Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 221901
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
301 PM EDT Thu Sep 22 2016
Low Pressure remains off the Carolina coast while high pressure
is centered over New England. A backdoor cold front will move
through the area Saturday. High pressure returns to the region
Sunday through early next week.
.NEAR TERM /THROUGH FRIDAY NIGHT/...
Fairly quiet weather continues across the area through Friday.
Scattered high clouds from low to our south continue to stream
northward across S MD and the Central Foothills of VA. Northward
extent hasn`t been captured well by model guidance...but general
trend is for clouds to thin as the move into high pressure. Added
some slight chance PoPs through the afternoon across these areas to
account for ongoing spotty showers. Elsewhere, it will remain mostly
sunny with only a few thin high-level clouds. Mostly clear skies
overnight might allow for some patchy radiational fog to develop
across the typically favored valley locations.
Remaining warm Friday with warm air advection ahead of cold front.
Limited cloud cover should allow for nearly full insulation...with
high temperatures a few degrees warmer than today and nearly 10F
above climatological normals.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Backdoor cold front pushes through the area Saturday morning. Models
often have a difficult time capturing sensible weather trends
(e.g., sky cover, temperature, winds) with backdoor cold fronts...so
have nudged these elements accordingly. Front is moisture starved,
so most areas will remain dry...though maintained slight chance PoPs
for a spotty shower over the higher terrain. Cloud cover will keep
temperatures cooler then previous days. Though, highs near 80s still
appear possible as cooler/drier air remains displaced further north
behind frontal boundary and doesn`t move in till later Saturday. Low
dewpoints will allow overnight low temperatures to fall into the L60s
across much of the area (50s across the north) Saturday into
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Deep ridging will traverse the region during the second half of the
weekend into early next week. The center of surface high pressure
will pass to the north and east of the region, so although high
pressure will be in control onshore flow will likely lead to
increasing low-level moisture and clouds.
An upper-trough will cut off over the upper Midwest and try to move
towards the area during the middle of next week, but the blocking
high pressure over the northwestern Atlantic will likely slow its
forward progress. The blocky/cutoff nature of the pattern lends to
greater than normal uncertainty in the forecast during this time.
.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
VFR conditions continue through the remainder of today. Fog
is possible tonight at the typically favored locations (e.g., CHO
and MRB) with IFR conditions possible. Could be some patchy fog
at other sites...though confidence in this is low at this time. VFR
expected Friday through Saturday night. Though, expect a sudden wind
shift to northerly as front moves through Saturday morning.
Sub-VFR possible Sunday into Monday as low clouds may
develop in onshore/easterly flow around 10 knots.
Winds remain below SCA values this afternoon through Friday night
with high pressure building into the area.
Small Craft Advisories are possible Saturday and Saturday
night with increased northerly flow behind frontal passage.
Easterly flow around 10 knots around high pressure over the
northwestern Atlantic should stay below Small Craft Advisory levels
Sunday into Monday.
Potential for minor coastal flooding on the evening tide cycle at the
more sensitive sites along the upper Potomac (e.g., DC/Alexandria).
Observations have been running slightly above forecast at these
sites, so confidence in reaching minor criteria is low and will need
to be monitored. Current forecast at Annapolis keeps levels below
minor flood stage this evening...though anomalies are gradually
rising so could be close to minor stage. Elevated tidal levels
remain at these sites after tonights cycle...though current forecast
keeps levels below minor flood stage.
Unusually warm weather has persisted over the area for
quite some time. Autumn-like temperatures will finally make an
appearance over the weekend likely bringing low temperatures at DCA
below 60 degrees for the first time since June 9th, or 104 days ago.
The record most consecutive days at or above 60 degrees in the
Washington DC area is 112 set in 2012.