Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1.5–3
You are likely to trigger large, destructive avalanches failing on weak snow in our snowpack. Importantly, these avalanches are pulling back into lower angled terrain above steeper slopes. These slides can be triggered from a distance away — giving you a reason to increase your travel margins. Two types of these slides can occur today:
1) A 1-3 foot thick slab avalanche large enough to bury you will be easy to trigger on many slopes today. Avalanches will break hundreds to thousands of feet wide across entire slopes and span multiple aspects. These slides will be at their largest and most destructive in areas where the wind has deposited additional snow. But sheltered slopes are in no way safe: dozens of these avalanches have occurred in wind-sheltered terrain, and on smaller slopes at lower elevations such as road cuts.
2) Avalanches mentioned above can step down to a layer of weak snow near the base of the snowpack creating slides that are likely unsurvivable. These slides will move the entire snowpack downhill. This layer of weak snow exists on all upper and most shaded middle-elevation slopes (W-N-E).
The most important thing to know about these avalanches is that you can easily trigger them from long distances away. They can break well above you on the slope and can be triggered from flat terrain at the base of steeper slopes.
(1/14/2024)
Many avalanches that failed this past week have pulled back onto low angle slopes.
Photo: Ben VandenBos