an even more potent
upper-level low digging into the Ohio Valley and Great Lakes on
Saturday. Downstream of the trough axis, we`ll be in a
favorable location for large scale ascent, with showers and
thunderstorms possible Saturday afternoon. The upper trough axis
will shift eastward to near our longitude by Sunday as an upper
low continues to deepen to the north of Lake Ontario. Most
solutions favor a cold front moving through either late Saturday
night or early Sunday. Drier low-level air will filter into the
region behind the front, with dewpoints dropping through the
60s on Sunday. That combined with the trough axis being located
overhead (leading to less large scale ascent), leads to most solutions
showing dry conditions locally. However, there still are a few
solutions that produce a passing shower or storm on Sunday.

Even drier air will advect into the area for Monday and Tuesday,
with dewpoints forecast to drop into the 50s. This will lead to dry
conditions, and also make it feel considerably less humid. High
temperatures each day Saturday through Tuesday will generally be in
the low to mid 80s at lower elevations, with 70s in the mountains.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Mid-level clouds wafting past KCHO to the north of a stalled
front as well as some subtle dry advection in the low levels may
keep fog to a minimum early this morning. However, if clouds
clear, brief L/IFR is possible. Elsewhere, VFR with light NW
flow is expected at the TAF sites through this morning.

Winds will gradually turn more southwesterly by this afternoon
with VFR conditions expected. Rain may approach the TAF sites
ahead of a cold front late tonight, with more numerous showers
and possible thunderstorms Thursday afternoon and evening.
Highest TS probs are near/east of I-95 terminals Thursday PM.
Some lower ceilings are possible, especially around MRB Thursday
morning. Showers may linger at CHO Thursday night and Friday,
along with potential lower ceilings.

Sub-VFR ceilings may be possible Saturday morning, before conditions
gradually improve back to VFR Saturday afternoon. Thereafter,
prevailing VFR conditions are expected through the weekend.
Temporary drops to sub-VFR conditions can`t be ruled out in
thunderstorms on Saturday or Sunday. Winds will be light out of the
southeast on Saturday, and then light out of the northwest on Sunday.

&&

.MARINE...
Light winds are expected through Friday. Northwest winds
become southerly by tonight. A brief enhancement is possible
along the Chesapeake Bay this evening due to channeling, but
prospects of advisory conditions are marginal at best. Winds
then shift back to the northwest and north Thursday and Friday
as a cold front pushes southward. This cold front may bring
some thunderstorms to the waters on Thursday into Friday. The
chance of thunderstorms has increased particularly for Thursday
afternoon, during which time gusty winds or a few waterspouts
are possible.

Sub-SCA level winds are expected this weekend, with winds generally
out of the southeast on Saturday, and then northwest on Sunday. A
shower or thunderstorm can`t be ruled out either afternoon.

&&

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

&&

$$

DISCUSSION...AVS/DHOF/KJP
AVIATION...DHOF/KJP
MARINE...DHOF/KJP