Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Fri Mar 01 2024

Valid 12Z Fri Mar 01 2024 - 12Z Mon Mar 04 2024

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

**Significant multi-day winter storm to produce extremely heavy
snowfall for the Sierra Nevada with widespread snow eastward to
the Rockies**

Deep upper low west of British Columbia this morning will continue
to advance southeastward into the weekend as a strong upper jet
punches into NorCal, favoring broad divergence aloft with
southwesterly flow bringing in moisture out of the Pacific. Cold
front has pushed into the northern Rockies/Great Basin and into
the northern Sierra where it will slow, stall, then dissipate as
another wave moves into the region overnight. Snow levels will
continue to fall into Saturday and early Sunday.  By then the
entire longwave pattern will start to relax and weaken as
precipitation starts to wane. Over the next two days, however,
several feet of snow are likely over the Sierra, driven by the
sustained moisture flux into the terrain at a nearly orthogonal
angle with impressive lift into/through the DGZ which will support
extremely high snowfall rates of 3-5"/hr along with strong winds
over 50-80+ kts. East of the Sierra, the broad SW flow will carry
moisture across the Great Basin to the central ID ranges and into
western WY along the lead cold front today, promoting heavy
snowfall into the mountains beneath the extended jet. By Saturday
into Sunday, increased westerly flow into the central Rockies will
favor a southward push of the snow across the NV ranges, the
Wasatch, and into the CO Rockies as the 130kt jet streak passes
through from west to east. By Sunday, another wave, albeit weaker,
will move into NorCal as heights rise across the west with its
passage, bringing in another round of snow.

Total snowfall will be extreme over the high Sierra, with max
totals over 10ft possible for the entire event. Even just on D1,
2-4ft+ is quite probable above 5000ft, and especially above
6500ft. WPC probabilities for at least 4 inches of snow are at
least 50% at elevations as low as about 3000ft or so.
Probabilities for at least a foot of snow are high (>70%) across
central ID and especially into the Tetons and Wind River Range in
WY. Into D2, the moisture plume will still lie across the Sierra
on a more westerly flow as the trough axis starts to come ashore,
nudging the axis of heaviest snow (still 2-4ft) over the central
to southern Sierra eastward across UT where WPC probabilities for
at least a foot of snow are highest in the Wasatch down into
southwestern UT. By D3, the highest probabilities for at least
another 6 inches of snow over the OR Cascades southward to the
northern/central Sierra, as well as across the CO Rockies.


...Northern (High) Plains...
Days 2-3...

Exiting shortwave out of the Rockies associated with the second
wave from the larger upper trough will lift through eastern MT
early Sunday and deepen as it rotates northward into southern
Canada. Surface low pressure is expected to deepen across/east of
100W with a favored area for snow on its NW side along the
US/Canadian border. Models have struggled with the evolution of
this system and its QPF placement/amounts, but the potential rapid
deepening of the system in the mid-levels as the upper jet swings
into the Upper Midwest suggests at least some potential of heavy
snow in the northern High Plains/northern Plains Sunday along a
surface trough axis, though mostly this will be across southern
Canada per the consensus. WPC probabilities for at least 4 inches
of snow are >10% along/north of I-94, and as high as about 70%
along the Canadian border.



The probability of icing of at least 0.1" is less than 10 percent.


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

--Heavy Mountain Snow Affecting Many Passes
Multiple feet of snow are likely (over 80% chance) for higher
elevations, especially above 5000 ft, including the Sierra Nevada
passes (such as I-80). Extremely heavy snow rates surpassing 3
inches per hour are likely.

--Blizzard Conditions Expected in Sierra Nevada
Very strong winds will cause significant blowing/drifting snow and
whiteout conditions, making travel impossible in the Sierra
Nevada. There is a high chance (over 70%) of substantial,
long-lasting disruptions to daily life in the higher elevations of
the Sierra Nevada through Sunday, where blizzard conditions and
5-12 ft of snow (and locally higher) are expected.

--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 likely down
trees and power lines, resulting in widespread power outages. 

--Cold Air Will Lower Snow Levels This Weekend
As the storm moves south, snow levels will lower into some
northern California and Sierra foothill communities. Much colder
air is forecast by the weekend, with temperatures 10-20 degrees
below normal.


Fracasso