Turnagain Pass Avalanche Forecast

Be aware of wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Strong Northwest winds this week have transformed a foot of new snow into variable surfaces. Ridgetops are scoured down to old anti-tracks, sastrugi or wind polished snow. Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. Shooting cracks may not be present until committed to a slope and the whole slab releases. Several weak layers have been preserved ~2 feet below the surface and could propagate a larger avalanche. (More on this below.) Although the sun is not expected today, keep in mind that its that time of year when radiation can make the snow more reactive on Southerly aspects. 

Scoured ridges and wind pillowed snow on Tincan following the big wing event this week. 

Triggering an avalanche 2+ feet thick is possible due to several weak layers buried within our snowpack. More potential exists on the Southern end of Turnagain Pass and Summit Lake zone where a shallow and weaker snowpack remains. This was evident on Wednesday during the wind event where numerous large avalanches released naturally near Silvertip Creek and in Summit Lake. In Turnagain Pass we have been tracking several weak layers buried 1-2 feet deep (facets and buried surface hoar) and both have been reactive in stability tests. This structure can be found on all aspects and will be easier to trigger in thinner areas of the snowpack. These slabs could be triggered in softer more protected snow or in places where the snow is harder and more supportable. Assess the terrain for consequences and remember that the bigger the terrain the bigger the consequences. There is still much uncertainty around this avalanche problem. 

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if you find the wrong spot above 3,000′ in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is also more pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Several observers this week have reported collapsing below 2500′ and is likey because of a layer of facets sitting on m/f crust. Photo of W aspect of Cornbiscuit at 2000′

 Large connected crown on a Northeast aspect near Silvertip Creek which released naturally some time between Tuesday and Wednesday during the wind event.