838
FXUS61 KLWX 130725
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
325 AM EDT Tue Aug 13 2024

.SYNOPSIS...
Tranquil weather conditions are expected through Thursday as
surface high pressure resides over the Northeast and Mid-
Atlantic states. Precipitation chances return by Friday and
into the weekend as a slow moving area of low pressure and
series of fronts cross the region. This system eventually exits
the coast by early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A frontal zone initially stretched out over the Carolinas has
drifted further south into the southeastern U.S. North of this
boundary, high pressure has taken charge as evidenced by light
winds across the local area. GOES-16 nighttime satellite imagery
depicts an axis of enhanced mid/high clouds pushing eastward out
of West Virginia. Regional radar imagery does show some weak
returns as light showers attempt to fall out of this deck. The
lack of rainfall being observed at upstream personal weather
stations suggests much of this is struggling to reach the
ground.

The layer of clouds overhead has kept temperatures a bit milder
than last night. As of 07Z/3 AM, most locations are reporting
temperatures in the 60s with a few spotty upper 50s in the cool
spots. The usual warm spots are inside D.C. and Baltimore where
low/mid 70s are being observed.

Heading toward daybreak, some patchy fog cannot be ruled out
over the Potomac Highlands if evaporative cooling from upstream
echoes can help raise local humidity values. Any such instance
of fog should quickly burn off as boundary layer mixing ensues.
Northwesterly flow continues in the column thanks to the deep-
layer cyclonic pattern. Within this flow regime, multiple
disturbances are embedded which should keep a steady stream of
clouds over the area. While most high-resolution models are dry,
an isolated pop-up shower could fire up over the Blue Ridge
Mountains this afternoon. Otherwise, expect a dry day over the
region with high temperatures in the upper 70s to low 80s.
Northwesterly flow also keeps dew points down which results in
much less humidity than mid-August typically offers.

High pressure remains a fixture over the area into the night.
The resultant light winds and mostly clear skies should make for
a decent night of radiational cooling. With that said, the
current forecast calls for mid/upper 50s from I-81 westward.
Those to the east are likely to see low/mid 60s readings.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Behind the conveyor belt of weak to modest impulses passing off
to the east, expect decent subsidence over the Mid-Atlantic
region on Wednesday. This will result in plenty of sunshine
along with a further warm up. Model soundings show deep mixed
layers punching into the 800-775 mb layer. In this setup, the
nature of the drier air mixing down can often lead to slightly
warmer temperatures than models suggest. As such, while
mid/upper 80s are currently being advertised, would not be
shocked to see a few 90 degree readings on Wednesday afternoon.
Another tranquil night lies ahead with seasonable temperatures.

Skies stay mainly clear to start off Thursday morning. However,
expect increasing clouds through the day ahead of the next
weather maker. Depending on the duration of unabated sunshine,
many spots could hit the 90 degree mark on Thursday. While a few
warm advection showers could reach the Allegheny Front Thursday
night, expect a mainly dry period. This shift to southerly flow
does slowly increase humidity levels heading toward the end of
the work week. Most spots will see overnight lows in the 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
On Friday, an upper trough will be exiting to the east while brief
weak upper ridging builds in over our area. Another trough digs into
the Ohio Valley/Mid-Atlantic Friday and into the weekend. The
arrival of this second trough is currently progged to coincide with
the exit of surface high pressure to the east and a low pressure
system moving into the Great Lakes/SE Canada.

The last few runs of guidance have trended a bit faster with the
arrival of warm frontal precip, and come into more agreement on
timing as well. However, there is still significant spread among
ensembles, with precip reaching the Alleghenies as early as late
Thursday night or as late as Saturday afternoon. That said, the
current most likely scenario appears to be precip moving into the
Alleghenies by Friday afternoon and expanding to the Blue Ridge and
northern Maryland through the evening. Coverage looks to be more
scattered with 30% PoPs elsewhere.

By Saturday, we`ll have better lift from the approaching trough and
ample moisture in the warm sector, so higher coverage of showers and
thunderstorms is likely. The cold front is progged to swing through
Saturday into Sunday, resulting in more widespread shower activity.
Surface high pressure is expected to build in behind the cold front
on Monday, but some showers could continue as a trailing shortwave
acts on lingering moisture.

Temperatures Friday and Saturday will depend on the timing of the
warm front, but are currently expected to be in the mid-upper 80s
for most of the area. Only a few degrees of cooling is anticipated
behind the cold front Sunday into Monday. Lows will be in the 60s
and 70s outside of the mountains for the duration of the
extended.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
VFR conditions can be expected at all terminals through Thursday
night. Any shower chances likely hold off until late Thursday
and be initially confined to the Alleghenies. With high pressure
in charge over the region, northwesterly flow persists. Some
afternoon gusts could push into the 10 to 15 knot range each day
before subsiding after dark. Southerly return flow ensues by
Thursday evening ahead of the next system.

VFR conditions are expected for most of Friday and Saturday, but
showers and thunderstorms could bring brief restrictions to
terminals, especially in the afternoon and evening hours. Winds
increase out of the south both days, and gusts to around 15 kts are
possible in the afternoon.

&&

.MARINE...
With high pressure sprawled over the region, expect mainly north
to northwesterly winds over the waterways through Thursday
afternoon. This is accompanied by a dry forecast. Given deep
mixing in the northwesterly flow regime, some afternoon gusts
could push into the 10 to 15 knot range. A shift to southerlies
is expected by Thursday evening into the night. Some channeling
effects could lead to a ramp up to around 15 knots over the
southern waters.

Winds increase out of the south Friday and Saturday and could
approach SCA criteria, especially with the aid of southerly
channeling in the afternoons. The open waters in the central and
southern Bay are the areas most likely to reach SCA criteria.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies remain low under light northwest flow. However, a
few sensitive sites may approach or reach Action stage during the
next few late night/early morning high tide cycles, such as Havre de
Grace and Annapolis, and possibly DC/SW Waterfront and Alexandria.
Winds turn southerly late this week behind a warm front which will
result in increasing tidal anomalies.

&&

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

&&

$$

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