Good morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Sunday, March 20th at 7:05 a.m. This information is sponsored by Blitz Motorsports and Yamaha and Grizzly Outfitters. This forecast does not apply to operating ski areas.
This morning it is snowing! Near Bozeman and Big Sky have 2-5”, there is an inch near West Yellowstone, and near Cooke City snow started after 6am with a trace so far. Temperatures are 20s to low 30s F and moderate southwest winds have decreased to 10-20 mph. Temperatures will be 20s F and drop to teens F this evening, and wind will shift to northwest and increase to 15-30 mph this afternoon. Snow will continue through mid-day. By this afternoon 3-5” are likely throughout the forecast area with 6-8” possible in some areas.
Heavy snowfall this morning followed by moderate northwest wind will make human triggered avalanches likely on wind-loaded slopes and possible on non-wind loaded slopes today. A person can trigger large, dangerous avalanches that break 1-3 feet deep on buried weak layers, or fresh drifts of snow up to a foot deep.
Over the last week avalanches were triggered by skiers near Cooke City (photo), Big Sky and in Hyalite (Wyoming Bowl video, Mt. Blackmore slide details), by snowmobilers near Buck Ridge (photo) and broke naturally throughout the forecast area (activity log). Yesterday Ian and I rode around Lionhead near West Yellowstone and noted very weak snow buried about a foot deep that was not yet unstable, but today’s snow could create a widespread instability (video). We have already seen these weak layers become unstable with snow earlier in the week and cause avalanches near Cooke City, the Bridgers, Hyalite and Big Sky, and today’s snow will cause more.
Avoid slopes with fresh drifts of snow. If you plan to ride or travel in steep terrain, first carefully assess the snowpack on safe, low-angle slopes similar to those you plan to ride. Dig down a couple feet to look for and test buried weak layers. Stay off steep slopes if you see natural avalanches or experience cracking and collapsing of the snowpack under your feet, skis or snowmobile. Avalanches breaking on persistent weak layers can be triggered from flatter terrain near or below steep slopes, so pay attention to what is above you and be cautious crossing underneath steep slopes.
If you get out, please send us your observations no matter how brief. You can submit them via our website, email (firstname.lastname@example.org), phone (406-587-6984), or Instagram (#gnfacobs).
Yesterday, March 19, two skiers were caught and one was killed in an avalanche near Steamboat Springs, Colorado (preliminary details). This was the fourth avalanche fatality in the U.S. in the past week and the fifteenth this season (https://avalanche.org/avalanche-accidents/).