Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 160931

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
531 AM EDT Fri Mar 16 2018

Low pressure will linger over the Canadian Maritimes through
Saturday. High pressure will build overhead today into tonight
before weak low pressure passes through the area Saturday. High
pressure will return for Sunday. Low pressure will impact the
area late Monday into the middle portion of next week.


Secondary surge of colder air is moving into the region this
morning as upper level disturbance moves overhead. This will
act to briefly induce some additional upslope snow showers along
and near the Allegheny Front this morning, but accumulations
will generally be less than one inch. In addition, some snow
showers are being observed out ahead of the surge, and some of
these will get into parts of western Maryland from Hagerstown to
Frostburg and the panhandle of eastern West Virginia. A quick
coating to half an inch of snow is possible, mainly on grassy
surfaces. Elsewhere, some additional clouds or a few flurries
will be possible in the early morning hours. Otherwise, a mostly
sunny and once again blustery day is expected with wind gusts
up into the 25-35 mph range, with the highest gusts across
northern and central Maryland. With high pressure gradually
building into the region, winds will be lighter further
southwest towards parts of central/western VA and WV.
Temperatures will be below normal, with highs in the 40s for
most locations, except around 50F in central VA towards
Charlottesville/Fredericksburg. With the wind, wind chills will
not out of the 20s/30s for most locations.


High pressure will crest overhead tonight, leading to decreasing
winds, dry conditions, and mostly clear skies. Some high clouds
will begin to increase aloft ahead of the next approaching
system, but they should be thin enough to not hinder radiational
cooling all that much. Lows should bottom out between 20-30F.

A fast moving low pressure system will then elongate and track
from near St. Louis Saturday morning east-southeastward
towards the NC/VA/TN region by late Saturday. Warm air advection
and isentropic lift will lead to precipitation overspreading
portions of the region Saturday morning, lasting into the
afternoon, and ending by the evening. Given the cold start to
the day and reservoir of cold air nearby across New England, at
least some wintry precipitation is expected. The northern extent
of the precipitation shield is still in question, as is the
thermal profile evolution, but a stripe of accumulating snow is
possible, in addition to some freezing rain/sleet Saturday
morning, before changing to rain Saturday afternoon. At this
time, the highest likelihood of seeing snow appears to be
portions of the highlands in eastern West Virginia and western
Maryland, with some light sleet/freezing rain accumulations
possible west of the Blue Ridge. That being said, uncertainty
remains. With the precipitation overhead through the day, highs
will likely not get out of the upper 30s/low 40s for much of the
region. If some areas don`t see precipitation, some mid 40s or
even a bit higher are possible.

Precipitation will taper off by Saturday evening as high pressure
builds back overhead Saturday night. Lows Saturday night will
fall back into the 20s to around 30F. Sunday should be a much
nicer day, featuring mostly sunny skies and highs back up into
the low to mid 50s.


Low pressure will likely track through the central CONUS Monday
and toward the Appalachians Monday night before transferring
its energy to a coastal low that will track up the Mid-Atlantic
Coast Tuesday into Wednesday before tracking toward New England
by Thursday.

A confluent zone in the upper-levels of the atmosphere will
continue to exist over New England between upper-level low
pressure over the Canadian Maritimes and high pressure over the
Great Lakes. This will build surface high pressure to our north
over New England. This will likely put our area on the cold side
of the storm with low pressure tracking through the Tennessee
Valley Monday and transferring its energy to a coastal low off
the Mid-Atlantic Coast Monday night into Tuesday. However, it
is the middle of March so there is still a question as to how
much cold air there will be for snow/wintry precipitation.
Latest deterministic guidance shows the potential for rain or
snow depending on subtle differences in the track of the low.
Latest ensemble guidance shows a multitude of solutions as far
as how strong the low will be and its exact track. Therefore,
it is too early to pinpoint exact details. As of now it is
increasingly likely that our area will be impacted by coastal
low pressure Monday night into the middle portion of next week.
There is even a possibility that the coastal low could hang
around nearby for a few days due to the blocking pattern
previously mentioned. Therefore...a prolonged period rain or
snow cannot be ruled out. Will continue to monitor over the next
several days as well as mentioning the possibility of wintry
weather impacting our area during this time.


VFR is expected through tonight with the main aviation weather
concern another day of gusty northwest winds with gusts 20-30
knots.  A period of light rain or mixed precipitation is likely
Saturday and this may bring some sub-VFR conditions, with the
highest likelihood at CHO. BWI/MTN have the lowest probabilities
of impact.

VFR then returns area-wide by Saturday night and continues
through at least Sunday night.

Low pressure will approach the Appalachians Monday before
transferring its energy to a coastal low later Monday night and
Tuesday. Rain or snow are likely Monday night and Tuesday with
subVFR cigs/vsbys.


Small Craft Advisory conditions are expected across all waters
through this evening with gusty northwest winds. As high pressure
builds across the waters tonight, winds will diminish and drop
below SCA criteria. Winds should then remain largely below
criteria through Sunday night, although a brief period of
marginal gusts may occur on Saturday across the northern
Chesapeake Bay.

Low pressure will approach the Appalachians Monday before
transferring its energy to a coastal low later Monday night and
Tuesday. Small Craft Advisories will likely be needed for the
waters Monday night and Tuesday.


More gusty winds are expected around low pressure over the
Canadian Maritimes. Somewhat chillier conditions are expected
as well with high temps in the 40s but fuels are drier compared
to recent days. The relative humidity will drop to between 15
and 25 percent across central Virginia and 20 to 30 percent
across northern Virginia, eastern West Virginia and Maryland.
The strongest winds will be displaced from the lowest RH values
(strongest winds over Maryland, northern Virginia and eastern
West Virginia). An enhanced threat for the spread of wildfires
is expected later this morning into early this evening given
the fact that fuels will be dry and RH values will be low. Will
issue a Special Weather Statement for areas where the winds are
expected to be strongest (Maryland...eastern West Virginia and
northern Virginia). Will leave central Virginia out for now
since winds will not be as strong...but it will be quite dry.


MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.


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