-- Discussion containing changed information from previous version are highlighted. --
971
FXUS61 KLWX 091339
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
939 AM EDT Thu May 9 2024

.SYNOPSIS...
A stationary boundary will reside across the area today. Troughing
will dig across the eastern US this weekend. High pressure will
build offshore early next week, with low pressure approaching
from the middle of the country during the middle of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
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Radar loop as of 9:30AM shows light rain showers tracking
northeast through the area with the heaviest precipitation
stretching from Cumberland MD down to Fredericksburg. Overall,
the severe weather threat has decreased significantly for today
with SPC removing the slight risk from our area. Stable air,
north of the frontal boundary draped across the area, will
limit severe potential, especially northeast of the area
stretching from Cumberland MD to just south of Washington DC.
The areas southwest of this line remain in a marginal risk for
severe weather with the potential to see scattered thunderstorms
this evening into tonight. Despite the severe risk decreasing
for today, the threat for heavy rain continues in the area north
of the front. South of the front, threats during potential
severe storms include damaging wind gusts of 60mph or greater
and large hail 1"+.

Previous Discussion Follows: Chances for showers will continue
through much of the morning into the early afternoon, although
coverage of these showers should be rather low. Thick overcast
will persist across the northern half of the area through the
day to the north of a stationary boundary that stretch from west
to east across the central Shenandoah Valley and central
Virginia. Less low cloud cover is expected to the south of the
boundary, which will allow temperatures to climb into the upper
70s to near 80. Further north, high temperatures in the 60s are
forecast to the north of roughly I-66/US-50.

A surface low will track from the mid-Mississippi Valley this
morning toward WV this evening. As this surface low approaches,
low-level forcing ascent in the vicinity of the surface boundary
will gradually increase, leading to increasing chances for
showers and thunderstorms. Model guidance shows that surface
based instability should remain confined to near/south of this
boundary across the central Shenandoah Valley/central VA.
Further north, no instability is expected through much of the
day, with only elevated instability developing after dark as the
surface low approaches from the west. As a result, the greatest
chance for strong to severe thunderstorms is expected to reside
in the vicinity of the boundary across the central Shenandoah
Valley and central Virginia. In those locations, model soundings
show around 1000 J/kg of MLCAPE and 50 knots of effective bulk
shear, with some limited low-level curvature in hodographs. As a
result, supercell, and all severe hazards appear possible in
that area. However, the tornado threat does appear minimal. In
terms of timing, storms may develop as early as mid-afternoon,
but the threat may persist through the evening as the surface
low and better forcing approaches from the west. Further north,
an elevated thunderstorm can`t be ruled out during the evening,
but the threat for severe thunderstorms appears to be low.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
A potent shortwave trough will track from the Ohio Valley
eastward toward the crest of the Appalachians during the day
Friday. Large scale ascent downstream of the trough axis will
lead to continued chances for showers across much of the
forecast area, with the most frequent showers expected to the
north of I-66/US-50. Temperatures will remain cool, with highs
in the upper 50s and lower 60s for most. Temperatures may be a
bit warmer across central Virginia (highs near 70), where
they`ll receive less in the way of rain.

The aforementioned shortwave trough will pass to our east
Friday night, but another shortwave will follow on its heels,
tracking into the Ohio Valley late Friday night. While showers
may linger through a portion of the night, a brief period of
clearing may move in between the two systems. If skies are able
to clear out for a time, some patchy fog may be possible in more
sheltered valleys. Overnight lows Friday night should be in the
40s for most.

Saturday should start out dry, but chances for showers will
increase during the afternoon once again as the next shortwave
disturbance approaches from the west. Chances for showers will
linger into the overnight as upper troughing builds overhead.
High temperatures on Saturday are generally expected to be in
the 60s, with overnight lows Saturday night in the 40s to lower
50s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Upper trough axis will begin to move further north of the area
during the day on Sunday. Some showers and isolated thunderstorms
will be possible, mainly north of I-66/US-50. This will be where
the better forcing is. Severe chances are limited at this time
for this particular event. Highs will be in the upper 60s to low
70s for most lower elevations, with 50s across the higher
terrain.

Drier air works in for the start of the workweek with high pressure
nearby. A mix of sun and clouds is expected with highs climbing back
up into the low to mid 70s for most areas. Moisture returns on
Tuesday and Wednesday ahead of an approaching low pressure system
from the south slowly moving further northeast. Expect on and off
periods of rain both days with isolated to scattered chances of
thunderstorms in the afternoon and early evening. Cannot rule out an
isolated severe thunderstorm with these systems, especially
Wednesday as the associated warm front continues to move further
north. Highs will continue to be in the low to mid 70s for areas
east of the Allegheny Front (60s). Lows will drop down mostly in the
60s during the middle part of the week.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
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Conditions are currently VFR at all terminals, but ceilings
should gradually drop throughout the day, becoming MVFR this
afternoon, and then IFR tonight. The exception will be CHO,
which should stay VFR through the day, before dropping to MVFR
and then IFR tonight. Showers will be possible on and off
throughout the day, and a thunderstorm may be possible at CHO
later this afternoon. During showers and thunderstorms, sub-VFR CIGs
and VSBYs are possible at all terminals.VCTS has been
introduced there to account for that possibility. A rumble of
thunder can`t be ruled out elsewhere this evening, but the
chance is far too low to mention directly in the TAFs. IFR
ceilings and chances for showers will linger through the day
tomorrow. Improvement back to VFR conditions is expected on
Saturday, but additional chances for showers will move back in
late Saturday afternoon into Saturday night.

Winds will be out of the east today, northeast tomorrow, north
tomorrow night, and then south on Saturday.

Occasional sub- VFR ceilings will be possible on
Sunday, especially for the northernmost terminals. Otherwise,
VFR conditions will persist with northwest winds gusting 15 to
20 knots at times during the afternoon. Winds turn more
southerly with VFR conditions in place for Monday.
-- End Changed Discussion --

&&

.MARINE...
Sub-SCA easterly winds are expected during the day today. These
easterly winds may near low-end SCA values for a time this
evening as low pressure passes to our south. Wind turn
northeasterly tomorrow, northerly tomorrow night, and then
southerly by Saturday afternoon.

SCAs may be needed Sunday into early Monday as a result of
strengthening pressure gradient near the waters. No other marine
hazards are expected during the long-term period.

&&

.TIDES/COASTAL FLOODING...
Southerly winds will allow for minor flooding across some sensitive
locations this morning. These levels will likely drop later today.
Additional minor flooding will be possible late tonight into Friday
morning for the high tide cycle. Levels should drop well off by
Sunday when offshore northwest flow kicks in across the area.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Coastal Flood Advisory until noon EDT today for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

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