Wind Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
A quick-hitting storm dropped 6+" of snow in this zone at the end of last week. On Saturday, on an off-duty ski day, I intentionally triggered an avalanche involving this snow (pictured at right/above). The slab that failed was 6-18" thick, up to 100' wide, and failed on a layer of weak snow (near-surface facets on a crust). The slide picked up speed quickly as it traveled downslope, eventually stopping 2,000' below where I triggered it.
Yesterday, on a recreational ski day near Banner Summit, my partners and I paid close attention to the snow surface, watching for signs of wind loading and slab stiffening and avoiding these areas where we found them. The slabs that we were avoiding did not look to be particularly large, but even small slabs of snow can do some serious damage to a soft-bodied human (all of us) in the wrong kind of terrain. Chris and his partner were nearby and they followed the same protocol. We all found better and much safer riding by avoiding these slabs.
If I headed out skiing or riding in this area today I'd still have my guard up. Here are a few reasons why:
- These slabs are sitting on a few different weak snow surfaces such as facets, crusts with facets, and surface hoar. These types of weak snow are slow to heal and can cause avalanches days to weeks after they have been buried.
- Continued wind loading this weekend, and another inch or two of snow overnight (accompanied by more wind) will form fresh drifts and help these older drifts to stay reactive to the weight of a skier or rider.
- Slabs that fail on these types of weak layers (called persistent weak layers) can do so in ways that surprise you. They may break wider than you expect and further above you than you might expect.
Your best bet for avoiding having a problem with these slabs today is to do what my group did yesterday: spend some time looking at the snow with an eye out for textures that indicate the wind has been at work (ripples on the surface of the snow, large pillowy dunes of snow, etc.). Pay attention to how the snow feels under your skis or your machine. If you are seeing signs of loading or feeling the slab stiffening, alter your course to somewhere with softer snow at the surface. You'll find better skiing and riding and much safer conditions, a real win-win.
(1/22/2022) North winds following Thursday's 6+" of new snow created sensitive wind slabs. These are failing on weak snow surfaces that formed during the ongoing dry spell. This wind slab was intentionally triggered in alpine terrain in the Sawtooths.
