Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 160757
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
357 AM EDT Sat Sep 16 2017

.SYNOPSIS...
High pressure will dominate the region through Sunday. Hurricane
Jose is forecast to move north along...but well offshore of...
the Atlantic coast early next week. See the National Hurricane
Center bulletins for the latest information on Jose.

&&

.NEAR TERM /THROUGH TONIGHT/...
A ridge of high pressure solidly in control of the eastern United
States early this morning. Above the ridge, there is just enough
weak warm advection and shortwave energy to induce a mid-cloud deck,
affecting much of Virginia as well as western Maryland and southwest
PA. Subsequently, where clouds are fog isn`t. That has kept fog
quite limited in coverage, focused on north-central Maryland and
parts of northern Virginia. Don`t believe that fog will be a rampant
issue through sunrise, as it does not appear as though the clouds
will be going anywhere.

For the daylight hours, believe we will have sufficient insolation
to erode the mid deck, but consequently have a cumulus field
develop. Have minimal instability...sufficient for a few showers.
Placement remains a challenge...synoptic scale guidance likely
overdone, and mesoscale guidance inconsistent. From a broader
perspective, the mountains and across northern Maryland seem to be
favored, but do not wish to go higher than 30 percent anywhere.

With little wind, airmass will remain fairly static. Perhaps we will
be a degree or two warmer than yesterday, owing mainly to daytime
heating.

Any showers should cease with sunset. Once again, fog potential will
be dictated by clouds. Don`t have a solid feel for where that
will/won`t be, but will entertain current thought of patchy fog
possible just about anywhere by dawn.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Since the weather regime will be similar Sunday, the forecast will
be about the same as well: early morning fog, daytime cumulus
developing, with a chance of afternoon showers.  The main difference
is a better indication for building instability across the
highlands... roughly I-81 west...perhaps as soon as mid morning. As
such, have morning showers for that area, and included a slight
chance of afternoon thunder as well.

From a synoptic standpoint, Monday will be similar as well. However,
the track of Jose will become more important. Forecast area may be
in the subsidence surrounding the cyclone, and have maintained a
more stringent PoP approach for the diurnal cycle.

Temperatures not far from a MOS mean. With dewpoints rising well
into the 60s, overnight lows will be muggy for September. Highs
aren`t that far from average.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
There is still some degree of uncertainty as to how the
tropical system, Jose, will affect our region Tuesday through
Tuesday night. The consensus of the computer models tend to keep
Jose well offshore of the Tidewater of Virginia and the
Delmarva as it moves northward and parallel to the East Coast.
Should Jose remain well offshore, about 250 miles offshore, then
the best case scenario will be dry conditions for most of our
region and a north wind becoming northwest around 10 mph with
gusts around 20 mph, mainly over the Chesapeake Bay. Consult the
latest bulletins from the National Hurricane Center on Jose.

As Jose either moves north toward New England or north then
northeast to the nearshore waters of the Eastern Canadian Maritimes
Tuesday night through Thursday, dry conditions will develop across
all areas. High pressure will build in Wednesday through Friday,
ensuring that we will have dry conditions and seasonable
temperatures.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
For the next several days, the key features will be similar: early
morning fog, then perhaps a few afternoon showers. In terms of
restrictions, the fog will be more meaningful.

Currently, an extensive mid-level cloud deck have precluded
widespread fog formation, although MRB has demonstrated some wild
fluctuations. Could have MVFR at IAD before sunrise as well.
Confidence at specifics for next couple of days too low to detail
here, just the potential is present.

Shower coverage should be limited, with low probability of an
airfield impact. The best chance probably will be Sunday PM at CHO
and MRB.

VFR conditions Monday through Wednesday night for all
terminals. This is dependent on Jose staying offshore. A track
closer to the coast or inland would significantly alter this
forecast.

&&

.MARINE...
Light flow this weekend, likely becoming onshore in the afternoon.
Winds will become increasingly northeast late Sunday into Monday as
Jose approaches the waters.

Based on the current forecast, likely will need a Small Craft
Advisory at some point Monday into Tuesday, and perhaps into
Tuesday night. Any track shift could alter this forecast,
resulting in either higher or lower wind speeds than currently
forecast.

No marine hazards expected Wednesday and Wednesday night.

&&

.TIDES/COASTAL FLOODING...
Water levels remain a little elevated. They should remain below
minor thresholds for the next couple cycles. By Sunday and
especially Monday, the approach of Jose may further elevate
them, resulting in minor flooding at sensitive sites. The
nighttime tide cycle is astronomically preferred. Depending on
how close the storm gets, moderate is not impossible, but
uncertainty on this is very high at the moment...as seen in the
forecast spread via SNAP-Ex.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

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



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