Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 110910
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
410 AM EST Sat Nov 11 2017

.SYNOPSIS...
Cold high pressure will dominate the region through Sunday. Low
pressure will affect the region Sunday night into Monday,
followed by another area of high pressure by Tuesday. Another
front may impact the region midweek.

&&

.NEAR TERM /THROUGH TONIGHT/...
Freeze warning continues through mid morning. The growing season
is terminated with this warning and no further frost/freeze
products will be generated until spring 2018. A PNS confirming
this has already been sent. Some spots may reach records - see
climate section below.

Canadian high pressure will continue to build overhead today
into tonight. Winds have been slowly diminishing and should end
up pretty light today. The very cold air aloft, however, will
not allow temps to rebound a whole lot, with many spots probably
getting stuck in the 30s, or barely reaching the low 40s.
However, with less wind and a decent amount of sun, it may in
fact feel more comfortable today.

Light winds expected tonight with high pressure still around -
however, high clouds may make their way overhead, and temps
aloft will be starting to rebound. So, all in all, not quite as
cold.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Approaching trough with weak surface low will be moving into the
Ohio Valley Sunday. As this occurs, a secondary low is expected
to start developing east of the mountains, with an energy
transfer to this low on Monday. As this low develops,
clouds will become common Sunday, and precipitation looks more
likely to break out across the region Sunday night. Right now,
given some moderation Sunday with warm advection aloft and a
light east flow at the surface, most of the region should see
rain. However, cold air damming could allow a period of mixed
precip west of I-95 and north of I-66 in western Maryland,
eastern West Virginia and far northwestern Virginia on Sunday
night. For now have included likely rain and chance
snow/sleet/freezing rain given high uncertainty, but may need to
put out advisories should the odds of freezing rain increase
sigificantly.

This system pulls out during the day Monday, with decreasing
clouds on a west wind during the afternoon. This should allow
even more moderation, particularly since the air mass behind the
system has more of a Pacific influence to it. This also means
that Monday night, despite some clearing, should not be as cold
as tonight, but some places could still drop below freezing.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure will pivot across the area Tuesday into Wednesday
bringing seasonable conditions. As the high moves offshore, a
weakening cold front will approach from the Ohio Valley. Upper-
level support will be weakening and lifting north during this
time, so the best chance of showers (albeit somewhat scattered)
will likely be confined to northwestern portions of the CWA.

A stronger upper trough/surface frontal system will approach
late in the week likely bringing more widespread chances for
precipitation, which looks to be mainly rain at this time given
the fact that the Mid-Atlantic will be solidly in the warm
sector.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
VFR through Sunday. Winds dropping below 10 knots and staying
light through Sunday.

Sub-VFR possible Sunday night as a storm system brings a period
of light rain, which could possibly be mixed with ice or snow
at MRB. Returning to VFR by Monday afternoon.

Mainly VFR Tuesday-Wednesday. Light flow under high pressure.

&&

.MARINE...
Winds will gradually diminish this morning as high pressure
builds overhead. SCA conditions should continue slowly winding
down, with sub-SCA by afternoon all waters.

Generally expecting sub-SCA tonight through Monday night, though
will need to watch a strengthening coastal low late Monday.
Winds could pick up enough to reach SCA levels as the low pulls
away.

No marine hazards expected Tuesday-Wednesday under high
pressure.

&&

.CLIMATE...
We took a look through the records earlier and found that there
has never been a case where DCA, IAD, BWI and the downtown
Baltimore station (currently DMH) has had their first freeze on
the same date. This is very likely due to the unusually warm
October followed by the severe cold snap we are now
experiencing, since in the more rural locations (particularly
IAD), radiational cooling usually brings a freeze much earlier
than at DCA and DMH. This year very narrowly prevented IAD from
reaching freezing in October (low of 33), allowing yesterday to
be the first freeze.

Record lows will still be possible early this morning. Here is
the forecast and the records for our three main climate sites:

DCA - Forecast 27 - Record 26 in 1973 and 1901
BWI - Forecast 22 - Record 21 in 1973
IAD - Forecast 19 - Record 16 in 1973

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Freeze Warning until 10 AM EST this morning for DCZ001.
MD...Freeze Warning until 10 AM EST this morning for MDZ004>006-011-
     013-014-016>018-503>508.
VA...Freeze Warning until 10 AM EST this morning for VAZ037-052>057-
     501-502-506.
WV...None.
MARINE...Small Craft Advisory until 6 AM EST early this morning for
     ANZ530>532-536-539>542.
     Small Craft Advisory until noon EST today for ANZ533-534-537-
     543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...DFH
AVIATION...RCM/DFH
MARINE...RCM/DFH
CLIMATE...RCM



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