20-21

<p>Yesterday near Bacon Rind, skiers triggered a very large avalanche from the safety of low angle terrain a long distance away (<strong><a href="https://www.mtavalanche.com/node/23991">photos and details</a></strong>). Multiple other groups in the southern Gallatin and southern Madison Ranges triggered large rumbling collapses that shook snow off trees hundreds of feet away (<strong><a href="https://www.mtavalanche.com/node/23983">photos and details</a></strong>). Dangerous avalanche conditions exist in the mountains south of Big Sky to West Yellowstone and human triggered avalanches are likely.</p>

<p>New snow from Wednesday night through yesterday morning totaled 18-26” equal to 1.5-2.2” of snow water equivalent (SWE). This <strong><a href="https://www.youtube.com/watch?v=n7ZW0JmstDA&amp;list=PLXu5151nmAvQDzKmH… from the southern Gallatin Range</a></strong> shows the new snow easily collapsing on a layer of surface hoar buried 1-2 feet deep, and a layer of weak, sugary depth hoar near the ground. Avalanches can break on either of these layers, propagate long distances and be triggered from low angle terrain below or adjacent to steep slopes. Today the avalanche danger is rated CONSIDERABLE. Keep a safe distance from slopes steeper than 30 degrees.</p>

<p>Since Thursday the mountains near Cooke City got 12-18” of low-density snow (0.9” SWE). Yesterday we heard of numerous natural avalanches (<strong><a href="https://www.mtavalanche.com/node/23997">details</a></strong&gt;), and group of skiers remotely triggered five small avalanches that broke below the new snow (<strong><a href="https://www.mtavalanche.com/images/21/skier-triggered-slide-west-cooke"…;). Another group triggered a small cornice from low angle terrain 20’ away (<strong><a href="https://www.mtavalanche.com/images/21/remote-triggered-cornice">photo</…;). This recent activity shows us the recent snow fell onto a weak surface, and creates a structure that makes avalanches possible to trigger. Avalanches could also break deeper on a weak layer of surface hoar or facets buried 24-30” deep that was responsible for a few snowmobile triggered avalanches last week (<a href="https://youtu.be/Ui1wdUHE56E"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/images/21/2-avalanches-sheep-mtn"><strong>p… of avalanches</strong></a>). Carefully assess the stability of the new snow and avoid steep slopes if you see cracking, collapsing or fresh avalanches. Avalanches are possible to trigger and the avalanche danger is MODERATE.</p>

<p>Friday night through yesterday morning the mountains near Big Sky and Bozeman got 7-11” of snow equal to 0.5-0.7” snow water equivalent (SWE). Yesterday this new snow avalanched naturally in Hyalite (<strong><a href="https://www.mtavalanche.com/images/21/natural-avalanche-maid-mist">phot…;) and near Big Sky (<strong><a href="https://www.mtavalanche.com/images/21/natural-avalanche-beehive">photo<…;), and on Friday afternoon a skier near Big Sky triggered an avalanche that propagated wide and broke into weak, sugary snow underneath (<a href="https://www.mtavalanche.com/images/21/dudley-creek-slides"><strong>phot…;). Yesterday Doug was climbing in Hyalite on his day off and witnessed numerous natural sluffs on the climb he was on. He made <strong><a href="https://youtu.be/qq8_qX60izk">this video</a></strong> that describes the weak interface below the new snow which is responsible for this avalanche activity. Today, the new snow resting over weak snow below means avalanches are possible to trigger. Wind will be stronger than yesterday, so expect fresh drifts could break wide and create large avalanches. Avalanche danger is rated MODERATE.</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>