522
FXUS61 KLWX 051910
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
310 PM EDT Fri Jul 5 2024

.SYNOPSIS...
A cold front will approach the area from the Ohio River Valley late
tonight into Saturday. The front will bring shower and thunderstorm
chances to areas west of the Blue Ridge tonight and to areas further
east Saturday. Humidity decreases Sunday in the wake of the front
with high pressure briefly building overhead. Heat, humidity, and
daily thunderstorm chances return early next week as high
pressure pushes offshore and several weak fronts push through the
region.

&&

.NEAR TERM /THROUGH TONIGHT/...
Scattered to broken fair weather cumulus accompanied by high
clouds have developed over the area early this afternoon.
Temperatures have risen into the 90s for most of the area, with
heat indices climbing to 100-110 from along the Blue Ridge to
the Bay. Heat Advisories and Excessive Heat Warnings remain in
effect until 8PM tonight.

Convection later this afternoon will be mostly limited to south
of I-66 and west of the Blue Ridge. Based on latest CAMs, storms
are expected to initialize along terrain near and west of the
Blue Ridge.

SPC still has us in a Marginal Risk for severe storms (1 of 5)
for areas along the Blue Ridge and west, with a Slight (2 of 5)
just to the west of our CWA. An MCS that is currently crossing
Kentucky is progged to move into our area this evening (or the
remnants of it). Hires guidance such as the HRRR maintains
somewhat organized convection through the mountains and into our
area as shortwave energy passes aloft, while other guidance is
less persistent with it. Will need to monitor the MCS closely as
it evolves, as severe potential this evening will be dependent
on if enough energy from the MCS persists into our area and tap
into instability in our area despite the loss of daytime
heating. Dry air aloft could keep us capped, or contribute to
potential downbursts if the energy granted from the remnant MCS
allows us to break the cap. As such, some storms this evening
could be strong to severe.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
On Saturday, an upper shortwave and associated surface low pressure
system are expected over the Great Lakes. By Saturday morning an
associated weak cold front is expected to approach from our
west and then slowly move through the area through Sunday
morning. Guidance continues to quickly fill in the upper trough
and takes it northeast, resulting in a continuing drier trend
for Saturday west of the Blue Ridge as the best forcing leaves
with it. Scattered showers and thunderstorms remain possible
Saturday afternoon and evening with PoPs focused east of the
Blue Ridge. This based on the current progged location of the
boundary, due to westerly flow behind the boundary drying from
downsloping, and along and east of the boundary having the
better forcing and moisture from southerly flow. We`re continuing
to monitor the potential for severe thunderstorms and isolated
flooding. Currently the I-95 corridor east is under a Marginal
ERO, but only a general thunder from SPC.

Additionally, Temperatures on Saturday are expected in the low
to mid 90s for most of the non-mountainous areas and heat
indices near 100-105 east of the Blue Ridge. We`re monitoring
the heat threat which could necessitate Heat Advisories, but
appears thresholdy at this time, and only for an hour or so.
Regardless, one can expect hot and humid conditions, with the
highest heat indices in the Virginia Piedmont and along the
waters due to the higher dewpoints.

The weak boundary stalls just to our east on Sunday morning.
Brief ridging looks to keep us mostly dry on Sunday, with highs
a little cooler than Saturday, but not as humid with dewpoints
in the 60s. Any showers and thunderstorms that do develop will
be restricted to near the stalled boundary, so far southern
Maryland in our area.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Synoptically, not too much of a change in the extended as we enter
the true crux of Summer. Upper level ridging/broad high pressure
will continue it`s influence over the north-central Atlantic while
broad upper level trough/low pressure over the central CONUS slowly
progresses east mid to late next week. Meanwhile, upper level low
pressure will continue to meander off the Carolina coast Monday
before washing out toward the middle of the workweek.

This will result in an uptick of moisture across the region along
with the threat of daily diurnally/terrain driven showers and
thunderstorms. Chances will be relatively low (25-50 percent each
day) with no large scale features to point to for widespread drought
busting rain.

A cold front looks to potentially cross the area Tuesday into early
Wednesday bringing with it the highest potential for widespread
rainfall. Even here precipitation chances have been capped to 50
percent or less given some uncertainty amongst the models. Severe
weather and even the potential for flooding could be an issue on
this day given the unstable airmass ahead of the boundary. Learning
machine probabilities also highlight this concern, so we`ll continue
to monitor.

High pressure builds back in behind the front Wednesday into the
weekend. Most of the area will remain dry during this time although
a few diurnally/terrain driven thunderstorms cannot be ruled out.
Temperatures will drop back close to seasonal norms during this
period.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions prevail through early this afternoon. Later this
afternoon, isolated showers and thunderstorms could develop
along the Blue Ridge. CHO and possibly MRB could see brief
restrictions but confidence is low given the limited coverage.
Heading into the evening, another round of convection is
possible, reaching the terminals around 01z-07z west to east if
it persists east of the mountains and through the loss of
daytime heating. Given the low confidence, kept it to VCSH
mention at the most. Will continue to monitor through the
afternoon, hopefully getting a better idea of how convection
will evolve in the next few hours.

Terminals can expect scattered diurnal showers and
thunderstorms once again on Saturday, but primarily along and
east of the Blue Ridge, so MRB might miss out on the action.

Prevailing VFR conditions are expected through Wednesday as the
influence of upper level ridging remains nearby. Shower and
thunderstorm chances are expected each afternoon and evening as a
series of weak fronts push through. Sub-VFR conditions are possible
for a brief period of time in and around these storms with a focus
on terminals west of the Blue Ridge Monday and further east Tuesday
as a cold front pushes through. High pressure briefly returns
Wednesday and into the weekend ahead. W/SW flow is generally
expected at 5-10 kts with occasional gusts to around 15 kts possible
in the afternoon (both Monday and Tuesday).

&&

.MARINE...
Southerly winds prevail through tonight, with varying from southwest
to southeast over parts of the water throughout the day. Southerly
channeling is expected to produce SCA winds in the middle portion of
the Chesapeake Bay between Smith Point and Drum Point this evening.
A Small Craft Advisory has been issued for those waters through
tonight, and it may need to be expanded a bit further up the Bay
this evening if winds are stronger than forecast. Otherwise,
sub-SCA winds gusting to around 10-15 knots. Mostly dry conditions
today, then scattered showers and thunderstorms are possible this
evening. Winds diminish heading into the weekend, but stronger gusts
remain possible during any scattered showers and thunderstorms over
the waters on Saturday. Sunday should be mostly dry, but will be
dependent on where the stalled cold front sets up in relation
to the waters.

Southerly channeling looks to become a concern for portions of the
waters Monday into Tuesday as the gradient tightens between upper
level low pressure off the Carolina coast and the incoming cold
front from the Ohio River Valley. SCA level winds return Tuesday
into Wednesday in the wake of the cold frontal boundary. High
pressure builds over the waters later next week.

&&

.TIDES/COASTAL FLOODING...
Generally light southerly to southwesterly flow will result in
elevated tide levels through the weekend. Vulnerable shoreline may
come close to minor flooding during the early morning high tides.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Heat Advisory until 8 PM EDT this evening for DCZ001.
MD...Heat Advisory until 8 PM EDT this evening for MDZ003>006-008-
     011-013-014-503>508.
     Excessive Heat Warning until 8 PM EDT this evening for
     MDZ016>018.
VA...Heat Advisory until 8 PM EDT this evening for VAZ025>031-
     036>040-050-051-053-054-501-502-505>508-526-527.
     Excessive Heat Warning until 8 PM EDT this evening for
     VAZ055>057.
WV...Heat Advisory until 8 PM EDT this evening for WVZ051>053.
MARINE...Heat Advisory until 8 PM EDT this evening for ANZ530.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ534-543.

&&

$$

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