FOUS11 KWBC 270735

QPFHSD



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





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