Snowpack and Avalanche Discussion
<p>Dangerous avalanche conditions exist in the mountains around Cooke City and human-triggered avalanches are likely. In the last week, snow fell every day totaling 18” equal to 1.5” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</a> (SWE). Winds gusted 45 mph yesterday, drifting snow onto slopes with weak layers buried 18-30” under the surface. Today, avalanches could range from relatively small to large. Saturday’s fatal avalanche broke approximately 800’ wide, flowed through two gullies and piled debris 15’ deep (<a href="https://www.mtavalanche.com/node/25906"><strong>photos and preliminary</strong></a><a href="https://www.mtavalanche.com/node/25906"><strong> details</strong></a>). An intentionally triggered avalanche on Ski Hill broke 15” deep and 30-50’ across. The likelihood of surviving a slide on the large end of this spectrum is not high. Utilize careful route-finding and largely avoid slopes over 30 degrees. Carefully assess the snowpack if you choose to enter steeper terrain. Avalanches will be most sensitive to triggers on or near terrain features with drifts from yesterday’s strong winds. The danger is rated CONSIDERABLE in Cooke City.</p>
<p>Human-triggered avalanches are possible in the mountains around Bozeman, Big Sky and West Yellowstone. The Bridger Range and the mountains around Big Sky received 9-13” of snow equal to 0.4-0.9” SWE with slightly less in the Northern Gallatin Range and Lionhead areas. In areas with more new snow, loose snow avalanches or sluffs will pack a punch as they gain significant volume. It is possible to trigger a dangerous slab avalanche where the wind has drifted the snow and where the new snow is sitting on weak layers buried 1-2’ under the surface. Scale up the slope size from Saturday’s rider-triggered avalanche near Two Top and you have a significant problem (<a href="https://www.mtavalanche.com/node/25924"><strong>photos and details</strong></a>). During last week’s field days to <a href="https://www.youtube.com/watch?v=Fdc8xGBt5RU&list=PLXu5151nmAvT1nrM2…;, <a href="https://www.youtube.com/watch?v=WyJv7snrlDM"><strong>Buck Ridge</strong></a> and the <a href="https://www.youtube.com/watch?v=uIJ0t3fBQDo"><strong>Bridger Range</strong></a>, we saw small avalanches that broke in the new and wind-drifted snow. As the winds shift to the east and increase through the day, expect drifts to form in abnormal locations.</p>
<p>Evaluate the snowpack carefully and avoid terrain features such as drifts, steep rollovers and terrain traps where avalanches are more likely or have more significant consequences. The danger is MODERATE.</p>
<p>The Southern Madison and Southern Gallatin Ranges received 1-3” of new snow equal to 0.1” of SWE. Yesterday’s strong winds drifted snow onto slopes with weak layers of facets and surface hoar buried 6-12” deep. It is possible to trigger an avalanche on slopes where recent drifts sit on top of weak layers. Outside of isolated instabilities, avalanches are unlikely on slopes without wind drifted snow.</p>
<p>Watch for signs of recent wind loading such as hard, drum-like slabs or cracking in the upper snowpack, assess stability and follow safe travel protocols. The avalanche danger is MODERATE on wind-loaded slopes and LOW on all others.</p>
<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
