284
FXUS61 KLWX 230745
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
345 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/...
A weak surface trough - responsible for yesterday afternoon and
evening`s showers and thunderstorms - was still evident in
surface observations early this morning roughly along the Blue
Ridge Mountains. This trough will likely sharpen some and drift
eastward toward I-95 through daybreak in response to a weak
perturbation aloft. These features coupled with elevated
instability are forecast to result in scattered showers and
possibly a couple of thunderstorms through mid-morning before
departing to the east. Lapse rates and instability aloft aren`t
particularly strong, and near-surface nocturnal stability is
present, so the prospects of severe weather through the morning
hours are relatively low.

Some clearing is expected in the wake of this morning`s
activity. 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.

&&

.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 /06Z THURSDAY THROUGH MONDAY/...
Mid and high level clouds are expected to prevent fog at the TAF
sites this morning despite the moist airmass in place. VFR is
anticipated, with brief reductions possible in showers pivoting
across with a mid-level wave this morning roughly 09-16Z. A few
thunderstorms are possible given elevated CAPE, but confidence
was too low to include with the 06Z TAFs. Amendments may be
needed for thunder or reductions in heavy showers this morning.

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.

&&

.MARINE...
Light south flow and showers are expected this morning,
becoming southwest this afternoon, then west to northwest
tonight through Friday. A period of showers and perhaps a
thunderstorm are forecast this morning. A couple gusts to near
gale-force can`t be ruled out if a stronger thunderstorm
develops. 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.

&&

.TIDES/COASTAL FLOODING...

Minor coastal flooding is possible at DC Waterfront and
Annapolis with the high tide cycle this morning. After the high
tide this morning, winds shift from southerly to westerly
allowing tidal anomalies to begin decreasing.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until 9 AM EDT this morning for MDZ014.
VA...None.
WV...None.
MARINE...None.

&&

$$

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