Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 3
Many large and dangerous human-triggered avalanches have occurred over the past several days, failing on a layer of faceted snow (a persistent weak layer, or PWL) that formed during the January/February drought. Avalanches failing on this PWL are 2-4' deep and well over 100' wide. The PWL can be found at all elevations on slopes facing west through north and east.
On Sunday, we added 0.4" to 0.9" of water with some wind-loading to this inherently dangerous snowpack structure.
A few additional notes of caution:
- Signs of instability may not always be present: you may or may not see or experience shooting cracks or audible collapsing.
- Tracks on the slope offer zero signs of stability. Avalanches can take out multiple existing tracks.
- You can trigger these avalanches remotely - from a distance or from below.
- Many avalanches have occurred at lower elevations below 8,000' such as this natural avalanche in Lamb's Canyon.
The good news is that Sunday's dense snow will provide safer and superb riding conditions on lower-angled slopes with nothing steeper above you.