Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 100909

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
409 AM EST Sat Mar 10 2018

A weak ridge of high pressure will build over the region today
through Sunday. Low pressure will pass south of the region
Sunday night and Monday, then move northeast out to sea Monday
night. High pressure will gradually build back into the region
as the week progresses.


Latest surface analysis depicts a ridge of high pressure
stretching from Hudson Bay south to Wisconsin then southeast
across the Mid-Atlantic and into the Atlantic. A stationary
front extends westward from North Carolina across Tennessee to
a wave of low pressure. From there, the stationary front
continues west across Kentucky, Missouri and Kansas, then turns
nth towards another low pressure located in southeastern
Montana. Aloft, a closed low dominates the Northeastern US but
is now centered over Atlantic Canada, while a weak shortwave is
crossing the Ohio Valley. A much stronger shortwave is over

For today, the main story is the ridge of high pressure over the
region at present. For most of the region, it will provide some
partly to mostly sunny skies, and some modest warm advection
since yesterday should allow temperatures to rise a bit more
than yesterday`s chilly readings. However, temps will still
struggle to reach 50, and it will still be cool for this time of
year. Over our southernmost counties in central Virginia, the
wave of low pressure in Tennessee will play a role. It is moving
east along the stationary front, and with the support of a
shortwave and jet streak, may produce a bit of light snow across
central and southern Virginia, most likely south of
Charlottesville. Any accumulations should be less than an inch,
and it is likely to completely melt by afternoon as the wave
passes east, precip ends and the sun comes back out.

Tonight, high pressure will nudge further south, with a bit of
cold advection. Combined with mostly clear skies, and we will
see another chilly night for early-mid March, with most places
in the 20s once again.


The focus of the short term continues to be the system diving
southeast from Montana today. It will team up with a weak wave
of low pressure in the southern Plains and start to tap Gulf
moisture by Sunday, then head east along the stationary front
towards the Carolinas. As it does so, we will start to see
increasing clouds, with precip likely to enter central and
western VA by early Sunday night. While a mix is possible early
thanks to milder daytime temperatures (mostly 40s), as the night
progresses, snow will become more likely across the region.
However, while guidance is certainly in better agreement
regarding this system`s evolution, with a majority of
operational models keeping heavy snow out of our region, many
still show some light accumulations, while a few ensemble
members in several ensemble suites still depict a heavy
snowstorm, particularly across the Shenandoah Valley but also
perhaps extending towards the metro. Given this potential, will
continue to run with chance of a winter storm in the HWO, but
confidence in a major storm is lower than it was yesterday.
However, it cannot be completely ruled out still. With snow
possible in many areas by morning, temperatures are expected to
be near or below freezing by late Sunday night.

The system will pull eastward off the coast during the day
Monday, with the chance of snow peaking during the morning and
rapidly decreasing by nightfall. Some upslope snow showers look
increasingly likely for the Allegheny Front Monday night, but
for most, whatever snow falls will be over and done with. Highs
Monday will depend on how quickly the storm pulls out, with 40s
most likely, and lows Monday night will again drop to freezing
or below in most areas.


Models in good agreement with the departing low pressure system
residing over the western Atlantic Tuesday morning, with
upslope snow showers along the Allegheny Front. Mid to upper
level troughing will reside over the northeastern U.S. through
Wednesday, as the aforementioned low pressure area lingers over
northern New England and Canadian high pressure builds over the
central U.S. Implications of this for our weather will be cold
and blustery conditions, with the chance for passing snow
showers Tuesday through Wednesday, primarily west of the Blue
Ridge, but a few flurries or snow showers east of the mountains
is not out of the question. As shortwave energy rotates around
the base of the trough, this will help provide sufficient lift
to generate increased cloud cover and snow showers. Expect highs
in the low to middle 40s, and lows in the 20s area wide. Factor
in the winds, it will feel like the 20s/30s during the day,
with wind chills in the teens to single digits over the higher
elevations at night.

By Thursday, Canadian high pressure will reside over the
southeastern U.S., and the mid to upper level troughing over the
northeastern U.S. will finally relinquish its position and
start migrating eastward. As a result, ridging will begin to
take hold over the eastern half of the U.S. to close out the
work week. A return flow over our region, as well as warm air
advection aloft, will help temperatures moderate towards weeks
end, seeing a return of the 50s/60s Friday and Saturday.
Conditions will remain mostly dry through the end of the period
as a cold front approaches from the west late Saturday.


VFR through Sunday with lighter winds today and Sunday than the
last few days. Significant flight restrictions are possible on
Sunday night into Monday, depending on the track of a low
pressure system which will pass to our south. A track far enough
north would cause IFR cigs and vis with rain and snow, but a
more southerly track could keep VFR conditions going. The
highest risk of IFR is at CHO, while the lowest risk is at MRB.

Periods of sub-VFR conditions will be possible Tuesday and
Wednesday as mid level shortwave energy moves over the region,
bringing the chance for passing snow showers. These episodes
will be brief, and most likely result in reductions to
visibility. Otherwise, predominate VFR conditions are forecast
through Thursday with strong northwest winds persisting and
gusting upwards of 20 to 25 knots.


Winds should generally be sub Small Craft Advisory level through
Sunday with high pressure ridging overhead. The chance of SCA
increases Sunday night and Monday as a low pressure system
passes to the south. Rain and snow are also expected with this
system, though the track will determine how far north the rain
and snow reach.

An extended period of Small Craft Advisory conditions appear
likely through Thursday as a strong pressure gradient will
reside over the waters. This will be in response to an exiting
low pressure system over the western Atlantic and building
Canadian high pressure to our west southwest.


MARINE...Small Craft Advisory until 6 AM EST early this morning for


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