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-- Discussion containing changed information from previous version are highlighted. --
347
FXUS61 KLWX 201333
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
933 AM EDT Wed Sep 20 2017

.SYNOPSIS...
A ridge of high pressure will remain over the eastern United
States through early next week. Hurricane Maria may approach the
coast of the Carolinas by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Upper-level ridge axis remains overhead this morning while an
upper-level disturbance approaches from the west. A deformation
zone overhead has allowed for mid-level clouds over the metro
areas this morning. A few sprinkles cannot be ruled out...but
clouds are expected to dissipate across these areas this
afternoon as deformation zone weakens.

A few popup showers are possible this afternoon into this
evening across the Potomac Highlands into the central Shenandoah
Valley as the upper-level disturbance approaches from the west.
However...instability will be limited and forcing with this
system is quite weak. Therefore...much of the time should turn
out dry. Elsewhere...partly to mostly sunny skies are expected
this afternoon and it will turn out quite warm with the upper-
level ridge overhead. Max temps will be in the mid to upper 80s
across most locations.

High pressure both at the surface and aloft will build over the
region as the upper-level disturbance shifts to the south
tonight. Patchy fog will again be a concern. Lows will be
mainly in the 60s.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
Northeast flow aloft will dominate Thursday through Friday night
as ridge builds to our west and Jose stalls to the east. Jose
should have little to no effect on our weather during this time,
so it will be unseasonably warm and humid, but dry, with the
ridging preventing any convection. Highs will be in the mid to
upper 80s, with lows in the 60s. Patchy late night and early
morning fog will be the main forecast concern, mainly in the
more rural, inland locations.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Ridge of high pressure will gradually strengthen through early
next week. Latest Euro is much stronger than GFS/GEFS with the
h5 ridge showing a 591 decameter ridge. No wx is expected as a
result. The first half of next week, flow will turn more onshore
north of Hurricane Maria. Latest Euro has trended westward and
slower with the track of Maria bringing it closer to the NC
Outerbanks, but so far models have been inconsistent on track
longitude thus far, limiting confidence. Please refer to NHC for
the latest on Maria.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
VFR conditions are expected through this evening with high
pressure in control.

Patchy fog will be a concern again over the next several late
night and early morning periods thanks to persistent high
pressure and light winds. Best odds same as early this morning
as described above. Other than that, should be VFR thru Friday
night.

VFR conditions through Sun with no sig wx.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Will continue with the SCA for the middle portion of the Bay and
lower Tidal Potomac River through late this morning...but it
will be marginal. Jose will move away from the area this
afternoon. Gusts will be close to SCA criteria...but the
forecast has them capped around 15 knots for now due to a
weakening gradient.

From tonight through Friday night, high pressure and light winds
will dominate, with no SCA concerns at present.

Light winds through the weekend. Winds will start strengthening
during the first half of next week as pressure gradient tightens
in response to approaching Hurricane Maria.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
-- Changed Discussion --
Water piled up near the mouth of the Bay from Jose over the
past couple days. Those anomalies have spread across the Bay
and Tidal Potomac River. Anomalies over 1 foot above normal
remain across the entire Bay...so elevated water levels are
likely to continue for at least the next couple tide cycles
through tonight...despite an offshore flow. Coastal Flood
Advisories are in effect from Annapolis southward and across the
upper Tidal Potomac River. A Coastal Flood Warning is in effect
for St Marys County where moderate flooding is expected.

Guidance continues to show elevated water levels for Thursday as
well.
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Coastal Flood Advisory until 11 AM EDT this morning for DCZ001.
MD...Coastal Flood Advisory until 6 PM EDT this evening for MDZ018.
     Coastal Flood Advisory until 10 PM EDT this evening for MDZ014.
     Coastal Flood Warning until 7 PM EDT this evening for MDZ017.
VA...Coastal Flood Advisory until 11 AM EDT this morning for VAZ054.
WV...None.
MARINE...Small Craft Advisory until noon EDT today for ANZ533-534-537-
     541-543.
-- End Changed Discussion --

&&

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