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 observed 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). Chris was in the northern Sawtooths on Saturday, where he 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 somewhat 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.
On Sunday, an experienced skier north of this zone remotely triggered a large avalanche that failed on a steeper slope adjacent to where he was skiing. He reported hearing wood breaking as the avalanche descended the slope. I looked at this slide and a few others yesterday, watch a video recapping what I saw here: Butterfield Avalanche. I was in the Gladiator Creek drainage on Sunday, investigating a large natural avalanche (photo at right) that appeared to have released within the past two days. You can watch a video describing what I found and why it is important here: Gladiator Creek Avalanche. The snowpack is a bit thinner in both of these areas, but not fundamentally different.
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. Recent natural and human-triggered avalanches confirm this fact. 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.