Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 131833
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
233 PM EDT Fri Oct 13 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/...
An onshore flow will continue around high pressure over New
England through tonight. Low-level moisture will remain trapped
underneath the subsidence inversion...resulting in more low
clouds along with areas of light rain/fog and drizzle. The best
chance for any light rain or drizzle will be along and east of
the Blue Ridge Mountains late this afternoon and tonight.

Across the central Shenandoah Valley into the Potomac
Highlands...the marine layer will be a bit thinner and with a
downsloping flow off the Blue Ridge Mountains there will be some
more breaks of sunshine this afternoon.

Max temps will top off on the 60s for most locations this
afternoon and min temps tonight will be in the 50s. Fog may be
locally dense tonight...especially along the ridge tops and
sheltered Valleys in the Shenandoah Valley and Potomac
Highlands.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
High pressure will extend into our area Saturday before moving
offshore Saturday night into Sunday. The building high pressure
will cause the marine layer to dissipate Saturday. Morning low
clouds and fog/drizzle will give way to sunshine...but it may
take a while into the afternoon hours for locations along/east
of the Blue Ridge Mountains. For locations farther west...clouds
and fog should dissipate in the morning. Max temps will be in
the 70s Saturday for most areas.

Mild conditions will persist Saturday night with a southerly
flow. A cold front will approach Sunday morning before passing
through later Sunday afternoon through Sunday night. Unusually
warm conditions are expected ahead of the boundary Sunday with
max temps in the 80s for many locations. A few showers will
accompany the frontal passage later Sunday afternoon across the
north and west...and across the rest of the area Sunday night.
Noticeably cooler conditions are expected behind the boundary
overnight.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
A strong cold front moving east across the Chesapeake Bay could
spawn a rain shower or two early Monday in the vicinity of
southern Maryland; otherwise, high pressure will build into the
region midday Monday through Friday. Dry conditions midday
Monday through Friday.

Temperatures should fall throughout the day Monday with the high
possibly occurring early Monday morning and the low occurring
just before midnight Monday night into early Tuesday morning. We
could see temperatures falling from the middle 60s early Monday
morning, through the 50s during the day, before getting into
the lower to middle 40s by late Monday evening.

As for Tuesday, temperatures will be about 5 degrees below
normal despite plenty of sunshine.

Wednesday, Thursday and Friday will be warmer with plenty of
sunshine despite starting off chilly in the morning.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
An onshore flow will persist through tonight before dissipating
Saturday. Low clouds and areas of fog/drizzle are expected
through Saturday morning before gradually dissipating Saturday
afternoon. MVFR conditions this afternoon are expected to drop
to IFR levels for most of the terminals tonight into early
Saturday morning. Cigs will gradually improve Saturday. High
pressure will move offshore Saturday night and Sunday. A
southerly flow is expected. Areas of low clouds and fog are
possible Saturday night into early Sunday.

A cold front will pass through late Sunday and Sunday night.
Showers are possible with the frontal passage and brief MVFR
conditions cannot be ruled out. A wind shift from the southwest
to northwest is expected with the frontal passage.

VFR conditions Monday through Tuesday night. Winds northwest 5
to 10 knots Monday, becoming light and variable Monday night
through Tuesday night.

&&

.MARINE...
An east to northeast flow will continue through tonight. The
gradient has subsided...but a Small Craft Advisory remains in
effect for the Maryland Chesapeake Bay south of Drum Point and
for the Tidal Potomac River south of Cobb Island. Gusts up to 20
knots are expected across these areas.

High pressure will build overhead Saturday before moving
offshore Saturday night through Sunday. A cold front will pass
through the water Sunday night. A Small Craft Advisory may be
needed for portions of the waters Sunday and Sunday night.

Small craft advisory possible Monday and Monday night. Winds
northwest 10 to 15 knots gusts to 20 knots. No marine hazards
expected Tuesday and Tuesday night. Winds becoming northwest
then southwest around 5 knots.

&&

.TIDES/COASTAL FLOODING...
A persistent onshore flow has caused tidal anomalies around 1.5
to 2.0 feet above normal. The onshore flow will continue to
weaken through tonight. However...the high anomalies persist
across all of the Bay so it will take a bit longer for the
anomalies to drop

Therefore...minor to moderate flooding is anticipated through
the high tide cycle Saturday morning. Coastal Flood Advisories
and warnings are in effect. Additional minor flooding is
possible later Saturday into Sunday.

&&

.CLIMATE...
A surge of warm air is expected Sunday ahead of the cold front.
We are not currently forecasting records, but we are expecting
temps to be close.

     Warm Temperature Records for October 15 (Sunday)...
     High             Warm Low
DCA  87 (1975)        67 (2008)
BWI  86 (1989, 1975)  66 (1941)
IAD  88 (1989)        64 (1985)

&&

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

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 7 AM EDT Saturday for DCZ001.
MD...Coastal Flood Advisory until 2 PM EDT Saturday for MDZ016-018.
     Coastal Flood Advisory until 10 AM EDT Saturday for MDZ508.
     Coastal Flood Advisory until 8 AM EDT Saturday for MDZ011.
     Coastal Flood Warning from midnight tonight to 4 AM EDT
     Saturday for MDZ014.
     Coastal Flood Advisory until midnight EDT tonight for MDZ014.
     Coastal Flood Advisory from 4 AM to 5 PM EDT Saturday for
     MDZ014.
     Coastal Flood Warning until 1 PM EDT Saturday for MDZ017.
VA...Coastal Flood Advisory until 2 PM EDT Saturday for VAZ057.
     Coastal Flood Advisory until 7 AM EDT Saturday for VAZ054.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight 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
CLIMATE...BJL
EQUIPMENT...BJL



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