Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1.5–2.5
Yesterday, a skier triggered a large avalanche near the Banner zone. Fortunately, they were able to ski off the moving snow. This avalanche likely failed about 2’ deep on the weak sugary facets that formed during the Jan/Feb drought.
Triggering similar avalanches today is most likely in recently wind-loaded terrain. The recent storms built slabs above multiple layers of weak facets, surface hoar, and crust-facet combinations on many middle and upper-elevation slopes. In the past week, there have been 12 reported human-triggered slides failing on these weak layers. These avalanches were all between 8500' and 9500' on NW-N-NE facing slopes with wind-affected surfaces.
Persistent Slabs can release in surprising ways. They can be much wider than expected and be triggered remotely—from flat terrain below, above, and to the sides of steep slopes.
Avoiding steep wind-loaded slopes is the best way to avoid trouble today, but recognize that avalanches are also possible in steep wind-sheltered terrain. Snowpack cracking and collapsing are clear signs of unstable conditions.
Additional Discussion: Whether a weak layer exists or not, the combination of recent snowfall and moderate to strong winds formed slabs that may remain sensitive to your weight. Look for wind-affected surfaces, dunes, or drifts. Feel for stiff slabs overlying weaker or softer snow. These often form near exposed ridgelines. These smaller wind slabs, once moving, are an effective trigger for the larger Persistent Slab avalanches described above.
(2/19/2026)
Very large avalanche on McDonald Peak in the southern Sawtooths. NE @ 9,500'.
Photo: Sawtooth Avalanche Center