17-18

<p>Since Friday, the mountains near Cooke City got over 3 feet of snow equal to 3.3” of <a href="http://www.or.nrcs.usda.gov/snow/about/swe.html"><strong>snow water equivalent</strong></a> (SWE). Strong westerly wind drifted this snow into slabs at least 2-4’ deep, which will avalanche naturally. These avalanches can run far into flat terrain and have the power to break large trees. Large, destructive avalanches were observed last week (<a href="https://www.youtube.com/watch?v=cj2Qhn1ldQA&amp;list=PLXu5151nmAvQSYtIf…;, <a href="https://www.mtavalanche.com/images/18/natural-avalanche-woody-ridge"><s…;), and on Saturday a skier triggered an 18” deep, 150’ wide avalanche on a low angle, wind loaded slope (<a href="https://www.mtavalanche.com/images/18/skier-triggered-slide-pebble-cree…;). Similar or larger slides are likely today. Avoid steep slopes and flat runout zones below, especially underneath heavily wind loaded slopes. Find safe riding on low angle slopes sheltered from the wind and not exposed to steep, wind-loaded terrain above. Large natural avalanches are likely today and the avalanche danger is <strong>HIGH</strong> on all slopes.</p>

<p>The northern Bridger Range has up to a foot of new snow equal to 1.1” SWE, though only 1-2” of new snow fell near Bridger Bowl. Avalanches are possible where dense new snow is deeper than 6-8”. On wind loaded slopes, slabs 1-3’ deep are likely and could avalanche naturally. More snow and wind today will increase the size and distribution and of these slabs. Avoid steep, wind loaded slopes and be extra cautious of all steep terrain where new snow is deeper than 6-8”. Avalanche danger is <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on non-wind loaded slopes.</p>

<p>The mountains near West Yellowstone and the southern Madison and Gallatin ranges got 3-4” of new snow equal to .5” of SWE. Strong westerly wind drifted recent snow into slabs up to a foot thick that are possible to trigger along ridgelines, cross-loaded terrain features, and the bottom of cliffs. Doug and I skied near Hebgen Lake yesterday, and our snowpack tests showed avalanches are possible on a layer of surface hoar buried 1-2’ deep, or on weak facets near the ground (<a href="https://youtu.be/2mj4jkCkEpc"><strong>video</strong></a&gt;). The surface hoar is not on every slope, and facets near the ground are difficult to trigger. Dig a hole to assess these layers before riding steep slopes. Today, avalanches are possible and avalanche danger is <strong>MODERATE</strong>.</p>

<p>The mountains near Big Sky and Hyalite got 2-3” of new snow overnight and 7-10” since Friday. Strong winds drifted this snow into fresh slabs that are possible to trigger. Over the weekend, skiers in Hyalite, Beehive, and the northern Bridger Range reported small natural and skier triggered wind slabs. Be cautious of wind loaded slopes near ridgelines and at the base of cliffs. Avoid riding above cliffs, dense trees, or other terrain traps to minimize consequences if caught in a slide. On non-wind loaded slopes the snowpack is generally stable (<a href="https://www.youtube.com/watch?v=-Kh4wvvQ3Wk"><strong>video</strong></a&…;). Avalanche danger is <strong>MODERATE</strong> on wind loaded slopes and <strong>LOW</strong> on non-wind loaded 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>

<p>The mountains near Cooke City have 2 feet of new snow equal to 2” of snow water equivalent (SWE) since Friday. Strong westerly winds drifted this snow into slabs 2-4 feet deep that will break naturally and be easy to trigger. These wind slabs are located below cornices along ridgelines, and lower on slopes along cross-loaded terrain and below cliffs (<strong><a href="https://www.mtavalanche.com/images/18/examples-wind-loaded-terrain">pho…;). Avoid travel on steep, wind-loaded slopes and minimize time in flatter terrain below. These avalanches could run far and have the power to break trees, similar to recent slides I saw on Thursday (<a href="https://www.youtube.com/watch?v=cj2Qhn1ldQA&amp;list=PLXu5151nmAvQSYtIf…;, <a href="https://www.mtavalanche.com/images/18/natural-avalanche-woody-ridge"><s…;). Yesterday, a skier triggered an 18” deep, 150’ wide avalanche on a wind loaded slope (<strong><a href="https://www.mtavalanche.com/images/18/skier-triggered-slide-pebble-cree…;), and similar or larger slides are likely today.</p>

<p>On non-wind loaded slopes avalanches are easy to trigger within the recent storm snow, and could break deeper and wider on a weak layer of surface hoar buried 3-4 feet deep (<a href="https://www.mtavalanche.com/images/18/propagation-surface-hoar-near-coo…;). Be extra cautious of all steep slopes, and practice conservative route finding and decision making. The safest bet is lower angle slopes sheltered from the wind, and not exposed to steep, wind-loaded terrain above. Avalanche danger is <strong>HIGH</strong> on wind loaded slopes and <strong>CONSIDERABLE</strong> on other steep slopes.</p>

<p>In the mountains near West Yellowstone and the southern Madison and Gallatin ranges, strong wind over the past 24 hours drifted recent snow into fresh wind slabs that are possible to trigger. Be cautious of wind loaded slopes along ridgelines, on cross-loaded terrain features, or along the bottoms of cliffs. On non-wind loaded slopes, avalanches are possible to trigger on a layer of surface hoar buried 1-2’ deep (<strong><a href="https://www.mtavalanche.com/images/18/ectp-12-bacon-rind">photo</a></st…;, <a href="https://youtu.be/thn9hnFUi4Y"><strong>video</strong></a&gt;), or on weak facets near the ground. These weak layers are not present or unstable on every slope. Dig a hole and assess these layers before riding steep slopes. Today, avalanches are possible to trigger and avalanche danger is <strong>MODERATE</strong>.</p>

<p>The mountains near Bozeman and Big Sky have 5-7” of new snow since Friday. Strong winds drifted this snow into small, fresh slabs that are possible to trigger. Yesterday, skiers in Hyalite, Beehive, and the northern Bridger Range reported small natural and skier triggered wind slabs. Be cautious of wind loaded slopes near ridgelines and at the base of cliffs. Avoid riding above terrain traps like cliffs or dense trees to minimize the consequences of being caught in a slide. On non-wind loaded slopes the snowpack is generally stable (<a href="https://www.youtube.com/watch?v=-Kh4wvvQ3Wk"><strong>video</strong></a&…;). Avalanche danger is <strong>MODERATE</strong> on wind loaded slopes and <strong>LOW</strong> elsewhere.</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>