Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Warm temperatures, fresh snowfall, and strong winds make it increasingly likely to trigger an avalanche on weak layers buried 1 to 3 feet deep. Southwesterly winds will deposit snow onto typical leeward slopes at upper elevations, adding further stress to weak layers.
You can trigger an avalanche on steep slopes or connected lower-angle terrain. Likely trigger points include slopes with obviously wind-affected snow, convex roll-overs, or rocks poking through the snow's surface.
Collapsing (whumpfing), shooting cracks, and a remotely triggered avalanche, have been concentrated in the Whitefish Range. Signs of instability may not always be obvious, and digging is the best way to identify if the slope you are on harbors a slab and a weak layer.
Today's snow and wind may be sufficient to produce fresh Wind Slabs. Small surface slides can trigger a larger avalanche on buried weak layers. Slabs 8+ inches thick can be hazardous in their own right. Steer away from wind-affected snow along ridges, below saddles, and in open bowls.
(2/13/2025)
A large natural avalanche triggered by a natural cornice fall from the ridge above. The intial debris stepped down to older weak layers as it ran down slope. SS-NC-D2.5R2-O
Photo: Flathead Avalanche Center
