Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Recent strong winds and light accumulations have built shallow slabs along ridgelines and these could be prime locations to trigger larger persistent slab avalanches. Triggering a large avalanche in more sheltered terrain is becoming more difficult, but not impossible.
The likelihood of triggering one of these large avalanches that break 1-3 feet deep on buried surface hoar or facets above the 2/7 crust has gradually decreased this past week. Our last known avalanche that failed on this persistent weak layer occurred on 2/28 on Darland Mountain (observation here).
We’re getting to a point where you may or may not receive any signs of instability before triggering a large, potentially unsurvivable avalanche. Just because there are tracks on a slope, it doesn't mean it's safe. The best way you can reduce your exposure to this tricky problem is to avoid steep open slopes greater than 30 degrees, especially where the wind has formed deeper drifts, such as beneath ridgelines or in rocky terrain.
(3/1/2026)
Snow machine triggered large (D2) persistent slab and self extricated on 2/28. Darland Mt. NE aspect, 6700 ft.
HS- AMu-R2-D2-O @ NE, 6700' Photo: Northwest Avalanche Center