Persistent Slabs
- Alta quota
- Limite del bosco
- Sotto il limite del bosco
- Probabilità
- Likely
- Dimensione
- 2
Human triggered avalanches failing on a buried persistent weak layer are possible on upper and mid elevation slopes. Strong south and west winds drifted tons of last week's nice powder into lee slope avalanche starting zones. Apparently, some avalanches can step down into buried persistent weak layers, involve large volumes of snow, and be quite dangerous and destructive. The cold weather Christmas week created sugary weak surface snow in many areas, in others a layer of surface hoar feathers was buried by the New Years Storm. Slopes with previously shallow snow cover are plagued by buried weak and sugary faceted snow. The additional weight from tons of recent snow and significant drifting was enough to reactivate the deeply buried October persistent weak layer on some slopes. You can still find this weak basal layer lurking on upper elevation slopes facing northwest, north and east.
- Some avalanches might be triggered remotely, from a distance or below.
- Smaller avalanches overrunning a slope with buried persistent weak layers could step down into old snow and initiate a much larger avalanche.
- Watch for and avoid stiffer drifted snow near ridge lines and in and around terrain features like cliff bands, scoops, gully walls, and sub-ridges.
- Avoid ridge top cornices, which can break much further back than expected and start avalanches on slopes below.
Sugary, faceted snow from a buried weak layer on a west facing slope at about 7000' (1-19-2020)