Good Morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast issued on Wednesday, December 18th at 7:30 a.m. Today’s forecast is sponsored by Grizzly Outfitters in partnership with the Friends of the Avalanche Center. This forecast does not apply to operating ski areas.
Snowfall last night left a trace to 2” in the Bridger Range, 3” in Hyalite, and 4-6” across the rest of the advisory area. This morning, temperatures are mid teens to mid 20s F and winds are west at 20-35 mph with gusts of 50-60 mph. Temperatures today will rise to the high 20s and low 30s F. Expect continued strong west winds at 30-50 mph. Snowfall will taper off this morning, with a possibility for another 1-2” in the mountains near Cooke City and West Yellowstone.
Doug rode in the Lionhead area yesterday and found a shallow, weak snowpack (video). Last night’s 6” of new snow will stress this very weak foundation to its breaking point. Triggering an avalanche on these weak layers near the ground is likely today. Expect slopes loaded by west winds to have the thickest slabs and touchiest conditions. Staying off of, and out from under, slopes steeper than 30 degrees would be a wise choice while waiting to see how the snowpack reacts to this new load. Cautious route finding will be key today as you could even trigger an avalanche from flat ground below steeper slopes. Venturing into avalanche terrain will require careful snowpack assessment before exposing yourself to any steep slopes. Triggering an avalanche is likely and the avalanche danger is CONSIDERABLE today.
The combination of last night’s new snow and strong west winds make triggering an avalanche likely on wind loaded slopes. Even before this new snow, avalanches continued to break on wind loaded slopes over the week since the last snowfall (see details on the Avalanche Activity page). The new snow will make it easier to trigger an avalanche and also increase the size and power of any slide you do trigger, particularly on wind loaded slopes.
The largest and most worrisome slides will break on a weak layer of facets that formed during cold, dry weather at the beginning of December. This weak layer was buried across the advisory area, as seen in these videos from the Bridger Range (video), Hyalite (video), Buck Ridge (video) and Taylor Fork (video). This weak layer is now buried 8-12” deep on non-wind loaded slopes. On wind loaded slopes, the weak layer is buried deeper (1-2’ deep) with a stiff slab of wind drifted snow above it. Give this newly loaded weak layer the respect it deserves by avoiding fresh wind drifts and digging to carefully assess the snowpack before committing to other steep slopes. Monday’s skier triggered avalanche on Bridger Peak, breaking in an area of wind-drifted snow, 6”-12” deep, 100’ wide, and running 2000’ (details) provides a good example of the type of avalanche you could trigger today.
Snowmobiler Avalanche Fatality in the Wyoming Range, Wyoming
From Bridger-Teton Avalanche Center (12/24): “A snowmobiler died two days ago in the Wyoming Range after triggering a small slab avalanche and getting pinned beneath his sled.” Check the BTNFAC website or avalanche.org for updated details. Our condolences go out to those involved.
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
January 2, Avalanche Awareness, 6-7:30 p.m. at REI, Bozeman. Pre-register at https://www.rei.com/events.
January 8, Women’s Specific Avalanche Awareness, 6:30-8 p.m. Story Mill Park, Bozeman.
January 9, 1-hr Avalanche Awareness, 7-8 p.m. Spire Climbing Center, Bozeman.
Every Friday and Saturday, Rescue Training and Snowpack Update. Friday 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.
Check out our new “Avalanches and Snowpits” menu item where we list all the reported avalanche activity.