Wind Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2
Acitve weather is returning after a couple days of quiet conditions. We are not expecting much snow during the day, but the increase in winds will increase avalanche danger, especially at elevations above 2500'. It will be easy to trigger an avalanche around a foot deep where the winds have drifted snow into reactive slabs. We may also see some natural avalanche activity as the winds increase. There is already plenty of soft snow on the ground available for slab building, so even if we don't see any snow today we are still expecting the likelihood of triggering an avalanche to increase. Wind slabs will be forming on top of a layer of surface hoar that formed during clear spells over the past few days, which may make them even more reactive.
This problem can be managed by avoiding steep, wind loaded terrain. Expect to find unstable conditions on steep slopes below ridgelines, convex rolls, and steep gullies. Warning signs like shooting cracks or collapsing are clear indicators of unstable snow. But, keep in mind that you will not always see this bull's eye data even when conditions are dangerous. This is the type of problem where the safer conditions will align well with the best skiing and riding. Look for optimal conditions on slopes that have remained sheltered from the winds with soft snow on the surface.
Persistent Slabs: There may be some isolated pockets of unstable snow from last week's series of storms. Although much less likely, this could produce a much bigger avalanche than the shallow wind slabs that form during the day today. One group experienced a large collapse on a layer of buried surface hoar about 1.5 feet deep in Goldpan yesterday (details here). While we do not believe this is a widespread problem, it is still worth assessing before committing to steep terrain.
(12/14/2024)
Fresh surface hoar on Seattle Ridge. This was the biggest we saw, but there was surface hoar from the road to the ridge. This will
Photo: Andrew Schauer