Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 231816

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
216 PM EDT Sun Oct 23 2016


The mid-Atlantic region is wedged between surface high pressure
building over the southeast U.S. and low pressure over Atlantic
Canada. A clipper system will push through the northeastern U.S. Monday
morning. High pressure will return for midweek. Low pressure will
approach from the west late in the week.



The autumnal cycle of cold fronts bringing temperatures down is
underway. After a very warm week a front moved through Saturday
which has brought temperatures back to more normal mid 60s values.

Although this is expected to not produce any precipitation tonight
the next system will be a fast moving short wave presently over
the Upper Great Lakes. This will track into PA overnight and off
the coast Monday morning. This will allow pressure gradient to
tighten overnight. Winds will become gusty...especially at higher
elevations...where gusts of 30 to 40 mph will likely overnight.

Lows will be 50-55 with exception of cooler at higher elevations.



High pressure builds into the Mid Atlantic Monday-Tuesday night.
Exepct a comfortable day Monday with highs of 65-70. Monday night
will see temps drop to the lower 40s...cooler at the higher
elevations...warmer in the cities.

Tuesday night high pressure will settle overhead providing
excellent radiation conditions. Have added patchy frost along the
M-D Line and west of the Blue Ridge as temps will likely fall into
the mid 30s. Would not be surprised to see frost advisories issued
with later releases.



Guidance is in reasonable agreement through Thursday, but begins
to diverge after that. At the beginning of the long term, we have
a deep closed low over Atlantic Canada and a weak ridge
extending from western Florida north to the Great Lakes, with a
shortwave further west in the upper Mississippi Valley. By Thursday
morning, all of these features shift east, with the closed low
moving into the western Atlantic, the ridge axis just east of our
region, and the shortwave over the Ohio Valley. By Friday, the first
shortwave passes northeast and a second stronger one is crossing the
area. By Saturday and Sunday, models diverge significantly, with
solutions ranging from a closed low to fast moving shortwaves.

In regards to sensible surface weather, high pressure will be off to
the north on Wednesday, likely leading to radiational cooling and at
least some areas of frost, if not perhaps a freeze in some spots.
Wednesday will then features some increase in high clouds looking
likely ahead of the next system. Clouds continue to thicken and lower
Wednesday night as a front approaches, with showers possible in
western areas late at night. This front then crosses the region late
Thursday or Thursday night with a continued chance of showers. The
front is east on Friday with high pressure trying to build back in,
though guidance showing a closed low is slower. Another weak
northern stream system may affect the area later in the weekend.

Temp-wise, we will remain seasonable to a bit below normal through
the long term as the Canadian influence and northern stream remain
more dominant in our weather.



VFR conditions expected tonight through Tuesday.

VFR to start Wednesday, but sub-VFR cigs and vis possible Thursday
as a frontal system moves through with rain. Improvements likely



SCA in effect for the Chesapeake Bay and lower Tidal Potomac
through Monday. SCA comes down overnight for the upper Potomac but
returns Monday.

Sub-SCA likely Wednesday, then SCA possible Thursday and Friday with
another frontal passage.


MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ530>534-
     Small Craft Advisory until 6 PM EDT this evening for ANZ535-
     Small Craft Advisory from 6 AM to 6 PM EDT Monday for ANZ535-


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