19-20

<p>Strong westerly wind is drifting 2-5” of recent snow into fresh slabs. These slabs are possible to trigger and can break large enough to bury or injure a person. Additional wind-loading today will push massive cornices closer to breaking. These overhanging waves of snow along ridgelines can be triggered by a person and break farther back from the edge than expected. A cornice fall or wind slab avalanche will thoroughly impact a slope and can trigger a deeper avalanche (<u><strong><a href="https://www.mtavalanche.com/images/20/hourglass-chute-crown">photo</a><…;). Be extra cautious of steep slopes with fresh drifts. Stay far back from the edge of ridgelines and avoid slopes below large cornices.</p>

<p>Although less likely than triggering a fresh wind slab, a scary possibility is an avalanche that breaks over 3-5’ deep on weak sugary snow at the base of the snowpack. On Thursday night in the northern Gallatin Range a trail groomer triggered and was damaged by an avalanche that broke 2-3’ deep on sugary snow near the ground (<u><strong><a href="https://www.youtube.com/watch?v=mpWviZprZZM&amp;feature=emb_logo">video…;, <u><strong><a href="https://www.mtavalanche.com/node/22269">photo and details</a></strong></u>). This and two natural avalanches last Wednesday (<u><strong><a href="https://www.mtavalanche.com/node/22257">photos and details</a></strong></u>, <u><strong><a href="https://www.mtavalanche.com/node/22293">photos and details</a></strong></u>) show the scary possibility and destructive consequences of triggering an avalanche on weak snow near the ground. Avoid steep slopes where the snowpack has potential shallow trigger points. Examples are lower elevation slopes with a relatively shallow snowpack, and where snow depth is more variable like rocky or heavily wind loaded slopes.</p>

<p>Today, fresh wind slabs and weak snow near the bottom of the snowpack create heightened avalanche conditions, and avalanches are possible to trigger. Avalanche danger is MODERATE.</p>

<p>Near West Yellowstone and Cooke City it has been several weeks since an avalanche broke on weak snow near the base of the snowpack. Evidence of this weak layer is not absent (<u><strong><a href="https://www.mtavalanche.com/node/22267">details</a></strong></u&gt;, <u><strong><a href="https://youtu.be/2IzNvRo0R3w">video</a></strong></u&gt;), but without new snow and wind to stress the snowpack large avalanches are unlikely. Today watch for small fresh wind slabs that could be hazardous if they push you into trees, confined gullies or over cliffs. Today avalanches are unlikely and avalanche danger is LOW. Low danger is not no danger. Remain diligent with thoughtful decision making, careful snowpack assessment and safe travel protocols (<u><strong><a href="https://youtu.be/9g-x7o56ek8">video</a></strong></u&gt;).</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></strong></u>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

<p>Recent human triggered and natural avalanches are evidence that potentially deadly avalanches can break deep in the snowpack. On Thursday, a trail groomer in the northern Gallatin Range triggered a slide that broke 2-3’ deep, 100’ wide and 600’ long on a west facing slope at 7,800’ elevation (<u><strong><a href="https://www.youtube.com/watch?v=mpWviZprZZM&amp;feature=emb_logo">video…;, <u><strong><a href="https://www.mtavalanche.com/node/22269">photo and details</a></strong></u>). The avalanche rolled and partially buried the vehicle, and the driver was unharmed. On Wednesday, natural avalanches broke 3-5’ deep in the Hourglass chute north of Bridger Bowl (<u><strong><a href="https://www.mtavalanche.com/node/22257">photos and details</a></strong></u>) and near Divide Peak in Hyalite (<u><strong><a href="https://www.mtavalanche.com/node/22293">photos and details</a></strong></u>). Avoid steep slopes where the snowpack has potential shallow trigger points. These include lower elevation slopes with a relatively shallower snowpack similar to where the groomer triggered slide occurred, and higher elevations where snow depth varies greatly like rocky, heavily wind loaded slopes or slopes with large cornices above.</p>

<p>Cornices are overhanging waves of snow along ridgelines and literally weigh a ton. They can be triggered by a skier or snowmobiler, break back farther from the edge than expected&nbsp;and make a good trigger for deep slab avalanches. The recent slide in The Hourglass was triggered by a large cornice (<strong><a href="https://www.mtavalanche.com/images/20/hourglass-chute-crown">photo</a><…;). Stay far back from the edge of ridgelines and avoid slopes below large cornices.</p>

<p>Last night’s 2-5” of snow equaled 0.1-0.5” of snow water equivalent (SWE) and with minimal wind does not greatly increase hazard today. Watch for cracking in the snow surface or blowing snow as a sign of unstable fresh drifts. Dry loose avalanches are possible where new snow is deeper. Today, weak snow near the bottom of the snowpack creates heightened avalanche conditions and avalanche danger is MODERATE.</p>

<p>Near West Yellowstone and Cooke City the snowpack is generally stable and avalanches are unlikely. Last night’s 1-3” of snow equaled 0.1-0.2” of SWE and adds minimal hazard. On Thursday skiers in Specimen Creek in the southern Gallatin Range got a collapse on weak snow near the ground (<u><strong><a href="https://www.mtavalanche.com/node/22267">details</a></strong></u&gt;). Yesterday, skiers in the same area dialed back their terrain choices after getting an Extended Column Test to propagate on 29 hits (ECTP 29). Weak snow near the ground has not produced an avalanche in these mountains for several weeks, but requires us to remain diligent with thoughtful decision making, careful snowpack assessment and safe travel protocols (<u><strong><a href="https://youtu.be/9g-x7o56ek8">video</a></strong></u&gt;, <u><strong><a href="https://youtu.be/2IzNvRo0R3w">video</a></strong></u&gt;). Today avalanches are unlikely and avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></strong></u>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>