Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
A mix of facets and crusts leftover from October snowfall make up the base of the snowpack on most middle and upper elevation slopes. This layer is at its weakest on the shaded (N) side of the compass but old snow exists on upper elevation slopes that face the sun as well. Avalanches failing on this old snow have been observed with each major precipitation event this winter (photo at right/above).
Yesterday, the professionals at Sun Vally Heli Ski experienced a large collapse to the west of this Zone when they landed their helicopter in a safe location and collapsed this layer of weak snow. Public observers traveling in the Galena Summit area have also reported triggering large collapses involving this weak snow in recent days. In steeper terrain these collapses are avalanches.
There are two things that make it somewhat less likely to trigger an avalanche on this layer today: the weak layer is buried beneath a very dense slab of snow, and we have not had major precipitation for almost a week. The weak snow is getting a bit of time to adjust to the slab on top of it and that same slab is making it hard for us to impact the weak layer with our weight. But, there is a huge divide between harder to trigger and impossible to trigger. Read the Forecast Discussion below.
(1/1/2022) This avalanche in Prairie Creek occurred sometime during or just after the Christmas storm. E/NE aspect at 9,500'.