Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 180803
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
403 AM EDT Sun Sep 18 2016
A weakening cold front will approach from the northwest today
before stalling over the Appalachians tonight through Monday
night. This front will dissipate on Tuesday. Another cold front
will move into the region and stall to our south later this week.
.NEAR TERM /THROUGH TONIGHT/...
The current surface analysis depicts a weak cold front is located
over the Great Lakes. High pressure has pushed well east of the
Atlantic Coast. Tropical Depression Julia remains centered off the
South Carolina coast. Aloft...high pressure is centered over the
western Atlantic with a shortwave trough moving east across the
The features to our west, namely the shortwave and cold front,
will move eastward today, while the depression will start sliding
northward along the coast. The combination of increasing tropical
moisture and approaching triggering mechanism means that
instability will grow markedly through the day and into
tonight...despite cloud cover. In addition...the southerly flow
will promote warmer air aloft...which should help boost surface
temperatures well into the 80s by this afternoon. As the trough
starts to move into this region late today and tonight...expect
plenty of showers and thunderstorms to develop. At this time with
limited shear...do not expect much in the way of severe
weather...though an isolated severe storm is certainly possible.
Heavy rain appears to be the bigger threat with potential training
of storms late today and tonight. The saving grace is the recent
run of very dry weather...with some areas of the metro having had
less than a half inch of rain over the last 31 days. This means
that it will take a lot of water to cause flooding...or that water
will have to fall very fast. Its certainly possible that it
does...but odds seem low enough to preclude issuance of a flash
flood watch just yet. Lows tonight will be in the 70s.
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The front appears to gradually dissipate over the Appalachians
before ever reaching us early this week. This means warm and
relatively humid air will remain in place. As the shortwave passes
Monday into Monday night the chance of showers and thunderstorms
will gradually decline...though the circulation of Julia will not
be far away so it will need to be watched for potential rainfall
especially in southern Maryland. Otherwise...Monday looks pretty
cloudy so dropped highs while Tuesday...well behind the
trough...should still be warm and mainly dry.
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Surface high pressure builds east across the northern Mid-Atlantic
Wednesday, lingering off New England Thursday into Friday. Wednesday
is definitely dry with a north wind. An onshore flow starts Thursday
and continues into the weekend. Low pressure may develop again along
the Carolina coast in the Friday/Saturday timeframe which may allow
some rain into the CWA. Cold front from a digging trough over
eastern Canada looks to approach the area over the weekend.
Dry and sunny conditions Wednesday through Friday would allow for
above normal temperatures, namely low to mid 80s maxima.
.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
MVFR vis not impossible early this morning with any patchy fog
though odds are looking lower right now with clouds overhead. Sub
VFR conditions possible later today and tonight with showers and
t-storms moving in from west/southwest. Conditions should improve
gradually through Monday with VFR returning Tuesday.
VFR conds prevail Wednesday through Friday as high pressure builds
east across the northern Mid-Atlantic (north wind Wednesday),
stalling off New England (onshore flow Thursday/Friday).
SCA expires at 6AM. May still see occasional gusts to 18 knots
over next few hours so will have to re-evaluate. Low level jet may
re-intensify so may need to add new SCA for late today/tonight.
Showers/t-storms also will be an issue later on today/tonight into
Monday. Sub-SCA more probable Monday/Tuesday.
High pressure builds east across the northern Mid-Atlantic Wednesday
with north winds before stalling off New England maintaining an
onshore flow Thursday/Friday.
South flow across the water has maintained positive water levels of
0.75 to 1.0 ft above astronomical prediction (normal). Minor coastal
flooding is expected to continue at the sensitive sites of
Annapolis, Straits Pt (St. Marys Co) and SW waterfront DC and
Alexandria at high tide through this evening. Coastal flood
advisories continue this time for Anne Arundel and St. Marys
DC/Alexandria have up to a 1.0 ft positive anomaly that may cause
minor coastal flooding at through high tide tonight. The day shift
will again be allowed to consult with MARFC before extending the
headline beyond noon.
Low pressure is expected to persist along the Carolina coast through
at least Tuesday with north winds delayed until Monday night at the
earliest. Expect elevated water levels and potential continued minor
coastal flooding at least through Monday.
DC...Coastal Flood Advisory until noon EDT today for DCZ001.
MD...Coastal Flood Advisory until 11 PM EDT this evening for MDZ014.
Coastal Flood Advisory until 8 PM EDT this evening for MDZ017.
VA...Coastal Flood Advisory until noon EDT today for VAZ054.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for