557
FXUS61 KLWX 160619
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
219 AM EDT Sun Aug 16 2026

.WHAT HAS CHANGED...
Thunderstorms over southeastern Ohio are prompting Flash Flood
Warnings and water rescues, and these storms are on pace to
reach western Maryland by daybreak.

&&

.KEY MESSAGES...
- 1) Severe weather and flash flooding are possible through
  tonight.

- 2) Thunderstorm chances return Wednesday night into Thursday.

&&

.DISCUSSION...
KEY MESSAGE 1...Severe weather and flash flooding are possible
through tonight.

Very active weather is expected over the next 12 to 24 hours,
with the threat for flash flooding, damaging wind gusts, and a
few tornadoes.

As of 06Z/2AM EDT, thunderstorms containing very heavy rain had
prompted several Flash Flood Warnings and water rescues in
southeastern Ohio. These thunderstorms are on track to reach
western Maryland (Garrett County) by daybreak/6AM EDT.

Will be closely evaluating the downstream environment into
Allegany County MD, as well as Mineral, Grant, Hampshire and
Hardy Counties in WV to see if the watch needs to be expanded to
cover this morning round of storms that have a history of
producing about 3 inches of rain in an hour.

The first shortwave of note which is the impetus for the
approaching complex has an impressive swirl on radar/satellite.
Given the orientation of the heaviest thunderstorms in this
complex, it appears that WNW to ESE training will continue as
this complex enters western MD. The signal for heavy rain
becomes a bit more diffuse as these storms cross the mountains
through mid to late morning, though a persistent convergence
axis is noted in obs/guidance trends in the above mentioned
areas (Allegany down to Hampshire/Hardy Counties).

To the east, strong moisture advection in the low levels should
cause at least scattered showers to break out by around or just
before day break across northern VA into central MD. Instability
is not as high here, so thunder and heavy rain may old off until
mid to late morning. Coverage of heavier storms looks a bit
lower and of less confidence this morning, though any heavier
rain could still bring about a conditional flood threat in
urban/poor drainage areas.

Guidance shows a relative lull in between the wave moving in
this morning and another stout shortwave (currently over IL)
moving through late this afternoon and evening. Upstream trends
between these waves in the Indianapolis area, however, show
convection initiating even in the middle of the night. This
seems indicative of sufficient WAA to result in rapidly
redeveloping convection at least in an isolated sense in between
these two waves at pretty much any point today.

Trends will need to be very closely monitored given the very
high PW airmass and potential for repeat/training thunderstorms.
Should this heavier activity train over any one area, 3 to 6
inches of rain would be possible on a localized basis. This
could cause scattered to numerous instances of flash flooding,
with considerable flash flooding possible in urban/poor drainage
areas or areas that have seen heavy rain recently. If and when
it becomes clearer where the greatest coverage of heavy rain
will set up, additional Flood Watches may be issued.

Regarding the severe weather threat, strong low-level winds
will boost SRH in a high moisture content environment. Wet
downbursts and brief spin ups would be possible in this
environment, with the tornado threat maximized along the slowly
lifting warm frontal zone - especially if any cell or cluster
interacts with/tracks along it. Shear is favorable for right-
moving (i.e. NW to SE) supercells if enough instability is
realized, and in those cases storms would be more apt to ingest
streamwise vorticity along the warm front (or residual outflow).

The wave this evening, though timed a bit after peak heating,
may pose the relative highest risk of damaging wind gusts due
to increased low-level flow orthogonal to what will probably a
linear type feature.

Convection (and corresponding severe/flood threats) may wane
only gradually tonight with continued low-level moist advection
beneath height falls aloft. This causes instability to remain
or even increase through the night.


KEY MESSAGE 2...Thunderstorm chances return Wednesday night into
Thursday.

As a cold front slowly moves across our area late Wednesday and
Thursday, shower and thunderstorm chances return across most of
our forecast region. Friday and Saturday, models continue to
depict a stalled front lying in our south, bringing sustained
chances for summer-time showers and thunderstorms. Currently,
it`s unclear if the position of synoptic features and
instability will be sufficient for hazardous weather. For now,
this will be a feature to monitor as the synoptic setup becomes
more defined. Temperatures may fluctuate a little depending on
what side of the front we`re on, but likely fall some by next
weekend, assuming the front pushes to the southeast.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Patchy low CIGS around FL015 have developed near KMTN. It is
unclear if this persists, as it may at least initially be driven
by local effects right along the Chesapeake Bay. Meanwhile, some
BR is noted at CHO, and will likely persist in some form until
rain moves in later this morning. Fog, especially dense fog,
seems unlikely given the increase in mid-level clouds. VFR is
likely to continue at the other TAF sites through 12Z, though a
few showers may develop near the metros and especially near MRB.
Lower (MVFR) CIGs may develop thereafter.

Active weather with multiple rounds of storms is expected
through tonight. The TAFs attempt to hone in on the highest
threat window for TS with a first wave this morning into early
afternoon, with a relative lull prior to a second wave late this
afternoon into the evening. It should be noted that, given the
airmass in place, a shower or thunderstorm could pop up at or
near a TAF site at basically any time. Persistent, backbuilding
convection is also possible, which could prolong restrictions
if/when TS move near or over a TAF site.

South winds through tonight become northwest Monday. Gusts of 15
to 20 knots are possible this afternoon. A few storms could
contain gusts of 30-50 kts on an isolated basis through evening.

VFR is expected Monday into Tuesday as high pressure builds,
though a pop up shower or storm is possible Monday until a cold
front crosses by evening.

Potential showers and thunderstorms re-enter the forecast late
Wednesday.

&&

.MARINE...
Light southeast winds early this morning become south and
increase by late morning. Gusts of 15 to 25 knots are expected,
and Small Craft Advisories are in effect for all waters through
early this evening. Gusts likely taper somewhat over the middle
and upper tidal Potomac River, but persist elsewhere through
much of the night.

Thunderstorms become increasingly likely through the day, and a
few may produce wind gusts of 35 to 50 knots. The storm threat
could linger through the night, with even some chances Monday
prior to the passage of a cold front that will turn winds to the
northwest. Dry weather and light winds are expected Tuesday as
high pressure builds.

Winds turn southerly on Wednesday, and channeling may bring marginal
SCA conditions along the bay during the evening/overnight. A cold
front may bring some thunderstorms on Thursday.

&&

.TIDES/COASTAL FLOODING...
Southerly winds will increase water levels through tonight.
Vulnerable shoreline such as the Annapolis waterfront could
approach minor flood stage during high tide through the night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory from noon today to 6 AM EDT Monday for
     MDZ008.
     Flood Watch from 6 AM EDT this morning through this evening
     for MDZ509-510.
VA...None.
WV...None.
MARINE...Small Craft Advisory from noon today to 6 AM EDT Monday for
     ANZ530>534-537>543.
     Small Craft Advisory from noon today to 8 PM EDT this evening
     for ANZ535-536.

&&

$$

DISCUSSION...DHOF/KJP/KVH
AVIATION...DHOF/KJP/KVH
MARINE...DHOF/KJP/KVH
TIDES/COASTAL FLOODING...DHOF