This is Alex Marienthal with the avalanche forecast for Monday, December 16th at 7:00 am. This information is sponsored by Knoff Group Real Estate, BWAGs and Bozeman Splitfest. This forecast does not apply to operating ski areas.
Since yesterday morning the Bridger Range received 8” of heavy new snow with 5-7” of lighter snow in Hyalite, Big Sky and Cooke City, and 2-3” elsewhere. Storm totals since Saturday night are:
10” snow/1.0-1.2” SWE - Bridger Range and Island Park
6-8” snow/0.4-0.8” SWE - Hyalite, Big Sky, S. Madison, West Yellowstone.
Yesterday wind was out of the west at 10-20 mph with gusts of 30-45 mph, and has decreased to 10-15 mph with gusts to 20-30 mph today. Temperatures are single digits to teens F this morning, and today will reach low 20s F. Snow is expected today, starting this morning near Island Park, West Yellowstone and Cooke City and this afternoon elsewhere. By tomorrow morning near Cooke City, Island Park and West Yellowstone could get 5-9” of snow with 3-6” elsewhere.
All Regions
Today human-triggered avalanches are likely, especially where strong wind has drifted snow into stiffer or deeper wind slabs, and where more snow falls and is drifted today. On non-wind loaded slopes avalanches are possible, as indicated by widespread avalanche activity yesterday, and due to the existence of buried weak layers.
Yesterday avalanches were triggered by skiers and broke naturally, with reports from all corners of our forecast area (avalanche activity page). Notably, skiers in the Bridgers (photos), Cooke City (photos), and Beehive (photo), and a rider between West Yellowstone and Island Park (photos), triggered avalanches from lower angle terrain below or adjacent to steeper slopes. A large natural avalanche was heard pouring over the cliffs on Saddle Peak in the Bridger Range as heavy snowfall peaked midday.
The slide near West Yellowstone and Island Park broke on surface hoar below the recent snow, while some slides were reported breaking within yesterday’s storm snow. Prior to yesterday’s snowfall weak layers were generally widespread, either on the snow surface or buried 4-12” deep (Cooke City photo, Taylor Fork video). These weak layers can cause persistent slab avalanches which will be wider, and possible to trigger from lower angle terrain, making them more dangerous and potentially surprising.
With more snow and moderate winds today, anticipate the size and distribution of potential avalanches to increase through the day. Heavy snowfall, or winds visibly drifting snow, are signs that stability may be getting worse.
Today, cautious route finding is essential. Avoid wind-loaded slopes steeper than 30 degrees. If you travel across or below any steep slopes carefully evaluate the terrain and snowpack for avalanche potential and consequences of a slide.
Avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on non-wind loaded slopes.
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar
Thursday, Dec 19 and Saturday, Dec 21, Companion Rescue Clinic at REI in Bozeman and History Rock. 6 to 8 pm on Thursday, 10 to 2 pm on Saturday.
Friends of the Avalanche Center: Fall Fundraiser!
We’re still counting on your support and the online Fall Powder Blast fundraiser is 79% of the way to our goal. Please consider making even a small donation HERE or via Venmo
We are sad to report that yesterday A motorized snowbiker was killed in an avalanche in the mountains northwest of Cascade, ID. Preliminary info here.