18-19

<p>In the Lionhead area near West Yellowstone and the southern Madison and Gallatin Ranges, the lower half of the snowpack is weak, sugary facets. This weak snowpack will struggle to support fresh drifts of snow that formed from strong southwest wind&nbsp;yesterday. Over the past week, Eric found this weak snowpack near Bacon Rind (<u><strong><a href="https://www.youtube.com/watch?v=3NMgoDNKUQg&amp;t=0s&amp;list=PLXu5151n…;) and Doug saw it near West Yellowstone (<u><strong><a href="https://www.youtube.com/watch?v=rQ7fzq4X1-4&amp;index=2&amp;t=0s&amp;li…;). Recently wind loaded, steep slopes are a likely place to trigger avalanches and should be avoided today. Non-wind loaded slopes are less unstable, but should be carefully assessed before riding. Avalanche danger is CONSIDERABLE on wind loaded slopes and MODERATE on non-wind loaded slopes.</p>

<p>In the mountains near Cooke City the snowpack is deeper and stronger than the other southern ranges, but it has buried weak layers and received more snow than elsewhere in the advisory area over the last week. I was riding near Cooke City the past two days and found two buried weak layers that were reactive in stability tests (<strong><a href="https://www.youtube.com/watch?v=u520iMxlXOQ&amp;list=PLXu5151nmAvRNl9ku…;, <strong><a href="https://www.mtavalanche.com/images/18/lulu-pass-snowpit-20-dec">photo</…;), and I observed widespread drifting snow yesterday (<strong><a href="https://www.youtube.com/watch?v=8Hp6eil66zY&amp;list=PLXu5151nmAvRNl9ku…;). Today, human triggered avalanches are likely on steep, wind loaded slopes where fresh drifts of snow added weight to buried weak layers. Avalanche danger is <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on non-wind loaded slopes.</p>

<p>The mountains near Bozeman and Big Sky got 2-3” of snow yesterday morning. Strong wind drifted this snow into fresh wind slabs that are possible to trigger today. A layer of weak, sugary facets is buried 10-12” deep&nbsp;and avalanches were triggered on this layer on wind loaded slopes over the past week (<strong><a href="https://www.mtavalanche.com/avalanche-activity">Avalanche Activity</a></strong>, <strong><a href="https://www.youtube.com/watch?v=mJRtrBZkgtY&amp;list=PLXu5151nmAvRNl9ku…;). Below this weak layer the snowpack is generally strong and avalanches breaking deeper are unlikely. Today, avalanches are possible and avalanche danger is rated <strong>MODERATE</strong>.</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>This morning, winds are blowing 30-50 mph in mountains near West Yellowstone. Strong winds combined with fresh snow will create thick wind drifts on slopes loaded by west-southwest winds. These drifts will be resting over a weak and fragile snowpack (<u><strong><a href="https://www.youtube.com/watch?v=rQ7fzq4X1-4&amp;index=2&amp;t=0s&amp;li…;, <u><strong><a href="https://www.youtube.com/watch?v=3NMgoDNKUQg&amp;t=0s&amp;list=PLXu5151n…;). Any steep slope with wind drifted snow will be highly susceptible to human triggered avalanches. Non-wind loaded slopes will be less prone to slides, but still need to be approached with caution.</p>

<p>The message is simple today: fresh snow, strong winds, and a weak snowpack will create dangerous avalanche conditions. &nbsp;The best defense against avalanches today will be terrain management. Avoid slopes steeper than 30 degrees and stay off low angle slopes connected to steep slopes above.</p>

<p>Today - fresh snow, strong winds, and buried weak layers make human triggered avalanches likely and the avalanche danger is rated <strong>CONSIDERABLE</strong>.</p>

<p>The primary avalanche problem today will be wind loaded slopes. This morning, winds are gusting over 70 mph on the summit of Lone Peak and 30-60 mph elsewhere. Strong west-southwest winds combined with a few inches of new snow will form a fresh batch of wind slabs that will be touchy to human triggers. On many slopes, wind deposited snow will be adding stress to a thin layer of facets buried in the upper foot of the snowpack.</p>

<p>Yesterday, Alex found this layer to be the primary avalanche concern in the mountains around Cooke City (<strong><a href="https://www.youtube.com/watch?v=u520iMxlXOQ&amp;t=0s&amp;list=PLXu5151n…;, <strong><a href="https://www.mtavalanche.com/images/18/lulu-pass-snowpit-20-dec">photo</…;). This is consistent with our field data and observations from the past few weeks (<strong><a href="https://www.mtavalanche.com/photos">photos</a></strong&gt;, <strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX…;). Today, watch for and avoid wind loaded slopes and pay attention to&nbsp;signs of instability such as cracking and collapsing. These are obvious clues the slope&nbsp;is unstable.&nbsp;Fortunately, the lower portion of the snowpack is mostly strong and stable which will keep instabilities isolated to new and wind-blown snow.</p>

<p>Today, dangerous avalanche conditions exist on wind loaded slopes which have <strong>CONSIDERABLE</strong> avalanche danger. Non-wind loaded slopes have <strong>MODERATE</strong> avalanche danger.</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>