474
FXUS61 KLWX 251857
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
257 PM EDT Wed Sep 25 2024

.SYNOPSIS...
Light rain and cloudy conditions persist through today and into
tonight. Weak front arrives Thursday with mostly dry conditions
expected. Hurricane Helene moves further north into the Gulf of
Mexico and into the southern Appalachians and Tennessee River
Valley over the next several days. Widespread rainfall possible
Friday, especially across parts of Central Virginia. High
pressure builds in from the north this weekend, but rain chances
remain into next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Off and on showers will persist through the remainder of the
day. Moderate to heavy rain may be possible at times for areas
along and west of the Blue Ridge. Cannot rule out a rumble of
thunder but confidence is low in this coming to fruition
locally. Rainfall amounts of 1 to 2 inches will be possible for
the aforementioned areas through tonight. Given the ongoing
drought concerns and the more prolonged periods of rain, the
flood threat should be fairly limited and localized heading into
early Thursday.

Afternoon highs will top out in the upper 60s to low 70s for
most areas aside from the Allegheny Front where low 60s will be
more common. For tonight, lows will only drop a few degrees
given the increased cloud coverage across the area.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A brief relief from the precipitation will take place on
Thursday as southerly flow builds in and a quick break between
the departing frontal boundary and the impacts associated with
Hurricane Helene. Cannot rule out a few isolated showers
Thursday afternoon but most areas should remain fairly dry for
the majority of the day.

Per the NHC forecast, Hurricane Helene makes landfall along the
northeast Gulf Thursday evening, then moves north toward the TN
Valley / Southern Appalachians Thursday night. Deep tropical
moisture moves into our area by early Friday morning, bringing
widespread rain/showers to central/northwest VA and surrounding
highlands. Models have trended weaker with a surface low moving
south from Canada, meaning most of the area is likely to see
high rain chances Friday into Friday night. The heaviest is
going to be along the eastern slopes of ridges south of
I-66/US-48, and in Central VA where 2-4" of rain is possible
with localized higher amounts. Localized flooding is possible
but confidence is low at this time given the track uncertainty.
The main circulation of Helene retrogrades west towards the Mid-
South as it interacts with the cutoff low, keeping the better
tornado environment to the west of the forecast area. Continue
to monitor our local forecast and the National Hurricane Center
as Helene continues to move further north.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
The remnants of Helene will continue to drift over the Tennessee and
lower Ohio River Valleys while being absorbed into a large cutoff
low this weekend. The cutoff upper level low will gradually fill and
weaken as over the Mid-South through early next week. With the low
nearby, and pieces of embedded energy pivoting around it, expect
increased chances for showers and perhaps a few thunderstorms
throughout the weekend into early next week. Some uncertainty
remains in regards to the placement of the cutoff low and
timing/placement of embedded pieces of energy pivoting around it.
The influence of surface high pressure over New England wedging
south along the Appalachians will play into the overall coverage of
precipitation as well. Overall not expecting any washouts this
weekend although abundant cloud cover and intermittent shower
chances will continue as remnant moisture from Helene overrides the
wedge high overhead.

The upper level low continues to fill and push to the east Monday
into Tuesday. Moist flow will likely remain with incoming troughing
and an associated cold front pushing out of the middle part of the
country. This deepening trough continues to show up on 12z
deterministic/ensemble model suites today and over past couple of
days. It`s exact amplitude, timing, and whether or not it cuts
off remains in question. Regardless, there is the potential for
a strong frontal passage during the Tuesday and Wednesday
timeframe providing additional shower and thunderstorm chances.
Drier conditions look to return wit high pressure by the latter
half of next week.

Due to the added cloud cover and cool air wedge, temperatures are
expected to remain at or below normal through Tuesday . Highs will
be around 80 Saturday with 60s and 70s Sunday into early next week.
Lows will fall into the 50s and 60s.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Sub-VFR conditions look to continue through Thursday as a
series of slow moving fronts cross the region. Still dealing
with a pseudo CAD wedge and a weak warm frontal boundary
gradually lifting north from central and southern VA. MVFR to
IFR (brief periods LIFR) ceilings will prevail through the
remainder of the day especially at terminals west of a line from
KBWI-KRIC. Light showers/drizzle will continue to work through
the corridor over the next 2-4 hours between now-21z/5pm.
Further west of KMRB and KSHD will continue to monitor the
progression of a line of moderate to heavy rain and embedded
thunderstorms working north along the incoming cold front from
the Ohio River Valley. This activity will gradually push east
later this evening and into the overnight hours reinforcing
reductions in vsbys and cigs across the area. IFR to possibly
LIFR CIGs are likely tonight into Thursday morning.

Conditions slowly improve Thursday as weak southerly flow ensue with
mid-level ridging overhead. Conditions should dry out for the
corridor terminals with perhaps a few showers and thunderstorms, mainly
at terminals along and west of a line from KMRB to KCHO/KSHD.
Ceilings should remain MVFR in these locations(IFR possible at
CHO for most of the day) with VFR further east. Winds will
remain light out of the east and southeast at 5-10 kts.

Sub-VFR ceilings are likely Thursday night into Friday as the
remnants of Helene work into the southern Appalachians. Widespread
rainfall is expected from this system with the heaviest at terminals
south of the corridor and down into southwest portions of VA.

Sub-VFR conditions are likely at times over the weekend into early
next week as remnant moisture from Helene continues to push over the
region. Wedging high pressure will keep abundant cloud cover and
shower chances in place through at least Monday. A few thunderstorms
are possible during this time.

&&

.MARINE...
A Small Craft Advisory goes into effect through this evening for the
Chesapeake Bay and surrounding rivers/tributaries, and the Lower
Tidal Potomac. Expect winds to gust up to 20 knots into tonight.

Winds will fall back below SCA levels tonight and remain at sub-SCA
levels through Thursday afternoon. The remnants of Helene approach
the area from the south late Friday into Saturday, with a surge of
east to southeast winds likely ahead of the tropical system. SCA
conditions are likely to develop Friday afternoon, and continue into
the weekend.

Depending on the evolution of low pressure approaching from the
OH/TN Valleys this weekend, onshore flow could be strong enough to
prompt the issuance of Small Craft Advisories at times. Uncertainty
is moderate to high at this time, and ranges from marginal SCA to
near gale-force.

&&

.TIDES/COASTAL FLOODING...
Decreasing astronomical tides will lead to slightly lower (though
still elevated) tides, with bouts of minor flooding likely around
times of high tide through Friday morning. The higher of the two
daily tides is during the overnight/early morning hours, and would
be susceptible to the most widespread minor to perhaps locally near
moderate tidal flooding.

By Friday, Helene will orbit around an upper low to the southwest as
high pressure holds firmly to the north. This pattern results in
enhanced onshore east to southeast flow at times through the
weekend, and has the potential to result in multiple rounds of
widespread minor to moderate tidal flooding through at least
Sunday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 6 AM EDT Thursday for DCZ001.
MD...Coastal Flood Advisory until 5 AM EDT Thursday for MDZ011.
     Coastal Flood Warning until 6 AM EDT Thursday for MDZ014.
     Coastal Flood Advisory until 1 AM EDT Thursday for MDZ016-017.
     Coastal Flood Advisory until 2 AM EDT Thursday for MDZ018.
     Coastal Flood Advisory until 9 AM EDT Thursday for MDZ508.
VA...Coastal Flood Advisory until 6 AM EDT Thursday for VAZ054.
     Coastal Flood Advisory until 1 AM EDT Thursday for VAZ057.
WV...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for
     ANZ531>534-537-538-542-543.

&&

$$

SYNOPSIS...ADM/KRR/EST
NEAR TERM...ADM/KRR
SHORT TERM...ADM/KRR
LONG TERM...EST
AVIATION...DHOF/ADM/EST
MARINE...DHOF/ADM/EST
TIDES/COASTAL FLOODING...LWX