Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2–3
Triggering a large, 1-4 foot thick slab avalanche that breaks widely remains a worrisome possibility on many slopes. Avalanche activity during major storms of the past two weeks was widespread, occurring on all aspects. Many slides in this zone failed on persistent weak layers in the upper and middle portion of the snowpack. You'll find a variety of weak layers here (crusts with facets on solar slopes, and facets without crusts on shaded slopes). On Tuesday, a large persistent slab avalanche was triggered from a distance, releasing on a heavily wind-loaded slope in Croy Canyon (observation).
You may or may not receive obvious feedback from the snowpack today. The first sign of instability may be the large, wide avalanche that you trigger. These slides can be triggered after dozens of skiers or riders have traversed a slope. Triggered slides are likely to break far above you, making escape difficult to impossible.
These weak layers have gained some strength and the likelihood of triggering a slide on them is gradually decreasing, but the consequences would be severe. Triggering a slide is most likely in steep, rocky, open, heavily wind-affected terrain (see photo at right/above).
(3/7/2024) This large avalanche was triggered remotely from the ridge. It released in a heavily wind-loaded gully on a weak layer of snow buried at the end of February. Croy Creek, NW @ 6,000'.