Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2–2.5
Recent Avalanches: We do not have any observations from yesterday so it is unclear if there was any new activity from this most recent storm. Several large avalanches were seen Friday on Seattle Ridge in Main Bowl, weather station bowl, Jr’s Bowl, and Warm-Up bowl. A skier was caught and carried in an avalanche on Sunburst on the same day, and skiers triggered multiple avalanches in the Tincan Trees (details here and here).
Yesterday's storm brought rain up to around 2500' or higher, along with strong winds and snow in the alpine. This is going to make it tricky to predict how the weak layers of buried surface hoar will respond. Here's what we know:
- People triggered very large avalanches on a layer of surface hoar that was buried about 1.5' deep by the Thanksgiving storm. This happened the day after the storm on Friday.
- Rain reached much higher yesterday than it did during the previous storm.
- That has added extra weight to the snowpack, and the weak layers have not had much time to change at all.
What we don't know is exactly how touchy those weak layers will remain. It is likely that all of that rain helped the cause stability-wise at mid and lower elevations because the snow above the weak layers is likely now either a thick crust or a wet and incohesive slab of mushy snow. But at some point there will be a transition from that wet mush to a heavy layer of new snow that will likely still be very reactive and capable of making big avalanches. We're not sure where that transition will happen, or how touchy those weak layers will remain today.
Approach steep terrain very cautiously for now. Be aware that these layers of surface hoar tend to exist in pockets, so even if you dig a pit and get a stable result you may still trigger an avalanche on a nearby slope. When these layers are the main concern, it's usually best to avoid big steep terrain, especially if there is any kind of terrain trap below.
