Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Advisory issued on Sunday, December 17th at 6:45 a.m. Today’s advisory is sponsored by Mystery Ranch and Stronghold Fabrication. This advisory does not apply to operating ski areas.
Since yesterday morning the mountains got 10” of low density snow in Hyalite, 3-5” in the Bridger Range and near Big Sky, and 1-2” elsewhere. Temperatures this morning are single digits to low teens F. Wind is westerly at 15-25 mph with gusts to 40 mph near Bozeman and Big Sky. Today, temperatures will be high teens to low 20s F with wind at 20-30 mph out of the west. Clear skies today will give way to increasing clouds this evening and the mountains could get 1-2” of snow by morning.
Near Bozeman and Big Sky, yesterday’s storm delivered 7-10” of low density snow equal to .3-.5” of snow water equivalent (SWE). I was in Hyalite yesterday where there was minimal wind and the main concern was soft slabs of new snow and dry loose avalanches on steep terrain (video). Today, strong westerly winds will drift new snow into slabs that are easy to trigger. These slabs could be 2-3 feet thick, and found near ridgelines as well as along the edges of cliffs and gullies. Avoid steep, wind-loaded terrain today.
On non-wind loaded slopes, soft slabs of new snow and dry loose avalanches are possible. These avalanches could run far and wide in very steep terrain, and on slopes where the previous snow surface is weak. On some slopes the new snow buried weak facets that formed during recent high pressure (photo, photo, video). Watch for signs of instability such as cracking and collapsing, and avoid slopes similar to where these signs are present.
Today, fresh wind slabs are easy to trigger and the avalanche danger is CONSIDERABLE on wind loaded slopes and MODERATE on all other slopes.
The mountains near West Yellowstone and Cooke City got 2-3” of low density snow yesterday. Moderate westerly winds will drift this snow into slabs up to a foot thick that are possible to trigger today. These slabs are most likely found near ridgelines. Evaluate terrain for the consequences of being caught in even a small slide. Approach wind loaded slopes with caution or avoid them altogether.
On non-wind loaded slopes the snowpack is generally stable and avalanches are not likely. The recent snow buried weak layers on some slopes, which will be a future problem, but pose minimal threat today without a significant load (photo, photo). Today, the avalanche danger is MODERATE on wind loaded slopes and LOW on non-wind loaded slopes.
If you get out and have any avalanche or snowpack observations to share, drop a line via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).
Upcoming Avalanche Education and Events
BOZEMAN
Dec. 21, Avalanche Awareness, 6-7:30 P.m. at Play It Again Sports, Bozeman
Jan. 12 and 13, Companion Rescue Clinic, Info and Register
Jan. 17, 18 and 20 or 21, Introduction to Avalanches w/ Field Day, Info and Register Here
Jan. 24, 25 and 27, Advanced Avalanche Workshop w. Field Day, Info and Register Here
Feb. 9 and 10, Companion Rescue Clinic, Info and Register
WEST YELLOWSTONE
Today and tomorrow, Snowmobiler Introduction to Avalanches with Field Course, Info and Register Here
Jan. 6, Avalanche Awareness, 7-8 p.m. at West Yellowstone Holiday Inn Conference Center
COOKE CITY
22 and 23 December, Weekly Current Conditions and Avalanche Rescue, 6:30-7:30 p.m. Friday @ the Super 8, and anytime between 10-2 on Saturday @ Lulu Pass road
A daily checklist is a great way to help prevent common mistakes or overlooking important data when travelling in the backcountry. This article from Backcountry Magazine discusses how to use and create your own backcountry checklist.