21-22

<p>Yesterday, the wind blew 20-30 mph in the Southern Gallatin and Southern Madison Ranges and the mountains around Cooke City and created 1-2’ drifts of snow on top of a weak layer of buried surface hoar. Human triggered avalanches are possible on slopes where recent drifts of snow and this weak layer overlap. Avalanches are unlikely on slopes missing one of these two ingredients, as Alex and Ian observed in the Taylor Fork prior to yesterday’s wind (<a href="https://www.youtube.com/watch?v=I6AleixLxTI&amp;list=PLXu5151nmAvT1nrM2…;). Triggered by a group of skiers on Friday, a shallow slide that propagated across a steep couloir near Cooke City indicates of the type of avalanche you could trigger today (<a href="http://www.mtavalanche.com/node/25595"><strong>photo and details</strong></a>). Luckily, the skiers were sheltered from the slide and were unharmed.</p>

<p>Indicators of instability such as recent avalanches or cracks shooting from your skis, board or sled are clear signs that you found the unstable combo and should retreat. If signs of instability aren’t as obvious, dig down to look for the <a href="https://www.mtavalanche.com/images/22/surface-hoar-layer-s-madison-rang… surface hoar</strong></a> and perform a quick stability test before entering steep terrain. Avalanches breaking on deeper weak layers are unlikely.</p>

<p>The danger is MODERATE on wind-loaded slopes and LOW on non-wind loaded slopes.</p>

<p>Dangerous, human-triggered avalanches are unlikely in the mountains around Bozeman, Big Sky and West Yellowstone. A weak layer of feathery surface hoar is buried under 6” of snow in the Lionhead area; however, the wind remained light and the overlying slab remains thin. In the mountains around Bozeman and Big Sky, strong winds created fresh drifts over the weekend, but wind-slabs like the one triggered on Saturday in the Northern Bridger Range have largely stabilized due to the lack of an underlying weak layer (<a href="https://www.mtavalanche.com/images/22/snowmobile-triggered-wind-slab-sm… of snowmobile triggered wind slab</strong></a>). Today, assess the snowpack for isolated areas of instability related to recent wind drifting and buried weak layers, follow safe travel protocols and be cautious on slopes where a small avalanche could sweep you into trees, rocks or off cliffs.</p>

<p>Overall, the snowpack is stable, and the danger is LOW.</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>

<p>Moderate winds out of the northwest to west will form fresh drifts of snow that can avalanche under the weight of a person. Snowfall on Thursday night dropped up to 9” of snow near Bozeman (0.8-1.3” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… Water Equivalent</a>) and 5-8” in the Madison Range (0.5<strong>-</strong>0.6” SWE). Near Cooke City got 6-8” since Tuesday (0.6” SWE).</p>

<p>Winds have been calm to light leaving the recent snow to be transported by today’s wind, except in the Bridger Range where moderate winds yesterday formed drifts which were easy to trigger with skis and snowmobiles (<strong><a href="https://www.mtavalanche.com/images/22/snowmobile-triggered-wind-slab-sm… of snowmobile triggered wind slab</a></strong>). Yesterday Ian and I went to Taylor Fork where wind was calm (<strong><a href="https://www.youtube.com/watch?v=I6AleixLxTI&amp;list=PLXu5151nmAvT1nrM2…;). We did not see signs of instability, but there was 8” of low-density snow that will be drifted into unstable slabs today. Be cautious of wind-loaded slopes, and avoid them if you see signs of unstable fresh drifts such as wind transporting snow across ridgelines, cracking across the snow surface or fresh avalanches.</p>

<p>Yesterday, a skier near Cooke City triggered a shallow, but wide avalanche in a steep couloir (<strong><a href="http://www.mtavalanche.com/node/25595">photo and details</a></strong>). A separate group of skiers near Cooke City dug down and had unstable test results break under the recent snow and chose a different objective. Layers of surface hoar or near surface facets were buried by the recent snow in the southern half of our advisory area which could make fresh drifts easier to trigger. If other signs of instability are not present, before riding steep slopes dig and do a quick stability test to look for unstable weak layers buried below the recent snow (<strong><a href="https://www.mtavalanche.com/images/22/surface-hoar-layer-s-madison-rang… of buried surface hoar</a></strong>). In addition, although unlikely, a much larger avalanche breaking on weak snow near the bottom of the snowpack could be triggered by a smaller avalanche or cornice fall.</p>

<p>Avalanches are possible today and danger is MODERATE on wind-loaded slopes. On non-wind loaded slopes avalanche danger is LOW.</p>

<p>The recent storm dropped 3-4” (0.4” SWE) near West Yellowstone. This is minimal weight added to a generally stable snowpack, and large avalanches are unlikely (<strong><a href="https://www.youtube.com/watch?v=g7Pl9-raU7g">video from Lionhead</a></strong>). Drifts will form from moderate west-northwest winds today which will be generally small and isolated hazards. Watch out for fresh drifts along ridgelines and in very steep terrain, above cliffs, or slopes where getting knocked off your feet by a small avalanche would have high consequences. Overall, large avalanches are unlikely and the avalanche danger is LOW.</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>