GNFAC Avalanche Forecast for Thu Jan 3, 2019

A well-developed layer of facets forms the foundation of the pack on most slopes in the southern Madison Range and mountains near West Yellowstone (video). This persistent weak layer was put under significant stress earlier in the week when it was loaded by 12-18” of new snow. On Tuesday, Doug rode in the Lionhead area and observed numerous natural avalanches that occurred during or immediately after the storm (video, photo). Since the storm ended on Monday, the snowpack has some time to adjust. Avalanches won’t be as easy to trigger today, but they still remain possible. All steep slopes should be considered suspect and approached with caution. It will be possible to remotely trigger slides from low angle or flat terrain. Keep in mind, if a slide does occur it will fail near the ground and likely be a large and dangerous.

Today, human triggered avalanches are possible and the avalanche danger is rated MODERATE.

There are two different scenarios going on in the mountains around Bozeman and Big Sky. In upper elevation terrain, the primary avalanche concern is wind loaded slopes. Areas loaded by west-northwest winds are the most likely to hold unstable conditions. Recently wind loaded slopes won’t be hair trigger, but still hold the potential to produce human triggered avalanches. Watch for rounded, firm pillows of wind drifted snow and approach these areas with caution. Fortunately, the snowpack lacks persistent weak layers at upper elevations, which will keep instabilities confined to new and wind-blown snow.

The second scenario is a shallow and weak snowpack on lower elevation slopes. Weak facets near the ground are now loaded by up to a foot of fresh snow. Widespread cracking and collapsing have been reported on Mt Ellis, Mt Wheeler, and lower terrain near Big Sky (video, photo). This is a clear indication unstable conditions exist where the snowpack is shallow and weak. Watch for signs of instability such as cracking/collapsing and avoid steep terrain where these signs are present.

Today, wind loading and weak layers make human triggered avalanches possible and the avalanche danger is rated MODERATE.

The storm over New Year’s did not produce much avalanche activity around Cooke City. A few small natural avalanches were observed on wind loaded slopes (photo), but in general the snowpack handled the load quite well. Although winds have been light the past few days, slopes loaded earlier in the week could still produce avalanches under the weight of a skier or rider. Watch for wind loaded slopes below ridgelines and cross loaded terrain features.  

A secondary, but not widespread problem involves facets buried mid-pack and near the ground (video, photo, video). These layers have not been highly reactive, but are worth assessing before jumping into avalanche terrain.

The snowpack is trending towards stability, but avalanches remain possible on wind loaded slopes which have a MODERATE avalanche danger. Generally safe avalanche conditions exist on non-wind loaded slopes which have LOW avalanche danger.

If you get out and have any avalanche or snowpack observations to share, contact us via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).