Good morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Sunday, March 12th at 7:00 a.m. This information is sponsored by Archer Construction and Gallatin County Sheriff Search and Rescue. This forecast does not apply to operating ski areas.
This morning there is no new snow. Temperatures are in the single digits to teens F. Wind is out of the southwest-west at 5-10 mph with gusts of 20-25 mph. Today will be mostly sunny with temperatures reaching high 20s F and southwest wind at 5-15 mph. The next chance for snow is late tomorrow through Wednesday.
On Thursday and Friday, the mountains near Cooke City, West Yellowstone and Big Sky received 10-14” of snow (1.0-1.5” of snow water equivalent) which was accompanied by strong to extreme westerly winds on Friday. Yesterday we received reports of over a dozen large natural avalanches that broke during or shortly after the storm (avalanche activity list). Some were up to 6 feet deep and destructive enough to break small trees (Fisher Mtn. near Cooke, Lionhead Ridge). A snowmobiler triggered a large slide on Crown Butte yesterday. The rider was not caught, and the slide appeared a couple feet deep and involved the recent snow (photo).
Today people can easily trigger large avalanches of wind-drifted snow, and slides could break deeper and wider on buried weak layers. Extreme winds affected most slopes and drifted snow into unusual places. The threat of avalanches on deeply buried persistent weak layers makes the situation more complex. Last week avalanches were triggered on weak layers that were buried in early January (Cooke City video), and the added weight of recent snow and drifts makes similar sized slides likely today. Keep your terrain choices simple and avoid travel on and underneath slopes steeper than 30 degrees. Large, human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.
The mountains near Bozeman got less snow, but strong winds created fresh drifts. Last week, skiers triggered a deep slab avalanche after a similar wind-loading event (Hyalite video, photo). Avalanches breaking deep on buried weak layers are possible today. Deep slab avalanches are tricky because signs of instability are scarce, and snowpits and stability tests may not provide clear information about instability. The best strategy is to choose smaller, simple terrain with minimal wind-loading and minimal consequences, or avoid slopes steeper than 30 degrees altogether. If you choose to ski or ride steep slopes, it is still worth digging to check for buried weak layers just in case.
Additionally, fresh drifts can avalanche under the weight of a person. On Friday, skiers in the northern Bridger Range saw a natural avalanche as the new snow was being drifted into fresh slabs (photo and details). Fresh wind slabs may be large enough to bury a person, but even a small slide will be harmful if it carries you into rocks, trees or over a cliff. Cracks shooting out in front of your skis or sled are clear signs that you’ve found an unstable drift that would avalanche on a steep slope. Today, avalanches are possible to trigger and avalanche danger is MODERATE.
Please share avalanche, snowpack or weather observations via our website, email (email@example.com), phone (406-587-6984), or Instagram (#gnfacobs).
Recent heavy snowfall and strong winds created dangerous avalanche conditions which still exist today. Freshly formed drifts can break at least 1-2 feet deep, and slides could break deeper in the snowpack. Avoid steep slopes and give them a wide berth if you’re traveling beneath them. See Dave’s video update from Friday for more travel advice.
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Saturday, 10 a.m. - 2:00 p.m. Avalanche Rescue Training, drop in for any amount of time. Round Lake Warming Hut, Cooke City. Free.
Loss in the Outdoors is a support group for those affected by grief and loss related to outdoor pursuits. Check out the link for more information.
A list of all avalanche activity from our forecast area is available HERE.