Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
Our latest snow has consolidated into slabs 1-2 feet thick in protected terrain and up to 2.5 feet thick on wind-loaded terrain. These slabs sit on various widespread weak snow layers that developed in early December. The widespread nature of these weak layers means avalanches may be triggered on any aspect at middle and upper elevations.
The odds of triggering an avalanche are greater on the north half of the compass - where weak layers are well-preserved and winds formed slabs up to 2.5 feet thick. Signs of wind-transported snow include drifts, cornices, and textured snow surfaces. Persistent slab avalanches may not show signs of instability and can be triggered remotely from above, below, or to the side of steep slopes. Use a wide safety buffer around steep slopes to address the uncertainty. Evaluate terrain carefully today. Even a small avalanche can have serious consequences.
Warming Discussion: Warm ambient temperatures can increase the sensitivity of avalanches. As temperatures increase throughout the day, the likelihood of triggering an avalanche also increases. Small wet loose avalanches are possible today on sun-facing slopes. These will generally not be large enough to result in injury or burial.
(12/17/2024)
Slab avalanche failing on old weak snow. 8700' E aspect
Photo: Alex Drinkard