Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Triggering a large avalanche up to 2 feet thick is possible where weak layers have been buried since the beginning of February. The current slab sits on a variety of weak surfaces, including crusts/facets on solar aspects and facets on shady aspects. This interface could be sensitive to the weight of a single rider or snowmobile. You are most likely to trigger an avalanche on very steep rocky slopes. Specifically, consider where the overlying slab might be thin and where you can more easily impact weak layers below - such as around the margins of wind-loaded slopes. Large triggers like snowmobiles, cornices, and small avalanches in more recent snow will increase the likelihood of triggering a large avalanche. Dig down and investigate layers in the top two feet of the snowpack, but keep in mind that buried weak layers from the January dry period will be as deep as 4 feet in wind-loaded areas and will not show any signs of instability like cracking or collapsing until an avalanche is triggered. Continue to travel safely by going one at a time around steep avalanche terrain and spacing out around terrain traps like creek beds and gullies.
Additional Discussion: Over the past 48 hours, Togwotee has received 2 - 3 inches of new snow with light winds from the west and south. Small wind slabs may form at upper elevations where winds have transported new snow. Continue to evaluate terrain where wind slabs typically form, such as ridgelines and leeward slopes. Small avalanches may have the ability to trigger a larger more destructive avalanche.
These creek drainages have previously avalanched, and debris was noted in the creekbed, in addition to these recent smaller cornice/wind slab avalanches. While Togwotee trends with Moderate hazard, terrain trap features like this should be considered cautiously or avoided altogether.
Photo: Bridger-Teton Avalanche Center
