Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2.5
Yesterday's storm brought another 6 to 8" new snow to the area, bringing storm totals to 8 to 12" snow over the past two days, equal to roughly 0.5 to 1" snow water equivalent. The weight of this new snow is adding stress to a touchy weak layer of buried surface hoar that has already produced avalanches that caught and carried two people earlier in the week at Turnagain Pass (details here, here and here), and one that came close on Mt. Alice (details here). With a day of quiet weather expected, there may not be obvious signs of this dangerous setup today. Don't let that fool you; conditions are dangerous, and there is a really good chance that a person can trigger a large avalanche. With a heavy load of snow on a known weak layer, the best option is to avoid steep terrain. 'Steep' terrain looks different for these surface hoar problems, which have a history of failing on low angle slopes. Keep in mind, this week we have seen multiple avalanches triggered remotely from low angle terrain connected to steeper slopes.
This surface hoar problem can be tricky to identify as you travel. In some cases you may be able to find it by taking a few seconds to dig into the snow with your hand, but now that it is buried a foot deep or deeper by multiple layers of snow it is getting harder to identify. We've also been finding it on some, but not all slopes. This means you might not find it in one spot then you could go around a corner and trigger a big avalanche. For now, the best way to manage this problem is to play it safe and stick to low angle terrain.
Loose snow avalanches will be easy to trigger today, and we should expect to see natural activity if the sun makes even a brief appearance. These have the potential of triggering a larger avalanche failing on that buried weak layer, and they may be dangerous enough on their own if they carry you through terrain traps like rocks or trees.
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)
Small slab on a small piece of wind-loaded terrain near Snug Harbor. This failed on a layer of buried surface hoar, which is now around a foot deep or deeper.
Photo: Andrew Schauer
