-- Discussion containing changed information from previous version are highlighted. --
992
FXUS61 KLWX 231405
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1005 AM EDT Thu May 23 2024

.SYNOPSIS...
A cold front will drop into the Mid-Atlantic through tonight,
then return northward as a warm front Friday. The front will
then meander north to south over the weekend, before being
overtaken by a stronger cold front Monday. High pressure looks
to build toward the area by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
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A residual surface trough responsible for last night`s activity
is continuing to spawn light showers across areas mainly east of
U.S. 15. There has certainly been a downtick in intensity of
such showers given no lightning in the past couple of hours.
Expect this activity to continue to press northeastward in time
before exiting into northeastern Maryland by late this morning.

Regarding the current thermodynamic profile as seen on the 12Z
IAD RAOB, some elevated instability is present in the 800-400 mb
layer. Additionally, the flow in the mid-levels is fairly
healthy while running in the 35 to 45 knot range. However, much
of the subsequent convection will depend on how quickly the area
can clear out.

The exact timing and extent of clearing remains a bit uncertain,
and will dictate the amount of instability that will rebuild
ahead of the next round of potential showers and thunderstorms.
Subsidence and a lack of stronger instability in the wake of the
morning activity will likely suppress convective initiation
through much of the afternoon. By late afternoon into this
evening, however, a stronger mid/upper wave and surface cold
front approach from the west. Mid-level flow attendant to this
wave looks strongest late this afternoon, with the highest
700-500 hPa flow split into two pieces - one over southern VA
and the other across northern PA. Still, effective shear around
30 kts combined with the forcing along the front will likely
result in a few clusters of semi-organized multicells or bands
of thunderstorms capable of producing several instances of gusty
to damaging winds and perhaps isolated/marginal hail given
modest mid-level lapse rates around 6-7 C/km. Given the
uncertainties in the extent of heating, and whether more
appreciable CAPE/convective initiation can overlap with the
better shear profiles, the severe weather threat this afternoon
and evening remains marginal. Conditionally, a more organized
band or two of thunderstorms could develop if stronger heating
is realized, or the incoming wave/front end up a bit stronger.

PWs are not overly high for late May, but the environment could
support rainfall rates around 1 inch per hour under the heavier
cells. Steering flow weakens a bit this evening, so any cell
mergers or brief training with flow parallel to the slowing
front this evening could pose a low-end flood risk. The more
robust CAMs produce localized swaths of 2-4 inches of rain, but
are rather random in their placement which is to be expected
with a modestly forced and somewhat conditional setup. If it
appears these higher totals will come to fruition and fall over
vulnerable areas with lowered FFG, a targeted Flood Watch may be
needed. The threat for this seems highest from around sunset
through late evening/midnight or so.

Otherwise, it looks like another warm and muggy day with highs
into the 80s and lows in the 60s amid light SW to W/NW flow.
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&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Shortwave ridging looks to crest over the area Friday. So,
despite the nearby front lifting back northward as a warm front,
shower and thunderstorm coverage may be rather sparse. It looks
like temperatures will be warmer Friday with more breaks of sun.

Another trough digs in from the Ohio Valley Saturday. Overnight
guidance trended a bit early in the diurnal cycle which would
lessen the convective threat somewhat, but this will be reliant
on what happens with convection upstream over the next few days.
Should the incoming wave slow down or become stronger, there may
be potential for a few strong to severe thunderstorms again. The
heavy rain threat will need to be monitored, as well, with the
meandering front nearby and rain anticipated in previous days.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Shortwave ridging will build again on Sunday keeping convective
cvrg isolated and mainly along the I-64 corridor.

Memorial Day still looks like a very active severe wx day and
the most active of all of next week. A deep upper level trough
over the Great Lks region will push a strong cold front through
the area Monday evening. Ahead of this front, widespread showers
and thunderstorms appear definite with the potential for a
significant severe wx episode given moderately strong bulk shear
values of 30-40kt, high instability, and moderately steep mid-
level lapse rates. GFS forecast soundings also indicate a
tornado threat with 0-3 km SRH of over 200 m^2/s^2, EHI of 2-4,
and high supercell composite values. The severe threat should
end by 06Z Tue with frontal passage. There could still be
instability showers Tue afternoon as upper trough axis pivots
through, but the deep moisture should have been shunted south
and east the night before.

Cooler and drier weather establishes for the middle and second
half of next week.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
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VFR is anticipated, with brief reductions possible in showers
pivoting across with a mid-level wave this morning roughly
through 16Z. Any threat for thunderstorms has become quite
minimal based on the latest presentation on radar and satellite.

Following this morning`s wave, subsidence may suppress
convective activity for much of the afternoon. It appears the
best chance for showers and thunderstorms will re-appear this
evening, most likely just after the evening push especially for
the metro terminals. Light SW winds today will become W/NW
tonight through Friday, then S Friday night through Saturday.

Shortwave ridging may suppress more substantial convection
Friday, with sparse coverage currently anticipated. Better
coverage is possible Saturday, though the exact evolution is
uncertain and will depend on the timing/amplitude of an incoming
wave that will be heavily influenced by prior day`s convection
upstream over the Ohio Valley.

Very active severe wx day appears on tap for Memorial Day with
all types of severe wx.
-- End Changed Discussion --

&&

.MARINE...
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Light south flow and showers are expected this morning,
becoming southwest this afternoon, then west to northwest
tonight through Friday. Light showers continue to track
northeastward across the area this morning. If any embedded
stronger storms were to develop, some 20 to 25 knot gusts
cannot be ruled out. Additional shower and thunderstorm activity
is anticipated this evening into tonight, with a subsequent
gusty wind threat which may require SMWs.

Shower and thunderstorm coverage looks sparse Friday afternoon
and evening, with higher coverage Saturday as winds turn back to
out of the south.

SCA conditions appear likely Sunday night through Tuesday. SMWs
are likely to be required on Memorial Day.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
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After the high tide this morning, winds shift from southerly to
westerly allowing tidal anomalies to begin decreasing.
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 10 AM EDT this morning for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...DHOF
NEAR TERM...BRO/DHOF
SHORT TERM...DHOF
LONG TERM...LFR
AVIATION...LFR/BRO/DHOF
MARINE...LFR/BRO/DHOF
TIDES/COASTAL FLOODING...BRO/LFR