Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 241356
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
956 AM EDT Wed May 24 2017

.SYNOPSIS...
Low pressure will impact the region through Friday.
Weak high pressure will build over the region Saturday. Another
low pressure system will impact the area on Sunday. Weak high
pressure builds over the region next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface ridge from high pressure along the New England coast
wedges into the area this morning. However...the high will move
offshore today and an easterly flow will continue to bring
unseasonably cool conditions for this time of year.

Low clouds remain trapped underneath the subsidence inversion
across central and southern areas this morning. There are some
breaks of sunshine across northern and central Maryland. Clouds
should fill in across all areas as overrunning increases ahead
of developing low pressure over the Ohio Valley. Max temps will
range from the 50s and 60s across central Virginia where cloud
cover is expected all day to the lower 70s in northern Maryland
where breaks of sunshine are expected through midday.

Low pressure will continue to deepen across the Ohio Valley tonight
while a closed upper low moves over the sfc low. Warm air advection
will increase in the low levels tonight and a soaking rain will
move back into the Mid-Atlantic region. Rainfall amounts around
one inch are expected for many areas...but locally higher
amounts along the eastern slopes of the Blue Ridge Mountains and
Potomac Highlands are possible due to a low-level easterly flow.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
The closed upper low and the sfc low will remain stacked over the
Ohio Valley Thursday morning. Low pressure will begin to
transition over the mtns Thursday. Lapse rates will increase
by Thursday afternoon and weak to marginal instability is
expected. Although shear profiles are very weak with the sfc low
overhead enhanced lift from a neg tilted upper level trough may
result in a few thunderstorms east of the Blue Ridge mtns. The
best chance will be across central VA/southern MD especially if
sfc heating is enhanced. Temps will range from the U60s/L70s
across the Highlands to the mid to upper 70s across the
Piedmont/DC Metro and east.

The sfc low and upper low will move to the north Thursday evening.
Any thunderstorm activity should be east of the Mid-Atlantic region
Thu night as post-frontal conditions are expected into Friday.
Vorticity rounding the backside of the upper low will likely move
across the Mid-Atlantic region into Friday leading to stubborn
clouds and the chance for showers. Clouds and showers will move to
the north by Friday afternoon and the sun will hopefully peak out
before dusk. A few showers may linger along the Allegheny Front.
Temps will reach the 70s across the region Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Weak ridge of high pressure sfc and aloft will build over the
area Fri night into Sat. Despite this, model guidance show
moisture overspreading the area from the west and even generate
light QPF west of the Blue Ridge.

A low pressure system near Chicago Sun morning will travel
northeast into Lk Huron by Mon morning pushing a cdfnt through
the area Sun night. Modest height falls and sfc pressure falls
will lead to convective development Sun afternoon with severe
t-storms possible especially east of the Blue Ridge and south of
I-66 & U.S. Hwy 50.

Dry westerly flow will prevail much of next week allowing for
longer breaks of dry weather.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Drier air has filtered in from the north and east allowing for
VFR conditions across most sites this morning. VFR conditions
will continue into this afternoon before low clouds return later
this afternoon and tonight. MVFR conditions will return later
this afternoon before falling to IFR this evening. The one
exception is KCHO where low clouds will likely hang around all
day. Did allow for cigs to improve to MVFR conditions for a
period late this morning into this afternoon...but confidence
in that is low. Widespread rain will also move into the area
this evening before coming to an end early Thursday morning.
However...additional showers and isolated thunderstorms are
possible Thursday afternoon.

Winds become westerly behind departing low pressure system
Thursday night-Friday. VFR conditions expected during this
time.

Rain possible late Fri night and Sat, then showers and t-storms
likely Sun afternoon with some possibly severe especially east
of the Blue Ridge.

&&

.MARINE...
Northeast winds will turn to the east this afternoon...but
speeds should remain below SCA criteria. The gradient tightens
tonight and E winds will increase across the MD Chesapeake Bay
and Lower Tidal Potomac. Rain returns tonight and continues
through Thu morning. A SCA is in effect tonight- Thu morning.
Low pressure moves over the waters Thursday afternoon and winds
will relax. There is a chance for thunderstorms Thursday
afternoon and SMW`s can not be ruled out mainly across the
southern waters. Scattered showers expected on Friday with
breezy conditions, gusting as high as 22 kt, which would require
a small craft advisory.

Gradient winds should remain below SCA levels Fri night into
early next week, but potential for strong/severe t-storms Sun
afternoon could generate locally high winds and waves.

&&

.TIDES/COASTAL FLOODING...
An onshore flow has caused elevated anomalies today...but since
the next high tide will be the lower of the two astronomical
norms and the flow will be light...minor flooding is not
expected this afternoon. Will have to watch sensitive areas such
as Straits Point in St. Marys County because it will be close.
The onshore flow will strengthen tonight and tidal anomalies
will increase. The next high tide will be the higher of the two
and the lunar phase is at a new moon...so minor flooding is
likely during the high tide cycle later tonight into Thursday
morning.

The flow will weaken and turn to the south Thursday before
turning southwest Thursday night and eventually to the west and
northwest Friday. Significant blowout should not occur until
later Friday...so minor tidal flooding is possible during the
high tide cycles Thursday through Thursday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT
     Thursday for ANZ530>534-537>543.

&&

$$
SYNOPSIS...BJL/LFR
NEAR TERM...BJL/HSK
SHORT TERM...HSK
LONG TERM...LFR
AVIATION...BJL/HSK/LFR
MARINE...BJL/HSK/LFR
TIDES/COASTAL FLOODING...BJL


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