Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Sat Mar 23 2019

Valid 00Z Sun Mar 24 2019 - 00Z Wed Mar 27 2019

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

Days 1-3...

A couple of systems will move across the Western US through the
forecast period, with a long duration heavy snow becoming more
likely in the ranges of northern CA. 

For tonight through Sunday, a shortwave trough will push onshore
northern California and the Pacific Northwest the move northeast
through portions of Idaho and northern Nevada. With favorable
forcing for ascent, the highest accumulations are expected in the
mountainous areas of eastern OR, southern ID, and the UT
Wasatch/Uintas. Light accumulations are also expected in northeast
MT where moisture convergence occurs within a mid level cyclonic
shear zone.  Initial temperatures are too warm for snow, so precip
type remains an uncertainty.

As the upper trough drifts northeast Sunday night, the
accumulating snow will move across the northern Rockies near the
ID/MT border and northwest WY, with light accumulations of 2-4
inches expected.

A shortwave trough pushes and accompanying upper jet maxima moves
into California Monday night into Tuesday. This will bring copious
amounts of moisture across northern CA. Several inches of snow are
expected with potential for a foot across the
Shasta/Trinity/Siskiyou/northern Sierra ranges on Day 2 (ending
00z Tue).  Consequently, the the highest probabilities are shown
in these areas.  The day 2 plus day 3 totals indicate 1-2 feet of
snow are expected in these areas, with locally higher totals.  The
NAM has slightly higher QPF and snow following a strong 130 kt jet
maximum on Tuesday morning.

On Monday afternoon and Mon night, a circulation off the Pacific
Northwest drives a warm front north across the OR/WA Cascades,
with an accompanying surge in moisture and lift from the front, as
well as a forecast 300 mb jet maxima streaming from southwest to
northeast that has embedded upper divergence maxima to produce
lift.
The snow tapers as the front moves north into Canada Tue.  There
is potential for several inches of snow in the WA Cascades.

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

Petersen