Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 200040
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
840 PM EDT Thu Oct 19 2017

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

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
An elongated area of high pressure stretches from the Deep
South northeastward across the southern Appalachians and off
the Mid-Atlantic coastline this evening. At the same time, a
weak cold front is tracking through the Ohio Valley into
Pennsylvania.

The weak front will push east-southeastward tonight, with its
tail end crossing the region overnight. Aside from a shift to
light northwest winds and a few added cirrus, no real sensible
weather impacts are expected with this decaying front. Although
as winds do turn to the northwest, there may be some terrain-
induced strato-cumulus along the Allegheny Front by morning.
Should still have decent radiational cooling tonight, but with
some added light winds and higher dewpoints, won`t be as ideal
as previous nights. Lows in the 40s to near 50F for most, except
low/mid 50s in the urban centers and along the shorelines of
the Chesapeake and Tidal Potomac.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
High pressure will gradually build back overhead for Friday and
Saturday, providing for mostly sunny skies, relatively light
winds, and mild temperatures. There may be some patchy fog each
late night/morning, but nothing widespread expected. Highs will
reach the low to mid 70s, with lows in the 40s/50s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
High pressure system will move away from the east coast on
Sunday. A cold front approaches from the west with a wave of low
pressure tracking northeast from the Gulf states towards the
Mid-Atlantic region Monday into Tuesday. This system will put an
end to the dry spell we`ve been experiencing, with
precipitation associated with it starting sometime on Monday
and remaining into Tuesday.

The pattern will evolve from warm and dry to cold and unsettled
as this system moves through, with some uncertainty on the
timing. In the upper levels, a large and deep trough will move
over the eastern CONUS Wednesday into Thursday. Guidance
suggests that this could bring some upslope showers on
Wednesday, and then dry into Thursday.

High temperatures on Monday will be between the low to mid 70s
decreasing into the 60s into Thursday.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Patchy fog possible at MRB/CHO/IAD over the next few mornings,
but chances are low and any fog would be brief. Otherwise, VFR
through Sunday night with relatively light winds under high
pressure.

Precipitation associated with a cold frontal system is then
expected later Monday into Tuesday, which could bring sub-VFR
conditions at times.

&&

.MARINE...
A weak cold front will cross the waters overnight. A pressure
surge behind the boundary will cause northwest winds to increase
toward morning. While a surface inversion will limit mixing and
wind gust potential along the shores, over the open warmer
waters, gusts in excess of 20 knots are possible late tonight
into Friday morning. Therefore, will leave Small Craft Advisory
in effect from through Noon Friday. Winds will drop below SCA
criteria by Friday afternoon and remain below through Sunday.

Southerly winds will increase out ahead of the next frontal
system Monday and Tuesday, and a Small Craft Advisory may be
needed.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until noon EDT Friday for ANZ531>534-537-
     539>541-543.

&&

$$
SYNOPSIS...MM
NEAR TERM...BJL/MM
SHORT TERM...MM
LONG TERM...IMR
AVIATION...BJL/MM/IMR
MARINE...BJL/MM/IMR



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