Area Forecast Discussion
Issued by NWS Sterling, VA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
FXUS61 KLWX 180737

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
337 AM EDT Mon Sep 18 2017

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


A ridge of high pressure extends from New England down the eastern
seaboard early this morning. A mid-level ridge extends up the
Appalachians. This tandem will lead to subsidence across the area.

Before we get there though, we`ll need to address early morning low
clouds and fog. There is still a fair amount of mid level clouds
across the area though, which is keeping fog localized. Like last
night, a bank of low clouds can be found across the Atlantic coast,
and NARRE/HREF suggest they will work inland again. Believe that low
clouds will dominate over fog given light but present flow.
Nonetheless, this will lead to a gray start to the day.

Eventually, the low-level moisture will burn off, but it may take
some time to do so. The relative lack of strong insolation, dry air
aloft, the lack of any shear, and subsidence (as already mentioned)
should combine to prevent showers today. The best chance (relatively
speaking) will be in the mountains where orographics and convergent
onshore flow will provide minimal lift. It will be plenty humid for
the season, as the northeast wind will assist dewpoints in reaching
70 degrees. Temperatures will be about the same...around 80 degrees.


By tonight, the forecast will begin to be influenced (indirectly) by
Jose, although the bigger influence (again, relatively speaking)
will be felt on Tuesday. Northeast/north winds will increase
tonight, especially near the Bay, with a fair amount of cloud cover
east of the Blue Ridge as well. Will be bringing a chance of showers
inland to the western shore by dawn Tuesday, with better chances
during the day on Tuesday. The inland reach of these showers likely
won`t spread west of I-95, but that is an aspect that is highly
conditional on the track of Jose, as well as how much the storm
expands as it weakens. A slight nudge westward would increase the
potential that an outer band could spread inland, providing a
soaking rain.

Am still keeping a solution of subsidence in the wake of the
cyclone, which will affect the forecast area Tuesday night and


Ridge of high pressure surface and aloft will build over the
region Thu through Sun as Jose remains well offshore. Tranquil
conditions are expected as a result. Temperatures will remain a
few degs above normal during this period. By early next week,
the ridge begins to weaken as a weakening post- tropical Jose
likely completes another loop and heads back to the mid-Atlc
coast. We`ll also be watching Hurricane Maria move into the
southwest Atlc during the second half of the week. Recent trends
indicate Maria may stay out to sea, but it is really too early
to tell at this time. Please refer to NHC for the latest on Jose
and Maria.


Once again, low clouds and fog are a concern for the morning push.
Unlike last night, there is a bigger contribution from mid clouds,
which is disrupting fog formation processes. Some guidance again is
providing high probabilities that low clouds will spread inland to
BWI and perhaps DCA. The odds aren`t as high as last night, and the
cloud deck is further removed from the area. However, the solution
is plausible. Have forecast IFR only at BWI; have kept cigs 010-015

Whatever does develop will slowly burn off through the morning. VFR
will prevail for the balance of the day.

Jose will make its nearest pass to the terminals late tonight
through Tuesday. Significant impacts will likely remain to the east,
but northeast winds tonight suggest there may be another round of
low clouds to deal with.  VFR should prevail Tuesday afternoon
through Friday, aside from perhaps early morning fog.


Although winds are weak early this morning, the pressure
gradient will be increasing today and tonight as Jose nears the
waters.The current alignment for Small Craft Advisories this
afternoon and tonight still appear on track; no changes were
made there. By Tuesday, the gradient will be at its strongest,
with several model solutions suggesting the gales will be
possible on the mid Bay. That is contingent on the track of
Jose. Have added a Small Craft to all Maryland and DC waters on
Tuesday since confidence in 20+ kt gusts high. Would not rule
out an upgrade to Gale Warning for a portion of this area.

Winds should stay generally below SCA Wednesday through Friday
under ridge of high pressure.


Water levels continue less than a foot above astronomical
predictions. This trend should gradually increase over the next
couple of days. At this point, St George Island will be the only
site forecast to consistently exceed minor flood, although Annapolis
and SW DC will come precariously close. Have added a short-fused
Coastal Flood Advisory for Anne Arundel county for the next couple
of hours. May need to do the same for SW DC for the early morning.
Otherwise, just caution stages with the current tide cycle.

Based on strong confidence in the trends, have extended the Advisory
for St Marys County for another three tide cycles, through the
daytime cycle Tuesday. Elsewhere, model spread precludes action at
this time. While moderate flood possible at sensitive locations,
confidence in this outcome at the low end of the spectrum.

Elevated water levels likely to be a concern through the end of the

MD...Coastal Flood Advisory until 7 AM EDT this morning for MDZ014.
     Coastal Flood Advisory until 4 PM EDT Tuesday for MDZ017.
MARINE...Small Craft Advisory from midnight tonight to 8 PM EDT Tuesday
     for ANZ531-532-539-540.
     Small Craft Advisory from 6 AM to 8 PM EDT Tuesday for ANZ530-
     Small Craft Advisory from 6 PM this evening to 8 PM EDT
     Tuesday for ANZ533-541-542.
     Small Craft Advisory from 3 PM this afternoon to 8 PM EDT
     Tuesday for ANZ534-537-543.


TIDES/COASTAL FLOODING...HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.