Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 AM EDT Fri May 06 2022

Valid 12Z Fri May 06 2022 - 12Z Mon May 09 2022


...Pacific Northwest...
Days 1-3...

Longwave troughing will settle into the West this weekend, with
two separate short waves or closed lows move through the region.
This will steadily lower snow levels during the three-day period,
but with decreasing precipitation as well as the moisture plume
sinks southward into California. First system will approach the
Oregon coast this evening as a 130+ kt jet streak moves into
central Idaho, promoting broad lift through the region. Focus will
lie over the central Washington Cascades southward through the
Oregon Cascades where more than a foot of snow is likely at the
highest peaks, but otherwise snow levels will be above 5000ft.
Several inches are likely over the central Idaho ranges into
western Montana.

Onshore flow will maintain at least lighter snow for the higher
elevations through Saturday before another system moves into the
area. A stronger compact mid-level closed low will approach the
Oregon coast Saturday afternoon as a 130 to near 150 kt jet noses
into northern California. This system will be a bit colder and
with heights lower than the first system, expect snow levels to
drop to around 2-3000ft in places. The favorable left exit region
dynamics supports another round of snow, some heavy, for the OR
Cascades but also extending southward into the northern California
ranges and parts of the Sierra including parts of the Klamath
Mountains. There is also an increasing signal for heavy snow to
spread eastward across the central Idaho ranges and toward
Yellowstone in northwest WY, near the Madison and Gallatin Ranges
in MT. For Day 3, WPC probabilities for 4 inches are slight (>10%)
down to around 3-4000ft in some places in OR and CA, but higher
(near 7000ft) over parts of MT into WY. 

For days 1-3, the probability of significant icing is less than 10
percent.

Fracasso/Taylor