23-24

<p>Triggering a dangerous slab avalanche that breaks 1-2 feet deep is possible. The poor structure of the snowpack across the advisory area is fundamentally the same, with a strong slab of recent snow resting on top of a thick layer of weak, grainy facets. Winds, especially in the Bridger Range, drifted last weekend’s snow onto some slopes where avalanches could break more deeply.</p>

<p>If you are traveling in the mountains of our advisory area, there is likely a persistent weak layer under your feet or sled. Detect it without a snowpit by noticing that you sink quickly to the ground below when you step out of your skis or off your snowshoes, board, or sled. We have highlighted these weak layers as our primary concern in nearly all of this season’s field <a href="https://www.youtube.com/playlist?list=PLXu5151nmAvSH326zVaU9KXJAPtvkIt-…;. Watch our videos from <a href="https://www.youtube.com/watch?v=eBYC04jLzjc&amp;list=PLXu5151nmAvSH326z…;, the <a href="https://www.youtube.com/watch?v=hE-tTtDuKyI&amp;list=PLXu5151nmAvSH326z… Range</span></strong></a>, <a href="https://www.youtube.com/watch?v=I2EByh1Yqa4&amp;list=PLXu5151nmAvSH326z… Park</span></strong></a>, <a href="https://www.youtube.com/watch?v=VB4oAyv7N34&amp;list=PLXu5151nmAvSH326z… Basin</span></strong></a>, and <a href="https://www.youtube.com/watch?v=Rv7NkQmnUnE&amp;list=PLXu5151nmAvSH326z… City</span></strong></a> for highlights within the last week. <a href="https://www.mtavalanche.com/snow-observations-list"><strong><span>Recent observations</span></strong></a> are filled with signs of instability, including the snowpack collapsing with whumphs, poor test scores, and one recent natural avalanche north of Cooke City (<a href="https://www.mtavalanche.com/node/29657"><strong><span>details</span></s…;). Allow these indicators to direct you to lower-angle terrain. Only consider slopes steeper than 30 degrees after thoroughly evaluating the snowpack for instability and the terrain for features that increase the consequences of a slide.</p>

<p>Slopes with recent drifts of wind-loaded snow are more prone to avalanches than those without. Winds, especially in the Bridger Range, built hard, drum-like slabs on some slopes at all elevations. Yesterday, during avalanche mitigation work, the Bridger Bowl Ski Patrol triggered slides with explosives that failed 2-3 feet deep on wind-loaded slopes. On Sunday, I toured north of Bridger Bowl and easily triggered small drifts (<a href="https://www.mtavalanche.com/images/23/wind-slab-avalanche-ramp"><strong… 1</span></strong></a>, <a href="https://www.mtavalanche.com/images/23/wind-loading-ramp"><strong><span>… 2</span></strong></a>).</p>

<p>Avoid specific slopes loaded by recently wind-drifted snow and travel in terrain less than 30 degrees if you observe signs of instability like recent slides, collapsing of the snowpack, shooting cracks, or unstable test scores (<a href="https://www.youtube.com/watch?v=Gk8W8nlUMpw"><span>learn about the extended column test in this video</span></a>).</p>

<p>The avalanche danger is MODERATE.</p>

<p>Winds in the Bridger Range are transporting the 6-8” of recent snow into stiff drifts likely to avalanche under the weight of human triggers today. Yesterday, my partner and I toured up the Ramp and arrived at the ridge just as these winds picked up. We found sensitive slabs of wind-drifted snow that cracked and avalanched readily (<a href="https://www.mtavalanche.com/images/23/wind-slab-avalanche-ramp"><strong… 1</span></strong></a>, <a href="https://www.mtavalanche.com/images/23/wind-loading-ramp"><strong><span>… 2</span></strong></a>, <a href="https://www.youtube.com/watch?v=hE-tTtDuKyI&amp;list=PLXu5151nmAvSH326z…;). Today, hard, drum-like slabs will be more dangerous than what we found yesterday. Expect and avoid wind-loaded slopes at all elevations, as the winds are nearly as strong at mid-elevations as on the ridge (<a href="https://www.mtavalanche.com/weather/stations/bridger-lift-midway-statio… Wx Station</a>, <a href="https://www.mtavalanche.com/weather/bridger/ridge">Ridge Wx Station</a>).</p>

<p>Persistent weak layers of sugary facets buried 1-2 feet deep make avalanches possible on all slopes, wind-loaded or not. Avoid terrain steeper than 30 degrees entirely if you observe signs of instability like recent avalanches, whumphs (collapsing), shooting cracks, and unstable test scores.</p>

<p><span>The danger in the Bridger Range is CONSIDERABLE. </span></p>

<p>This weekend, the mountains around Island Park, West Yellowstone and Big Sky received 5-8” of new snow, with 2-3” south of Bozeman and near Cooke City. Persistent weak layers buried 1-2 feet deep near the bottom of the snowpack are nearly universal across the advisory area and make human-triggered avalanches possible. Alex and Doug got confused by the calendar the last two days, celebrating Groundhog Day rather than Christmas, titling their videos from Island Park and Lionhead Ridge, “<a href="https://www.youtube.com/watch?v=I2EByh1Yqa4&amp;list=PLXu5151nmAvSH326z… Weak and Unstable</span></strong></a>” and “<a href="https://www.youtube.com/watch?v=eBYC04jLzjc&amp;list=PLXu5151nmAvSH326z…’s Not Better Yet</span></strong></a>.” Skiers in Cooke City and the Northern Gallatin Range have experienced whumphing collapses in the last two days and reported a recent avalanche north of Cooke City (<a href="https://www.mtavalanche.com/node/29657"><strong><span>observation Cooke</span></strong></a><strong>, </strong><a href="https://www.mtavalanche.com/node/29681"><strong><span>observation N. Gallatin</span></strong></a>). Our <a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>avalanche log</span></strong></a> has many red flags indicating instability associated with buried weak layers across the advisory area.</p>

<p>Avoid avalanches by traveling in terrain gentler than 30 degrees if signs of instability like recent slides, whumphs (collapsing), shooting cracks, and unstable test scores are present (<a href="https://www.youtube.com/watch?v=Gk8W8nlUMpw"><span>learn more about the extended column test in this video</span></a>).</p>

<p><span>Today, human-triggered avalanches large enough to bury or injure a person are possible, and avalanche danger is MODERATE.</span></p>