Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
A weak layer buried 1 to 2 feet deep exists on shaded slopes. You could trigger an avalanche on this layer remotely from a shallower slope below or further back on a ridgeline than you expect. Slab thickness will increase with elevation and in wind-affected areas.
The best way to manage this problem is to let the surface crust thickness dictate your travel plans. A hard, stout, supportable crust that is beneath the few inches of recent snow is the safest route to go. Travel in places where you need sunglasses and your skis or machine are not breaking through more than 3-4 inches of snow. If you choose to ride in shaded terrain (i.e., better ski conditions), keep the slope angle low to provide a margin of safety.
(2/4/2026)
A recent, rollerball-initiated persistent slab avalanche (D2) in the Flathead Range. (Paola Ridge). 6800' - SE
Photo: Michael Reavis