Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Recent storms built 2-2.5' thick slabs above weak layers of facets and facet + crust combinations. Observations indicate that these layers are most likely to cause trouble on steep, middle and upper-elevation slopes facing the northern half of the compass.
Before triggering an avalanche, you may not experience obvious signs of instability like snowpack cracking and collapsing or whumpfing. Avalanches could be triggered remotely, from lower-angle terrain above, below, or to the side of steep slopes. Persistent Slabs can release in surprising ways and break much wider than expected.
The best way to manage this problem is to stick to lower-angled slopes and simple, forgiving terrain free from terrain traps like cliffs, trees, or creek bottoms.
Additional Discussion: Today's snowfall and moderate wind may form thin, fresh wind slabs in areas exposed to the wind. Look for these near ridgelines, along steep mid-slope gullies, and on aprons below cliffs. Cracking is a great indication that you've found a sensitive slab.
(3/18/2025) Very large slab avalanche on Williams Pk, Sawtooth Mountains. Photo: Sawtooth Avalanche Center