18-19

<p>This is the first significant snow in a week, although it seems a lot longer than that. The 3-4” of snow measures 6-10% density; aka powder. The last 7 days of sunshine, frigid temperatures, and clear nights created a weak surface of small, sugary facets, and some feathery surface hoar (<strong><a href="https://www.mtavalanche.com/images/18/surface-hoar-southern-gallatin-ra…;) which are now buried. This interface of new and old snow is our #1 concern. I do not expect avalanches to break in deeper layers or step down. Alex found this to be the case in Buck Ridge (<strong><a href="https://www.youtube.com/watch?v=nd-L5OJBGYw&amp;index=5&amp;list=PLXu51…;) and I found similar conditions around Cooke City (<strong><a href="https://www.youtube.com/watch?v=ILYeYyN0TWU&amp;list=PLXu5151nmAvRNl9ku…;

<p>Over the last few days wind slab avalanches have been isolated and small. Yesterday, an ice climber triggered a wind slab in Hyalite (<strong><a href="https://www.mtavalanche.com/images/18/hyalite-wind-slab-10-dec">photo</…;) and on Sunday skiers near Bridger Bowl found the snow easily broke under a wind-slab in their stability test (<u><strong><a href="https://www.youtube.com/watch?v=wGONRwZiOys&amp;list=PLXu5151nmAvRNl9ku…;). A few inches of new snow and increasing wind, especially in areas where a weak layer was buried, will increase the potential for triggering slides. Wind-loading will occur all day. Assess all slopes because even a small avalanche can be deadly. To get a visual idea of what we are currently finding in the backcountry, check out our YouTube <strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX…;, <strong><a href="https://www.mtavalanche.com/photos">Photos</a></strong&gt;, and <strong><a href="https://www.mtavalanche.com/snowpits">Snowpits</a></strong&gt;. For today, the avalanche danger is rated MODERATE since triggering avalanches is possible.</p>

<p>The snow structure near West Yellowstone is especially worrisome. The entire depth is 1-2 feet of weak, sugary facets that will not support much of a snow load (<u><strong><a href="https://www.youtube.com/watch?v=hl5lygIF7s4&amp;index=9&amp;list=PLXu51…;). Last night’s 3 inches will be blown into thicker drifts that could avalanche into deeper layers or even break at the ground. The slopes in Lionhead are uniformly weak and avalanches may be wide. Eric is down there today and he’ll have an update for tomorrow’s forecast. For today, the avalanche danger is rated MODERATE since the new snow and wind-loading are making human triggered avalanches possible. &nbsp;</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

<p>Doug rode in the mountains near Cooke City yesterday and dug multiple snowpits. He found 2.5 to 4 feet of stable snow (<strong><a href="https://www.youtube.com/watch?v=ILYeYyN0TWU&amp;list=PLXu5151nmAvRNl9ku…;, <strong><a href="https://www.mtavalanche.com/images/18/four-feet-snow-near-wolverine">ph…;), and saw a couple small avalanches from last week (<strong><a href="https://www.mtavalanche.com/images/18/loose-avalanche-crown-butte">phot…;, <strong><a href="https://www.mtavalanche.com/images/18/loose-avalanche-crown-butte">phot…;). The snowpack near Bozeman and Big Sky is similarly deep and generally stable (<u><strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX…; and <u><strong><a href="https://www.mtavalanche.com/snowpits">snowpits</a></strong></u&gt;). Near West Yellowstone the snowpack is 1-2 feet deep, sugary and weak (<u><strong><a href="https://www.youtube.com/watch?v=hl5lygIF7s4&amp;index=9&amp;list=PLXu51…;). Avalanche activity last week was confined to small slides of new and wind-drifted snow (<u><strong><a href="https://www.mtavalanche.com/avalanche-activity">Avalanche Activity</a></strong></u>), and the mountains have not had new snow or wind-loading since last Tuesday.</p>

<p>Isolated areas of unstable snow are possible where small slabs of wind-drifted snow formed on top of weak, low density snow (<strong><a href="https://www.mtavalanche.com/images/18/natural-wind-slab-hyalite-0">phot…;). Ice climbers triggered a small wind slab in Hyalite on Friday (<strong><a href="https://www.mtavalanche.com/images/18/ice-climber-triggered-small-wind-…;), and yesterday skiers out-of-bounds near Bridger found an 8” wind slab that collapsed and propagated with eleven taps in their stability tests (unstable test result) (<strong><a href="https://www.youtube.com/watch?v=wGONRwZiOys&amp;list=PLXu5151nmAvRNl9ku…;). Be cautious of wind loaded slopes and assess terrain for consequences of being caught in even a small slide. A lack of recent snow and wind, and a generally stable snowpack make avalanches unlikely to be triggered today, and avalanche danger is rated <strong>LOW</strong>.</p>

<p>Check out our <u><strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX… videos</a></strong></u> and <u><strong><a href="https://www.mtavalanche.com/snowpits">snowpit profiles</a></strong></u><strong> </strong>on our website for a snapshot of the snowpack structure across our advisory area.</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>