Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 4
There is a persistent weak layer (PWL) of old faceted snow near the ground with 3-10' of snow on top of it. This PWL exists on mid and upper elevation slopes facing west through north and east. It does not exist on south-facing slopes as any early season snow melted away and December snowfall landed on bare ground. This PWL has been fracturing and producing large, dangerous avalanches over the past few weeks.
The PWL is slowly gaining strength and adjusting to the dense, deep slab on top. Although it is unlikely a human could trigger an avalanche that fails in the PWL, it is possible you could trigger a large and dangerous avalanche in isolated areas such as steep, rocky terrain where the snowpack is thinner.
Yesterday, my very-experienced touring party looked down an untouched 34° northeast facing slope and decided the possibility of an avalanche with catastrophic consequences simply wasn't worth it. We moved to a similarly-untouched slope less than 30 degrees in steepness and rode perfect powder.