Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2–3
The storm early last week added more load to our well-established persistent weak layer that is now buried around 2-3 feet deep in this zone. The highest concentration of natural avalanches occurred in the drainages near Smiley Creek (example) and in the far Western Smokys, but slides also occurred in the Sawtooths.
On Wednesday and Friday of last week, riders remotely-triggered avalanches in the Western Smokys (photo, photo). I was in the northern Sawtooths yesterday, where I found a 2.5' thick, dense slab atop a layer of sugary facets that was showing little signs of improvement. With the weak layer in this zone more deeply buried, it may be more difficult to trigger a slide than in other portions of the forecast area. But if you do trigger an avalanche, it's likely to be a big one that will be difficult to survive.
There are two key factors that point to this instability being especially long-lasting and unpredictable: 1) the buried weak layer is especially bad, and 2) this weak layer has been very slowly loaded over the past three weeks. As time goes by and the obvious signs of instability diminish, it requires more and more discipline to choose appropriate terrain—read more on that in the Forecast Discussion below. We urge backcountry skiers and riders to continue to choose low angle slopes and to pay extra attention to the terrain they're "connected" to. Remotely triggering an avalanche from below, above, and to the sides of steep slopes remains a very real possibility.