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000
FXUS61 KLWX 060757
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
357 AM EDT Thu May 6 2021

.SYNOPSIS...
High pressure will build in from Canada today. Low pressure and
its associated cold front will approach tonight before passing
through Friday. High pressure will build toward the region
Saturday through Saturday night before low pressure and its
associated warm front possibly impact the area Sunday. A cold
front will pass through Monday and high pressure will return for
the middle portion of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A northwest flow behind a cold front has ushered in much cooler
conditions compared to recent mornings. A Freeze Warning remains
in effect until 9 AM for western Highland and western Pendleton
counties, where most of the freeze conditions are expected for
elevations above 3kft. A steady wind and some stratocu clouds
will prevent any widespread frost from developing.

For the rest of today, surface high pressure will build over the
region while an upper-level trough remains overhead. The upper-
level trough will be broad today, so the dry air advection and
subsidence associated with the high will provide a dry day along
with some sunshine and cool conditions for this time of year.
Any leftover stratocu deck should thin out this morning from the
dry air advection, but there will be some high clouds as a
jetmax rotates around the trough, passing through our area this
afternoon. Max temps will range from the 40s and 50s along the
ridge tops to the 60s for most other locations.

The upper-level trough over our area will become sharper tonight
as two distinct jet streaks and vort maxes begin to phase. This
will result in low pressure that will develop near the coast of
the Carolinas (with the southern stream system), and another
low will develop over southwestern PA (with the northern stream
system). A boundary will set up between these two systems, and
an onshore flow will develop ahead of them. However, much of
tonight should be dry since the boundary and the onshore flow
will remain weak. Perhaps there may be a few showers toward
morning near the Allegheny Front. Cool temperatures will persist
with min temps in the 40s for most locations (30s in Allegheny
Highlands) along with a sct/bkn high and mid-level cloud deck.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
The upper-level trough will continue to strengthen and turn
negatively tilted as the northern and southern stream jet maxes
(see discussion in tonight period for details on those) continue
to strengthen and phase. The boundary that will be connecting
the two surface lows will pass through the area Friday, and with
strengthening dynamics, that means the onshore flow and moisture
advection will strengthen ahead of this system as well.
Therefore, showers are expected to develop, and some showers may
be locally heavy along with a possible isolated t-storm. Latest
guidance is showing MUCAPE increasing a bit due to the moisture
advection and colder air aloft from the strengthening trough.

The showers along with the clouds and onshore flow will cause
very cool conditions for this time of year with max temps in the
50s and 60s (40s in the mountains). Friday will be a wet,
dreary, and chilly day.

This system will exit Friday night, and a northwest flow will
bring more chilly conditions for this time of year. However, it
should dry out for most areas. Although a few showers may
persist in the evening near the Bay and through the night
along/west of the Allegheny Front due to an upslope flow. In
fact, some snow showers are possible along the ridge tops of the
Allegheny Highlands. There should be enough of a west to
northwest flow along with stratocu clouds that frost will not be
widespread Friday night despite the chilly conditions. However,
temps may drop below freezing along/west of the Allgheny Front.

The upper-level trough will remain over the region Saturday,
bringing more chilly conditions, and there may even be a few
showers due to limited instability and a shortwave passing
through. High pressure may briefly build overhead Saturday
night. There will be a limited period of radiational cooling
Saturday night before more clouds move in ahead of the next
system, but some frost and freeze conditions are possible near
the Allegheny Highlands and perhaps into some of the valleys
west of Interstate 95 (confidence very low at this time).

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A very cool and wet Mother`s Day is in store for the area as
overrunning rains develop ahead of low pressure center over the mid
Mississippi River Valley. Heaviest rainfall amounts are expected on
the western slopes of the Appalachians Sun afternoon and evening
where 1 to 2 of rain are possible. Rain should begin to taper off
late Sunday night as low pressure crosses the area and should exit
the area Monday morning with frontal passage.

Upper level convergence behind exiting trof will allow sfc high
pressure to build into the area Monday night through the middle of
next week supporting fair weather conditions. Showers will likely
return for the second half of next week as upper level flow
amplifies east of the MS River and broad sfc low pressure develops
over the Southeast. Large spread is seen among global models in
regards to amplitude, timing, and evolution of this trof pattern,
but anticipate an unsettled wx pattern to unfold for the second half
of next week with more rain chances.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
VFR conditions are expected through today along with northwest
winds. More VFR conditions are expected tonight, but showers
will develop Friday along with subVFR conditions (possible IFR).

A northwest flow will develop behind a cold front Friday night
into Saturday along with more VFR conditions (there may be
isolated to scattered showers around during this time). High
pressure will settle overhead Saturday night.

Flight restrictions are likely Sunday/Sunday night with low
cigs and reduced visibilities in rain. Breezy conditions likely
on Monday on NW winds behind frontal passage.


&&

.MARINE...
High pressure will build over the waters today. An SCA is in
effect for the waters early this morning, and portions of the
waters through this morning, but winds should diminish below SCA
criteria this afternoon through tonight.

A cold front will pass through the waters late Friday.
Widespread showers will develop ahead of the boundary Friday and
continue into Friday evening. An isolated t-storm cannot be
ruled out either. An SCA for northwest winds will likely be
needed for portions of the waters Friday night and Saturday.
High pressure will build overhead Saturday night.

SCA conditions are likely Sunday through Tue with the strongest
winds expected on Monday. Risk of gales remains low at this
time.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...Freeze Warning until 9 AM EDT this morning for VAZ503.
WV...Freeze Warning until 9 AM EDT this morning for WVZ505.
MARINE...Small Craft Advisory until noon EDT today for ANZ530>534-
     537>543.
     Small Craft Advisory until 6 AM EDT early this morning for
     ANZ535-536.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...LFR
AVIATION...BJL/LFR
MARINE...BJL/LFR