Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Persistent slab avalanches are dangerous and can catch even the most experienced backcountry travelers by surprise. We also know that fresh wind slabs formed on open slopes near and above treeline Tuesday and that you're likely to find deeper slabs below ridgelines in areas closer to the Cascade crest. As you start to transition both in elevation and aspect, look for evidence of firmer wind transported snow, avoiding terrain steeper than 30 degrees in these areas. Give yourself an extra buffer while traveling along ridgelines and in terrain connected to steep open slopes above.
Observers have reported a layer of weak snow (facets 1.0-1.5mm) resting on a crust that formed in the past week. Near the Cascade Crest, you can find this weak layer about 10-20 inches (25-50cm) below the surface. On Monday, observers in the Highway 2 corridor near Lost Lake, as well as close to Stevens Pass, reported collapses up to 100ft in diameter and snowpack tests that indicated propagation.
Sticking to treed terrain, lower angle slopes without overhead exposure or windward aspects will help you travel safely on Wednesday.
(12/14/2020) Observers found up to 8 inches of snow over a facet crust combo near Lost Lake. They reported whumphs as big as 100ft across on this weak layer.