17-18

<p>The Lionhead area near West Yellowstone has an unstable snowpack and dangerous avalanche conditions. It is possible to trigger avalanches 2-4’ deep across entire slopes. A weak layer of facets 1-2’ above the ground has shown clear signs of instability for three weeks. There have been snowmobile triggered avalanches and large collapses almost daily (<a href="https://www.mtavalanche.com/images/18/remote-trigger-lionhead"><strong>…;, <a href="https://www.mtavalanche.com/images/18/snowmobile-triggered-avalanche-li…;), and three people killed in avalanches nearby since the start of 2018.</p>

<p>Saturday, I was on Lionhead Ridge&nbsp;and found stable results in stability tests, then collapsed the entire surrounding low angle slope as we left our snowpit (<a href="https://youtu.be/y8O0iWplhS0"><strong>video</strong></a&gt;). Signs of instability are slowly becoming less obvious, and these large avalanches will get harder to trigger. The first person on a slope may not trigger a slide, while a large, deadly avalanche could be triggered by the second, third, or 30^th person. Avoid steep slopes and terrain below. Avalanche danger is <strong>CONSIDERABLE</strong> on all slopes.</p>

<p>In the Bridger, Gallatin, and Madison Ranges strong wind overnight drifted recent snow into slabs 1-3’ deep. These slabs are easy to trigger, and likely found near ridgelines and the edges of cliffs and gullies (<a href="https://www.mtavalanche.com/images/18/fairy-lake-wind-slab"><strong>pho…;, <a href="https://www.mtavalanche.com/images/18/small-avalanche-wind-loaded-slope…;). On Saturday, a skier triggered and was carried hundreds of feet in a wind slab on Naya Nuki peak in the Bridger Range. Yesterday on the Throne, a skier triggered and was caught in a wind slab (<strong><a href="https://www.mtavalanche.com/images/18/skier-triggered-wind-slab-throne"…;), and other skiers reported easily triggering a 2-3’ deep, 50’ wide slab. Near Cooke City, wind overnight remained light, but fresh slabs are possible if wind increases today. Yesterday a rider saw a recent natural avalanche on the wind loaded, east face of Mt. Abundance (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-mt-abundance">p…;). Avoid recently wind loaded slopes today and assess the terrain for consequences of even small slides.</p>

<p>Snow on Friday buried a weak layer of surface hoar (<a href="https://www.mtavalanche.com/images/18/buried-surface-hoar-lionhead"><st…;), and in some places near surface facets. We have found these layers to be unreactive in stability tests and show no signs of instability at Mt. Ellis, Hyalite, Lionhead, and Taylor Fork. However, uncertainty exists and these layers are assumed guilty until proven innocent. Dig 1-2’ to rule out these weak layers before riding any steep slope (<strong><a href="https://www.mtavalanche.com/images/18/taylor-fork-surface-hoar">photo</…;).</p>

<p>Avalanches breaking on facets 2-4’ deep are becoming less likely, but are possible and could be large. This weak layer is most unstable and likely to trigger where the snowpack is 3-5’ deep or less. Doug found unstable test results on this layer at Taylor Fork yesterday (<strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQSYtIfyQP-gMYrlfja6Ls…;), and Eric found similar in the northern Madison Range last week (<strong><a href="https://youtu.be/Z5zkCJfIfdI">video</a></strong&gt;). Be cautious of steep slopes where the snowpack is relatively shallow or highly variable.</p>

<p>Today, avalanche danger is <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on all other slopes.</p>

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