Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 161455

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1055 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.


Behind our morning snow showers, skies are becoming mostly
sunny and it is once again blustery day with expected wind
gusts up into the 30-40 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 30-40
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.


Winds have proven stronger than expected across locations just
upstream of the waters, so raised a Gale Warning thru the rest
of the day for all waters. We drop back to Small Craft Advisory
this evening, then as high pressure builds across the waters
later 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 from 6 PM this evening to midnight EDT
     tonight for ANZ530>543.
     Gale Warning until 6 PM EDT this evening for ANZ530>543.


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