Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Advisory issued on Sunday, December 3rd at 7:00 a.m. Today’s advisory is sponsored by Gallatin Valley Snowmobile Assoc. and Yellowstone Ski Tours. This advisory does not apply to operating ski areas.
NEW THIS SEASON: Regional Conditions Pages with region specific weather info, webcams, photos, videos, snowpits and more. Links at top of advisory and in the ‘advisory’ dropdown menu.
Since yesterday morning the mountains got 3” of new snow near Cooke City with 1-2” in the southern Madison and Lionhead Ranges. At 4 a.m. temperatures are low 30s F and wind is south to southwest at 10-20 mph with gusts to 45 mph. Temperatures will fall to low 20s and teens F today. Wind will be southwest at 15-30 mph this morning, then shift to the north-northwest at 5-15 mph this afternoon. Snow showers will begin this morning with periods of heavy snowfall expected today and through tonight. By morning the mountains will get 8-15” of snow near Big Sky, Hyalite, and West Yellowstone with 15-20” possible in the Bridger Range and near Cooke City.
The main avalanche problem today is unstable slabs that will form from new snow and wind through the day. Fresh wind slabs will be easy to trigger and found near ridgelines and along the edges of gullies. These slabs will grow larger as snow falls through the day. As snow piles up, watch for obvious signs of instability like cracking and collapsing, blowing and drifting snow, and natural avalanches. Avoid nearby, similar avalanche terrain if these signs are present. In the absence of obvious signs of instability, dig 1-2 feet deeper than the new snow and assess stability before committing to avalanche terrain.
Aside from new snow and wind today, the snowpack is generally stable and lacks widespread persistent weak layers. Eric went to Big Sky yesterday to look at the massive avalanche that patrol triggered with explosives on Thursday (photo, photo, photo). The slide broke 6-10 feet deep on a weak layer of depth hoar on a north facing slope around 11,000’. This isolated, lingering instability is an outlier within our area’s generally stable snowpack, but a reminder that avalanches are still possible (video). Cornices are large right now (photo, photo), and they could break under the weight of a person and be a perfect trigger for a large avalanche like the one at Big Sky. Travel far back from the leeward, corniced edge of ridgelines and minimize time on slopes below them.
A generally stable snowpack makes avalanche danger LOW this morning. Heavy snowfall and moderate wind today will form unstable slabs that are easy to trigger, and avalanche danger will increase to MODERATE this afternoon.
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).
Get Avalanche Smart Video Series
The Avalanche Center and Friends group work hand-in-hand to bring you daily avalanche information and education. This last video in series of 4 shows how we create a culture of being safe in the backcountry: Get Avalanche Smart – Episode 4: The GNFAC
Upcoming Avalanche Education and Events
BOZEMAN
Dec. 6, Avalanche Awareness, 6-7:30 p.m. at REI Bozeman
Dec. 7, Avalanche Awareness and Beacon Practice, 6-8 p.m. at Beall Park, Bozeman
Dec. 13, Avalanche Awareness, 6:30-8 p.m. at Gallatin Valley Snowmobile Association, 4-Corners
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
HELENA
7 December, Avalanche Awareness, 6-7:30 p.m. at Basecamp, Helena
WEST YELLOWSTONE
Dec. 14 and 15, Snowmobiler Introduction to Avalanches with Field Course, Info and Register Here
COOKE CITY
8 and 9 December, 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.
Check out our playlist of videos from last April’s Professional Development Workshop. The topic of the day was “Avalanche Science, Avalanche Stories”.