Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Fri Mar 22 2019

Valid 00Z Sat Mar 23 2019 - 00Z Tue Mar 26 2019

...Ranges of CA/Great Basin/Rockies...

Days 1-3...

Several systems will move into the West through the forecast
period bringing rounds of snow in the mountains.

The first is an upper low that crosses CO Friday.  Light to
moderate snow is expected along the track of the low and
accompanying mid level deformation zone from the front range into
the foothills of CO.  Snow tapers early Sat as the low moves east
on the Plains, where temperatures are forecast to be too warm for
snow.

Modest snows are expected in the ranges of northern CA across
northern NV, and eastern OR as a 700 mb wave moves onshore in
OR/northern CA and progresses inland, with ascent as enhanced 700
mb relative humidity and vertical velocity are forecast in advance
of the wave. A high risk for 4 inches is indicated in the high
Sierra terrain.

On Day 2 Sat night-Sunday, a period of snow occurs within the
cyclonic shear zone and upper divergence maxima cross the ranges
of northeast OR, southern ID to adjacent northwest WY.  This wave
is forecast to gradually shear with time, as low level convergence
fields weaken Sunday, resulting in a low probability of heavy snow
anyplace. Several inches are expected in the UT Uintas due to the
orographic lift plus synoptic lift from the approaching upper
trough.  A moderate to high risk of four inches is indicated, but
primarily a low risk of 8 inches.

Yet another system will then approach California Sunday night-Mon
on day 3.
The upper level circulation and core of coldest air is north of
CA, so the deep layer west southwest flow makes it likely the
valley areas will stay warm and snow is expected at higher
elevations of the mountains.  Several inches of snow is expected
in the Sierra Nevada range in CA, in response to a period of with
upper divergence maxima and low-mid level warm/moisture advection.
Since the band of enhanced moisture and lift last several hours
but not for a longer duration, heavy snow potential is somewhat
limited. Snowfall probabilities are low to moderate for 8 inches
in the Shasta/Trinity/Siskiyou/Sierra ranges.

...Interior New York/Northern New England...
Day 1...

A low drifting northeast across the Maine coast tonight into New
Brunswick tomorrow will combine with an upper low crossing
interior NY/New England to bring another round of snow before
ending as the low departs Sat.
Cold advection on NW flow has developed. It will lower snow
levels, with initial mid level frontogenesis and deep moisture
leading to moderate to heavy snowfall accumulations in the
Adirondacks, St Lawrence Valley, and northern Green Mountains.  As
the synoptic system gradually pulls away, an emphasis on upslope
flow providing the source of lift is expected, which has led to
lake enhanced snow developing over Lake Ontario.  Several inches
are likely in the areas along the eastern and southeast shore
downstream from lake Ontario, with accumulating snow showers
extending into the northwest Catskills, and then the Berkshires of
MA. Lesser accumulations are likely as far SE as the Worcester
Hills.

The probability of significant freezing rain is less than 10
percent.

Petersen