Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2–3
Rain and heavy wet snow have loaded the weak layers in our snowpack. .6 to 1.30'' of snow water equivalent (SWE) overnight is a sizable load and will add weight and stress to multiple weak layers. The Jan 2 persistent weak layer-made up of buried surface hoar, faceted snow, and/or a crust/facet combo-has been reactive in multiple avalanche cycles over the past 2 weeks. Avalanches that occur today could step down to weak faceted snow located much deeper in the snowpack around the Dec 19 rain crust or on the depth hoar at the ground. Naturally or human triggered avalanches could occur today resulting in large and destructive avalanches 2 to 6+ feet deep.
Recent avalanches, long shooting cracks, snowpack collapse, or whumpfing sounds are indications of unstable persistent slabs in the immediate area. These avalanches could be remotely triggered from low angle terrain above, below, or off to the side of a steeper slope. The only effective way to manage a persistent slab avalanche problem is avoidance. If recreating in the backcountry today, carefully choose terrain that is well under 30 degrees in steepness and not connected to any steeper terrain nearby.
(1/14/2024)
Remotely triggered avalanche from group on ridgeline, Jan 14. Shallenberger Ridge, Donner Summit area.
