Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Sun Mar 24 2019

Valid 12Z Sun Mar 24 2019 - 12Z Wed Mar 27 2019

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

Days 1-3...

3 mid-level impulses will bring snow to the West through the
forecast period. The first is a weak shortwave lifting northeast
from the Great Basin into Montana before shifting eastward early
Monday morning. A broad but modest Pacific Jet will follow
immediately in the wake of this feature, and the combination of
diffluence and height falls/PVA will produce modest ascent from
the Colorado Rockies northward through the Northern Rockies and
into the Washington Cascades. This system is weak and moves
quickly, so total snowfall will be light, with the highest
probabilities for 4 inches in the terrain above 5000 ft in the
Uintas, Rockies, Sawtooth, and ranges of NW WY.

As this first system moves out, a more potent trough will lift
onto the Northern California coast and eject into western Canada
Monday night, followed quickly by a third impulse encroaching on
the California coast late on day 3. The best moist advection and
synoptic ascent due to jet level diffluence will focus in the
Northern Sierra of California D2/D3, as well as the
Shasta/Trinity/Siskiyous as 700mb flow becomes southerly
/orthogonal/ to the ranges producing intense upslope forcing. Day
2/3 totals may eclipse 3 feet in the Sierra, and 2 ft near Shasta,
and WPC probabilities show moderate to high risks for 12 inches
each day. Further to the north, snowfall will spread across the
high terrain from northern NV into ID/MT/WA/OR as a jet rotates
cyclonically around the trough keeping this region in the
favorable LFQ for ascent. This combined with subtle 850-700mb fgen
in response to a weak front will produce moderate snowfall, but a
relatively warm airmass will keep snow levels above 4000 ft
outside of the Washington Cascades. WPC probabilities are moderate
for 6 inches only in the Cascades, with lesser accumulations
likely across the other ranges.


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

Weiss