Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 3
The entire snowpack is faceted through on shady aspects, providing a variety of weak layers. The immediate layer of concern is the old snow surface from before the storm on the night of February 11. This is the most sensitive of our many weak layers, and the easiest to trigger. Out of the wind zone, the weak layer does seem to be adjusting to the new load. However, it remains possible to trigger a soft slab avalanche that will initially be about ten inches deep. On steep, continuous slopes, these relatively shallow avalanches can entrain enough snow to step down into more deeply buried weak layers, causing a deeper, more dangerous avalanche.
On slopes that have seen recent drifting, the most prominent weak layer of concern is buried two to three feet below the surface. On these slopes, you are likely to trigger avalanches that will initially be up to three feet deep and will almost certainly step down (possibly to the ground), causing very large and destructive avalanches. Keep it simple and avoid slopes steeper than 30 degrees.
