Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 212359
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
759 PM EDT Wed Sep 21 2016

.SYNOPSIS...
High pressure will build over the region through early
Thursday then weaken through Friday. A cold front will move
through the area early Saturday. High pressure builds again over
the region early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
A few light showers are seen on radar over southern MD and the
Fredericksburg area, but these are expected to dissipate early
tonight as high pressure builds in and air mass dries out. Biggest
question for tonight is whether high clouds will thin out and
skies become clear. Latest 12Z ECMWF and HRRR simulated cloud IR
imagery show high clouds sticking over the area around much longer
than earlier runs with clearing not indicated now until after
midnight or early Thu. Fog is not expected as models show sfc
dewpoints dropping tonight.

A few high clouds still possible Thu if the ECMWF is correct, but
any high clouds are likely to be thin enough for a mostly sunny
day. High pressure will be in control, although it will be
weakening.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
Weak high pressure in control during this period. Temperatures
are expected to warm up into the upper 80s and possibly reach 90F
in a few spots on Fri.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Surface cold front will likely have passed south of the region by
Saturday morning, behing pushed along by a 1030+ mb high pressure
center originating near Hudson Bay Canada. The center of this high
and coolest air will pass over New England, but much cooler
weather is expected over the Mid-Atlantic as well especially
during the second half of the weekend into early next week.

Onshore flow may result in elevated humidity and low clouds and
drizzle especially early next week. The operational GFS runs have
been the quickest with an approaching cold front next week but have
been trending slower towards a GEFS/EC blend. A slower solution
seems more likely given the large blocky nature of the high pressure
center that will be stationed just northeast of the region next
week. This should keep more substantial rain chances at a minimum
through much of the forecast period.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
VFR conditions next 24 hrs, except for possible 3-5SM mist at
KCHO.

Mainly VFR expected Saturday with northerly winds 10 to 15
knots. Sub-VFR possible later in the weekend with lower clouds as
winds become easterly around 10 knots.

&&

.MARINE...
Winds will gust to around 15kt in the lower Bay through midday
Thu before they begin to diminish.

A pressure surge, aided by northerly channeling, will likely
push winds into Small Craft Advisory territory on Saturday. Winds
should gradually diminish and veer to the east Saturday night into
Sunday.

&&

.TIDES/COASTAL FLOODING...
Water levels running less than a foot above astronomical normals,
but departures are on the rise. Nonetheless this is proving to be
enough to flirt with minor inundation thresholds at sensitive
locations. Forecast has been running right on track...adding
confidence for the upper tidal Potomac. Have added DC and
Alexandria to the Coastal Flood Advisory. Anne Arundel County
continues. Allowed St. Mary`s County to expire at 8pm.

Elevated water levels persist through the rest of the week due to
low pressure off the Carolina coast.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory from 11 PM this evening to 2 AM EDT
     Thursday for DCZ001.
MD...Coastal Flood Advisory until midnight EDT tonight for MDZ014.
     Coastal Flood Advisory until 8 PM EDT this evening for MDZ017.
VA...Coastal Flood Advisory from 11 PM this evening to 2 AM EDT
     Thursday for VAZ054.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...LFR
LONG TERM...DFH
AVIATION...LFR/DFH
MARINE...LFR/DFH
TIDES/COASTAL FLOODING...HTS/LFR


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