Good morning. This is Doug Chabot with an early season avalanche information bulletin issued on Monday, November 21 at 7:30 a.m. This bulletin is sponsored by a Montana FW&P Recreation Trails Grant. Please remember that uphill traffic is not allowed at Big Sky or Moonlight Basin Ski areas. Uphill traffic is permitted at Bridger Bowl, but backcountry snow conditions exist. Our next bulletin will be issued Wednesday morning.
Since the last bulletin on Saturday morning the northern mountains have been dry while the southern areas got dusted with Cooke City getting two inches. Mountain temperatures have substantially warmed from the single digits to high teens as ridgetop winds blew westerly at 20-30 mph. By tomorrow, moist air on a west flow will bring some clouds and a trace to one inch of snow in the south as the northern mountains stays dry and mostly sunny. Temperatures will continue to warm today and Tuesday, but west winds will increase. The rest of the week looks dry and unimpressive for snowfall.
Over the weekend many folks got into the backcountry, with the greatest numbers skiing in the Hyalite drainage of the northern Gallatin Range. Yesterday, my partner and I toured above Hyalite Lake. With three feet of snow on the ground at 9,000 feet it’s one of the deeper snowpacks besides Cooke City. It also has one of the more unstable snowpacks. My stability tests (ECTP21,Q1 x2) broke clean on two inches of facets sitting on an ice crust near the ground (video, photo, snowpit). Although facets are found in most of our advisory area, they are under the most stress where the snow is deepest. We saw a large natural avalanche on a northwest facing slope that broke near the ground and ran 400 feet wide. Nearby, skiers on Friday triggered another slide from low angled terrain while on Saturday other groups got multiple collapses and shooting cracks, all signs of instability.
Skiers sent in observations and snowpits from many areas. Some bulls-eye data outlining instability include skiers unable to isolate a column around Frasier Lake in the northern Bridgers. If a block of snow naturally falls down after cutting away all four sides, you’ve got a problem. This indicates very unstable conditions. In the northern Madison Range, the Big Sky Ski Patrol continued to get avalanches breaking on facets during their control work (photo). Further south, two reports from near West Yellowstone reported collapses and cracks shooting across the slope.
Some thoughts on our snowpack:
1. The snowpack structure is weak. A foundation of unbonded snow is creating avalanche danger in the backcountry.
2. Areas with more snow are more unstable.
3. Avalanche activity, collapsing and cracking are signs that you should ski elsewhere.
4. Even without fresh snow, wind loading can contribute to instability. (photo)
5. This week, in the absence of storms loading the snowpack, I expect signs of instability will decrease making stability analysis trickier.
My advice is to be conservative in the backcountry. The winter is young and the snowpack is undeniably weak, and in many places unstable. Enjoy a tour, but don’t needlessly place yourself at risk for a few scrappy turns. Be patient. It’ll get better…maybe.
Eric will issue the next avalanche bulletin Wednesday morning.
We are not issuing avalanche danger ratings yet because we only have limited snowpack data. We need your backcountry observations to help us. Any snowpack or avalanche information is especially valuable this time of year. If you get out, please drop us a line at mtavalanche@gmail.com or leave us a message at 587-6984.
Tuesday, November 22, WEST YELLOWSTONE
Avalanche Awareness and Dozen More Turns movie at the Holiday Inn at 6 p.m. before the Backcountry Film Fest.
Wednesday, November 30, BOZEMAN
Introduction to Avalanches with Field Course at MSU. Wednesday and Thursday evening lectures with a field course on Saturday. More info at http://www.mtavalanche.com/education/classes/workshops