19-20

<p>The Lionhead area near West Yellowstone has dangerous avalanche conditions. On Tuesday close to a foot of new snow fell onto a weak snowpack. It was the largest snowfall of the season and measured .8-1” of <u><a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a></u>. This snow came in with strong southwest wind and drifted at the ridgelines. A thick, sugary layer of weak snow at the ground will struggle to support the weight of the new snow, which Alex shows in this <strong><a href="https://youtu.be/Fd3eKZDCkB4">video</a></strong&gt; and<strong> <a href="https://www.mtavalanche.com/images/19/shallow-and-unstable-lionhead">ph…;. Triggering avalanches with a snowmobile or skis is likely, even from a distance. This weak layer is widespread and connects many slopes allowing an avalanche to propagate far and wide. Stay clear of runout zones (the bottom of slopes). Today is a day to play in the flats, far away from the edges of steep slopes. For today, the avalanche danger is rated CONSIDERABLE on all slopes.</p>

<p>Since Tuesday, the mountains surrounding Big Sky, south to Taylor Fork and Cooke City received 5-7” that drifted at the ridgelines. Yesterday, these wind-drifts avalanched with ski cuts and the same possibility remains today. Furthermore, a weak layer buried 1-2 feet under the surface holds the potential to avalanche. We have gotten reports from the Big Sky area, Bacon Rind and Cooke City that point to a strengthening snowpack; however, this thin layer of weak facets should not be forgotten. Although the likelihood of triggering slides is decreasing we still advocate testing the snowpack before giving a slope a thumbs up. Our videos in <a href="https://youtu.be/gxj7yMOxTsc">Taylor Fork</a>, <a href="https://youtu.be/Fd3eKZDCkB4">Beehive</a&gt; and <a href="https://youtu.be/MOUWPWg2J4A">Cooke City</a> are instructive. Go ahead, binge watch a few. Not only will you make better decisions, you’ll sound smart to your friends. For today, given the need to evaluate the snowpack and a possibility of triggering slides, the avalanche danger is rated MODERATE.</p>

<p>Since Tuesday, 2-3” of low density snow fell in the mountains around Bozeman. This was not enough to increase the avalanche danger. Overall the mountains have a stable snowpack and safe avalanche conditions. A minor exception to this are small, isolated wind drifts at the ridgeline which could be triggered. On Tuesday I went into the northern Bridger Range and found 3 feet of stable snow in my snowpit, although we had to navigate an very thin snowpack to get there (<strong><a href="https://youtu.be/JB8Uc77wUZk">video</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/19/thin-snowpack-northern-bridgers">…;). For today, the avalanche danger is rated LOW.</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>The avalanche danger in the Lionhead area near West Yellowstone has risen substantially. Yesterday 8-12” of snow measured .8-1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE), the largest snowfall of the season. The snowpack has a thick layer of weak, sugary snow at the ground that will avalanche. Southwest wind gusted to 40 mph during the storm and wind drifts at the ridgeline may have already slid or are dangerously close to doing so. Triggering avalanches is likely, even from far away, like the bottom of a slope. Alex and I rode into this area on Sunday and determined the snowpack would fail to hold the weight of this amount new snow (<strong><a href="https://youtu.be/Fd3eKZDCkB4">video</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/19/shallow-and-unstable-lionhead">ph…;). Avoid being on or underneath avalanche terrain. For today, the avalanche danger is rated HIGH on any slope that has been wind-loaded and CONSIDERABLE on all others.</p>

<p>The mountains around Big Sky, Taylor Fork and Cooke City have two things in common: they received 4-5” of new snow totaling .4” of SWE, and they have weak layers 1-2 feet under the surface. These layers are sometimes breaking in stability tests which we saw during our field investigations in Taylor Fork on Monday (<strong><a href="https://youtu.be/gxj7yMOxTsc">video</a></strong&gt;) and Beehive Basin on Sunday (<strong><a href="https://youtu.be/Fd3eKZDCkB4">video</a></strong&gt;). On Saturday, a large avalanche occurred south of Cooke City on a wind-loaded slope (<strong><a href="https://www.mtavalanche.com/node/21323">details and photo</a></strong>). Alex’s <strong><a href="https://youtu.be/MOUWPWg2J4A">video</a></strong&gt; from Cooke City outlines our general concerns over much of the forecast area: weak layers exist, some slopes are unstable, and the best way to determine stability without obvious clues such as cracking, collapsing or recent avalanche activity, <em>is to dig and test</em>. For today, the avalanche danger is rated MODERATE since triggering avalanches is possible. &nbsp;</p>

<p>For Christmas, the Bridger and northern Gallatin Ranges got 2” of snow, a cosmetic upgrade.&nbsp; Yesterday, my partner and I went into the <strong><a href="https://www.mtavalanche.com/node/13952">Throne</a></strong&gt; in the northern Bridger Range. We found 3 feet of stable snow at 8200’, but getting to that elevation required snowmobiling and skiing on mere inches of snow (<strong><a href="https://youtu.be/JB8Uc77wUZk">video</a></strong&gt;). We dug on this slope 3 weeks ago yet the snow depth is the same and the layers have gotten stronger (snowpits: <strong><a href="https://snowpilot.org/node/18267">12/2</a></strong&gt; and <strong><a href="https://snowpilot.org/node/19239">12/24</a></strong&gt;). Until we get more snow avalanches are unlikely in the mountains around Bozeman. For today, the avalanche danger is rated LOW on all slopes.</p>