Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
You could trigger wide, 1-3 foot thick avalanches where wind formed slabs above weak snow (facets, crust + facet combos, and isolated surface hoar) that developed during a month-long, January-February drought. The weak layers are ugliest on NW-N-NE-E aspects, both above and below the middle-to-upper elevation transition.
Thursday's remotely triggered avalanche in the White Cloud Mountains is a good reminder that Persistent Slab avalanche problems are slow to heal and can involve surprisingly soft slabs; this avalanche released several days after any snowfall. Snowpack cracking and collapsing are clear signs of unstable conditions. However, a lack of these obvious warning signs doesn't mean you're in the clear.
Persistent Slabs can release in surprising ways:
- They can break above you
- Avalanches may be much wider than expected
- You can trigger them from a distance—above, below, or to the sides of the avalanche crown
What's the easiest way to reduce the chances of finding trouble? Avoid steep, middle and upper elevation slopes facing the shady side of the compass (NW-N-NE-E) if you suspect or feel that a slab (stiffer, but not crusty, snow) has formed. Triggering large avalanches is much less likely where the upper 1-2 feet of the snowpack is soft and fluffy.
Additional Discussion - Wind Slabs: In typically windy, upper elevation and alpine terrain, the last storm formed wind slabs above slick crusts and hard, wind-hammered surfaces. Although these slopes do not have any glaring weak layers below the slabs, the weight of a skier or snowmobiler could be enough to trigger an avalanche. Be on the lookout for large dunes or drifts, clear signs the wind has transported a lot of snow. Although likely to be small, these slides can have big consequences in big terrain.
(2/10/2026) Slab avalanches near Elizabeth Lake in the Northern Sawtooths. NE @ 8,800'.
Photo: Sawtooth Avalanche Center