Good Morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Wednesday, December 6th at 6:45 a.m. Today’s advisory is sponsored by Alpine Orthopedics and Knoff Group Real Estate. This advisory does not apply to operating ski areas.
At 5 a.m. under clear skies, there’s no new snow, just wind (15-25 W) and temperatures of 10-15F. Winds in the Bridger Range have lessened from yesterday’s speeds of 35 mph that swirled from all directions. Today will be clear with temperatures reaching the mid-20s. High clouds will slide in from the NW tonight, and temperatures will drop into the teens. A high pressure ridge will dominate through the weekend and block any chance of snow.
The story in the Bridger Range is simple: yesterday’s strong wind blew Sunday and Monday’s 16” of new snow into wind slabs that avalanched on many slopes. The winds were unusual and did not come from any one direction. They swirled around and mostly hit mid to lower elevation terrain. The Bridger Bowl Ski Patrol was able to avalanche wind slabs with ski cuts all over the mountain, not just the ridgeline. The slabs were sliding on the Thanksgiving ice crust and did not break into deeper layers. In general, the old snow underneath this crust is strong and stable (video).
Avoid slopes where wind drifted snow has formed slabs. Shooting cracks and recent avalanches are warning signs of instability. For today the avalanche danger is rated CONSIDERABLE on all wind-loaded slopes and MODERATE on all others.
In the mountains around Hyalite, Big Sky and Cooke City, westerly wind blew at the ridgelines with many upper elevation slopes stripped bare as others grew cornices (photo). A skier up Hyalite noted that several cornices broke at ridgelines but did not trigger avalanches. Though slopes are generally stable (snowpits, video of Buck Ridge) it is possible to trigger small wind slabs near ridges or in gullies. For today, the avalanche danger is rated MODERATE on all wind-loaded terrain and LOW on all other slopes.
The southern Madison Range, southern Gallatin Range, and mountains around West Yellowstone have a stable snowpack that could handle the new snow from Sunday (6”). Winds blew at the ridgelines after the storm but these slabs bonded to the old snow surface and are unlikely to move. For today the avalanche danger is rated LOW since they have generally safe avalanche conditions.
Upcoming Avalanche Education and Events
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
7 December, Avalanche Awareness, 6-7:30 p.m. at Basecamp, Helena
Dec. 14 and 15, Snowmobiler Introduction to Avalanches with Field Course, Info and Register Here
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.
Emily Wolfe, board member of the Friends, wrote a great article in Mountain Outlaw about a local woman, Leslie Martin, who survived an avalanche in the Sawtooths in 2009 that killed her husband. http://ow.ly/NWsX30h1Puk