Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Mon Oct 27 2025

Valid 12Z Mon Oct 27 2025 - 12Z Thu Oct 30 2025


...Northern/Central Rockies...
Day 1...

Persistent moisture on confluent west to east flow impinging into
the Northwest will be acted upon by height falls/PVA through the
last in this series of shortwaves moving from ID into MT and WY
today into tonight. This feature will be quickly followed by
shortwave ridging in its wake, bringing an end to precipitation by
the end of D1. Snow levels will remain relatively low, around 3500
ft west, 4500 ft east, with several inches of snowfall likely above
these levels, leading to at least scattered pass level impacts.
WPC probabilities D1 indicate a high chance (>70%) for additional
snowfall above 6" in the Tetons and Big Horns, with light snow
accumulating to a few inches likely in the CO Rockies, the
Northern Rockies, and even into the higher Black Hills.


...Washington Cascades...
Day 2...

A potent, but progressive low pushes across the BC coast Tuesday
night with a trough axis extending south over Washington State. A
brief period of enhanced moisture noted in regional soundings will
result in transient but heavy precipitation, driven by a narrow
corridor of intense 700-600mb fgen late Tuesday night. The
strongest fgen appears to efficiently intersect the DGZ, which will
deepen as colder air floods eastward behind the accompanying
shortwave. While the heaviest precip will likely occur with snow
levels around 8000 ft limiting pass-level impacts, they will crash
quickly, aided by the heavy precipitation rates, to around 4500 ft
before precipitation wanes. This results in WPC probabilities for
more than 4" of snow reaching 70-90% across the highest terrain of
the WA Cascades, with a few inches of snow likely at Washington
Pass.


The probability of significant ice across the CONUS is less than
10 percent.


Weiss