Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 191443
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
943 AM EST Fri Jan 19 2018

.SYNOPSIS...
High pressure to the south will dominate the weather through
the weekend. A storm system and cold front will cross the region
late Monday and early Tuesday. High pressure will return by the
middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Surface high pressure is located across the southeastern CONUS
this morning. The only weather impact comes from a band of
cirrus, which is greatly filtering the sunshine west of I-95.
Have added this into the database, although expect improvement
through the afternoon. It could impede the temperature rise, but
based on yesterday that could balance the forecast out. No other
changes at this time.

For tonight, the high will remain along the Gulf Coast. A few
cirrus may cross the area while winds become light. Have lows
ranging from the mid 20s to lower 30s. It could be colder in
spots if prolonged decoupling occurs, as dew points will still
be in the teens/lower 20s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
High pressure will continue eastward off the southeast coast
into the Atlantic over the weekend, resulting in continued
west/southwest flow and mild weather. Saturday will be
(aesthetically) the better day of the weekend with plentiful
sunshine and temperatures into the 50s across much of the area
(maybe even 60 for Charlottesville- Fredericksburg). Low level
moisture return around the high will begin to encroach on the
Appalachians by Saturday night. Given the shallow nature, any
precipitation likely remains west of the divide and would likely
be very light rain. There`s still a chance temperatures could
be just below freezing, supported by forecast soundings but less
so in GEFS/SREF/WPC FZRA probabilities. However, continued warm
advection will end any limited ice threat by daybreak Sunday
(if not much sooner).

Any light rain will likely remain west of the Allegheny Front
Sunday. However, lower clouds may spread east of the mountains
as well, particularly northern parts of the area. Combined with
surface flow that may become more southeast than southwest,
temperatures will likely be a little cooler than Saturday. The
question is just by how much, and where the dividing line
between 45-50 and 55-60 degree temperatures will be. A backdoor
cold front may drop into northeastern parts of the area by
Sunday night, which could lead to some light rain or drizzle.
Low temperatures will be in the upper 30s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
At the start of the long term, a warm front will be lifting
north across the region as low pressure strengthens to our west
across the Corn Belt. Southerly flow will be enhanced south of
the front, and temperatures stand a shot at reaching the 60s
across a decent portion of the area on Monday. A little rain is
possible as the front lifts north, most likely near the PA
border and most likely earlier in the day.

EC and to a lesser extent the GFS is now hinting that a triple
point low may try to develop along the approaching cold front as
it crosses our region later Monday night. This would enhance
the rainfall and increase the risk of potential convection. Will
need to monitor this in case it looks like a low-end squall
line with heavy rain and gusty winds could develop as the system
passes. Monday night will remain mild, at least through the
time of cold frontal passage, with temps staying in the 50s,
perhaps even low 60s, much of the night.

The front pushes east of the region as we head through Tuesday,
with steady or falling temps and rain ending. Some upslope
rain/snow showers may linger along the Alleghany Front through
the whole day, however. Despite the falling temps, they should
stay fairly mild for late January, with readings unlikely to
drop severely.

This is due to the incoming high behind the system having more
of a Pacific origin, versus the recent high pressures which have
dropped southeast from Canada. Therefore, while Wednesday and
Thursday look to be dominated by this high, it should only be
close to normal for late January, versus the recent cold
outbreaks which dropped temps 10-20 degrees below normal each
time. With the high overhead, Wednesday and Thursday should turn
out dry with some sun as well.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
No aviation concerns are expected through Saturday as high
pressure moves along the Gulf Coast. Winds will be between west
and south, and generally less than 10 kt.

Low level moisture return begins Saturday night and definitely
Sunday into Sunday night. Best case is scattered to broken low
VFR, although SREF indicates decent probabilities of MVFR by
Sunday, especially northern parts of the area (metros included),
and a greater chance of IFR by Sunday night with possible light
rain/drizzle.

Cig and vis restrictions look likely by Monday night into
Tuesday as a cold front moves across the region, bringing
periods of rain.

&&

.MARINE...
Winds will remain between west and south through the weekend as
an area of high pressure moves from the Gulf Coast off the
southeast coast. Mixing (both due to warm air temperatures and a
subsidence inversion aloft) will likely keep winds less than 15
kt, although there could be some near-SCA gusts near the shore
of the northern Bay today and again Saturday.

SCA looking likely at some point Tuesday as a cold front
crosses the region.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS/ADS
SHORT TERM...ADS
LONG TERM...RCM
AVIATION...ADS/RCM
MARINE...ADS/RCM



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