697
FXUS61 KLWX 200800
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Wed Aug 20 2025

.SYNOPSIS...
High pressure to the north will continue to funnel cool and
moist air into the region off the Atlantic Ocean this morning. A
cold front will approach the region through the day before
pushing through tonight. This will help to drag Hurricane Erin
well offshore of the Atlantic coast. Weak high pressure builds
across the region late in the week into Saturday. An area of low
pressure will track toward Hudson Bay over the weekend. The
associated cold front will move through early next week. In the
wake, a strong dome of high pressure slowly approaches from the
Midwest.

&&

.NEAR TERM /THROUGH TONIGHT/...
The early morning surface analysis shows a continued cold air
damming (CAD) signature extending from Quebec down along the
spine of the Appalachian Mountain chain. To the south, a wavy
frontal zone remains along the eastern North Carolina coast back
toward/along the Appalachians. Continued easterly onshore flow
has favored a persistent thick stratus deck over the entire
area. Many locations are seeing overcast skies down to around
500-1000 feet, locally a bit lower in a few spots. While lift is
generally weak, the degree of low-level saturation has caused
areas of light drizzle. This could be enough to squeak out a
hundredth or two of precipitation. Any instance of patchy fog is
more tied to the terrain with low clouds obscuring portions of
the Alleghenies.

The low dewpoint depressions currently being observed should
change very little through the first half of the morning. The
CAD wedge remains in place while gradually being eroded through
the day. While the day will start with temperatures in the 60s,
a return to much warmer weather resumes as the boundary lifts
northward as a warm front. This is forecast to eventually put an
end to the prolonged onshore flow and a return to more
summertime conditions.

Based on the latest high-resolution model package, it appears
the Alleghenies are first to get into the expanding warm sector.
This ultimately favors convective intiation along these
mountains by early in the afternoon. Aided by local orographic
effects and surface-based CAPEs around 1,000 to 1,500 J/kg, a
few storms could become slightly stronger in nature. However,
the limited vertical shear should mitigate any notable severe
threat. As storms move off the terrain, updrafts are likely to
weaken while tracking toward the Shenandoah Valley. Farther
downstream, some residual onshore flow north of the front will
limit any convective threats. However, given uncertainties in
the position of this front, will maintain a slight chance for
thunderstorms during the afternoon to early evening hours.

After topping out in the low/mid 80s today (70s across the
mountains), a slightly milder night lies ahead. The wavy frontal
system across the region begins to pull away to the southeast as
a cold front. As this occurs, northeast to easterly flow returns
allowing for another round of low clouds tonight. This comes
with residual showers and some patchy fog. However, any fog
should be more intermittent in nature given the increase in
northeasterly breezes. Nighttime lows fall into the mid 60s to
low 70s, slightly cooler in the mountains.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
On early Thursday morning, Hurricane Erin will be in the process
of recurving around a subtropical ridge. Its position is
forecast to be well offshore of the Carolinas. However, the
expansive nature of this hurricane coupled with interactions
with the nearby synoptic front will lead to a further expansion
of wind fields. This becomes most evident closer to the
Chesapeake Bay where north-northeasterly winds pick up in
strength. Gusts up to 20 to 30 mph are possible, perhaps up to
35 mph over far southern Maryland. The net northerly flow will
aid in another cool down with high temperatures in the mid 70s
to low 80s (60s to low 70s for the mountains). This comes with
mostly cloudy skies and passing showers which track toward the
southwest. However, do anticipate plenty of dry time given
showers should be more scattered in coverage. Any thunder
chances are relegated to the Alleghenies down toward the I-64
corridor.

Drier conditions lie ahead into Thursday night with northerly
gusts around 10 to 15 mph. Forecast lows will mainly be in the
low/mid 60s, with a few spotty upper 50s in the mountains and
near the Mason-Dixon Line.

As Hurricane Erin continues to pull further away from the coast
on Friday, any synoptic wind influences become less evident. The
associated longwave trough will pull out into Atlantic while the
next system tracks across Manitoba/western Ontario. Sitting in
between these features allows for a period of weak height rises.
This helps raise temperatures a bit along with increasing
sunshine. Friday`s highs push up into the upper 70s to low 80s
(5 to 10 degrees cooler for the higher terrain). Another cool
night lies ahead underneath mostly clear skies. Forecast lows
generally range from the upper 50s to mid 60s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure moves further offshore on Saturday, allowing return
southerly flow to bring warm temperatures back closer to normal
(though still only in the low to mid 80s). A potent shortwave trough
digs through the Great Lakes over the weekend. There is some
uncertainty with how much forcing reaches our area Saturday, but
there may be enough height falls, increasing moisture, and terrain
circulations to result in scattered showers and thunderstorms.
Activity is most likely to focus west of the Blue Ridge.

While there is some uncertainty in the timing, a cold front will
approach the area on Sunday. The chance for showers and
thunderstorms will be highest this day as higher dew points pool
ahead of the front. There is some potential for severe thunderstorms
given increasing wind profiles aloft. Modest instability will be the
limiting factor. Some guidance is slow to move the front eastward
Monday, but the highest chance of rain should be east of the area.
If not Monday, then definitely Monday night and Tuesday will feature
the arrival of cooler air and lower dew points. Highs Tuesday will
be in the upper 70s and lower 80s as dew points drop to the 50s if
not upper 40s under mostly sunny skies.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Most terminals continue to see IFR ceilings given the persistent
easterly onshore flow. Some places are even seeing occasional
reductions to LIFR (400 feet) at times. Lift within the
saturated layer is even producing light drizzle at times.
Restrictions likely remain in place through the early afternoon
before the stalled frontal system eventually returns northward
as a warm front. Some afternoon convection is possible across
the higher terrain. A few of these storms could approach the
I-81 corridor. Thus, have maintained a PROB30 group for
thunderstorms at KMRB between 19-23Z. Otherwise, scattered
showers may impact other terminals downstream.

The frontal system pulls away as a cold front overnight which
allows for a return of onshore flow to the area. Low ceilings
(IFR) are possible again tonight into Thursday morning. However,
these should be shorter lived as winds turn more north-
northeasterly in response to the track of Hurricane Erin well
offshore. North-northeasterly gusts across the more eastern
terminals could push into the 20 to 25 knot range on Thursday.
Winds remain slightly elevated into Thursday night, but with VFR
conditions. Tranquil weather is expected on Friday as weak high
pressure builds in.

VFR conditions are likely to prevail this weekend. Will need to
monitor the development of thunderstorms each afternoon that could
bring brief periods of sub-VFR to any affected terminal. Sunday
looks to have the highest chances for strong thunderstorms as a cold
front tracks across the area.

&&

.MARINE...
While sub-advisory caliber winds are expected through the day, a
ramp up is likely as the cold front exits and the influence of
Hurricane Erin offshore. This leads to a need for Small Craft
Advisories across all waters late Wednesday into Thursday. The
north-northeasterly gusts will be highest over the southern
Chesapeake Bay (25 to 30 knots). There is even perhaps times
where the gusts near gale force. This aspect of the wind
forecast will continue to be monitored. Some lingering 20 knot
gusts are possible the first half of Friday before diminishing
into the evening and night.

Winds are forecast to remain below SCA levels this weekend, though
each evening will bring the opportunity for southerly channeling in
the middle Chesapeake Bay and lower Potomac River. This could bring
a few hours of near-SCA winds to those areas. Additionally,
scattered showers and thunderstorms each afternoon to evening will
pose a threat to mariners from gusty winds and lightning
strikes.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies will steadily rise for the next 24 hours as
onshore flow strengthens in response to Hurricane Erin tracking
east of the area. While some coastal flood headlines are in
effect now, additional advisories are likely needed to account
for high tides through tonight. The winds turn northeast then
north by Thursday morning, which will allow water levels to
rapidly drop Thursday afternoon into Friday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until 8 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 2 PM EDT this afternoon for
     MDZ018.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...BRO
NEAR TERM...BRO
SHORT TERM...BRO
LONG TERM...KRR
AVIATION...BRO/KRR
MARINE...BRO/KRR
TIDES/COASTAL FLOODING...BRO