Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

000
FXUS61 KLWX 171837
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
237 PM EDT Sun Sep 17 2017

.SYNOPSIS...
Warm high pressure will remain over the eastern United States
this week. Meanwhile, Hurricane Jose is expected to track
north off the coast of the eastern United States Monday through
Wednesday. Refer to the National Hurricane Center`s website
hurricanes.gov for the latest on Jose.

&&

.NEAR TERM /THROUGH TONIGHT/...
Large scale upper-level ridge will remain over the eastern
United States while a weak upper-level trough remains situated
over New England into the Mid-Atlantic. High pressure along the
New England Coast will extend south into the Mid-Atlantic
through tonight.

The onshore flow around the high has allowed for more moisture
and it remains unseasonably warm due to the large scale upper-
level ridge. Max temps this afternoon will be in the lower to
middle 80s for most areas. This has led to some
instability...but it remains limited due to a strong subsidence
inversion. Isolated to widely scattered showers are expected
this afternoon and early evening due to the limited
instability...but much of the time will be dry and we will
continue to leave thunder out of the forecast due to the strong
subsidence inversion keeping convection low topped.

Any showers will dissipate around sunset this evening. Areas of
low clouds and fog are likely late tonight as moisture gets
trapped underneath the nocturnal inversion. Fog may be locally
dense. A light onshore flow suggests that there may be a better
chance of low clouds vs. fog east of the Blue Ridge...but
perhaps a better chance for locally dense fog vs. low clouds
west of the Blue Ridge.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
High pressure will continue to wedge into the area from New
England Monday and there will be a weakness overhead in the
large scale upper-level ridge. Therefore...more of the same is
expected when compared to recent days. Areas of low clouds and
fog will burn off by late morning...and more unseasonably warm
conditions are expected with max temps in the lower 80s across
most areas. Shower coverage will remain isolated to widely
scattered and most areas will end up dry.

Jose will move north up the Mid-Atlantic Coast Monday night
through Tuesday night. Jose is most likely to remain far enough
offshore to prevent any significant impact on our area. Outer
bands of rain will make a push toward our CWA during this time.
Will keep slight chance pops across our eastern areas. As of
now...it appears that much of the time will be dry and that most
rainfall should stay to our east. However...should Jose track
just a bit farther west then a soaking rain is possible across
our eastern areas. Will have to closely monitor the track of
Jose over the next couple days. For the latest information
regarding the track of Jose...please refer to the National
Hurricane Center`s website hurricanes.gov.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Wednesday-Friday: By 12Z Wed...Jose will have weakened to a
tropical storm and moved well north of the area. Subsidence
expected on the periphery of Jose over our area could allow
temps to spike up on Wed even with northerly winds.

By Wed night into Thur...a large upper-level high pressure
system over the Great Lakes will build eastward...but just how
far east will depend on the the future track of Jose of the New
England coast. For our region, weak high pressure is expected
in the wake of Jose for the remainder of the work week Thursday
and Friday. Temperatures are expected to average above normal
Wednesday through Friday. With northerly/northeasterly winds
expected Wed-Fri, would also expect to see some locally dense
fog set up in favored valley locations...and even the
DC/Baltimore metro areas could see locally dense fog around
sunrise (or just after) for an hour or two.

There`s a suggestion in some models of a weak backdoor cold
front poised to the north of our region early Friday. This front
will sag southward on Friday...and could bring a cooler and more
moist maritime influence to the northeastern and eastern zones
Friday. This front would dissipate late Friday.

For the weekend...surface ridge of high pressure extending from
New England into North Carolina will control the weather.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
Cigs should gradually improve to VFR levels by mid-afternoon
with cigs above 3kft. VFR conditions are likely this
evening...but more low clouds and fog are likely late tonight
into Monday morning. IFR and subIFR conditions are possible.

Cigs/vsbys should improve Monday morning. An onshore flow will
continue Monday night through Tuesday night. Low clouds are
possible during this time...especially during the overnight and
morning hours.

Expect mostly VFR conditions through the extended with IFR to
locally LIFR visibilities in early morning fog at IAD/MRB...and
MVFR/IFR fog for BWI/DCA/CHO/MTN terminals.

&&

.MARINE...
An onshore flow will continue through Monday morning...but
winds should remain below SCA criteria. The gradient will
strengthen as Jose moves north off the Mid-Atlantic coast later
Monday through Tuesday night. A Small Craft Advisory will likely
be needed for the waters during this time. A Gale Warning may be
needed for portions of the waters as well...especially across
the southern Maryland Chesapeake Bay late Monday night through
Tuesday.

Small craft winds possible Wednesday depending on how fast Jose
moves away. The pressure gradient will diminish Wednesday
afternoon...and sub advisory winds/waves are expected for the
remainder of the week.

&&

.TIDES/COASTAL FLOODING...
Onshore flow will continue through tonight...but it will be
light. Elevated water levels around one half foot to three
quarters of a foot above normal are most likely. This will cause
water levels to be close to minor flooding thresholds for
sensitive areas. Confidence remains highest for Straits Point in
St Marys County where a Coastal Flood Advisory remains in
effect. Annapolis and Washington DC will also be close
overnight into early Monday morning and this will have to be
monitored throughout this evening.

The onshore flow will strengthen a bit for Monday into early
Tuesday as Jose moves north off the Mid-Atlantic Coast. Water
levels will likely increase and there is a better chance for
minor tidal flooding...especially during the preferred high tide
overnight Monday into early Tuesday. Depending on how close the
storm gets, moderate is not impossible, but uncertainty on this
is very high at the moment.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until 3 AM EDT Monday for MDZ017.
VA...None.
WV...None.
MARINE...None.

&&

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.