Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 011432

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1032 AM EDT Sat Oct 1 2016

Low pressure over Ohio/Indiana will lift north toward Michigan
today. A weak cold front will cross the area Sunday night, bringing
drier conditions for Monday. High pressure will prevail for the
middle of the week.


Cutoff area of low pressure continues to spin across the mid-Ohio
Valley. It will slowly migrate north toward Michigan today-tonight.
While the deep moisture should be fleeting, low-level flow is still
be from the east. This is resulting in areas of drizzle, with
numerous showers occurring in a theta-e ridge across the eastern
part of the area. Elevated instability has been analyzed, with a
few lightning strikes near the Bay. Have added thunder to the
forecast across the eastern part of the CWA where this instability
is expected to reside through the afternoon. There are mixed
signals how many showers can redevelop once the dry slot continues
its northeast progression.

Clearing skies to the SW should be able to work their way into
the central foothills/central Shenandoah valley and adjacent
ridges during the afternoon. However, northeast progress is
looking less promising, and have added to the cloud cover through
the day. With cloudier skies and persistent showers, high
temperatures have been lowered several degrees.

There will still be enough humidity at the surface (and on the
ground) that any clearing skies tonight would likely lead to fog
during the overnight. Have that as a part of the database.


As the upper low lifts Sunday, it will send a subtle cold front our
way Sunday night or perhaps Monday morning. Introduced a stray
shower across northern Maryland/Potomac Highlands Sunday PM. Aside
from a little vorticity, there is little convergence or forcing to
work with. There is no evidence to warrant PoPs above slight chance.
Do have a period of broken clouds, which likely will be the best
visual cue of a frontal passage.

Northwest flow behind this front Monday will scour out the low-level
moisture. Skies should become mostly sunny. Pleasant temps 70-75
during the day, 50s at night.


Nose of strong high pressure...centered over the far NE CONUS...will
extend southwestward into the mid-Atlantic and remain the dominate
influence on Mid-Atlantic weather through much of the long term
forecast. As such, expect cloudy/cool/drizzly conditions as
persistent east/northeast onshore flow develops and strengthens
Tuesday afternoon through the end of the week...resulting in a
classic/hybrid CAD scenario. Model guidance is notorious for over-
forecasting high temperatures and being too optimistic with cloud
cover in CAD scenarios. Thus, began the process of nudging high
temperatures down and cloud cover up.

Tropical Cyclone Matthew perhaps near the Atlantic coast late next
week. Even the far more aggressive GFS family has the center of
circulation off the South Carolina coast at 00Z Saturday...the end
of this forecast period. ECMWF much further south at that
it keeps center of circulation well offshore.
these extended time scales location uncertainty is extremely high.


Flight restrictions prevail across the terminals early this morning.
IFR dominates with occasional dips into LIFR. With such
variations, some amendments are likely, but overall improvement
should be slow.

As drier air attempts to filter in, ceilings/vsbys should lift. MVFR
does seem within reach, more so to the southwest. Believe clouds
will part, giving CHO VFR. Do not have high confidence of VFR
north/east of there, which would include MRB and IAD, but it is

Clearing skies late today/tonight over a wet ground with light winds
suggests that there will be fog potential overnight. International
TAFs have MVFR/IFR in place, with additional details forthcoming.

There will be a weak cold front Sunday night. However, no
anticipated restrictions anticipated. Therefore, VFR conditions
forecast Sunday through Monday.

SUB-VFR conditions...due to low ceilings...could begin to develop as
early as Tuesday afternoon, as CAD scenario becomes established in
the persistent/strengthening onshore flow. Potential for flight
restrictions remains through much of the remainder of the week.


Gusts up to 20 kt continue on the Bay/lower tidal Potomac,
including the southern reaches of the Maryland waters. Given
strong winds just off the surface, think these winds will at least
be possible through the afternoon, so have extended the SCA until
6 PM. Guidance does indicate there may be some decrease by this
afternoon. Have also added thunderstorms to the forecast, based on
recent observations and analyzed elevated instability.

East flow this morning will become south tonight. Wind speeds should
diminish to 10 kt or less by midday. Light winds continue on
Sunday ahead of a cold front. The main thing that the front will
do is swing winds to the northwest for Monday. Still do not have
gusts higher than 10 kt.

Strengthening onshore flow develops Tuesday afternoon as pressure
gradient tightens...with a small craft advisory looking probable.
Wind possible remain AOA SCA through much of the remainder of the
week as CAD remains entrenched.


Tide forecasts remain on track this morning. Will analyze headline
decisions/extensions by mid-afternoon.

Tidal anomalies continue to run around 1.5 feet above normal at most
sites...with northeasterly winds beginning to weaken a bit. Forecast
generally on track. Though, made a few changes based on

Annapolis: Left current headlines as is...While morning tide cycle
could fall short of moderate flood stage...there is still a
possibility of reaching it in the evening tide cycle. Will wait to
decide about the Coastal Flood Watch until confidence increases.
Regardless, solid minor flood expected through Sunday`s tide cycles.

Straits Point: Left headline as is...moderate flooding expected
through tonight`s high tide cycle...minor flooding expected Sunday.

Baltimore/Solomons/Dahlgren/DC/Alexandria: Left headlines as
is...solid minor flood stage over the next two cycles. Could be near
minor for Sunday`s cycles...though confidence is currently low. Will
re-evaluate at subsequent forecast cycles.

Havre De Grace: Forecast keeps tides closer to action stage over
the next two tide cycles.


DC...Coastal Flood Advisory until midnight EDT tonight for DCZ001.
MD...Coastal Flood Advisory until 8 AM EDT Sunday for MDZ018.
     Coastal Flood Warning until noon EDT today for MDZ014.
     Coastal Flood Watch until 10 PM EDT this evening for MDZ014.
     Coastal Flood Warning until 8 PM EDT this evening for MDZ017.
     Coastal Flood Advisory until 8 PM EDT this evening for MDZ016.
     Coastal Flood Advisory until 2 AM EDT Sunday for MDZ011.
VA...Coastal Flood Advisory until 8 PM EDT this evening for VAZ057.
     Coastal Flood Advisory until midnight EDT tonight for VAZ054.
MARINE...Small Craft Advisory until 6 PM EDT this evening for


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