Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
317 AM EST Fri Feb 03 2023

Valid 12Z Fri Feb 03 2023 - 12Z Mon Feb 06 2023


...Great Lakes and Northeast...
Day 1...

In the wake of the potent shortwave trough and arctic cold front
passage, the anomalously cold and deep mid/upper low will skirt
through the Great Lakes and Northeast over the next couple of
days. Northwesterly to westerly flow will bring modest lake effect
snowfall to the eastern U.P. and downwind of Lake Ontario today
through tonight. WPC probabilities for 2" or more approach 50 to
70 percent with a slight signal for 4"+ across the far eastern
U.P. of Michigan.

...Western U.S....
Days 1-3...

A pair of weather systems over the next 3 days will bring
unsettled and active weather to the region with the threat of
heavy mountain snow for portions of the Western U.S. through
Sunday night. A compact shortwave trough will move from just
offshore the California coast to northwest Washington today
through tonight. The favorable forcing for ascent across the
region combined with an axis of higher moisture transport
positioned southwest to northeast will help bring widespread
precipitation to the region stretching from northern California to
western Washington. A relatively warmer system, snow levels will
limit accumulations to the higher terrain of northern CA to
western WA, but there are still high probabilities for 8"+ across
the WA Cascades and Olympics with the peaks likely to see
accumulations between 1-2 feet.

A stronger system then approaches the western U.S. late Saturday
night through Sunday night with the approach of a mid/upper level
low that tracks through/south across California during the day
Sunday. This system will have greater moisture transport, although
still modest levels of IVT and marginally above normal PW values.
The lack of a significant cold air mass in place will generally
keep snow levels higher and this should limit the greatest
accumulations to the higher terrain areas of the OR/WA Cascades
down through the Sierra Nevada. Nonetheless, with copious amounts
of QPF to work with and a broad/prolonged period of favorable
ascent will support heavy snowfall particularly late Saturday
night through Sunday. The latest WPC probabilities are moderate
for 8"+ across the OR Cascades and northern CA ranges while peak
at 90+ percent for the Sierra Nevada. For the Sierra Nevada,
isolated totals greater than 2 feet are likely during the day 3
period. Some of that moisture does begin to spill eastward across
the Intermountain West and Rockies including the central/northern
Idaho ranges, northwest Montana, WY Tetons, and Wasatch Mountains
where probabilities for 6"+ reach 30 to 60 percent late in the day
3 period.

Taylor