Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
The most likely places to get an avalanche are northerly and easterly facing slopes if they have been loaded by recent winds. On these slopes avalanches may break 1-2 feet deep on a persistent weak layer of facets generally found about a foot above the ground.
Yesterday Craig and I rode out of Mill Hollow and we found two things: (1) The snowpack is generally weak & rotten & full of facets. Even the snow surface has faceted which made for great skiing conditions. (2) Strong winds occurred on Wednesday & Thursday from the west and north. Further north just east of Bear River in Mill Creek, Ted Scroggin found similar conditions and has a great report here.
What does all of this mean? Below treeline, the snowpack is basically one big persistent weak layer lacking a slab on top to create an avalanche. Near treeline snow depths increase some, and there is more of a slab on top of the weak snow. Without loading from significant snowfall, weak facets buried in the snowpack aren't as sensitive as they were last weekend except in places loaded by recent winds.
Photo - north aspect near 10k feet. Snow layers near the shovel blade are snow that fell in November and early December. The weakest snow is the obvious stripe of facets near the top edge of the shovel blade. That stripe of weak snow sits on a decomposing crust. Snow near the shovel handle is the slab that can create an avalanche. Slopes with the added weight of wind drifted snow on top of this layering are the ones most likely to avalanche.