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000
FXUS61 KLWX 110127
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
927 PM EDT Wed Apr 10 2024

.SYNOPSIS...
A frontal system will approach from the west through Thursday.
Potent low pressure and its associated cold front will cross the
area Thursday night. High pressure will return Friday night
into Saturday, then another frontal system may approach Sunday
into Monday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Weak PVA and isentropic ascent are resulting in a couple areas
of light showers across central Virginia/far southern Maryland
and far western Maryland. However, low levels are still
relatively dry, and deeper moisture and stronger forcing are
still well west of the area, ahead of low pressure in the lower
Mississippi Valley. Therefore any showers will be light
overnight with isolated to scattered coverage. A large period of
time should be dry for most areas though. Some more organized
shower activity may approach the Appalachians toward daybreak.
With mostly cloudy skies in place, another very mild night is in
store with temperatures only falling to the mid 50s to lower
60s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
Rain chances increase further Thursday morning as a frontal
system inches closer to the region, but the bulk of
precipitation likely arrives Thursday afternoon. Strong
southerly winds are expected to develop ahead of the approaching
cold front, which could reach 25 to 35 mph or so.

The upper trough that is currently digging into the MS River
Valley will lift northeastward towards the Great Lakes, becoming
negatively-tilted into Thursday evening/night. Given the amount
of pre-frontal showers and clouds, instability looks to be hard
to come by, especially with the timing looking to be later in
the evening into Thursday night. However, given height falls
aloft and anomalous low-level moisture, 200-400 J/kg ML/SBCAPE
still looks achievable. This, combined with increasing low-level
flow to 50+ kts at a few thousand feet AGL (especially late at
night Thursday into early Friday morning) could be enough for
low-topped convection capable of bringing down damaging wind
gusts or spinning up a brief tornado or two. The greatest
potential for any severe weather appears to be Thursday night.

Along with all of this, given the very warm and moist air mass
in place, these storms will be capable of very heavy rainfall
as well. Ensemble guidance suggests that PWAT values could be in
the 1.75-2+ inch range. While the period of heaviest rainfall
should move through rather quickly, there could still be an
isolated flooding threat, particularly in areas of poor
drainage/lowered FFG given recent rainfall.

Given the strong LLJ at a few thousand feet, the crest of the
Blue Ridge Mountains in VA as well as along and west of the
Allegheny Front will likely experience downsloping gusts to 50
MPH (from a S/SE direction) Thursday into Thursday night.

For Friday, the primary trough will swing through the region.
This will bring with it the chance for additional showers and
thunderstorms, especially first thing in the morning when the
LLJ/forcing are strongest. Additionally, cooler temperatures
and gusty southwest winds can be expected on Friday. Winds will
most likely be around 20 to 30 mph with gusts up to 45 mph
possible, especially in showers. Highest winds will be for
those in the western portions of the forecast area, especially
at higher elevations. High temperatures will be a few degrees
cooler than previous days with temperatures in the 60s for most,
with those west of the Blue Ridge Mountains in the upper 40s to
upper 50s.

Conditions begin to dry out more by the late evening to the
early overnight hours Friday night with lows in the upper 30s
for the mountains and 40s to around 50 further east.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
A departing low pressure system to the north coupled with an
approaching high pressure to the south will bring gusty winds
across the area for the weekend. Wind Advisories may be needed
Saturday, especially along and west of the Blue Ridge for the
potential for 40+ knot wind gusts. Mostly sunny skies are
expected for the day with highs in the 60s for most areas with
mid to upper 50s expected along the Allegheny Front. Winds will
diminish slightly by the evening hours with overnight lows
dropping down into the mid to upper 40s with mostly clear skies.

By Sunday, a surface low pressure system will move in across the
Great Lakes with an associated warm front crossing the area locally.
A few light showers will be possible, mainly across the northern
third of the area depending on the placement of the warm front.
Highs will rise into the mid to upper 70s for the afternoon
hours with winds remaining elevated (gusts 20-30 knots) but
weaker than Saturday`s expected winds.

A cold front is expected to stall just off to the north of the area
by Monday and continuing through Tuesday, leading to some low
PoPs both days for mainly the western areas. Highs will be in
the mid to upper 70s to even some low 80s across central VA and
southern MD for the afternoon hours both days. Overnight lows
will drop down into the 50s to low 60s each night with winds 10
to 15 knots.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
VFR conditions are expected through most of the night. Sub-VFR
ceilings approach around or just after daybreak, except a few
hours earlier at CHO. Isolated to scattered light rain showers
are possible overnight, but not enough chance of an impact to
include in the TAFs.

CIGs lower further and shower chances increase Thursday, with a
few thunderstorms and LLWS possible as well as a LLJ
strengthens. The strongest LLJ should pass overhead late
Thursday afternoon into very early Friday morning, and this is
when convection may be most likely. However, with forecast
instability to be weak, confidence is not high enough to include
thunder in the TAFs yet.

Otherwise, light S/SW flow is expected through tonight AOB 10
kts, increasing to 10-20 kts with gusts to 30 kts Thursday into
Thursday night. Convection may bring down stronger winds given
50+ kts a few thousand feet AGL Thursday night. Winds turn to
the west Friday but remain elevated/gusty, with additional
showers or a thunderstorm possible as an upper trough swings by.
VFR conditions should return Friday afternoon/night as drier
air moves in behind the low/trough.

VFR conditions are expected Saturday into Sunday with gusty westerly
winds 25 to 30 knots throughout the afternoon and evening hours
especially. KMRB and terminals further west towards the Allegheny
Front may gust 40 to 45 knots at times depending on the
strengthening pressure gradient over the area. Some light showers
may allow for brief sub-VFR conditions during the afternoon
Sunday.

&&

.MARINE...
Light S/SW winds are expected through early Thursday morning,
though a few gusts of 15-20 kts are possible during the second
half of the night. Winds are expected to increase Thursday into
Thursday night, 15 to 25 kts with gusts to 30 kts. While there
is some uncertainty in boundary layer mixing Thursday morning
and resulting gusts, there is enough agreement in computer
guidance that the start of the Small Craft Advisory has been
moved up to 8 AM.

Despite a very strong LLJ, warmer air over cooler water should
preclude widespread or persistent gale conditions outside of
showers and thunderstorms Thursday afternoon through Friday,
though this may need to be re-evaluated if frequent shallow
convection is able to bring down those the stronger winds from
just above the surface. A Gale Watch is in effect Friday night
into Saturday when stronger large scale flow may result in more
widespread or persistent gale conditions.

Small Craft Advisory caliber winds are expected both Saturday
and Sunday, with gales possible Saturday. Westerly winds gust
25-35 knots over the waters on Saturday before shifting to
southerly on Sunday and gust 15-20 knots.

&&

.TIDES/COASTAL FLOODING...
Southerly flow will increase through Thursday night. Light flow
will lead to a gradual increase in tide levels through tonight,
then stronger flow and approaching strong low pressure will
result in a more significant increase Thursday into Thursday
night. The highest tides are expected late Thursday night
through Friday morning, and this is when widespread minor to
localized moderate tidal flooding would be most likely. However,
if onshore flow is a bit stronger, tides could easily end up a
foot or so higher than currently forecast. This would result in
more widespread moderate tidal flooding (perhaps as early as
late tonight, with near major for the most vulnerable areas).
Coastal flood headlines are being updated this evening based on
the latest forecast.

Westerly flow should cause a decrease in tide levels Friday
afternoon into Saturday, though the flow is west instead of
northwest which may result in some residual elevated water
levels sloshing around the Chesapeake Bay and tidal Potomac
River a little longer than is typical behind a front.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Watch from Friday morning through Friday
     afternoon for DCZ001.
MD...Wind Advisory from 11 AM to 11 PM EDT Thursday for MDZ001.
     Coastal Flood Advisory from 6 AM Thursday to 2 AM EDT Friday
     for MDZ014.
     Coastal Flood Watch from late Thursday night through Friday
     afternoon for MDZ014.
     Coastal Flood Advisory from 2 AM Thursday to 2 AM EDT Friday
     for MDZ017.
     Coastal Flood Watch from late Thursday night through Friday
     morning for MDZ017.
VA...Coastal Flood Watch from Friday morning through Friday
     afternoon for VAZ054.
     Wind Advisory from 6 AM to 8 PM EDT Thursday for VAZ503.
     Wind Advisory from 2 PM Thursday to 2 AM EDT Friday for VAZ507-
     508.
WV...Wind Advisory from 11 AM to 11 PM EDT Thursday for WVZ501.
     Wind Advisory from 6 AM to 8 PM EDT Thursday for WVZ505.
MARINE...Small Craft Advisory from 8 AM Thursday to 6 PM EDT Friday for
     ANZ530>543.
     Gale Watch from Friday evening through Saturday afternoon for
     ANZ530>543.

&&

$$

SYNOPSIS...DHOF
NEAR TERM...ADS
SHORT TERM...DHOF
LONG TERM...ADM
AVIATION...ADS/DHOF/ADM
MARINE...ADS/DHOF/ADM
TIDES/COASTAL FLOODING...DHOF