Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
A persistent weak layer of faceted snow that developed during the cold dry period in mid November exists on aspects that face W-N-SE. You are more likely to trigger an avalanche on slopes facing NW-N-E, where wind drifted snow has built thick slabs on top. These hard slabs are 1-4' thick and can produce very large, deep, and potentially deadly avalanches. The snowpack has become quiet. You will not observe obvious signs of instability as you travel today, however a poor snowpack structure still exists. This is when things get tricky. Typically during December in a continental snowpack these types of instabilities take a long time to heal. I am still traveling conservatively. If you are stepping out into moderate terrain you should do so cautiously. It is wise to avoid complex terrain and terrain traps. It is possible trigger an avalanche on:
- Slope margins where the slab is more thin and the weight of a rider is more likely to trigger the weak layer
- Shallow, rocky areas with a thin snowpack
- Steep convex rollovers
You can avoid this avalanche problem by keeping your slope angles below 30 degrees, ride slopes that are heavily anchored by dense trees, or ride South facing slopes that do not harbor this dangerous persistent weak layer.
