Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
426 PM EDT Wed May 1 2024

Valid 00Z Thu May 02 2024 - 00Z Sun May 05 2024

...Northern Rockies and Oregon Cascades...
Day 1...

Mid-level low pressure remains centered over southern Saskatchewan
through tonight while a reinforcing trough rounds the low, crossing
from the ID/WY border this afternoon and becoming the dominant low
on Friday north of Minnesota. A second reinforcing trough from the
northeast Pacific crosses the PacNW coast tonight.

Flow wrapping around this low pushes into the eastern slopes of the
northwest MT Rockies/around Glacier NP this evening, shifting
southeast over the west-central MT ranges (like the Big and Little
Belts) late tonight that continues through Friday morning. Snow
levels through Day 1 are generally 4000 ft over this area. Day 1
PWPF for >6" are 50-80% for the Lewis, Mission, and Big/Little
Belts. 12Z HREF mean snow rates generally peak around 1"/hr with
this generally moderate precipitation.

The wave reaching the PacNW coast tonight brings a swath of late
night locally moderate precip along the Oregon Cascades with snow
levels ranging from 4500ft in the northern OR Cascades to 6000ft in
the southern. Day 1 PWPF for >6" is generally 40-80% for the higher
Cascades.


...Cascades through Sierra Nevada...
Day 3...

A deep, closed low tracks south of the Gulf of Alaska Thursday and
approaches the PacNW coast late Friday then tracks over the OR/CA
coast Saturday. Snow levels will drop from around 7000ft with the
track of this low. The low track has been rather uncertain in
recent days, but with the 12Z global model suite, there is decent
certainty with the mid-level low center tracking into northern NV
through Saturday night. Snow levels of generally 5000-6000ft can be
expected over the Cascades/Sierra Nevada during the heaviest precip
Friday night/Saturday. Day 3 PWPF for >6" are generally 40-70% for
the southern OR Cascades/CA Cascades/Shasta-Siskiyou and
northern/central Sierra Nevada. Onshore flow would continue through
Saturday night, maintaining decent snow rates through that time for
similar areas.


The probability of significant icing is less than 10 percent.


Jackson