Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 221434
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1034 AM EDT Sun Apr 22 2018

.SYNOPSIS...
High pressure over the Great Lakes will slowly move east into
the Northeast U.S. by tonight. 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.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface high pressure will continue to dominate the day today
with dry conditions, light northeast to southeast winds, and
temperatures approaching normal for this time in April. More
middle level clouds will move in across the region this
afternoon as a weak upper level 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 upper level 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 40s will be anticipated.
Winds will remain light from the southeast.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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. Highs will again be generally in the 60s, with cooler
readings in west-central VA where rain may arrive in the
afternoon, while warmer readings towards the metro. Rain is
likely to spread across the region by late Monday night as the
system to the southwest closes in.

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 may 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.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected through Monday with light and variable
winds, becoming southeast 5 to 10 knots 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 northwest.

&&

.MARINE...
No marine hazards expected through Monday morning. 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 starts Monday afternoon through Monday
night for the middle bay and lower Potomac, and likely to expand
northward Tuesday and Tuesday night. Winds southeast becoming
east 10 to 15 knots with gusts 20 knots Monday afternoon
through Monday night, with gusts perhaps approaching 30 knots
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.

&&

.TIDES/COASTAL FLOODING...
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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 1 PM Monday to 6 AM EDT Tuesday for
     ANZ534-537-543.

&&

$$
SYNOPSIS...KLW/RCM
NEAR TERM...KLW/RCM
SHORT TERM...KLW/RCM
LONG TERM...BKF
AVIATION...BKF/KLW/RCM
MARINE...BKF/KLW/RCM
TIDES/COASTAL FLOODING...BKF



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