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321
FXUS61 KLWX 031831
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
231 PM EDT Fri May 3 2024

.SYNOPSIS...
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A backdoor cold front will sink south of the area tonight. The
boundary will return north as a warm front Sunday into Monday
before secondary cold front approaches and stalls near the area
for the middle and latter portions of next week.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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High pressure remains centered over the New England coast this
afternoon while an upper-level ridge axis is slowly moving off
to our east. An upper-level trough is building over the central
CONUS and a backdoor cold front is currently located near the
Potomac Highlands into central Virginia.

The backdoor boundary will most likely stall out near the area
through late this afternoon before eventually pushing off to
our south and west tonight as high pressure strengthens along
the New England Coast.

As convergence strengthens along the backdoor boundary into this
evening, this will combine with moisture advection (southerly
flow aloft around periphery of the high) and instability,
triggering some showers and thunderstorms over the Allegheny
and Potomac Highlands into the Shenandoah Valley. This activity
will likely advect eastward into the metro areas late this
evening and overnight. A rumble of thunder is possible overnight
as well due to limited elevated instability above the marine
layer.

Low clouds and noticeably cooler conditions are expected
overnight as the onshore flow continues behind the backdoor
cold front. Lows will be in the 50s for most areas, with upper
40s in portions of northern Maryland.
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&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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The backdoor boundary will remain to the south and west through
Saturday night while high pressure remains centered near the New
England Coast. An onshore flow will continue during this time
while warm and moist air overruns the marine layer in response
to an upper-level trough pushing into the Midwest. This will
result in plenty of clouds along with periods of rainfall and
unseasonably cool conditions. There may be some breaks in the
rain, but for most of the time near and west of Interstate 95,
there will be some rain around. Perhaps there will be some more
breaks east of Interstate 95 where the overrunning moisture may
not be quite as deep.

The overrunning moisture will deepen Saturday night into Sunday
morning as the boundary begins to push north as a warm front,
and the low-level flow develops a fetch from the Gulf of Mexico.
Therefore, more rain is expected.

The warm front will move into the area Sunday while a weak
upper-level trough axis passes through. More unsettled
conditions are expected with showers and perhaps even a couple
thunderstorms. Sunday afternoon will turn out a bit warmer and
more humid as well, but temps still near and below climo. Highs
will range from the 60s north of the boundary in northern MD
into the metro areas/eastern WV/northern VA to the 70s south of
the boundary. The upper-level trough axis will move off to the
east Sunday night while the surface boundary remains nearby.
While a few showers are possible, coverage of precipitation
should wane behind the departing trough axis. There may be areas
of dense fog overnight with plenty of low-level moisture and
light winds.
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&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
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The unsettled weather pattern is likely to continue across the
region for virtually all of next week. Nearly zonal flow aloft
favors numerous passing shortwaves that bring enhancements to the
daily afternoon showers and thunderstorms. Even at night, isolated
showers/storms are possible given the increased moisture and
lingering elevated instability.

At the surface, a stalled frontal boundary is likely to be just
north of the area Monday, slide south to around I-70 Monday night,
then be pushed back north of the area through mid week. However, any
change in the position of the stalled front could result in higher
or lower rain chances than currently forecast for some areas. A
stronger shortwave trough is forecast to cross the area Wednesday
night into Thursday, possibly bringing some heavier rainfall and
stronger storms to the area.

Afternoon highs in the upper 70s to low 80s Monday and Tuesday warm
to the mid 80s Wednesday and Thursday. Very mild overnight lows in
the 60s each night due to increased dew points and cloud cover.
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&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions are expected through late this afternoon along
with dry conditions. Low clouds will develop due to an onshore
flow with MVFR conditions developing most likely between 2 and
5Z and IFR conditions developing overnight. Showers are likely
to develop overnight, and a thunderstorm cannot be ruled out
between 5 and 9z due to elevated instability.

IFR/subIFR conditions are expected most of the time Saturday
through Saturday night along with periods of rain and drizzle.
There may be a few breaks of MVFR conditions Saturday afternoon.
More unsettled conditions are expected Sunday morning with
IFR/subIFR cigs/vsbys. Cigs/vsbys should improve some Sunday
afternoon, but areas of low clouds and dense fog may cause more
subIFR conditions Sunday night. Showers are likely Sunday with
perhaps a few showers. Precipitation coverage should wane Sunday
night, but a few showers are possible.

Unsettled weather looks to continue for the start of next week.
Scattered showers and thunderstorms are likely each afternoon, with
more isolated activity during the overnight and mostly dry in the
morning. A heavy shower/storm moving over a terminal could result in
brief sub-VFR conditions. Outside of shower/storm activity, VFR
conditions are expected.
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&&

.MARINE...
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A pressure surge behind a backdoor cold front will cause
easterly winds to gust around 20 to 25 knots into this evening.
A Small Craft Advisory is in effect.

The gradient will subside a bit overnight through Saturday, but
an SCA remains in effect over the Bay and lower Tidal Potomac
River. It will be marginal though with gusts around 15 to 20
knots. The Small Craft Advisory continues Saturday night for the
Bay as well as the middle and lower Tidal Potomac River due to
onshore flow winds ahead of an approaching warm front.

The warm front will move into the area Sunday into Sunday night.
More SCA conditions are possible during this time.

West to southwest winds around 5-10 knots at the start of next week
as the unsettled weather pattern continues. Scattered afternoon
showers and thunderstorms are likely each afternoon. Any stronger
storm could produce wind gusts to 35 knots and lightning strikes. A
weak frontal boundary dips south into the northern Chesapeake Bay
Monday night, then lifts north of the area Tuesday. Otherwise, winds
are forecast to remain below SCA conditions.
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&&

.TIDES/COASTAL FLOODING...
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Onshore flow will persist through early next week. This will
raise water levels and keep them elevated during this time,
causing minor tidal flooding for many locations. Moderate tidal
flooding is possible around Annapolis and St. Marys County with
the high tide cycle late Saturday night, and again late Sunday
night into Monday morning.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 8 AM EDT Saturday for DCZ001.
MD...Coastal Flood Advisory from midnight tonight to 5 PM EDT
     Saturday for MDZ014.
     Coastal Flood Watch from late Saturday night through Sunday
     morning for MDZ014.
     Coastal Flood Advisory from 9 PM this evening to 2 PM EDT
     Saturday for MDZ017.
     Coastal Flood Watch from Saturday evening through Sunday
     morning for MDZ017.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ530>534-
     537>543.
     Small Craft Advisory until midnight EDT tonight for ANZ535-536.
     Small Craft Advisory from 6 PM Saturday to 6 AM EDT Sunday for
     ANZ536.
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&&

$$

SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...KRR
AVIATION...BJL/KRR
MARINE...BJL/KRR
TIDES/COASTAL FLOODING...BJL