Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220759

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
359 AM EDT Sun Apr 22 2018

High pressure over the Great Lakes will slowly move east into the
Northeast U.S. by Sunday night. This high will move offshore Monday.
A low pressure system will bring unsettled weather to the region
Monday night through the middle of the week.


High pressure will influence dry conditions overnight with some
cirrus clouds streaming across much of our region through
daybreak. There could be some middle level clouds along the Mason-
Dixon region, but dry conditions will linger. Temperatures
overnight will not be as chilly as recent nights with lows in the
upper 30s to lower 40s. Winds will be light and variable

High pressure will continue to dominate the day today with dry
conditions, light northeast to southeast winds, and seasonably cool
temperatures for this time in April. There should be more middle
level clouds move in across the region today as a weak disturbance
slides across us from northwest to southeast. We can`t rule out a
sprinkle or a brief shower, but for the most part, dry conditions
should prevail. High temperatures today will reach the lower to
middle 60s. A couple of degrees cooler over the ridge tops
of the Potomac Highlands and the Blue Ridge Mountains.

A weak ridge of high pressure will build back into the region
tonight after the weak disturbance departs to the southeast. Dry
conditions with clouds breaking and low temperatures dropping down
into the middle 40s will be anticipated. Winds will remain light
from the southeast.


High pressure will move off of the East Coast Monday as a cut-off
low pressure system moves up the East Coast from the Southeast
U.S. Winds will persist out of the southeast ahead of the low
pressure system. Clouds will thicken through the day Monday.
Temperatures will modify some into the middle 60s. Some light rain
could overspread the region from the southwest to northeast later in
the day Monday into Monday night. The first areas to encounter this
rain will be the central Shenandoah Valley.

As the cut-off low and a couple of pieces of upper level energy move
into the mid-Atlantic region Tuesday, additional rounds of light to
moderate rain will develop and overspread most of the region. This
rain should gradually taper to showers Tuesday night and end from
southwest to northeast. However, the ending time may be
delayed as the next upper level disturbance will be quick on the
heels of the Monday night and Tuesday low pressure system.
Temperatures will be about 5 to 10 degrees cooler Tuesday due to
cloud cover and rainfall and about 5 to 10 degrees milder Tuesday
night due to the same two factors.


Lingering shower activity will be ongoing Wednesday morning as
low pressure resides on the eastern periphery of our CWA, likely
in the vicinity of the Delmarva Peninsula. This area of low
pressure will also be receiving lift and support from the mid to
upper level troughing overhead, and associated shortwave energy
heading toward the New England states. There should be a
downward trend in rain coverage during the daytime hours on
Wednesday before another shortwave quickly on the heels of the
aforementioned features helps enhance additional shower
activity Wednesday evening. Highs and lows Wed/Wed night will
remain below normal thanks to ample cloud cover and shower
activity, reaching the low to middle 60s during the day and
upper 40s to near 50 at night.

More of a drying trend is looking likely on Thursday as we will
see weak surface high pressure build in to the region and along
with weak upper level ridging overhead and our area remains in
between the exiting system over New England and the next low
pressure/shortwave digging across the upper Midwest. Continued
slightly below normal temperatures expected Thursday and
Thursday night, maybe a touch cooler than Wednesday with a
light northwest flow and weak/brief cold air advection aloft
early Thursday.

Surface low pressure and an associated upper level cut-off low
will swing across the Great Lakes region Thursday night. There
is a good deal of global model discrepancy at this time on the
strength and timing of this feature. Operational GFS trending
more progressive and stronger, while the operational ECMWF is
slower and weaker. Regardless, ensembles do agree upon a broad
mid to upper level trough winning out once again over the Mid
Atlantic and Northeast through the first half of the weekend.
Will maintain chance POPs the latter half of Friday into
Saturday for much of the area with near normal temperatures for
late April.


VFR conditions expected overnight through Monday with light and
variable winds, becoming southeast 5 to 10 knots this
afternoon and tonight. Winds southeast around 10 knots Monday
and Monday night. MVFR conditions are possible at the CHO
terminal Monday night with some light rain approaching from
the southwest.

MVFR conditions possible at all terminals Tuesday and Tuesday night
due to light to moderate rain. Winds east 10 to 15 knots Tuesday
becoming northeast 5 to 10 knots Tuesday night.

Periodic MVFR/IFR conditions expected Wednesday and Wednesday night
with an unsettled weather pattern bringing increased rain chances to
the terminals. Light northerly winds of 10 knots or less are
anticipated. A return to VFR flying conditions forecast Thursday
into Thursday night as weak high pressure builds over the area, and
winds remain light at less than 10 knots out of the west


No marine hazards expected overnight through Monday. Winds will be
light and variable, becoming southeast around 10 knots this
afternoon and tonight. Winds southeast 10 to 15 knots Monday. Small
craft advisory conditions possible Monday night through Tuesday
night. Winds southeast becoming east 10 to 15 knots with gusts up to
20 knots Monday night and Tuesday. Winds becoming northeast
10 to 15 knots gusts to 20 knots Tuesday night.

Sub SCA conditions forecast over the waters Wednesday and
Wednesday night as low pressure crosses the Delmarva and exits
to the northeast. Marginal SCA gusts possible Thursday morning
in the wake of the exiting low pressure system, but weak high
pressure is expected to build over the waters the second half of
Thursday and into Thursday night, delivering lighter winds.


As low pressure approaches the waters from the southeastern U.S.
late Monday into Tuesday, a persistent onshore flow will
develop. This will yield increasing tidal anomalies, and
the possibility of coastal flooding toward the middle part of
the work week.




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