Wind slabs

CBAC2020-21 Observations

Zone: Northwest Mountains

Date of Observation: 12/20/2020

Name: Zach Guy

Subject: Wind slabs

Aspect: South East, South

Elevation: N/ATL


Spotted a few more recent persistent slab avalanches fitting the usual pattern.

Weather: Moderate ridgetop winds. High clouds thinned through the day.

Snowpack: Rec skiing on southerly aspects to take a break from looking at persistent slabs. We had to manage for small windslabs that were easy to identify and avoid. Wind drifted slabs were 8” to 10” thick near treeline, easy to produce cracking on moderate slope angles. Above treeline, wind slabs were up to 18” thick and harder (1F) and more stubborn. These were all cracking on lower density snow from earlier in the week. We also got several rumbling collapses on lower angle terrain where buried sun crusts (2 feet deep) are thinner than on steep aspects. The basal structure transitions from a strong crust on steep south to a thinner, weaker, more collapsible crust on ESE.   We avoided drifts and stayed on more southerly pitches with no avalanche activity.