Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Sunday’s storm snow fell on various weak surfaces (facets, crust + facet combos, and isolated surface hoar) developed during a month-long drought. Triggering a large persistent slab avalanche is possible, as evidenced by recent observations of natural and human-triggered slab avalanches. You're most likely to find trouble in recently wind-drifted terrain. Assume that weak faceted layers exist beneath the storm snow on NW-N-NE-E aspects at middle and upper elevations, increasing the chances of triggering a slide.
Snowpack cracking and collapsing or whumpfing 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, break wider than expected, and be remotely triggered by releasing above, from the side, or from flat terrain near steep slopes. Your best way to play it safe today is by avoiding steep slopes facing the shady side of the compass where you suspect or feel a slab has formed.
Additional Discussion - Wind Slab: Sunday's storm also came in with wind that built 1-3 foot thick slabs in upper elevation and alpine terrain. Pay attention to the snow you are traveling through; if it is becoming denser or deeper, you are probably moving through a wind slab. They can feel hollow or drum-like, which indicates that they are sitting atop weaker snow and should be avoided when on a steep slope. You can dramatically decrease the chances of finding trouble by avoiding steep, wind-loaded slopes.
(2/10/2026)
Slab avalanches on McDonald Pk in the southern Sawtooth Mountains. There are crowns under the cornices at the top of the photo, as well as under the cliffs. E and SE aspects 9,500-9,700'.
Photo: Sawtooth Avalanche Center
