Wet snow avalanches are today’s main concern and will probably consist of small wet loose avalanches that involve the top few inches of snow. If crusts on the surface of the snowpack fully melt, the snowpack below is wet and unsupportable, so wet loose avalanches could gouge multiple feet deep into wet snow or larger wet slab avalanches could be triggered. Plan to be off and not below sunny slopes steeper than 30 degrees before the surface crusts melt and the snowpack becomes wet and unsupportable. On shady, high elevation slopes, it is still possible to trigger large persistent slab avalanches that break on weak snow that formed in January and February.
Wet loose avalanches may be a few inches deep as surface crusts melt through the day. If surface crusts fully melt, wet-loose avalanches could gouge deeper into the saturated, wet snowpack below, and Wet Slabs will also be triggered.
Persistent slab avalanches are most likely on high elevation, shady slopes where the snowpack stayed drier during last week's heat.
Yesterday morning the surface of the snowpack was solidly frozen after four nights and days without freezing, and daytime high temperatures were 10-20 degrees cooler than the previous four days. Sunshine and above freezing temperatures softened the snow surface on slopes that receive direct sun and lower elevation slopes, and the snow stayed frozen on higher and shadier slopes.
Today, I expect generally similar conditions as yesterday. Temperatures are slightly warmer, but the snow surface should be re-frozen this morning on most slopes that were previously wet. Warmer daytime temperatures might cause wet snow instabilities to develop faster today, but they might be working against cloudier skies that slow down the melting effects of the sun.
Wet snow avalanches are today’s main concern and will probably consist of small wet loose avalanches that involve the top few inches of snow. If crusts on the surface of the snowpack fully melt, the snowpack below is wet and unsupportable, so wet loose avalanches could gouge multiple feet deep into wet snow or larger wet slab avalanches could be triggered. Large wet slab avalanches broke naturally near Big Sky earlier in the week (Cedar Mt. 1, Cedar Mtn. 2), and near Cooke City a couple days ago (Woody Ridge, Town Hill). Yesterday, skiers in the northern Bridger Range reported a large wet slab that broke naturally on Friday evening or Saturday (observation), and skiers near Cooke City reported similar recent wet avalanche activity (observation).
Plan to be off and not below sunny slopes steeper than 30 degrees before the surface crusts melt and the snowpack becomes wet and unsupportable. If you sink into wet snow deeper than a couple inches, or see rollerballs and pinwheels on the snow surface or fresh natural wet avalanches, it is time to find lower angle or shadier slopes
On shadier, high elevation slopes, it is still possible to trigger large persistent slab avalanches that break on weak snow that formed in January and February. Carefully assess the snowpack and terrain for potential buried persistent weak layers. These are most likely on high elevation, northerly facing slopes where the snowpack stayed drier during last week’s heat. On Friday near Emigrant Peak skiers triggered a 3-5 foot deep, thousand foot wide avalanche on a north facing slope (observation).
Stay alert for cornices along ridgelines as they have been losing strength from the heat and breaking easily. Give cornices plenty of space if you’re travelling above them on ridgelines and be cautious of slopes below cornices during the heat of the day.
Avalanche danger is MODERATE throughout the forecast area.
