Bridger Range

In the Bridger Range, buried persistent weak layers are less widespread, so there are less slopes with a recipe for persistent slab avalanches. Dig down to look for weak layers near the ground before committing to steep slopes. Be on alert for Wet Loose avalanches if you find a wet, unsupportable snowpack.

The primary problem is large persistent slab avalanches that can break 2-5 feet deep on weak snow near the bottom of the snowpack. Additionally, wet loose avalanches are a concern in the northern half of the forecast area, near Bozeman and Big Sky, where at 6am temperatures are already above freezing at 11,000 feet.

Near Cooke City there has been widespread avalanche activity. Many large avalanches broke on weak layers buried below thick slabs of snow that fell over the last couple weeks. Yesterday I saw at least six avalanches that were not previously reported and happened within the last 48 hours (video). Many of these broke naturally as slopes were being loaded by wind-drifted snow, and on Thursday a snowmobiler triggered a huge slide from low angle terrain below a big steep slope, he was fully buried and fortunately found and dug up quickly with only minor injuries (Daisy Pass avalanche).

Yesterday near Big Sky, ski patrols easily triggered large persistent slab avalanches. This type of activity has been a daily occurrence as they’ve been doing mitigation work on a snowpack that is currently similar to what exists in the backcountry. This is evidence that, despite a couple days without new snow and wind-loading to stress the snowpack, a skier or rider can still easily trigger a large persistent slab avalanche.

Avalanche danger is CONSIDERABLE at all elevations near Cooke City, and at upper and middle elevations in the N. Madison and N. Gallatin Ranges. Choose your route to avoid slopes steeper than 30 degrees and stay out of the lower angle terrain directly below steep slopes.

In the Bridger Range, buried persistent weak layers are less widespread, so there are less slopes with a recipe for persistent slab avalanches. In the S. Madison Range, S. Gallatin Range, and near West Yellowstone and Island Park, less recent snowfall has restricted the persistent slab problem to higher elevations and makes triggering a large slide less likely. If you plan to travel on steep slopes in these areas, dig to the ground and look for weak layers buried near the bottom of the snowpack. Avoid steep slopes if you find this poor snowpack structure. The avalanche danger is MODERATE in these areas.

Wet loose avalanches are unusual for mid-December, but worth a mention with unusually warm temperatures. Yesterday, cooler temperatures kept the snow mostly frozen and minimized chances for wet snow, but today is warmer. Be especially alert for wet loose avalanches on steep sunny slopes with exposed rock outcrops, and where even a small slide would have high consequences like on ice climbs or above cliffs.