Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 4
There is a persistent weak layer (PWL) of old faceted snow near the ground with 3-10' of snow on top of it. This PWL exists on mid and upper elevation slopes facing west through north and east. It does not exist on south-facing slopes as any early season snow melted away, and December snowfall landed on bare ground. This PWL has been fracturing and producing large, dangerous avalanches over the past few weeks. I would continue to avoid steep slopes on the north half of the compass. Head to the southerly (sunny) slopes if you want to ride steep terrain. Ok, let us pick a danger rating together: Let's decide between CONSIDERABLE vs. MODERATE. Please start with the (Travel Advice) column. Think about the consequence and size of the avalanches right now and how we would need to move in the mountains. I think the travel advice fits better for CONSIDERABLE vs. MODERATE as we have dangerous avalanche conditions, and I would be cautious and conservative.
Next column (Likelihood of Avalanches), we've seen the frequency (the number of avalanches) decrease over the past few days. The weak layer is now buried deep, and therefore it's harder for us to affect that weak layer. For that reason, I think the Likelihood of human-triggered avalanches is possible and NOT likely. I think MODERATE works better here. Think of it in odds. You now have a 2 out of 10 chance vs. an 8 out of 10 chance of triggering an avalanche. The Likelihood has decreased, but the consequence remains the same. Drew Hardesty has a video explaining this HERE.
Finally, the (Avalanche Size & Distribution), I don't think large avalanches only exist in isolated areas. In fact, there is a very specific terrain where you can trigger a large or very large avalanche. And we know that's on slopes that face west to north to east at the mid and upper elevations. Therefore I think the Avalanche Size & Distribution fits better for CONSIDERABLE vs. MODERATE.
At the start of the morning, it's tough determining what the actual danger rating is, especially, when everything doesn't fit nicely into the North American Danger Scale. However, two out of the three columns match better to CONSIDERABLE so I am sticking with that.