000
FXUS61 KLWX 100121
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
921 PM EDT Tue Apr 9 2024

.SYNOPSIS...
High pressure will remain offshore through the middle of the
week while a frontal system approaches from the west. Potent low
pressure and its associated cold front will cross the area
Thursday night. High pressure will return Friday into Saturday,
then another frontal system may approach Sunday into Monday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
EVENING UPDATE...
Some spotty showers have been observed in the area during the
afternoon and early evening, but not much precipitation has made
it to the ground. A few more isolated showers are possible in
the next few hours and a few rumbles of thunder can`t be ruled
out, but the better shower activity doesn`t arrive until after
midnight.

Previous discussion follows...
Scattered showers and a thunderstorm or two may develop in
response to the increasing heat/moisture heading into early
evening, lingering and lifting NE into the evening near a
lifting warm front. There is several hundred J/kg CAPE present,
but most of it is centered below -10 C so thunder prospects
remain a bit uncertain. Temperatures will remain mild through
the night.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
A warm front will lift through the region early Wednesday.
Showers are likely around daybreak, with perhaps an elevated
thunderstorm or two. Instability is going to be limited, so not
expecting anything strong/severe, but wouldn`t be shocked to
hear some thunder.

With height falls encroaching on the region, the warm front
actually won`t change temperatures much, especially with clouds
around. High temperatures will likely be a couple degrees
cooler on Wednesday.

Wednesday night, a few showers are possible with a weak impulse
of upper-level energy rotating around the upper ridge still
shifting off to the east. However, thinking much of the night
will be dry especially east of the Blue Ridge.

Rain chances increase quickly Thursday morning as the frontal
system inches closer to the region, but the bulk of
precipitation most 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 had been 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 may be somewhat
limited, especially with the timing looking to be later in the
evening into Thursday night. Most guidance has around 300-400
J/kg of CAPE, which when combined with a strengthening low-level
wind field may be enough to bring gusty or even damaging winds
to the surface. Deep layer shear of 50-70 knots is expected. If
anything does manage to become organized and surface-based,
damaging wind gusts are possible. This would likely be with the
main line of convection just ahead of the FROPA 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 - unusually high for mid April. 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.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
A deep upper low centered just north of the Great Lakes on
Friday will continue to allow deep, low-level moisture to reside
across the Mid-Atlantic. Showers and isolated thunderstorms
will persist through much of the day on Friday with highs in the
low to mid 60s across most of the lower elevations along and
east of the Blue Ridge. Slightly cooler conditions are expected
further west towards the Allegheny Front. Winds out of the
southwest may gust to 25 to 40 knots at times for the
afternoon. QPF totals will be fairly low on Friday, with most of
the heavier precip having occurred on Thursday. Conditions
begin to dry out more by the late evening to early overnight
hours Friday night with lows in the upper 30s for the mountains
and 40s to 50 further east.

High pressure across the deep south will begin to influence the area
by Saturday while the gusty winds will persist another day. Highs
will be in the upper 50s to upper 60s for the afternoon with minimal
chances for precipitation. Lows drop back down into the 40s to near
50 Saturday night with continued dry conditions expected. By Sunday,
a warm front associated with a low pressure system near the Great
Lakes will move into the area. This will increase moisture
availability to the area along with warmer temperatures Sunday
afternoon. Highs will climb into the low to mid 70s for most areas
aside from 60s in the mountains and along the MD/PA border. Cannot
rule out a stray shower throughout the day but a total washout is
not expected at this time.

The associated cold front will cross portions of the area sometime
early Monday and will allow for a slight increase in the potential
for a few showers across the area overnight Sunday through early in
the day on Monday. Highs may be a couple degrees warmer compared to
Sunday with winds out of the west gusting 15 to 20 knots at times.
Seasonably mild overnight lows Monday night will be in the mid
to upper 40s across most locations.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are expected through at least this evening
overall, though showers or a brief thunderstorm could result in
isolated brief VSBY restrictions. Confidence in TS remains too
low to include in the TAFs as of mid afternoon, though potential
is relatively higher at IAD/DCA 22Z-01Z or so. Light S/SW flow
is expected into tonight as shower activity becomes a bit more
widespread. Some guidance hints at patchy fog overnight into
early Wednesday AM.

SW flow becomes SE Wednesday through Thursday, with stronger
flow and some LLWS expected Thursday as a LLJ intensifies. Sub-
VFR conditions are likely especially Thursday into Thursday
night with showers and a few thunderstorms.

Sub-VFR conditions are possible Friday as showers and thunderstorms
impact the terminals through the early to middle portion of the day
before drying out by the evening. Winds out of the southwest will be
gusty (25-35 knots) throughout the day. VFR conditions return
Saturday as high pressure influences the area, but winds will
remain elevated out of the southwest.

&&

.MARINE...
Light S/SW flow is expected into Wednesday, increasing Wednesday
night through Thursday night. Despite very strong low-level flow
just above the surface, air temperatures much warmer than the
water temperatures will create near surface stability and reduce
efficient mixing, likely keeping gusts in the SCA range outside
of showers and thunderstorms through Thursday.

High-end small craft caliber winds are most likely Friday and
Saturday with an elevated pressure gradient over the waters.
Gale-force winds are possible at times, especially across the
northern waters of the Chesapeake Bay either day. An SMW may be
issued Friday as a result of thunderstorms crossing the waters.

&&

.TIDES/COASTAL FLOODING...
At or near minor flooding of vulnerable shoreline locations is
expected through Wednesday. Thereafter, a marked increase in
tide levels is forecast by the guidance (especially the ETSS,
SFAS and CBOFS; P-ETSS is even higher, with ESTOFS a bit lower
in most areas). This is due to increasing southerly flow ahead
of strong low pressure passing to the west (from the Ohio River
Valley into the eastern Great Lakes). Widespread minor to
moderate flooding is looking increasingly likely Thursday into
Thursday night, before westerly winds cause a reduction in tide
levels Friday. The higher envelope of guidance shows a few
things of note: (1) moderate for 2-3 tide cycles late Wednesday
night through Thursday evening at typically more vulnerable
locations, (2) widespread moderate Thursday evening/night, and
(3) potentially major flooding for vulnerable locales Thursday
evening/night. Guidance can sometimes overdo the magnitude of
surface winds in southerly flow due to poor mixing of warm air
over cooler water, so at this time the most likely forecast
hedges a bit below the mean of available guidance.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 2 AM EDT Wednesday for DCZ001.
MD...Coastal Flood Advisory until 6 AM EDT Wednesday for MDZ017.
VA...Coastal Flood Advisory until 2 AM EDT Wednesday for VAZ054.
WV...None.
MARINE...None.

&&

$$

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