Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1.5–3
Expect to trigger a 1-2 foot thick Persistent Slab avalanche in areas sheltered from the wind. As you climb into windier terrain you could trigger a slide up to 5 feet thick. These avalanches will break wide and may fail in unusual locations. Anticipate remotely triggering these avalanches a large distance away from where they release.
We've observed dozens of Persistent Slab avalanches over the past week—many of which were human-triggered. Assume this problem exists on all upper and middle elevation slopes and shadier aspects at low elevations. Avalanches are failing on a variety of weak layers; surface hoar and/or facets on shaded slopes and a crust + facet combination on sunnier slopes.
The avalanches described above could "step down" to an additional weak layer of snow near the ground. This basal weak layer exists on upper elevation slopes and shaded middle elevation slopes. Avalanches that break down into this snow are likely to be unsurvivable (video).
(1/18/2024) These natural avalanches buried the highway near Galena Summit. They failed on E to SE facing slopes between 8,800 and 9,300'.