Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 3
Old October snow that was on the ground before Thanksgiving has become a persistent weak layer of sugary, faceted snow crystals. This layer has produced widespread slab avalanches since snowfall around Thanksgiving. The slab on top of this weak layer is now 2-4 feet thick. This avalanche problem is labeled "persistent" because it doesn't go away and takes a long time to heal.
I wouldn't touch any slope harboring this persistent weak layer. There are two ways to know if this layer exists. First is to know the direction (aspect) the slope faces. Second is to dig a quick snowpit on an adjacent low angle slope. If you find weak sugary snow at the ground, pick a different slope. You have to be a detective to determine which slopes have this old snow and which do not.
I'm rating the avalanche danger at CONSIDERABLE based on the travel advice which is "careful snowpack evaluation, cautious route-finding and conservative decision-making." ALSO, southerly winds drifted some snow onto northerly facing slopes yesterday and added just a little more stress to this weak layer.