Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Certain
- Size
- 2–3.5
Many flavors of large destructive avalanches—wet, dry, slabs, loose, wind-driven, etc.— are likely to release on their own today. The travel advice is simple: stay out of the way. Read the Forecast Discussion below for details on specific avalanche problems other than the Persistent Slab problem described here.
What is it? Powerful, 2-5 foot thick avalanches are a near certainty. Snowfall, wind-blown snow, and rain will overload the buried weak layers (sugary facets or crust + facet combinations) that produced hundreds of avalanches and tragically resulted in an avalanche fatality in recent days. Many slides will release naturally, on their own. Some avalanches will probably be over 1000' wide.
Where is it? Given that we've received snowfall all but one day since February 26th, the slabs exist on almost all slopes that have not already avalanched. Many of the slopes that avalanched last weekend have "reloaded" with fresh, dense slabs. The weak layers are also widespread.
How can you recognize it? Avalanche terrain includes slopes steeper than about 30 degrees and areas below steep slopes.
How can you manage it? Stay off of and out from beneath slopes steeper than 30 degrees. Persistent weak layers can fail unpredictably and break significantly wider, deeper, and higher on slopes than you might expect, producing much larger avalanches. Smaller loose snow and storm slab avalanches can trigger larger persistent slab avalanches lower on slopes. You could remotely trigger avalanches from gentle terrain far above, below, or to the sides of steep slopes.
(3/11/2023) This very large persistent slab avalanche was observed in the Boulder Mountains. It failed over 3,000' wide, wrapping around SE-E-NE aspects between 10,000' and 10,800'.