This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Monday, December 3rd at 7:30 a.m. Today’s advisory is sponsored by Gallatin County Search and Rescue in partnership with the Friends of the Avalanche Center. Please remember that uphill traffic is not allowed at Big Sky or Moonlight Basin ski areas. It is permitted at Bridger Bowl until the ski area opens, but backcountry conditions exist within the ski area boundaries.
Since yesterday morning Carrot Basin Snotel site in the southern Madison Range picked up 1.4 inches of SWE (snow water equivalent) while Madison Plateau and Fisher Creek are showing close to one inch of SWE. That translates to nearly a foot of new snow. The mountains around Bozeman and Big Sky picked up 2-4 inches of snow.
At 4 am temperatures are in the teens to low 20s and winds are blowing 10-20 out of the WNW. Today, a westerly flow will keep skies partly to mostly cloudy and winds will continue to blow 10-20 out of the west. Temperatures will warm into the mid-20s to low 30s. No precipitation is expected today.
Cooke City Southern Madison Range Southern Gallatin Range
Lionhead
What state are we in? Normally this time of year we're used to cold temperatures and dry snow. That's not what we encountered yesterday during our trip to the Lionhead (video). In fact, we entered an environment far more akin to a coastal climate such as Washington or Oregon. With pouring rain in West Yellowstone and thick, cement-like snow above 8,000 ft., it was difficult to believe we were in Southwestern Montana.
This warm and wet weather pattern has not been good to low elevation terrain, turning the already anemic snowpack into piles of slush. But above 8,000 feet, 2-3 feet of heavy, dense snow has fallen over the past four days (photo, video). This heavy load has put the snowpack to the test, and to our delight no avalanches have been triggered or observed during this storm cycle in the mountains around Cooke City and West Yellowstone.
Today, wind loaded slopes are the primary avalanche concern. Instability is isolated, so avalanche activity should stay confined to steep, upper elevation slopes with north through east aspects.
Avalanches within the storm snow are also possible. Density changes within the top 1-2 feet of the snowpack could act as temporary weak layers, making avalanches possible on slopes steeper than 35 degrees (snowpit).
Today, the avalanche danger is rated CONSIDERABLE on wind loaded slopes steeper than 35 degrees. All other slopes have a MODERATE avalanche danger.
Bridger Range Northern Madison Range Northern Gallatin Range
Yesterday, a snowmobiler triggered an avalanche off Buck Ridge south of Big Sky. Information is limited, but it sounds like the slide was triggered on a north facing, wind loaded slope. The avalanche likely ran on a layer of facets at or near the ground.
Although persistent weak layers are not pervasive, they can be found in isolated areas. Shadier, upper elevation slopes (north through east) are the most likely to have faceted crystals buried beneath the snow surface. This poses a problem since north and east facing slopes received the heaviest wind load over the past few days.
Fortunately, snow amounts have been lite and loading has stayed confined to upper elevations. Slopes directly below ridgelines or cross loaded gullies will be the most likely to produce an avalanche. Digging to the ground to assess the snowpack structure and stability is a good idea before committing to steep slopes. This typically can be done in less than 5 minutes since the snowpack is only a few feet deep.
Today, human triggered avalanches remain possible on wind loaded slopes which have a MODERATE avalanche danger. Non-wind loaded slopes have a LOW avalanche danger.
Doug will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations drop us a line at mtavalanche@gmail.com or call us at 587-6984. Thank you.
Snowmobiler Introduction to Avalanches with Field Course in Billings at Hi-Tech Motor Sports on December 12 and 13, 6-9 p.m. and the field course on January 20 in Cooke City. Sign up for this class HERE
Snowmobiler Introduction to Avalanches with Field Course in West Yellowstone on December 20 and 21. Sign up for this class HERE.
Snowmobiler Introduction to Avalanches at Greenup Performance in Black Eagle near Great Falls, MT, December 8, 9 a.m. to 2 p.m. FREE.
FREE 1 hour lectures:
December 3, Northern Lights Trading Company, Bozeman, 7 p.m.
December 12, REI in Bozeman, 6:30 p.m.