Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 AM EST Sat Mar 02 2024

Valid 12Z Sat Mar 02 2024 - 12Z Tue Mar 05 2024

...West Coast & Northern/Central Rockies...
Days 1-3...

**Significant multi-day winter storm producing extremely heavy
snowfall in the Sierra Nevada**

Deep trough and embedded upper low will move into the West Coast
this morning, continuing an onslaught of extremely heavy snow over
the Sierra Nevada during the first part of the D1 period. Nose of
the 130kt jet streak into the northern Sierra will lie atop
impressive lift through the column into the DGZ, maximized by
well-aligned upslope flow, to continue to yield snowfall rates of
3-6"/hr this morning in the Sierra, slowly sinking southward into
the afternoon and easing in intensity. However, another wave of
heavy snow will move through the northern to central Sierra this
evening with rates of 1-4"/hr. WPC probabilities for another 12
inches of snow today through 12Z Sun are around 100% in the high
Sierra (where 2-3ft+ will be common), and >50% above about 3000ft.
To the north and east of the Sierra, incoming troughing will
promote widespread snowfall over much of the Northwest/Great Basin
into the northern/central Rockies as snow levels lower regionwide.
WPC probabilities for at least 8 inches of snow are highest in the
NorCal ranges, the higher Cascades in OR into southern WA, across
the NV ranges, into the Wasatch northward to the Tetons/Wind River
Range, and as far east as the CO Rockies.

Into D2, the leading front and height falls will move into the
Plains while a trailing stream of vorticity (all the way back to
southern Alaska) will continue to feed into NorCal and associated
with a more elongated jet streak. Snowfall rates will be much
lower than with the current system, on the order of 1-2"/hr,
supporting more isolated totals in excess of 8 inches or so. WPC
probabilities of at least 8 inches are highest (>50%) above about
4000ft as snow levels bottom out with the passage of the cold core
aloft.

By D3, another system within the very northern side of the
relentless troughing will dive into the Pacific Northwest,
focusing snowfall primarily over the OR Cascades into the NorCal
ranges (Klamath, Shasta/Siskiyous). WPC probabilities for at least
6 inches of snow on D3 are highest (>50%) from the southern WA
Cascades southward to the northern Sierra as snow levels slowly
rise. Strong westerly flow will also favor the Blue Mountains into
the central ID ranges with spillover precip.


...Northern High Plains...
Days 1-2...

Leading height falls associated with the western system will swing
into the Black Hills overnight tonight into early Sunday, deepen
in response to upper jet buckling over southern Canada, and take
on a negative tilt as it forms a closed low over ND Sunday
evening. A surface low will move out of northeastern WY across SD
and lift northward through the Red River Valley of the North in
Canada by late Sunday afternoon. Temperatures are fairly marginal
across the High Plains though dew points are in the teens closer
to the Canadian border. Frontal boundary south of the ND/SD border
will lift northward as a warm front as the surface low approaches,
promoting an area of mixed precip and some light icing over
central/eastern ND into northern MN. WPC probabilities for at
least 0.10" icing are around 10-25%. Northwest of the surface low
and closer to the mid-level center will be an area of light to
moderate snow, enhanced by a surface trough/deformation axis
extending into the Canadian Prairies. Wrapped up evolution of the
system will promote at least a brief extension of a TROWAL into
the region, though the heaviest snow will be over Canada (roughly
200 miles north of the border) where the pivot point will have the
longest residence time. WPC probabilities for at least 4 inches of
snow are highest (near 90%) along the Canadian border in far
northern/northwestern ND, and trail off from north to south to
about 10-20% near I-94 in western ND and also into far
northwestern MN.


***Key Messages for the Major Western Winter Storm***

--Heavy Mountain Snow Continues
Extremely heavy snow rates of 2-6 inches per hour are ongoing in
the Sierra. Total snow accumulations of 5-12ft, especially above
5000 ft, are forecast through late Sunday. Many passes across the
Sierra are closed as of early Saturday. Avalanches are
increasingly likely.

--Blizzard Conditions in the Sierra Nevada
Strong winds gusting 60-80 mph, locally over 100 mph at the
highest peaks, will cause significant blowing and drifting snow
and whiteout conditions, making travel impossible in the Sierra
Nevada. Substantial, long-lasting disruptions to daily life are
expected in the higher elevations through Sunday.

--Widespread Damaging Wind in the Western U.S.
Wind gusts of 55+ mph are forecast across much of the West,
particularly across higher elevations and the Intermountain West,
where 75+ mph gusts are possible. These winds will cause difficult
travel, and likely down trees and power lines, resulting in
widespread power outages.  

--Colder Temperatures and Lower Snow Levels
As the storm moves south, snow levels will lower to bring
accumulating snow down into many valleys. Much colder air is
forecast this weekend, with temperatures 10-20 degrees below
normal.

Mullinax