Persistent Slabs
- Alta montaña
- Límite del bosque
- Bajo el límite del bosque
- Probabilidad
- Unlikely
- Tamaño
- 2–3
Triggering a persistent slab avalanche is unlikely but not impossible. Persistent weak layers (facets, facets and crusts, isolated surface hoar) exist in the bottom and middle of the snowpack on nearly all slopes. Know that they are under your feet or sled. Warm and dry conditions last week finally gave these weak layers some time to rest, but they did not magically go away.
The SAC forecasters have avoided large, consequential, upper elevation avalanche terrain in this zone since mid-December, and we still don't trust it. You're most likely to find trouble on very steep (approaching 40 degrees), rocky, wind-affected slopes. Terrain like this is most common at upper elevations and especially in the alpine. Because these weak layers are deeply buried on many slopes, slides failing on them could be large and destructive.
ADDITIONAL DISCUSSION: Isolated wind slabs may have formed in "extreme" terrain over the past couple of days. Though small, these slabs could be sensitive to your weight. Calm, clear weather today could produce some small, sun-induced loose snow avalanches in very steep, rocky terrain, most likely on E-S-W aspects. Think about the consequences of being caught in even a small slide before committing to serious, exposed terrain.
There's still a small chance of triggering a persistent slab avalanche, primarily in terrain like shown in the photo—very steep, rocky, and wind-affected. Pole Creek area.