-- Discussion containing changed information from previous version are highlighted. --
825
FXUS61 KLWX 291415
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1015 AM EDT Wed May 29 2024

.SYNOPSIS...
A cold front will move through the area tonight. In the wake of
the front, high pressure will gradually build in from the Great
Lakes through Saturday, before retreating offshore early next
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
KLWX radar loop as of 945AM shows showers tracking east along
the Alleghenies towards the Blue Ridge. To the west of the area,
additional rain showers can be seen over West Virginia and
approaching the western portions of the forecast area. Looking
at visible satellite, cloud cover is increasing as cumulus
clouds develop west of the Blue Ridge. Sunny skies can be seen
along and east of the Blue Ridge, but cloud cover is expected to
increase in these areas late this morning into the early
afternoon. 12Z CAMs are indicating a more organized line of
showers and thunderstorms, moving through the area from 2PM to
10PM, with slightly more favorable conditions. CAPE values
nearing and exceeding 500J/kg and 30-40 knots of shear are not
overly favorable, but are slightly increased from overnight.
Will continue to monitor as the previous forecast package
remains on track with late morning to afternoon convection.

Previous discussion follows:
Most recent CAMs show these showers and thunderstorms
organizing and growing upscale in a north-south oriented line
along the leading edge of stronger forcing for ascent attendant
to the approaching mid- level shortwave. This initial line
should gradually track eastward, impacting areas to the west of
the Blue Ridge during the late morning and early afternoon
hours, and then locations to the east of the Blue Ridge during
the mid-late afternoon hours. Additional showers and storms
should develop in the wake of this initial line, and gradually
rotate across the forecast area during the late afternoon and
evening hours.

The parameter space that storms will be moving into doesn`t
look overly threatening, with only around 200-400 J/kg of MLCAPE
ahead of the initial line, and relatively weak flow in the
boundary layer. Flow does increase markedly in the mid-upper
levels, but storms should somewhat low-topped, making effective
shear values only around 20-30 knots. Strong surface heating
this morning beneath sunny skies, and rapid cooling in the mid-
levels will lead to steep low-level lapse rates (nearly dry
adiabatic in the 0-3 km layer), with somewhat of an inverted-V
profile in the boundary layer ahead of the initial line. As a
result, storms may be capable of producing gusty winds in spite
of the unimpressive CAPE/shear parameter space, especially if
they become well organized in a linear fashion. CAMs (which are
usually underdone with convective winds) show a lot of gusts in
the 30-40 knot range with this initial line of storms. Some
small hail also can`t be ruled out, given very low freezing
levels and some CAPE present through the hail growth zone. The
threat for both gusty winds and small hail should be minimized
in the wake of the initial line, within an environment
characterized by more saturated profiles. Some brief heavy
downpours may be possible with the storms today, but flooding
isn`t anticipated in an environment with low PWAT values (around
1 inch) and enough flow in the mid- upper levels that storms
should stay progressive in nature.

Any leftover showers and storms should rapidly weaken and lift
off toward the northeast this evening with loss of daytime
heating. Clouds will be on the decrease as well, and winds will
start to pick up out of the northwest as a cold front crosses
the area. Some patchy fog may be possible later tonight in some
of the most sheltered valleys, but most locations should
maintain enough wind to preclude fog formation. Low temperatures
overnight will generally be in the 50s.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Yet another shortwave trough will descend down in northwesterly
flow from the Great Lakes during the day Thursday. This final
shortwave will move overtop a very dry boundary layer, with
dewpoints only in the 40s in the wake of tonight`s cold front.
Despite the moisture starved boundary layer, ascent tied to this
shortwave should lead to an uptick in cloud cover Thursday
afternoon, and may even produce a few showers or even a brief
thunderstorm, especially across central Virginia. Highs on
Thursday will be in the low to mid 70s.

Thursday`s shortwave will progress off to the east Thursday
night into the day Friday. As large scale subsidence start to
increase in the wake of the departing trough, high pressure will
start to build in from the Great Lakes. Sunny skies and light
northerly winds are expected during the day Friday. High
temperatures will reach into the low-mid 70s, and we`ll have a
dryness to the air more typical of early spring, with dewpoints
holding in the upper 30s and lower 40s.

Clear skies are forecast for both Thursday night and Friday
night. There should be enough of a pressure gradient to maintain
a light wind across much of the area Thursday night, but
sheltered mountain valley may decouple late in the night. As the
surface high moves closer Friday night, more locations should be
able to decouple. The combination of clear skies, light winds,
and low dewpoints should lead to ideal radiational cooling
conditions, and a very chilly night to start off the month of
June. Most locations should see low temperatures in the 40s, but
cooler mountains valleys may drop back into the 30s and
potentially even see some frost.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure will nearly be overhead early Saturday
and continue to slowly move further southeast. Dry conditions with
mostly sunny skies are expected for the day with highs in the upper
70s to low 80s. By Saturday night, clouds will increase a bit with
lows dropping down into the low to mid 50s for most areas.

As the high drifts further east and a series of shortwaves moves
near the Mid-Atlantic, expect clouds to increase along with
precipitation chances to return. For now, high temperatures will be
in the upper 70s to low 80s Sunday into Monday with renewed rain and
thunderstorm chances each afternoon and evening especially. Warmer
air returns Tuesday into midweek next week, with highs climbing into
the low to mid 80s for most areas. Best chances for active, strong
storms may be Tuesday given the latest guidance. We will continue to
monitor this threat over the next several days.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Prevailing VFR conditions are expected through Friday. Showers
and thunderstorms this afternoon may lead to temporary drops to
sub-VFR conditions. Mid-afternoon looks to be the most likely
time for thunderstorms at most of the terminals, and VCTS has
been timed out as best as possible at the individual TAF sites.
Showers and thunderstorms will winds down this evening with loss
of daytime heating. Drier conditions are expected tonight
through Friday. Winds will be out of the west today, northwest
tonight into tomorrow, and then out of the north on Friday.

VFR conditions are expected Saturday into Sunday with high pressure
nearby or overhead. A slight chance for a few thunderstorms is
possible later in the day on Sunday for some of the western
terminals like KCHO and KMRB.

&&

.MARINE...
Sub-SCA westerly winds are expected over the waters today, but
SMWs may be possible as storms move over the waters later this
afternoon into this evening. A cold front will cross over the
waters later tonight, with winds shifting to out of the
northwest behind the front. Winds may near low-end SCA levels in
northwesterly flow later tonight into the day tomorrow. Lighter
northerly flow is expected over the waters on Friday.

Winds will be below SCA criteria Saturday into Sunday with nearly
calm winds on Saturday turning southerly on Sunday while remaining
light. Cannot rule out an isolated thunderstorm over the waters
Sunday afternoon/evening.

&

.TIDES/COASTAL FLOODING...
Offshore flow will continue through Thursday. This will lead to
lower water levels. No tidal flooding is expected through
Thursday, but Annapolis and DC may potentially reach Action
Stage around high tide.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...KJP
NEAR TERM...AVS/KJP
SHORT TERM...KJP
LONG TERM...ADM
AVIATION...KJP/ADM
MARINE...KJP/ADM
TIDES/COASTAL FLOODING...KJP