20-21

<p>From Big Sky to West Yellowstone 1-2 feet of weak, sugary snow on the ground will struggle to hold the weight of fresh drifts that formed from strong westerly wind. Last week Ian was in Taylor Fork and found unstable, soft drifts (<strong><a href="https://www.youtube.com/watch?v=eAZKRKDi-pg&amp;list=PLXu5151nmAvQDzKmH…;), and Doug triggered a 1 foot deep soft slab on a small slope near West Yellowstone (<strong><a href="https://www.mtavalanche.com/node/23272">photo</a></strong&gt;). On Friday, we got reports of multiple slides triggered by snowmobiles, groomers, snowplows, and by explosives at the ski resorts (<a href="https://www.mtavalanche.com/images/20/groomer-triggered-road-cuts"><str…;, <a href="https://www.mtavalanche.com/images/20/small-snowmobile-triggered-slides…; </strong><a href="https://www.mtavalanche.com/images/20/snowplow-triggered-slide-near-big…;).</p>

<p>Due to the very poor snow structure, slabs that grew over the last week have not stabilized and remain easy to trigger. Avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on non-wind loaded slopes. Near West Yellowstone, heavy snowfall and wind today will increase the avalanche danger to CONSIDERABLE. Avoid travel on or underneath steep, wind-loaded slopes.</p>

<p>Near Cooke City, avalanche danger is elevated due to new snow and strong wind that will create fresh slabs. Today, these slabs are possible to trigger and large enough to bury or badly injure a person. Expect stability to decrease through the day as more snow and wind grow larger slabs. Be extra cautious of wind-loaded slopes where thick drifts form. The snowpack near Cooke city is 3-5 feet deep and generally lacks widespread buried weak layers (<a href="https://www.youtube.com/watch?v=71V0bipTxfY"><strong>video</strong></a&…;). However, we have seen and heard evidence of weak snow buried 1-2 feet deep on some slopes. This includes a few avalanches west of Cooke City last week which broke 100 feet wide on a layer of sugary snow (<a href="https://www.mtavalanche.com/node/23292"><strong>photo</strong></a&gt;). Today the avalanche danger is MODERATE.</p>

<p>In the mountains near Bozeman, strong westerly winds over the last 24 hours formed thick drifts that are unstable on steep slopes. These drifts can’t be trusted to hold the weight of a person because the snowpack below has widespread sugary weak layers (<strong><a href="https://www.mtavalanche.com/images/20/snowpit-bridger-29-nov">photo</a>…;, <strong><a href="https://www.youtube.com/watch?v=JrjrgTLRff0&amp;feature=youtu.be">video…;). Avoid steep wind-loaded slopes today. These can range from hard slabs near ridgelines to soft slabs in the trees. On non-wind loaded slopes, a lack of new snow to form a slab over the weak foundation makes avalanches unlikely. If you are unsure which slopes are wind-loaded, be cautious of any slope steeper than 30 degrees. Today the avalanche danger is MODERATE on wind-loaded slopes and LOW on other slopes.</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>Strong winds have grown existing drifts and also built new drifts of cohesive snow sitting on a weak foundation. Yesterday (before the winds picked up) we got reports of multiple slides triggered by snowmobiles, groomers, snowplows, and with explosives at the ski resorts (<a href="https://www.mtavalanche.com/images/20/groomer-triggered-road-cuts"><str…;, <a href="https://www.mtavalanche.com/images/20/small-snowmobile-triggered-slides…; </strong><a href="https://www.mtavalanche.com/images/20/snowplow-triggered-slide-near-big…;). These slides were generally small, but are a clear indication that the snow is unstable and that the conditions for larger slides exist. The very strong winds have likely built drifts in unusual places further below ridgelines than is typical. Continued strong winds today will continue to build new drifts, so stay on alert for changing conditions through the day. Avoid steep, windloaded slopes.&nbsp;</p>

<p>Human triggered avalanches are likely on wind-loaded slopes and the avalanche danger is CONSIDERABLE. On all other slopes the avalanche danger is MODERATE.</p>

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<p>There is less new snow available to drift in the Bridger and Northern Gallatin ranges. Drifts will generally be thinner and more isolated, but no less dangerous where there is a thick slab of wind drifted snow. Weak snow in the lower snowpack is widespread, so anywhere these drifts form they are likely to be unstable. Unfortunately, these weak layers will not stabilize quickly, so plan to stay on alert for them for the foreseeable future. Watch for and avoid heavily wind-drifted slopes.</p>

<p>The avalanche danger today is MODERATE on wind-loaded slopes and LOW on all others.&nbsp;</p>

<p>Wind drifts of new snow are also the primary concern around Cooke City, In general, drifts are not building on top of snow that is as weak as in other areas. However, there are spots with weaker snow, as evidenced by several natural slides that broke west of Cooke City earlier in the week (<a href="https://www.mtavalanche.com/node/23292"><strong><u>photo</u></strong></…;). Alex was in Cooke yesterday and recommended digging below the new snow to find out what it’s sitting on before riding steep slopes (<a href="https://www.youtube.com/watch?v=71V0bipTxfY"><strong><u>video</u></stro…;) Today, human triggered avalanches are possible and 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><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>