Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 4
The most dangerous and likely problem is large slab avalanches breaking on persistent weak layers near the ground. On Thursday along the Mirror Lake highway, I triggered cracks shooting 100 feet in front of my sled which told me if I had been on a steeper slope, I would have triggered an avalanche (observation, video)
The good news is that the snowpack in the Uinta Mountains has gotten a lot deeper after last weekend's series of storms. The bad news is that snowfall made the slab much thicker and more dangerous. In places where the slab is thickest, avalanches will be harder to trigger because it is harder to impact weak snow near the ground. However, thin spots or rocky areas are often good trigger spots.
A scary combination exists on slopes loaded by recent winds near the top but with a thinner snowpack near the bottom of the slope where an avalanche can be triggered.
The photo below shows weak snow near the ground, and how a snowmobile can stay on top of the snowpack. However, there are a lot of different ways for a sled or a skier to impact the weak layer. Because the snowpack is not the same depth across a slope, it's easy to hit a thin spot and trigger an avalanche. Tracks on a slope DO NOT mean it is stable.
Ted Scroggin who knows the Uinta Mountains better than anyone added these words of wisdom: "To me, these are tricky conditions, there were some natural avalanches, some slopes have filled back in, and things look and feel good to go. Normally this time of year we are starting to venture out more on bigger slopes, but the current snowpack is still not to be trusted even though conditions feel great under our sleds and skis."