Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
Recent storm snow and wind blown snow exists over the top of a buried persistent weak layer in many areas of the forecast region. This weak layer is widespread in below and near treeline terrain and isolated in above treeline areas on W-NW-N-NE-E aspects. The persistent weak layer is buried up to 1 foot deep with whumpfing sounds, cracking, and unstable snowpack test results reported throughout large parts of the forecast area over the last 2 days. Where this weak layer is present makes up a large percentage of the overall useable terrain with our early season shallow snowpack. Human triggered avalanches remain possible today with the potential for wide propagation, remote triggering from any connected terrain, and mid slope avalanches. Additional load from the storm forecasted for tonight and tomorrow is expected to cause this weak layer to fail in some areas.
Managing a persistent slab avalanche problem is challenging. We know we have a poor snowpack structure and there are many signs of instabilities, but we haven't seen any avalanche activity. The only way to effectively manage this avalanche problem is to use terrain to avoid areas where this problem is located until it goes away. Limit terrain choices to under 30 degrees, avoid avalanche run out zones and any connected terrain which may be steeper that could be remotely triggered. Consequences of any avalanche continue to remain elevated due to shallow snowpack conditions and exposed obstacles.