Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
A layer of surface hoar buried 1-2’ deep can be found across our forecast area. Although this layer has been buried for three and a half weeks, it continues to produce obvious signs of instability. On Saturday, in the Salmon River Headwaters, a rider remotely triggered a small slope from below (photo). In the weeks since it was first buried, even small storms and wind events have been enough to reactivate this layer.
Dealing with persistent weak layers is challenging and frustrating. Even as the snowpack gives us fewer and fewer obvious signs of instability, the possibility of triggering a slide remains. Read more about how I think about dealing with this type of problem in the forecast discussion section below. Persistent slabs can fail in surprising ways and break wider than expected. And, as the slide on Saturday illustrated, they may be triggered remotely—from above, below, and to the sides of steeper slopes.
Additional Discussion
On Friday and Saturday, moderate to strong N-NW winds built fresh wind slabs. This weekend, multiple groups of skiers and riders saw signs of instability associated with these fresh slabs. They’ve had a bit of time to bond to the surfaces they are on, so the likelihood of triggering one has decreased. The larger concern now is the additional stress that they are adding to the weak snow buried underneath.