Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
A widespread, well-preserved buried weak layer was responsible for two rider-triggered slab avalanches in the Whitefish Range this past week. This layer lies within the top foot or so of the surface in sheltered terrain and around two feet deep on wind-loaded slopes.
The recent heat wave has stiffened surface snow into a cohesive slab on polar aspects and a crust of varying strength on sunny slopes. You may not notice signs of instability, such as cracking or collapsing, before triggering a slide. This problem is notorious for riders remotely triggering slides from flat terrain above, to the side, and below steep slopes.
This is a near-surface problem, and hand pits are a useful tool for confirming the presence of a buried weak layer.
Sticking to a supportable crust will minimize the risk of impacting the weak layer. Choose low-angle slopes that are not connected to steep slopes in areas without a crust.
Wet Loose: Today's forecasted rain may wet previously dry snow, resulting in small wet loose slides. If the freezing line rises above expectations, this problem will become more widespread.
(2/3/2026)
Riders were ascending a northerly-facing slope when they triggered this thin, soft slab. This avalanche likely failed on a buried weak layer.
Photo: Flathead Avalanche Center