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.
These avalanches are currently tricky because they don't always offer immediate signs of instability and it's easy to be lured onto slopes with other tracks, particularly when snow depths and snow tests might be pointing in the direction of "stable".
The PWL is slowly gaining strength and adjusting to the dense, deep slab on top. Although the likelihood that a human could trigger an avalanche that fails in the PWL continues to decrease, the consequences of a deep and deadly avalanche remain high. This remains particularly possible in areas that the slab atop the facets is thinner, such as steep rocky terrain where the overall snowpack is thinner or on an old repeater slope that still has facets at the ground. While we are trending in the right direction, we are not out of the woods yet, and I would continue to avoid traveling on or below steep west through north through east facing slopes.