Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 180741
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
341 AM EDT Wed Oct 18 2017

.SYNOPSIS...
High pressure will remain across the Mid Atlantic through the
rest of the week and this weekend. A low pressure system may
affect the region early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure is located directly over the region this morning.
Some patchy fog is possible through sunrise, mainly in the
river valleys. Cirrus currently across Kentucky may cross the
sky this afternoon, and a light south wind will develop as the
high drifts to the southeast. A moderating low level airmass
will lead to high temperatures on either side of 70 degrees.

An upper level trough will cross the area tonight, although it
will have little impact other than some additional cirrus. Dew
points will be a little higher, and some locations may be able
to hold onto a light south wind since the high will be to the
southeast. Thus expect any frost to be much more isolated, with
most locations in the upper 30s to mid 40s...and lower 50s in
the cities.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
The center of the high will remain generally to our south and
southwest Thursday into Thursday night. The tail end of a
decaying cold front/low level trough over New England will clip
the area Thursday night, but bring little more than a few clouds
and a wind shift to the northwest. The upper level pattern will
amplify (west coast trough/east coast ridge) Friday into Friday
night, with the surface high expanding back to the north and
east.

High temperatures will continue to warm through the 70s.
Overnight lows will be in the 40s for most, with 50s in the
cities. Greater variation is likely Friday night though with a
more favorable radiational cooling set up.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure will be centered overhead or just to the northeast
on Saturday morning, providing light winds and mostly clear
skies. After a cool (but not as chilly as this morning) start,
it will warm into the 70s with plenty of sun. The high will
shift eastward off the coast by Sunday, with more of a
southerly flow - however, the gradient will remain weak, so not
a whole lot of change in sensible weather. A little warmer, a
few more high clouds, that`s likely all the difference between
Saturday and Sunday. Overall, ideal weekend weather,
particularly for autumn.

Guidance still shows a cold front and wave of low pressure
moving toward the region early next week, but are a bit less in
sync than last night. The GFS is significantly slower than the
EC in bringing the upper low and its associated surface wave
northeastward into the region, causing Monday to be drier on the
GFS than on the EC, with a faster drying trend as we head into
the middle of the week on the EC than on the GFS. Overall, will
keep chance of showers, and heavy rain remains possible, given
strong wave and potential for training along the stalling front.
Both models also still show a very deep trough digging over the
eastern US behind the system for mid-late week next week. This
is something that would likely end the growing season across
much of the region, while also perhaps trying to get a few snow
flakes flying, especially in our higher terrain. Still, there`s
a long time to watch this.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
High pressure will remain in control through the end of the
weekend. Given regional observation trends, inserted a short
period of MVFR BR this morning at MRB and CHO, although this may
ultimately be pessimistic. Can`t rule out a similar scenario
any morning this week, but guidance doesn`t look terribly
favorable. Otherwise only passing cirrus is expected with winds
less than 10 kt.

&&

.MARINE...
High pressure will remain nearby through Thursday with light
southerly winds developing. A weak front will pass by to the
north Thursday night, which will turn winds to the northwest.
Potential for Small Craft Advisory conditions will be dependent
on mixing, so the greater chance would be over the more open
waters. Winds will subside during the day on Friday as high
pressure moves back overhead, which will then generally persist
through the weekend.

&&

.TIDES/COASTAL FLOODING...
Anomalies have risen to around one-half to three quarters of a
foot above normal. This should keep water levels below minor
flood thresholds but it will be close for the sensitive sites of
Straits Point, Annapolis, and Washington DC. Water levels will
need to be monitored.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Frost Advisory until 9 AM EDT this morning for DCZ001.
MD...Frost Advisory until 9 AM EDT this morning for MDZ003>006-013-
     016-017-502>507.
VA...Frost Advisory until 9 AM EDT this morning for VAZ028>031-
     036>040-050>057-501-502-505-506.
     Freeze Warning until 9 AM EDT this morning for VAZ025>027.
WV...Frost Advisory until 9 AM EDT this morning for WVZ050>053-055.
MARINE...None.

&&

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



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