644
FXUS61 KLWX 151353
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
953 AM EDT Sat Aug 15 2026

.WHAT HAS CHANGED...
The earlier Dense Fog Advisory will be allowed to expire at 10
AM.

&&

.KEY MESSAGES...
- 1) Severe thunderstorms and some instances of flash flooding
  are possible on Sunday.

- 2) Seasonably warm conditions and daily shower and
  thunderstorm chances are expected through Monday, before
  another round of storms are possible on Thursday.

&&

.DISCUSSION...
KEY MESSAGE 1...Severe thunderstorms and some instances of
flash flooding are possible on Sunday.

Overnight model guidance has come into a broad consensus
regarding the synoptic evolution for Sunday.

In the upper levels, a belt of seasonably strong westerlies
will persist from the upper Great Lakes across the Saint
Lawrence Valley into the Northeast and Canadian Maritimes. Broad
ascent on the equatorward side of this jet will persist much of
the time from early Sunday morning through late Sunday night.

Meanwhile, a pair of mid-level shortwaves, likely augmented by
upstream convection over the Midwest and Ohio Valley, will track
across the Mid-Atlantic on Sunday. Although timing remains a
bit uncertain, most guidance now agrees on an initial wave and
attendant enhanced lift/flow during the morning. This initial
wave may slow on its exit during the afternoon, only to be
followed by another stout wave during the late afternoon and
evening. W/NW flow in the 700-500 hPa layer increases to 30-40
kts, possibly higher depending on how these waves are deepened
by convection that occurs today/tonight upstream.

In the low levels, flow will also increase. This will allow a sharp
rise in theta-e, with PWs rising from around 1.75" at 03Z Sun to
near 2.25" by 09Z Sun. Further increases are progged through Sun
evening. Low-level/steering flow will lie parallel to a slowly
northward lifting warm front expected to bisect the area, so despite
the increased flow, backbuilding/repeating convection seems
plausible. Training plus the high PW airmass yields a threat for
excessive rain and flooding, perhaps mitigated a bit by ongoing
drought east of the Appalachians.

Areas that have seen recent heavy rain, or typical poor
drainage/urban areas would be rather susceptible to any such
excessive rainfall amounts. Of note, the 00Z HREF 3-hr PMM has
50-70% chance of exceeding 1" in the vicinity of western MD
early Sunday morning as a presumably weakening MCS treks into
the region. The probs for 3" are less than 10%, but recent heavy
rain in this area could raise at least a conditional flood
concern as early as the predawn hours on Sunday. Probs for 1"
and 3" in 3 hours are notably higher east of the Blue Ridge
during the afternoon hours. The latest HREF only goes out until
early Sunday evening, but guidance such as the NAM and extended
RAP suggest a further increase in PWs, low-level flow, and
SBCAPE Sunday night suggesting a lingering heavy rain threat.

In addition to any heavy rain threat is the potential for bands
of strong to severe thunderstorms. Increased flow down into the
low levels would be favorable for organized line segments
capable of mixing down damaging wind gusts in any organizing
cold pools. The saturated profiles could result in water loading
downdrafts, though the lack of mid-level dry air may keep DCAPE
low putting a ceiling on just how high damaging wind gusts can
get (most likely in the 50-65 mph range). The increased low-
level flow and SRH coupled with moist profiles could lend to the
threat of a few tornadoes as well.

Although the prospect of early morning clouds and precip may at
first glance seem to preclude a higher potential for heating and
severe weather later in the day, the high low-level moisture
content coupled with steady height falls aloft means that
heating will not need to be as robust to result in sufficient
CAPE for strong to severe convection, especially given the shear
that will be present.

Some severe weather or flood threat may persist into the night
given the above listed factors.


KEY MESSAGE 2...Seasonably warm conditions and daily shower and
thunderstorm chances are expected through Monday, before
another round of storms are possible on Thursday.

High pressure building across southern Quebec down into New
England will favor a mostly quiet day for the area today. An
onshore component to the winds should favor a mix of clouds and
sun through the day. Highs will rise into the mid/upper 80s with
any shower/thunderstorm chances confined to the Potomac
Highlands across the central Shenandoah Valley toward I-64.
Recent high-resolution models are showing an MCS racing across
the Ohio Valley late today. Some of this could leak across the
Alleghenies, but confidence remains low.

As Sunday`s cold front tracks offshore, upper-level zonal flow
bringing drier air from the Great Lakes persists over the Mid-
Atlantic through midweek, creating a break in the rain and
thunderstorms. While temperatures and dewpoints drop a few
degrees by Tuesday in the wake of the front, temperatures should
gradually increase again in the latter half of the week as high
pressure builds overhead. Prior to high pressure building,
additional convection is possible Monday but with a likely
lesser threat of severe weather or flooding.

Meanwhile, an upper-level trough will begin to form over the
Northern Plains and then track across the Great Lakes late in the
week, with a strong cold front potentially moving through the Mid-
Atlantic between Thursday and Friday. Medium-range algorithms are
already highlighting a potential for severe thunderstorms with this
system. However, severe probabilities currently vary widely across
models, with CSU ML probabilities highlighting only a marginal 5%-
15% probability as of the 12Z model runs while the WxNext2 Mean AI
outlook is already showing a 30%-45% probability. Deterministically,
the GFS/ECMWF also have not quite aligned on the timing and
placement of the trough 7 days out. Should this setup
materialize, storms capable of heavy downpours and damaging
winds would be possible. As drought conditions continue to
improve area-wide, localized flooding becomes more of a concern
with any thunderstorms that form in the region. For now, this
will be a feature to continue to monitor as the synoptic setup
becomes more defined.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions are expected for today as high pressure builds
over New England into southern Quebec. Any shower chances are
likely confined to those west of the Blue Ridge and south of
I-66. A decaying MCS could move through late tonight, but there
is plenty of uncertainty at this point. Sunday presents itself
as a much more active weather day which would include some
convective-driven restrictions. Ahead of the approaching cold
front, southerly winds pick up in strength with afternoon gusts
to around 15 to 20 knots. Convection could loom into Sunday
night and Monday morning which would support additional sub-VFR
conditions. Conditions turn drier for later in the day as the
cold front moves off toward the southeast.

Prevailing VFR conditions are anticipated at terminals Tuesday
through Wednesday. Light northwest winds shift southerly on
Wednesday.

&&

.MARINE...
Background wind fields remain below advisory threshold through
early Sunday. Ahead of a cold front, southerly winds increase in
earnest which will carry gusts to around 20 to 25 knots. This
likely requires Small Craft Advisories from Sunday afternoon
into the overnight hours. Additionally, there will be an
increasing risk of strong to severe thunderstorms, many of which
may need Special Marine Warnings. Sunday likely presents itself
as the most hazardous day to be on the waters, particularly
from the afternoon onward. Convection may continue into Monday
morning before the storm threat and winds drop off through the
day.

Winds stay below SCA thresholds on Tuesday. Beginning Wednesday
afternoon, wind gusts pick up to marginal SCA thresholds before
diminishing overnight. Northwest winds shift southeast by Wednesday
morning.

&&

.TIDES/COASTAL FLOODING...
Water levels are largely expected to stay below Action Stage
through Saturday. The potential exception could be Annapolis,
which could reach Action Stage at the higher of the daily tides.
Water levels will start to increase in southerly flow on
Sunday, with Annapolis potentially approaching Minor Flood
Stage.

&&

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

&&

$$

DISCUSSION...BRO/DHOF/CJL/KJP/SRT
AVIATION...BRO/DHOF/SRT
MARINE...BRO/DHOF/SRT

NWS LWX Office Area Forecast Discussion