Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2
Poor snowpack structure exists on all aspects at middle and upper elevations. This includes layers of buried surface hoar and facets around a crust. Recent strong-extreme winds from the west may have overloaded these weak layers, and the zone will now experience rapid warming on Saturday.
This is an atypical snowpack setup that we don't often experience in the WA Cascades, so you can't roll out your typical playbook to recreate with. All steep open terrain is suspect, including moderately treed areas where strong wind has snuck its way in. Avalanches could be triggered from below or next to steep slopes. A change to denser feeling snow underneath your equipment is a good indication that it has been influenced by the wind. Cracking, collapsing, and recent avalanches are also a red flag indication to stay off steep slopes.
We have uncertainty around this problem due to a lack of observations, so take some time to poke around for more info in the specific area you plan to recreate. You can dig small hand pits and pull on blocks of snow to see how easily overlaying slabs break free from weak snow underneath. Small, steep test slopes or convex features can help gauge the reactivity of the upper snowpack. But given snowpack variability, be cautious about extrapolating your results too broadly.
It might be more likely to trigger smaller fresh wind slabs independent of buried weak layers. However, the potential consequences of being caught and carried are the same. You should be concerned about triggering true wind slab avalanches in the same places where you could trigger a larger persistent slab avalanche.
(2/22/2026)
A small, remotely triggered avalanche in the Buillon Basin area, failing 14-16" deep on buried surface hoar.
Photo: Sam Clairmont