485
FXUS61 KLWX 200739
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
339 AM EDT Mon May 20 2024

.SYNOPSIS...
High pressure overhead will move offshore through Wednesday. A
cold front will approach from the Ohio River Valley Wednesday
night, then cross the Mid-Atlantic Thursday. The front will
likely stall just to the south, and meander nearby through the
upcoming weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early morning satellite imagery reveals areas of fog, some
dense, developing over much of the region. A few patches of
stratus were meandering about, as well. This is due to lingering
low-level moisture in light onshore flow.

Fog and low clouds should lift a few hours after daybreak,
eventually becoming mostly sunny this afternoon. Subsidence
beneath high pressure should keep the region dry, with any very
low chances for showers likely staying west of the Appalachians.

High temperatures are expected to reach the upper 70s to lower
80s across most of the area today once the sun comes out. Low
temperatures tonight are expected to fall into the 50s with some
patchy fog or low clouds possible once again overnight.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
High pressure will move offshore Tuesday into Wednesday. Ridging
aloft will still be present Tuesday, and this may act to cap
convection. However, just enough lift from added terrain
circulations could pop a shower or thunderstorm later in the
afternoon on Tuesday mainly west of I-81 in eastern WV.

The ridge will begin to break down a bit on Wednesday, but with
the main forcing from the incoming trough/cold front still well
to the west, convection should remain isolated and generally
confined to west of the Blue Ridge late Wednesday afternoon.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
To the south of a deep upper trough tracking across Quebec will
be a series of lower amplitude waves that race toward the Mid-
Atlantic region on Thursday. As this occurs, a slow moving cold
front is expected to push through the local area by midday into
the evening hours. There is fairly strong mid/upper support with
a belt of 500-mb west-southwesterlies around 40 to 50 knots.
This is accompanied by ample right entrance region jet dynamics
within a jet streak running between 100 to 110 knots. The key
parameter that will dictate the degree of severe weather threat
is the instability. At this point, even global ensembles are
showing around 1,000 to 1,500 J/kg of surface-based CAPE on
Thursday. This would be more than adequate to support severe
convection given the extent of vertical shear in the profile.
However, as usual, the near to short term trends of cloud cover
which inhibits convective potential will need to be monitored
ahead of the event. Besides the threat for showers and
strong/severe thunderstorms, it should be a very warm day with
decent humidity owing to persistent south-southwesterlies.
Forecast highs are in the mid/upper 80s, with heat indices
approaching the low 90s. The frontal boundary eventually slides
off to the south by Friday morning.

In the wake of this frontal system, temperatures and dew points
drop off some to finish out the work week. Shower and
thunderstorm chances do return later in the day on Friday as
this boundary re-approaches the area from the south. This leads
to a period of unsettled conditions heading into the weekend.
The position of this frontal zone and amplitude/strength of
disturbances aloft will dictate the degree of threats to the
local area. General low-amplitude troughiness persists upstream
which would tend to support this semi-active convective pattern.
Daily chances of showers and thunderstorms are shown in the
forecast package for this weekend. Temperatures remain fairly
close to average for late May standards.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Fog and patchy low stratus will affect most TAF sites through
12-14z this morning. Some fog may be dense, especially for KCHO,
KMRB, and KIAD. IFR is likely for all TAF sites until an hour or
two after daybreak with light SE flow. Conditions should improve
to VFR 14-16z with continued light SE flow. Additional fog or
low clouds could develop again mainly after midnight tonight.

Prevailing VFR is expected Tuesday into Wednesday outside of any
patchy late night/early morning fog/low clouds with continued
light S/SE flow. A shower or thunderstorm could approach KMRB
late Wednesday afternoon, but otherwise it should be dry.

A slow moving cold front tracks through the Mid-Atlantic region
on Thursday. The threat for showers and thunderstorms will favor
periods of sub-VFR conditions. This is accompanied by some
degree of severe weather risk given the parameter space at hand.
The area terminals should gradually dry out from west to east
during the evening and into the night. Initial west-
southwesterly winds will give way to northwesterlies by late
Thursday into portions of Friday. This boundary does not stay
to the south very long as it returns northward as a warm front.
Ultimately this supports some additional shower and
thunderstorm chances into Friday, and thus some possible
restrictions.


&&

.MARINE...
Generally light south to southeast winds are expected through
Wednesday, though some channeling/river or bay breeze
enhancement is possible during the afternoon and evening each
day. This should stay entirely sub SCA through tonight given
high pressure moving overhead, with some marginal/sporadic SCA
gusts possible late Tuesday afternoon into early evening. By
Wednesday afternoon, the gradient tightens a bit with high
pressure more firmly offshore, raising the prospects for
channeling and SCAs.

Background winds should stay below Small Craft Advisory levels
on Thursday on Friday. However, this comes with a caveat as
strong to severe thunderstorms may impact the local waters on
Thursday, possibly into Thursday night. There is certainly a
risk of Special Marine Warnings along with a threat of frequent
lightning with any of the convection. As the cold front
responsible for this activity settles to the south on Friday
morning, winds will be out of the west-northwest. This boundary
does return northward as a warm front which may bring additional
showers and thunderstorms on Friday.

&&

.TIDES/COASTAL FLOODING...
Elevated water levels are expected to persist through the middle
of the week with persistent light onshore (S/SE) flow. Minor
flooding is likely along vulnerable shoreline particularly
during the overnight/early morning high tide cycles (the higher
of the two astronomically). The higher end of the guidance
envelope approaches moderate flooding at Straits Point and
Annapolis, but this seems unlikely given the light flow.

Winds turn offshore behind a cold front Thursday, which will
cause a subsequent decrease in water levels.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 9 AM EDT this morning for DCZ001.
MD...Coastal Flood Advisory until 7 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 3 AM EDT early this morning for
     MDZ017.
VA...None.
WV...None.
MARINE...None.

&&

$$

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