Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- 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. Even though many slopes in this zone had already avalanched during the Solstice storm, the more recent storm still produced some noteworthy slides (example, example).
Following the storm, Ben and I found the weak layer buried beneath a 3' thick, dense slab. Despite the weight of the slab, the weak layer showed little sign of strengthening or being "squashed". When I stepped out of the pit, we felt and heard an extremely large collapse. While playing in a meadow yesterday, sledders in this zone felt a huge collapse that they likened to an "earthquake". With the weak layer buried beneath a thick, dense slab, 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.