Good morning. This is Dave Zinn with the Gallatin National Forest Avalanche Forecast on Tuesday, December 27th at 7:15 a.m. This information is sponsored by the Avalanche Alliance and onX. This forecast does not apply to operating ski areas.
Winds from the south to southwest are blowing 20-35 mph with temperatures in the 20s F near West Yellowstone and Cooke City and in the 30s F in the mountains near Bozeman and Big Sky. Cooke City got 4” of new snow with an inch near West Yellowstone.
Today, temperatures will be in the 30s F in the northern ranges and in the 20s F in the southern ranges. Winds will blow 25-40 mph from the south to southwest. Precipitation will increase this morning with 10-12” of snow around West Yellowstone, 8-10” near Cooke City, 2-4” in Big Sky and south of Bozeman, and 1-2” in the Bridger Range by tomorrow morning. Precipitation will begin as rain at lower elevations and in the northern portions of the advisory area.
Dangerous avalanche conditions exist in the mountains around Cooke City and West Yellowstone. Cooke City has received 8” of wet snow in the last 48 hours, with 2” near West Yellowstone. Strong winds from the south to southwest are gusting to 55 mph and blowing snow into unstable drifts at many elevations and aspects that are likely to avalanche. A storm bringing 4-8” of snow during the day will increase the danger on all slopes. In addition, two weak layers buried one foot deep and near the ground make much larger avalanches possible.
Yesterday, a splitboarder riding just outside our advisory area near Cooke City intentionally triggered an avalanche breaking 6-18” deep and saw cracks shooting from the nose of his board (observation and photos). Similar to what Alex and Doug found at Lionhead this weekend (video, observation), a boarder in Republic Creek confirmed seeing a reactive weak layer buried a foot deep (observation).
Careful route finding and snowpack evaluation are essential. Avoid all steep, wind-loaded slopes, and expect the danger to increase with today’s snow. The avalanche danger is CONSIDERABLE.
The avalanche story is complicated in the Madison, Gallatin and Bridger Ranges where problems including rain and wet snow at lower elevations, new snow during the day, strong winds creating unstable drifts and two weak layers buried a foot deep and near the bottom of the snowpack make avalanches possible.
Yesterday, a skier near Big Sky triggered “whumphing” on a slope indicating unstable weak layers (observation). I found a weak layer of near-surface facets buried a foot deep at Mount Blackmore and saw the wind drifting snow (video). Another group at Blackmore got unstable results with their test propagating on the near-surface facet layer. Alex confirmed multiple weak layers at Buck Ridge and saw recent avalanches (video). And the Big Sky Ski Patrol noted “very sensitive” slabs of wind-drifted snow 4-6” deep during routine mitigation.
Today, precipitation will begin as rain at lower elevations. Yesterday, on our drive down Hyalite Canyon, we observed small wet snow avalanches on the roadcuts. Any rain will have a destabilizing effect on the snowpack.
Keep your head on a swivel looking for signs of instability because human-triggered avalanches are possible, and the danger is rated MODERATE.
Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).
Dangerous avalanche conditions exist in the mountains around Strong winds are gusting to 55 mph and blowing snow into unstable drifts at many elevations and aspects that are likely to avalanche. A storm bringing 4-8” of snow during the day will increase the danger on all slopes. Two weak layers buried one foot deep and near the ground make much larger avalanches possible. Today, careful route finding and snowpack evaluation are essential.
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Thursday, December 29, 6:30 p.m., Avalanche Presentation and Raffle (great odds of winning!) at MAP Brewing in Bozeman. Free.
January 4 + field day on January 7 or 8, Avalanche Fundamentals for Snowmobilers, Information and pre-registration HERE.
January 4 + field day, Avalanche Fundamentals for Skiers and Snowboarders, Information and pre-registration HERE.
Every 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, for those affected by grief and loss related to outdoor pursuits. Check out the link for more information.
Please consider donating to the Friends of GNFAC Annual Fundraiser.
There are new avalanche beacon checkers at Portal Creek and the trailhead to Denny Creek/ Lionhead Ridge. Thank you the Gallatin Valley Snowmobile Association and Hebgen District FS snow rangers for installing these community resources.