17-18

<p>The Lionhead area near West Yellowstone has a weak, unstable snowpack and large avalanches are possible. Avalanches breaking on weak facets 3-5 feet deep are getting more difficult to trigger, but can fracture across entire slopes and have high consequences (<a href="https://youtu.be/nQ5ZZBJLC-4"><strong>video</strong></a&gt;). The best plan is to avoid steep slopes and be extra conservative when riding in and below avalanche terrain. Southwest winds drifted recent snow into slabs and grew large cornices near ridgelines. These are possible to trigger and add stress to buried weak layers. Avalanches are possible today and could be large. The avalanche danger is <strong>MODERATE</strong> on all slopes.</p>

<p>The mountains received steady, small snow storms over the past week and soft powder is plentiful. Strong west-southwest wind drifted recent snow into slabs 6-18” thick near ridgelines and along the edges of cliffs and gullies. Yesterday, skiers near Big Sky and in the Bridger Range found wind slabs easy to trigger. In the last week, skiers and snowmobilers have triggered wind slabs through the advisory area (<a href="https://www.mtavalanche.com/images/18/small-wind-slab-3rd-yellowmule"><…;, <a href="https://www.mtavalanche.com/images/18/skier-triggered-wind-slab-throne"…;), and a large natural avalanche was observed near Cooke City (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-mt-abundance">p…;). Similar avalanches are possible today. Avoid pillows of wind drifted snow and seek terrain sheltered from the wind. Stay far back from the edge of large cornices along ridgelines, and avoid slopes below or approach with extra caution.</p>

<p>Avalanches breaking on weak, sugary facets 1-2’ off the ground are difficult to trigger, but possible on some slopes. We continue to get unstable test results on this layer (<a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQSYtIfyQP-gMYrlfja6Ls…;), and yesterday skiers observed an old avalanche crown in the Bridger Range that may have failed on this layer (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-northern-bridge…;). This layer is most unstable where the snowpack is shallower or depth is highly variable. Evaluate individual slopes carefully before riding avalanche terrain. Yesterday I found a weak layer in my snowpit that was only visible after it produced an unstable result in my test (<strong><a href="https://youtu.be/gKvrr5JHODA">video</a></strong&gt;), which provided evidence to find different or low angle terrain.</p>

<p>For today, avalanches are possible and avalanche danger is <strong>MODERATE</strong>.</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>

<p>The Lionhead area has the weakest snowpack structure in the advisory area. Facets buried 1-2’ off the ground still hold the potential to propagate a fracture and produce large persistent slab avalanches (<a href="https://www.mtavalanche.com/images/18/ski-hill-snowpit-profile-23-jan">… profile</strong></a>). The likelihood of triggering a slide on this layer is decreasing <a href="https://youtu.be/nQ5ZZBJLC-4"><strong>video</strong></a&gt;, but the consequences remain high. Although conditions are gradually improving, careful snowpack evaluation and conservative decision making remain essential when traveling in steeper terrain.</p>

<p>Additionally, new snow and wind have formed thick wind slabs that will be touchy to human triggers. Stay clear of wind loaded slopes near the ridgelines and look out for cornices that have grown significantly over the past few weeks. Give these large overhanging chunks of snow a wide berth both above and below the ridgelines.</p>

<p>For today, the avalanche danger is rated <strong>CONSIDERABLE</strong> on all wind-loaded slopes and <strong>MODERATE</strong> elsewhere.</p>

<p>The combination of new snow and wind will make wind slabs today’s primary avalanche problem. Strong winds out of the west-northwest have formed sensitive wind drifts on leeward slopes (<a href="https://www.mtavalanche.com/images/18/small-wind-slab-3rd-yellowmule"><…;, <a href="https://www.mtavalanche.com/images/18/skier-triggered-wind-slab-throne"…;). Winds have been strongest along the ridgelines, but have also worked their way into lower elevation terrain. Watch for pillows of wind drifted snow and avoid consequential terrain if there is evidence of recent wind loading.</p>

<p>A secondary concern is sugary facets 1-2’ off the ground. This layer is not widespread, but can be found in isolated areas (<a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQSYtIfyQP-gMYrlfja6Ls…;). Doug got unstable results on this layer in the Taylor Fork on Sunday and skiers north of Bridger Bowl and in the southern Gallatin Range also got unstable test results on Wednesday. Variability between slopes is not unusual, so it’s important to evaluate individual slopes carefully before committing to avalanche terrain.</p>

<p>For today, new snow and wind is creating a <strong>CONSIDERABLE</strong> avalanche danger on wind-loaded slopes. All other slopes have a <strong>MODERATE</strong> avalanche danger.</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>

<p>Lionhead has a poor snowpack structure because it has a weak foundation of sugary facets (<strong><a href="https://www.mtavalanche.com/images/18/ski-hill-snowpit-profile-23-jan">… profile</a></strong>). With time these layers are gaining strength and the likelihood of triggering slides is decreasing, which I am happy about, but these facets 1-2’ off the ground make me uneasy. Eric and I rode and dug pits on Tuesday and outlined our cautious optimism in this <a href="https://youtu.be/nQ5ZZBJLC-4"><strong>video</strong></a&gt;. Additionally, wind yesterday and last night have formed thick wind slabs that will easily avalanche today. Stay clear of ridgelines as a rider or skier can break cornices far from the edge and trigger slides. For today, the avalanche danger is rated <strong>CONSIDERABLE</strong> on all wind-loaded slopes and <strong>MODERATE</strong> elsewhere.</p>

<p>The wind is strong, gusty and loading slopes. At the ridgelines it is blowing S-SW, but will be swirly everywhere else. Gullies, road cuts, roll-overs and other fetches will have wind drifts that can avalanche. Riders up Buck Ridge triggered a small wind slab which served as a warning that they could trigger bigger slides up high (<strong><a href="https://www.mtavalanche.com/images/18/small-wind-slab-3rd-yellowmule">p…;). Wind-loading was also noted by skiers in the Bridger Range, up Hyalite, and in the southern Gallatin Range. With the Lulu Pass weather station reading 50 mph gusts, I’m certain Cooke City has many wind-loaded slopes. Let us not forget that over the weekend two skiers in the Bridger Range separately triggered wind-loaded slopes, one near the ridge and one at a lower elevation (<a href="https://www.mtavalanche.com/images/18/skier-triggered-wind-slab-throne"…;).</p>

<p>A secondary concern is weak, sugary snow 1-2’ off the ground. Although most slopes are stable, a few are not. I found this instability on one slope in Taylor Fork on Sunday (<a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQSYtIfyQP-gMYrlfja6Ls…;), and yesterday skiers north of Bridger Bowl and in the southern Gallatin Range also had unstable test results in their snowpits when this layer propagated during an Extended Column Test. Variability between slopes is not unusual so we dig and test, which is what these parties did. In the absence of other signs of instability, one poor test result is enough to turn around.</p>

<p>For today, strong wind is creating a <strong>CONSIDERABLE</strong> avalanche danger on wind-loaded slopes. All other slopes have a <strong>MODERATE</strong> avalanche danger.</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>