Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2.5
The Valentine's Day surface hoar layer remains a concern for large parts of our advisory area. Chances of triggering a large avalanche on this layer remain high as the winds pick up and we see a few more inches of new snow today. This layer is buried 1 to 2 feet deep on average, and is starting to take a little more work to identify as it gets buried deeper. It seems to be most problematic in areas that were sheltered from winds during the early February dry spell, at elevations above 1500'. It was responsible for several avalanches last week, including two events that caught and carried people on Seattle Ridge in Turnagain Pass (more details here, here and here) and one near-miss on Mt. Alice (details here).
From what we've seen over the past week, the weak layer exists across most of the forecast area, but it does not exist on every slope. This slope-scale variability can make it hard to assess conditions on a specific piece of terrain. You could easily dig a quick pit and see no signs for concern, then move a few hundred feet away and trigger a big avalanche. With that kind of uncertainty and the high likelihood of triggering an avalanche, the best bet for now is to avoid steep terrain. We've seen multiple avalanches triggered remotely from low-angle terrain connected to steeper slopes. Keep this in mind as you travel, and be aware of steep overhead terrain.
Loose snow avalanches will become more likely if the sun pokes through the clouds. There is around a foot of soft snow on the surface now, which will probably start releasing naturally if it heats up before it has a chance to settle. This may trigger a larger avalanche failing on that buried weak layer.
Cornices have been growing with continued winds and new snow. These can fail naturally, and they are easily triggered by the weight of a person. Avoid spending time below them, and give them plenty of space if you are traveling along ridgelines.
Glide Avalanches: Glide cracks are still on the move, and we still don't know when they will release. These avalanches are very large and very unpredictable. The only way to manage them is to avoid spending time under open glide cracks.
(2/27/2025)
We found this buried surface hoar in most of our hand pits in wind-sheltered terrain. It was smaller in terrain that was exposed to the winds.
Photo: Andrew Schauer
