Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
Weak layers buried two to three feet deep are the culprit of recent instability in the upper snowpack, with the most reactive slopes found near the tree line down to about 5,000 feet. Buried surface hoar is still the most well-preserved on north to east-facing slopes, while sunnier aspects have a breakable crust with faceted grains looming above and below it. Although deeper weak grains are showing initial signs of strengthening, they still remain vulnerable to failure if impacted from the "not-so-sweet" spot of a slope.
We've struggled to paint a common sense pattern of weak layer distribution across aspects/ elevations within our forecast zones. Given the slab depth above these layers, triggering an avalanche could result in a large, wide-breaking, and dangerous slide. Backcountry users are still reporting warning signs like collapsing and cracking, though avalanche activity has diminished significantly. Our persistent problem is steady as she sails for now, but slab depth appears to directly influence triggering potential and ultimate avalanche size.
(2/2/2025)
An example of shooting cracks that extends across the slope. This is a warning sign that a cohesive slab of snow can fail under the weight of a skier or snowmobiler.
Photo: Micah Krmpotich