20-21

<p>The snowpack in the mountains around West Yellowstone, Big Sky and Bozeman all have a similarly weak structure with a slab of new and wind-drifted snow sitting on top of a weak foundation of sugary facets. A structure like this does not inspire confidence even as the likelihood of human-triggered avalanches goes down as we become further removed from our last snowstorm. The analogy Doug and I made yesterday at Lionhead was that skiing or riding in steep terrain right now is like playing Russian Roulette, but with fewer chambers loaded (<strong><a href="https://www.youtube.com/watch?v=rWeNgK6_PTs&amp;feature=emb_title">vide…;). This analogy applies equally in this portion of our advisory area where we have seen continued signs of instability such as:</p>

<ul>
<li>Two large collapses (“whumps”) and unstable test results on our tour at Lionhead Ridge yesterday</li>
<li>Two large deep slab avalanches triggered by the YC Ski Patrol during yesterday’s avalanche mitigation. One was 600’ wide and 3’ deep, the second broke 5’ deep</li>
<li>Two different tourers reported loud “whumphs” and shooting cracks in the Southern Gallatin Range</li>
<li>A large unintentionally triggered avalanche on the Football Field just south of the Bridger Bowl Boundary on Christmas Day (<a href="https://www.mtavalanche.com/node/23396"><strong>photos and details</strong></a>)</li>
</ul>

<p>These events correspond to what we have observed in the field. Go through this <strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQDzKmH5K3ZS8Gg3DzwsZ3…’s field video library</a></strong> for discussions about our field observations.</p>

<p>Today, utilize thorough snowpack evaluation and careful route selection that avoids steep terrain. Human triggered avalanches remain a scary possibility and the danger is rated MODERATE.</p>

<p>While the danger rating is the same in Cooke City as in our other areas, the avalanche problem is different because the foundation of the snowpack I s generally strong. Human-triggered avalanches failing 2-3’ deep within the new and wind-drifted snow from the last week of snowstorms are possible in steep, rocky terrain. Watch our videos and read about recent avalanche activity to get an idea of what is possible (<a href="https://youtu.be/bHZazXX4EXM"><strong>video</strong></a&gt;, <a href="https://youtu.be/Ava7FSUx9kY"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/node/23352"><strong>details</strong></a&gt;). The new snow will continue to stabilize but remain vigilant by following safe travel protocols and carrying avalanche rescue gear. Today, watch for signs of instability such as shooting cracks and evaluate the upper few feet of the snowpack by digging and performing a stability test before committing to any avalanche terrain. The 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>

<p>Near Bozeman and Big Sky, dangerous avalanche conditions exist due to 6-9” of new snow adding 0.5” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE) to a weak snowpack. A 1-2 foot thick layer of weak, sugary facets on the ground avalanched and collapsed under the weight of new snow earlier this week (<a href="https://www.mtavalanche.com/images/20/natural-avalanches-bridger-peak">…;), and today’s new snow makes similar avalanches likely.</p>

<p>On Friday, a skier in the Bridger Range triggered a large slide on the Football Field path of Saddle Peak (<a href="https://www.mtavalanche.com/node/23396"><strong>photos and details</strong></a>), and a skier in Hyalite triggered a large, rumbling collapse on a low angle slope (<a href="https://www.mtavalanche.com/node/23404"><strong>details</strong></a&gt;). Yesterday, Ian and I went to the northern Bridger Range and found a snowpack similar to what exists in Hyalite, near Big Sky and West Yellowstone, with a thick layer of weak facets on the ground (<strong><a href="https://www.youtube.com/watch?v=OYjGdWjKAzc&amp;list=PLXu5151nmAvQDzKmH…;

<p>Today’s new snow creates dangerous avalanche conditions on steep slopes, especially where thicker drifts of snow formed from west-northwest wind. The snowpack this year holds some of the weakest snow we have seen, and has shown it can’t be trusted. Careful terrain selection is your best defense. Today the avalanche danger is CONSIDERABLE.</p>

<p>The snowpack in the southern Madison Range and Lionhead area near West Yellowstone has a similar poor structure as the mountains near Bozeman and Big Sky, and they received 3-4” of snow equal to 0.3-0.4” of SWE. It is possible to trigger avalanches on sugary persistent weak layers 1-3 feet deep. Last weekend, Dave and I saw avalanches and weak facets in Taylor Fork (<a href="https://youtu.be/IUb9ub26y1o"><strong>video</strong></a&gt;), and he and Doug triggered a couple avalanches at Lionhead (<a href="https://www.mtavalanche.com/node/23324"><strong>details and video</strong></a>). Be extra cautious of wind loaded slopes, and avoid steep slopes if you suspect weak, sugary snow exists on the ground. Today the avalanche danger is MODERATE.</p>

<p>The mountains near Cooke City got 5” of new snow equal to 0.3” of SWE. The snowpack there is 4-6 feet deep with a stronger foundation than the rest of our advisory area. Earlier in the week, 2 feet of heavy snow fell and we had reports of natural and skier triggered avalanches (<a href="https://youtu.be/bHZazXX4EXM"><strong>video</strong></a&gt;, <a href="https://youtu.be/Ava7FSUx9kY"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/node/23352"><strong>details</strong></a&gt;). Today, watch for instabilities in the new snow and on freshly wind-loaded slopes. Avalanches could break 2-3 feet deep below the storm snow that fell early last week. Today the avalanche danger is MODERATE. Be cautious of steep, wind-loaded slopes and carefully assess the stability of the last week’s snow before riding slopes steeper than 30 degrees.</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>