859
FXUS61 KLWX 161402
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1002 AM EDT Fri Aug 16 2024

.SYNOPSIS...
Dry weather continues for most locations outside of the mountains
through this evening as high pressure pushes offshore. A warm front
will lift into the region this evening before pushing north tonight.
Shower and thunderstorm chances increase this weekend with a cold
front slowly crossing the region. The front will push east of the
region Monday with cool Canadian high pressure settling in Tuesday
into the middle of next week.


&&

.NEAR TERM /THROUGH TONIGHT/...
It`s a day of transition as we get back to the commonplace of
summertime heat and humidity as well as the daily threat for showers
and thunderstorms. Weak upper level ridging over the Mid-Atlantic
and surface high pressure will continue to push offshore today with
an incumbent area of low pressure and warm front approaching from
the Great Lakes and Ohio River Valley. As a result, expect an uptick
in mid to high level clouds east of this Blue Ridge this morning and
into the afternoon with showers further west. As the afternoon
progresses, expect increasing coverage (scattered to numerous) for
showers and thunderstorms over Alleghenies due largely in part to
shortwave energy shifting east from the Ohio/Tennessee River Valley
and increased diffluent upper level flow aiding in a bump of low
level moisture across the region. Areas east of the mountains will
likely remain dry through this evening with any shower and
thunderstorm chances holding off until late evening and overnight as
a southerly low level jet develops and warm front lifts through the
region.

The severe weather threat today appears to be low with the highest
instability values remaining along and west of the Appalachians.
Even with that said, one or two strong storms could be on the
stronger side of things although cloud cover should help in being a
limiting factor. The primary threat with storms today will be
locally heavy rainfall. This is especially true west of Blue
Ridge where several rounds of shower and thunderstorm activity
look to push through heading into the overnight hours. The
flooding threat remains very low given several days of dry
weather leading up to this event combined with current drought
concerns.

Temperatures today will range from the mid 70s over the mountains to
around 90 in the I-95 corridor where more sunshine will filter
through. Lows tonight will fall back into the upper 60s and low 70s
given increased moisture on southerly low level flow.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Saturday will be interesting with the area solidly in the warm
sector by the afternoon. Recent high res guidance has continued
to slow the system, and actually nearly stalls the cold front
over our area for the weekend. With a decaying MCS east of the
Alleghenies Friday night/Saturday morning, we`re presented with
a problem that our area often is: the previous day`s convection
and any lingering cloud debris in the morning/afternoon will be
key for convection. The environment appears more favorable with
around 1500-2000 J/kg of CAPE during peak heating and 30-40
kts, all with the cold front parking along the I-81 corridor.
SPC maintains a Marginal risk (1/5) for along and west of the
I-95 corridor Saturday. We will continue to monitor, but
currently looks to be a typical "conditional severe" set-up for
us.

The story will be similar Sunday with very little movement
eastward of the cold front meaning the environment won`t change
much. If anything, it appears we have more favorable shear as
the upper trough swings into the Mid-Atlantic. SPC continues
the Marginal into Sunday for I-95 and east.

Along with the severe threat, another concern is potential
flooding. WPC currently has most of the area outlined with a
Marginal risk (1/5) for Excessive Rainfall Saturday, and then
adds a Slight (2/5) for the Baltimore metro and northeast.
Northeast MD recently got a good amount of rain (before and
during Debby), so the signal for repeated rounds of rainfall in
this area with the cold front stalled to the west bares
monitoring.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Models continue to advertise a highly amplified hemispheric wave
pattern with a deep upper trough across the eastern U.S., while a
broad ridge remains over the Four Corners and Southern Plains. The
fact this longwave trough sits over the Eastern Seaboard is what has
shielded the coastline from direct impacts from Hurricane Ernesto.
The latest National Hurricane Center forecast track keeps this
tropical system well offshore (east of 70W). Looking more locally,
despite the surface cold front moving off the coast early Monday,
the trailing upper trough will keep convective chances around. This
comes with a mixed bag of clouds and sun. Forecast high temperatures
stay fairly close to mid-August climatology, generally topping out
in the mid 80s. For cooler conditions, the mountains will see
readings in the low 60s to mid 70s. Most opportunities for showers
and thunderstorms should wane after nightfall given the loss of
heating. Nighttime conditions turn progressively cooler owing to a
strengthening of the northwesterly flow. Low temperatures should
range from the upper 50s to mid 60s east of the Blue Ridge, to
mainly 50s off to the west.

For Tuesday through Thursday, Canadian high pressure brings a
pattern shift to the eastern U.S. With surface pressures expected to
be around 1024-1026 mb, this is easily 1.5 sigma above average. As
expected with such an anomalous anticyclone, temperatures will
return to below normal with significantly reduced humidity. On
Tuesday and Wednesday, many locations will barely crack the 80
degree mark. This comes with dew points that stay in the low/mid
50s. Strong subsidence within the column favors mainly sunny skies
each day. Heading into the night, there should certainly be a bit of
a chill in the air, particularly well west of I-95. From the Blue
Ridge westward, a number of areas drop into the low 50s with some
mid/upper 40s along the Alleghenies. For the I-95 corridor, upper
50s to low 60s are more likely.

Heading toward the latter part of the work week, a gradual warming
trend is expected. Although global ensemble box-and-whisker plots
indicate some temperature spread, the general trends support this
forecast. The dry pattern persists through Thursday, perhaps even
into Friday if the dome of high pressure lingers another day.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
VFR conditions during the day today with winds increasing out
of the south. Rain chances increase west to east today, but
precip is unlikely to reach any of the 6 main terminals until
Friday evening or later. In the event showers and thunderstorms
do reach any of the terminals, expect brief restrictions. Winds
could gust 15-20 kts Friday afternoon, as well as overnight with
the development of southerly LLJ.

Showers and thunderstorms are expected Saturday behind a warm
front and ahead of a slow moving cold front, particularly in
the afternoon and evening. Some storms could be strong to
severe. Similar to Friday, these could bring restrictions to
terminals, and gusts to 15-20 kts are possible outside of
thunderstorms before winds diminish overnight. Sunday will be
similar with no sensible change in air mass.

With the upper trough remaining overhead, the continued threat for
showers and thunderstorms may yield some restrictions on Monday
afternoon/evening. As the trough exits, winds shift from westerly to
northwesterly late Monday. Northwesterly breezes could gust up to 15
to 20 knots on Tuesday, particularly during the afternoon hours.
Expect VFR conditions on Tuesday with mainly sunny skies.

&&

.MARINE...
Winds increase out of the south on Friday and Small Craft
Advisories are in effect Friday night. SCA conditions likely continue
through Saturday afternoon and evening, and possibly into Sunday
as we remain in persistent southerly flow. Additionally,
showers and thunderstorms possible Friday and through the
weekend and could bring stronger gusts to the waters. Stronger
storms could require Special Marine Warnings on Saturday and
Sunday.

Given the lingering threat for showers and thunderstorms, conditions
may be hazardous at times over the waters on Monday, particularly
during the afternoon to evening hours. Most activity decays into the
night with winds increasing out of the northwest. A breezy
northwesterly wind on Tuesday may require Small Craft Advisories
over all waters. However, conditions will be dry, accompanied by
plenty of sunshine.

&&

.TIDES/COASTAL FLOODING...
Nearly calm winds early this morning has led to a spike in tidal
anomalies. Most locations feature such anomalies between 0.4 to 0.6
feet. With southerly warm advection ensuing through the weekend,
expect multiple opportunities for coastal flooding during high tide,
particularly at more sensitive sites (i.e., Havre de Grace,
Annapolis, and D.C. Southwest Waterfront). Based on the latest
forecast, the most likely times for Minor flooding would be the
early morning high tides (higher of the two astronomical high tides)
this weekend. Thereafter, some reduction in water levels is expected
by late Sunday into Monday as winds shift to westerly.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory from 6 PM this evening to 4 PM EDT
     Saturday for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to 4 PM EDT
     Saturday for ANZ530>534-537>543.

&&

$$

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