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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 271825
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
225 PM EDT Sat May 27 2023

.SYNOPSIS...
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Dry conditions look to continue through tonight with high pressure
remaining north of the region. High pressure will slide offshore
late tonight while coastal low pressure pushes northward from the
Carolinas. Rain chances will increase Sunday and persists through at
least Tuesday. High pressure builds back in by the middle part of
next week with above average temperatures.
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&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Dry conditions are expected through this evening. Plenty of sunshine
across the area, though noticeably denser cirrostratus begins to
fill in south of I-66 this afternoon/evening. There is so much dry
air in the low to mid-levels of the atmosphere that any precip
moving into the central VA Piedmont this evening is likely to be
virga. Although, cannot rule out some drizzle or a very light
shower.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
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An extratropical low east of the Savannah will steadily move north,
moving inland along the Carolina coastline sometime over the next 12-
24 hours. This low is developing in a broad area of strong 1000-
925mb frontogenesis, and is also begin aided by a developing large
cutoff low over the Southeast U.S. To the north, high pressure
offshore of southern New England will become stretched out, though
retain its influence across that region through Monday.

The entire complex of the surface low, area of frontogenesis, and
mid/upper cutoff low will meander over the southern Appalachians and
Carolinas on Sunday, then shift toward coastal NC/VA late Sunday
into Monday. Moisture slowly advects northward into our area over
the next couple of days, however it is going to take some time to
erode the large amounts of dry air currently in place. As a result,
rain chances were reduced for most of the area Sunday, especially
north of I-66 where it should remain mostly dry (though cannot rule
out a stray shower or drizzle at times).

The best rain chances are going to be Sunday evening through Monday
night as the surface low moves into central NC/southern VA and the
main area of frontogenesis lifts north into our area. Even then, the
highest rain chances are going to be along/south of I-66, with much
lower chances near the MD/PA border. Overall the rain looks to be
light, with embedded moderate showers at times. A few thunderstorms
are possible each afternoon, though the highest chance for that is
also on Monday.

Abundant cloud cover keeps afternoon temps below normal Sunday, with
highs forecast in the mid 60s in central VA/central Shen. Valley to
lower 70s along the MD/PA border. Temps a bit more uncertain for
Memorial Day due to rain/cloud mix, though likely to also be below
normal in the upper 60s to low 70s. Overnight lows in the 50s.
-- End Changed Discussion --

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
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The extended period will be a tale of two seasons with near normal
to slightly below normal temperatures to start the period followed
by early Summer heat to round out the workweek.

Synoptically, the upper level pattern will remain fairly wavy/blocky
with a broad closed upper level low weakening over the Carolinas
drifting northeast into our region midweek. This will keep
temperatures at or below average through at least Wednesday with
periods of showers and even a few thunderstorms during the afternoon
and evening hours. No washouts are expected between this period
although considerable model spread as the low gradually fills and is
nudged to the east with the trough flattening over Canada and a
broad diffuse area of high pressure aloft building southward over
the eastern U.S. This will lend to a reduction in precipitation
chances each day starting with Tuesday afternoon and continuing into
the end of the workweek.

By Thursday and Friday, temperatures will trend upward while
precipitation chances continue to decrease. Once again, this will be
highly dependent on weakening low pressure kicking offshore and the
strength of high pressure building aloft. Although model guidance
differs consensus suggests that the high pressure system will win
out yielding warm and muggy conditions across the region.
Temperatures will head back above average Thursday and Friday with
highs approaching 90 degrees. Precipitation chances remain low, but
are not zero with a focus over the mountains and along the bay
during the afternoon and early evening hours. With the high nearby
overall forcing remains subtle at best, but something to watch with
some of the modeling continuing to drop a backdoor cold front into
the region Friday into Saturday. The front would further enhance
convection although 12z guidance suggests a FROPA beyond peak
heating time period late Friday into Saturday.

Forecast confidence in the long term periods remains moderate due to
large model spread for both precipitation chances and temperatures
within the mid and late week period.
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&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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VFR conditions are expected through tonight, with only increasing
high-level cirrus as low pressure over off the South Carolina
coastline moves northward.

Lower CIGs are expected to reach CHO late tonight, likely producing
MVFR conditions with a low chance for IFR conditions. Dry air still
in place along/north of I-66 is likely going to keep CIGs at VFR
from IAD/DCA northward on Sunday. Scattered showers at CHO, with
just light rain possible elsewhere for Sunday.

The main period for more persistent rainfall and possible CIG/VSBY
restrictions is going to be Sunday night into Monday evening as the
remnants of the surface low over the Carolinas moves into southern
VA.

MVFR to IFR cigs along with periodic showers and thunderstorms will
likely continue through Tuesday evening as closed low pressure
drifts offshore. Sub-VFR conditions may linger into the first half
of Wednesday although confidence remains low with low pressure
moving offshore and high pressure building. Higher confidence for
VFR conditions returning late week.
-- End Changed Discussion --

&&

.MARINE...
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Winds steadily increase through the afternoon as pressure gradient
over the region increases, in response to a developing area of low
pressure off the South Carolina coast and high pressure offshore of
southern New England. Gusts up to 25-30KT will be possible in the
lower bay, and around 20-25KT elsewhere. Winds diminish slightly
overnight, likely falling below SCA criteria in parts of the
northern bay and upper Tidal Potomac.

A second surge in winds is forecast Sunday morning into afternoon.
Winds fall below SCA criteria late Sunday night.

The surface low over the Carolinas drifts north through the weekend,
eventually reaching southern VA where it opens into a weak/broad
trough. Winds are forecast to be just below SCA criteria, but it is
possible some gusts up to 20KT occur in the lower bay Monday
afternoon.

SCA level winds will persists into Tuesday in northeast flow as
cutoff low pressure gradually relinquishes it`s grip over the
region. By Wednesday, the pressure gradient looks to relax, allowing
for lighter winds still from the northeast direction. These
conditions will likely continue into Thursday and Friday as high
pressure builds from the north. Winds will switch to the south and
southwest Thursday before turning to the south and southeast
Friday.
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&&

.TIDES/COASTAL FLOODING...
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Low tidal anomalies will keep tidal levels below Action Stage
at all locations for the high tide cycle this afternoon.
However, there are higher anomalies in the southern bay, which
will move up the bay tonight as winds weaken. Sensitive
locations are likely to reach Action Stage over the next 2-3
tide cycles, and tidal levels might near Minor Flood at DC
Waterfront and Straits Point Sunday afternoon.
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&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 2 PM EDT Sunday for ANZ530>532-
     538>540.
     Small Craft Advisory until 8 PM EDT Sunday for ANZ533>537-
     541>543.
-- End Changed Discussion --

&&

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