20-21

<p>Buried persistent weak layers make human triggered avalanches possible today. A layer of weak, sugary snow near the ground is buried 2-3 feet deep on many slopes and has produced large avalanches this season. The most recent reported was triggered by a snowmobiler Tuesday in the southern Madison Range (<strong><a href="https://www.mtavalanche.com/node/23867">photos and details</a></strong>). On Thursday Doug and I found this layer on Buck Ridge, in addition to a thin layer of surface hoar buried 8-10” deep (<a href="https://www.mtavalanche.com/images/21/poor-snowpack-structure"><strong>… of layering</strong></a>). The sugary snow near the ground broke in our stability test which reminds us it remains unstable and is not going anywhere (<a href="https://youtu.be/fUK0nUTBSvU"><strong>video</strong></a>,<strong&gt; </strong><a href="https://www.mtavalanche.com/images/21/muddy-crk-profile-jan-21"><strong… profile</strong></a>). The surface hoar is not on all slopes, but the sugary depth hoar near the ground is on most.</p>

<p>Light wind with a couple inches of snow the last few days combined with continued calm, clear weather today gives weak layers a reprieve from additional load. Triggering an avalanche is becoming more difficult, but the possibility and consequences require careful terrain selection and diligent snowpack assessment. Be cautious of travel on and underneath slopes steeper than 30 degrees. Large avalanches are possible to trigger and the avalanche danger is rated MODERATE.</p>

<p>In the mountains near Cooke City a layer of surface hoar buried 12-18” deep produced avalanches, cracking and collapsing over the last week. On Tuesday, snowmobilers triggered an avalanche on this layer in Sheep Creek (<strong><a href="https://www.mtavalanche.com/node/23858">details</a></strong&gt;), and near Goose Lake skiers saw 2 human triggered slides that we suspect broke on this layer (<a href="https://www.mtavalanche.com/node/23857"><strong>details and photo</strong></a>). Additionally, a weak layer of sugary, faceted snow buried 2-3 feet deep exists on some slopes. Dave rode near Cooke City last Sunday and Monday and traveled as if these weak layers are on all slopes (<a href="https://youtu.be/J9oQHYge_gM"><strong>video1</strong></a&gt;, <a href="https://youtu.be/J9oQHYge_gM"><strong>video2</strong></a&gt;). Although these layers do not exist on all slopes, you can avoid avalanches by avoiding slopes steeper than 30 degrees. Otherwise, you have to diligently assess the snowpack which starts with a thorough review of recent avalanche activity (<strong><a href="https://www.mtavalanche.com/avalanche-activity">activity log</a></strong>) and media from the region (<strong><a href="https://www.mtavalanche.com/forecast/cooke-city">Cooke regional page</a></strong>), and should include digging to look for these layers before riding steep slopes. Today avalanches are possible and 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>The snowpack from the Bridger Range to West Yellowstone is weak, not getting any stronger and gives me a headache. The problem is a thick layer of weak, sugary facets at the ground called depth hoar. This layer is 1-2 feet thick and is responsible for collapses, whumpfs and many avalanches (e.g. <a href="https://www.mtavalanche.com/node/23867"><strong><u>Tepee avalanche</u></strong></a>). A secondary problem is a thin layer of feathery surface hoar crystals about a foot down (<a href="https://www.mtavalanche.com/images/21/poor-snowpack-structure"><strong>… of layering</u></strong></a>). While the depth hoar is on most slopes, the surface hoar is not. Yesterday, Alex and I rode around Buck Ridge, found it, and added it to our list of concerns. We also saw 7+ avalanches from 5-7 days ago (<a href="https://www.mtavalanche.com/images/21/4-avalanches-near-mcatee-basin"><…;). In our stability test we were able to break the weak snow at the ground which caught our attention and should erase any fantasy thinking about this layer getting stronger&nbsp; (<a href="https://youtu.be/fUK0nUTBSvU"><strong><u>video</u></strong></a>,<strong…; </strong><a href="https://www.mtavalanche.com/images/21/muddy-crk-profile-jan-21"><strong… profile</u></strong></a>). A snowpack with depth hoar is not to be trusted.&nbsp;</p>

<p>Low snowfall and slopes stripped by wind has created a thin snowpack (<a href="https://www.mtavalanche.com/images/21/wind-scoured-mcatee-basin"><stron…;). Thin and weak go hand-in-hand. Folks will continue to trigger an occasional avalanche if they get unlucky or careless. Continue to dig and look for surface hoar and test the weak snow at the ground, but no matter what I find I’m hesitant to get into avalanche terrain.&nbsp;</p>

<p>Given the poor snow structure, recent avalanche activity and two weak layers in the snowpack, the avalanche danger is rated MODERATE.</p>

<p>The mountains around Cooke City have 3” of new snow, enough to improve riding conditions without increasing avalanche danger. These mountains have two layers of concern: feathery surface hoar crystals buried 12-18” deep and a thin layer of weak grains 3 feet under the surface. These layers are not on every slope and there is no quick and easy way to find them without digging. On Tuesday, snowmobilers triggered this layer in Sheep Creek and luckily escaped getting caught, and near Goose Lake skiers saw 2 human triggered slides (<a href="https://www.mtavalanche.com/node/23857"><strong><u>details and photo</u></strong></a>). Dave and his partner were in these mountains Sunday and Monday and treated slopes as though these layers were on every one. His 2 videos explain what to look for (<a href="https://youtu.be/J9oQHYge_gM"><strong><u>video1</u></strong></a&gt;, <a href="https://youtu.be/J9oQHYge_gM"><strong><u>video2</u></strong></a&gt;). For today, the avalanche danger is rated MODERATE since a person could trigger a slide on one of these weak layers.&nbsp;</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><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>