Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
The weak snow interface that we've been tracking in the upper snowpack; buried surface hoar and near-surface facets, remain the focus of our avalanche forecast. This interface was buried on 12/8 with over 2' of storm snow falling over several days. After some settlement, if you can still find these layers, they are likely 1-2' down near or below treeline.
The most recent signs of instability involving these layers include shooting cracks in White River Canyon on Monday. The last known avalanches on these layers occurred on Sunday when we received numerous public observations (thank you for submitting!) that reported widely propagating slab avalanches as well as snowpack test results highlighting this layer. Most significantly, a skier was caught, carried and partially buried after being strained through trees that day. Fortunately, the skier was uninjured and self-extracted.
Moving past the storm cycle and into the middle of this week, we have limited snowpit data that suggests the weak snow interface may be gaining strength, less likely to trigger, and harder to identify.
This is not your usual storm-driven avalanche problem. Persistent slab avalanches can be killers and stick around longer than other avalanche problems. They can break widely across slopes, around terrain features and can be triggered from much lower angled terrain below. Until we can put this problem to bed with more confidence, you'll need to continuously assess this layer as you travel throughout the landscape. Look and listen for red-flag indicators like whumpfs or rolling collapses. While a snowpack test won't give you a green light, you can use snowpack tests to gain information and help rule out terrain. Check out the video for more info.