NWS updated
The air aloft is cold enough to support snow, and despite the
warm conditions this afternoon, there should be enough dry air
for wetbulb cooling to take place, causing any rain or rain/snow
mix at the onset to change to snow for most areas. Even still,
temperatures will be marginal at the surface near to perhaps
even a degree or two above freezing across the metro areas and
southern MD, to perhaps near or a degree/two below freezing near
the Mason-Dixon Line and the higher elevations. Also, with the
warm conditions leading up to the event, that will affect the
SLR`s as well. Therefore, the accumulating snow will be
dependent on the heavier snowfall rates, which are possible
given the stronger frontogenetical forcing that is showing up in
much of the guidance. The banding snow may overtake the marginal
temperatures for a period Sunday morning, causing the snow to
accumulate. Have continued with the Winter Storm Warnings for
the Metro areas as well as northern and central Virginia, and
central Maryland. These areas have the best chance for heavier
precipitation with temps close enough to freezing for 3-6" most
likely. Farther west across the northern Shenandoah Valley into
the Potomac and Allegheny Highlands, Winter Weather Advisories
are up for 2-4" of snow most likely. Temperatures will be colder
leading to higher SLR`s, but the better chance for heavier
snowfall rates will be to the east. Across southern MD, a Winter
Weather Advisory is in effect. Despite the heaviest
precipitation rates across this area, temps will be a little
warmer causing snow to mix with rain at times.
The confidence in the forecast is lower than it would typically
be because, the snowfall accumulation will be dependent on
exactly where the heavier bands of snow setup since temps are
marginal.
Precipitation will move out of the area Sunday afternoon and
most areas will rise well above freezing, causing any snow that
does stick to melt. The one exception will be along the ridges
of the Allegheny Highlands.