Island Park

Human-triggered avalanches are possible where snow from recent storms sits on weak layers buried 1-2 feet deep. This recipe is most prevalent on middle- and upper-elevation slopes. Dig, test, and evaluate slopes for instability before considering travel on steep slopes. Seek out terrain sheltered from the wind and where recent snow fell on bare ground for safer conditions.

Cooke City

Near-constant snowfall has created dangerous avalanche conditions in the mountains around Cooke City. Snow ended yesterday afternoon, and we allowed the avalanche warning to expire. But make no mistake, you are likely to trigger a large, destructive avalanche if you venture into steep terrain.

Persistent slab avalanches failing on weak layers near the ground should drive your decision-making today. Recent slides on Miller Mountain, where a group triggered a distant slope, and a slab breaking close to the ground on Henderson Mountain are two good examples among many. Yesterday, guides triggered multiple whumphing collapses as weak layers collapsed (observation). Today, skiers and riders can remotely trigger slides from a distance while traveling in flatter terrain, so caution is required when steep slopes are above your group.

If large, persistent slab avalanches aren’t enough for you, wind slab avalanches large enough to bury or injure skiers and riders are likely on wind-drifted slopes.

Careful and conservative route-finding that avoids slopes steeper than 30 degrees is the name of the game. The avalanche danger is CONSIDERABLE on all slopes.

Bridger Range - Gallatin Range - Madison Range - Lionhead Area - Island Park

The snow and avalanche story is fundamentally the same from the Bridger Range south through the Madison and Gallatin Ranges, in the Lionhead Area, and Island Park. Recent snow is sitting on weak layers buried 1-3 feet deep. The amount of recent snowfall, more around Bozeman and Big Sky, and less near West Yellowstone and Island Park, drives the differences in danger (Buck Ridge video).

Persistent slab avalanches breaking near the ground on weak, sugary snow are the primary problem. Since Thursday of last week, we received nearly two dozen reports of avalanches and close calls (avalanche activity log), such as a rider who was carried in an avalanche on Buck Ridge in the N. Madison Range (details) and a skier who triggered a slide near the Apron within the boundaries of Bridger Bowl (details). With less snow in the Lionhead and Island Park areas, there were fewer avalanches, but on Tuesday, I was surprised by instability at Lionhead (video).

Warm temperatures are limiting drifting, but avalanches tend to be more likely on commonly wind-loaded slopes below corniced ridgelines and in upper-elevation terrain, whether they break as wind slabs or persistent slab avalanches.

Dig, test, and evaluate for weak structure/ instability before considering slopes steeper than 30 degrees, and then rigorously follow safe travel practices. Seek out terrain sheltered from the wind and where recent snow fell on bare ground for safer conditions. The danger in the Bridger, Madison, and Gallatin Ranges is CONSIDERABLE on upper-elevation slopes, MODERATE at middle-elevations, and LOW in lower-elevations.

The Lionhead and Island Park areas have MODERATE danger at upper- and middle-elevations, and LOW danger at lower-elevations.

Bozeman Ice Fest

I am annoyed to mention this in December, but with above-freezing temperatures, wet snow surfaces, and warming rock bands, wet loose avalanches may occur. These will be relatively small, but ice climbers getting out in Hyalite Canyon for Ice Fest should watch for roller-balls and pinwheels that indicate increasing instability. Retreat if the steep terrain above your position is becoming unstable.