19-20

<p>Today’s 3-5” of new snow (0.3-0.4” <u><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a></u>) does not increase avalanche danger, but creates some additional hazard. Fresh drifts of snow are possible to trigger. These drifts are larger where more snow fell, and will grow today with moderate wind. Be cautious of wind loaded slopes near ridgelines, identifiable by rounded pillows of snow or overhanging cornices (<strong><a href="https://www.mtavalanche.com/images/20/natural-wind-slabs-maid-mist">pho…;). Cracking of the snow surface around your feet is a sign fresh drifts are unstable and to avoid steep wind loaded slopes. Even a small slide can be deadly in the wrong terrain, and could be a trigger for a larger avalanche.</p>

<p>A less likely, but larger avalanche is possible to trigger breaking at least 2-4 feet deep on sugary weak snow near the base of the snowpack. I wrote this <u><strong><a href="https://www.mtavalanche.com/blog/2019-2020-mid-season-snowpack-summary-… snowpack summary</a></strong></u> to review the poor snowpack structure and recent large avalanches. It is more difficult to trigger one of these large avalanches than it was a week ago, but the consequences are large. Conservative decision making and cautious route finding are advised.</p>

<p>There are fewer warning signs like collapses that tell us the weak, sugary snow is buried deep below our feet, but red flags are not entirely absent. We know a poor snowpack structure exists on many slopes. We continue to get unstable extended column test results (<strong><a href="https://www.mtavalanche.com/images/20/flathead-pass-profile-26-jan">sno… profile</a></strong>). On Thursday a skier had a big collapse north of Bridger (<u><strong><a href="https://www.mtavalanche.com/node/21731">details</a></strong></u&gt;), and on Friday Big Sky ski patrol triggered a large slide on weak snow near the ground (<u><strong><a href="https://www.mtavalanche.com/node/21746">details and photos</a></strong></u>). Several large skier and snowmobiler triggered avalanches last weekend are a reminder of what is possible (<u><strong><a href="https://www.mtavalanche.com/photos">photos</a></strong></u&gt;).</p>

<p>Avoid heavily wind loaded slopes, where large slides can be triggered from thinner areas of the snowpack (<u><strong><a href="https://www.youtube.com/watch?v=MsjmwmAH7Ww&amp;list=PLXu5151nmAvSbcbVf…;). Some slopes have a shallower, sugary weak snowpack where avalanches can break wide though maybe not as deep. These might not be as large as the deep hard slabs, but are easier to trigger and still deadly. Friday on Mt. Ellis I found the shallowest weakest snowpack in our area which will become unstable with a few more inches of snow (<u><strong><a href="https://www.youtube.com/watch?v=-iokOWUdQ3s&amp;list=PLXu5151nmAvSbcbVf… Doug and I found a similar structure on one of the shallower slopes in Taylor Fork (<strong><a href="https://www.mtavalanche.com/images/20/taylor-fork-profile-26-jan">snowp… profile</a></strong>).</p>

<p>Today avalanches are possible to trigger and avalanche danger is MODERATE. Carefully assess snowpack and terrain before riding on or underneath steep slopes.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong></u&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

<p>Weak layers near the base of the snowpack are at least 2-4 feet deep and make large avalanches possible to trigger. The last reported human triggered avalanches in the backcountry were six days ago (<strong><a href="https://www.mtavalanche.com/node/21706">details</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/node/21707">details</a></strong&gt;). Over the last week the mountains got a few inches of snow equal to 0.5-0.7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE) with 1” SWE near Cooke City. Deeply buried weak layers can adjust to this small addition of weight, but they remain close to breaking under the weight of a human or cornice fall. I wrote this&nbsp;<strong><a href="https://www.mtavalanche.com/blog/2019-2020-mid-season-snowpack-summary-… snowpack summary</a></strong> to review the current poor snowpack structure and recent large avalanches.</p>

<p>It has become more difficult to trigger a huge avalanche on sugary snow near the ground, but the consequences are large and call for conservative travel. We have seen fewer signs of instability, such as collapsing and cracking, but large skier and snowmobiler triggered avalanches last weekend are fresh in memory. See our <strong><a href="https://www.mtavalanche.com/photos">photos</a></strong&gt; page for a look at large avalanches last weekend.</p>

<p>Recent warning signs are not entirely absent. On Thursday skiers north of Bridger Bowl had a slope collapse which sent them home for clean underwear (<strong><a href="https://www.mtavalanche.com/node/21731">details</a></strong&gt;). On Friday the Big Sky ski patrol used explosives to trigger a deep avalanche on weak snow near the ground (<u><strong><a href="https://www.mtavalanche.com/node/21746">details and photos</a></strong></u>). Yesterday a skier saw a recent natural avalanche on Alex Lowe peak in Hyalite (<strong><a href="https://www.mtavalanche.com/images/20/small-slab-alex-lowe-pk">photo</a…;). We continue to find and get reports of unstable extended column test scores even where weak layers are buried very deep.</p>

<p>Avalanches can break deep and wide on weak layers near the ground if a trigger hits the right spot. Avoid heavily wind loaded slopes, where large slides can be triggered from thinner areas of the snowpack (<u><strong><a href="https://www.youtube.com/watch?v=MsjmwmAH7Ww&amp;list=PLXu5151nmAvSbcbVf…;). Carefully assess snowpack and terrain before riding on or under steep slopes. If you see a poor snowpack structure or expect a bad outcome, then find lower angle terrain.</p>

<p>On Friday I was at Mt. Ellis where the snowpack is the shallowest in our advisory area (<u><strong><a href="https://www.youtube.com/watch?v=-iokOWUdQ3s&amp;list=PLXu5151nmAvSbcbVf…;). It looked like much of our forecast area did at the start of December. When a supportable slab forms from new or wind-drifted snow large avalanches will be easy to trigger.</p>

<p>Today, large avalanches are possible to trigger and avalanche danger is MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong></u&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>