Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
You can trigger an avalanche in previously wind-drifted snow which breaks on weak layers buried around two to four feet deep. The most problematic areas are near and above-treeline slopes facing north though northeast to east, where drifted snow forms a stiff slab above cohesionless layers near the ground. Look for and avoid slopes with evidence of wind-drifting, such as stiff or sculpted surface texture, drumlike or hollow-sounding snow, fresh cornice growth, or lens-like pillows. Anticipate loose wet avalanches on sunny slopes at lower elevations as the day progresses, and plan to be off of these slopes before afternoon or sooner if you see roller balls or wet surface snow. Slopes less than about thirty degrees without steep terrain above offer safer options.