It is still possible to trigger Persistent Slab avalanches, particularly on upper elevation and shadier slopes, and those that have been recently wind loaded. Dig to look for weak layers near the ground and assess any you find. Smaller, Wind Slab avalanches are a secondary concern.
This problem will be more likely at upper elevations, but the weak layer can also be found at mid elevations and it is worth digging down and evaluating it.
Large avalanches breaking on weak layers near the ground remain the major concern across most of the region.
Riding in the Lionhead area yesterday, I saw evidence of many large avalanches, breaking deep and wide, some of which had broken in the last couple days (video, observation). I was surprised to find avalanches breaking even in areas that had thick rain crusts above the weak layers at the ground. Even without much loading over the last week, I still don’t trust the snowpack near West Yellowstone and Island Park. Recent avalanches clearly indicate that triggering large slides remains possible and if you do they’ll be large and dangerous. If you’re going to venture onto slopes steeper than 30 degrees, choose smaller slopes and those without rocks, trees, gullies, or other obstacles beneath them.
It’s been a bit longer since we saw many large avalanches in the northern Madison and northern Gallatin Ranges.The last reported avalanches were the day after Christmas (observation).Still, avalanches on weak layers near the ground are still possible (Alex’s video from yesterday on Mt. Blackmore). It’s definitely still worth digging down, looking for weak layers near the ground, and assessing any you find.
Near Cooke City, the weak layers have been buried deeply by the consistent snowfall throughout December (photo). This means that it’ll be harder to affect these layers and trigger a slide, but also that any slide that you do trigger would be really large and dangerous. Last Monday’s avalanche on Chimney Rock is a good reminder of the size and power of these slides. Avoid thin areas near rocks that are the most likely trigger points.
Wind Slab avalanches are a minor, secondary concern across most areas. It snowed 3-6” across the region on Thursday night and Friday morning. South and west winds drifted this snow into thicker drifts on some slopes. With the warm temperatures, I expect any drifts that formed to be fairly well bonded at this point, but watch for cracks shooting out in front of you as a clear sign that you’ve found an unstable drift.
In the Bridger Range, the avalanche danger is LOW. Persistent Slab concerns are minimal. Wind Slabs are the primary concern, but won’t be widespread or reactive.
The avalanche danger is rated MODERATE across the rest of the advisory area.
