Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 121833
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
233 PM EDT Thu Oct 12 2017

.SYNOPSIS...
High pressure over New England will extend into the area through
Saturday before moving offshore Sunday. A cold front will push
into the Mid Atlantic Sunday night followed by a return to high
pressure early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure over New England will extend south toward our area
through this tonight. An onshore flow has allowed for low- level
moisture to be trapped underneath the subsidence
inversion...resulting in low clouds along with patchy
drizzle/light rain. Upper-level ridging will increase a bit this
afternoon and evening while a trough digs into the western
CONUS. This will allow for the low-level flow to veer toward the
southeast...causing warm and moist air to overrun the surface
cool air in place. Therefore...light rain and drizzle are likely
to increase in coverage...especially for locations along and
east of the Blue Ridge Mountains into the eastern Panhandle of
West Virginia and western Maryland. This is where there will be
an upslope component to the low-level flow. Areas of light
rain/drizzle are possible over the Shenandoah Valley as well but
coverage may not be as widespread this afternoon due to a
downslope flow off the Blue Ridge Mountains.

Upper-level ridging will continue to build overhead tonight and
this may shrink the marine layer a bit overnight...causing
overrunning to diminish. Therefore...coverage of rain will
likely diminish but areas of drizzle and fog will continue
overnight. Min temps will be in the 50s across most areas to the
lower 60s in southern Maryland.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
High pressure over New England will continue to extend south and
west into our area through Saturday morning. An onshore flow
will continue and moisture will remain trapped underneath the
subsidence inversion...resulting in low clouds along with areas
of light rain and fog/drizzle. High pressure will begin to move
offshore Saturday and some sun may break out as the marine layer
thins out...but confidence is low for this happening along/east
of the Blue Ridge Mountains. Max temps will be well into the
70s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
A cold front will push across the eastern Ohio Valley into the
mid-Atlantic region Sunday into Sunday night. Ahead of the front,
there is a chance for rain showers, mainly Sunday night into
Monday morning. High temperatures ahead of the front, on
Sunday, will reach the lower to middle 80s. As the front passes,
temperatures will cool late Sunday through Monday.

High pressure is expected to build into the region Sunday night
through Thursday. Dry conditions and cooler temperatures
expected Monday afternoon through Thursday.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
An onshore flow will continue to cause low-level moisture to be
trapped underneath the subsidence inversion...resulting in low
clouds along with areas of light rain/drizzle through Saturday
morning. Mainly IFR conditions are expected...but periods of low
end MVFR conditions are possible as well. Cigs should improve
later Saturday...but confidence is low at this time. Areas of
low clouds/fog may develop again Saturday night as a southwest
flow ushers in plenty of moisture.

VFR to MVFR conditions possible with any rain showers Sunday
night and Monday morning. Otherwise, VFR conditions will be
expected at the terminals. Wind southwest 5 to 10 knots Sunday,
becoming northwest around 10 knots gusts up to 20 knots Sunday
night through Monday night.

&&

.MARINE...
A pressure surge has caused gusty east to northeast winds today.
High pressure will continue to extend south and west into our
area into this evening. A Small Craft Advisory is in effect for
all of the waters. Winds should gradually diminish later tonight
through Friday...but a Small Craft Advisory remains in effect
for portions of the waters. High pressure will build overhead
Saturday before moving offshore Saturday night.

No marine hazards expected Sunday. Small craft advisories are
possible Sunday night through Monday night. Winds southwest
around 10 knots Sunday, becoming northwest 10 to 15 knots
gusts 20 knots Sunday night through Monday night.

&&

.TIDES/COASTAL FLOODING...
Onshore flow will continue through Friday. Minor Coastal
Flooding is likely. A Coastal Flood Advisory is in effect for
the Maryland Chesapeake Bay from Anne Arundel County southward
through tonight. The advisories may need to be extended north
into the Potomac River and northern Bay for the high tide cycle
later tonight. Coastal Flood Advisories will likely be needed
Friday into Saturday as well. Moderate flooding cannot be ruled
out...especially near Straits Point. A Coastal Flood Watch may
be needed for the high tide cycle Friday night.

&&

.EQUIPMENT...
The NWS 88D Sterling radar (KLWX) will be down during the day
from 7 AM through 5 PM through Saturday this week. This is for
nationally scheduled maintenance on the radome. Our surrounding
88D radars as well as FAA terminal radars will be operational
during this downtime.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory from 6 PM this evening to 2 AM EDT
     Friday for MDZ018.
     Coastal Flood Advisory from 10 PM this evening to 3 AM EDT
     Friday for MDZ014.
     Coastal Flood Advisory from 6 PM this evening to 2 PM EDT
     Friday for MDZ017.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ531>533-
     539>541.
     Small Craft Advisory until midnight EDT tonight for ANZ530-535-
     536-538-542.
     Small Craft Advisory until 6 PM EDT Friday for ANZ534-537-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...KLW
AVIATION...BJL/KLW
MARINE...BJL/KLW
TIDES/COASTAL FLOODING...BJL
EQUIPMENT...BJL



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