20-21

<p>In the mountains south of Big Sky to West Yellowstone new snow has added significant weight to a snowpack that contains multiple buried weak layers, and dangerous avalanche conditions exist. Since Wednesday night these mountains got 18-26” of snow equal to 1.5-2.1” of snow water equivalent (SWE). Avalanches large enough to bury or injure a person are easy to trigger within the new snow, especially where yesterday’s moderate to strong southwest wind formed thicker slabs (<a href="https://youtu.be/mky_kON6nKU"><strong>Dave’s video</strong></a><strong> from Lionhead</strong>). Larger avalanches can break deeper on buried weak layers and could be triggered from lower angle terrain below and adjacent to steep slopes. On Thursday, skiers in the southern Gallatin Range triggered a large collapse in low angle terrain (<strong><a href="https://www.mtavalanche.com/images/21/large-collapse-s-gallatin">photo<…;). Today the avalanche danger is rated CONSIDERABLE. Conservative decision making and cautious route finding are essential.</p>

<p>Near Big Sky and Bozeman, 3-6” of low-density new snow (0.3-0.4” SWE) and light to moderate west-northwest wind formed fresh slabs that can be triggered by skiers and riders. Yesterday afternoon a skier in the northern Madison Range triggered an avalanche in the new snow which propagated wide and broke deeper into weak sugary snow below (<strong><a href="https://www.mtavalanche.com/images/21/dudley-creek-slides">photo</a></s…;). Today similar human triggered avalanches are possible, especially on wind-loaded slopes. The avalanche danger is MODERATE due to fresh drifts adding weight to a weak snowpack.</p>

<p>Near Cooke City, since Thursday morning the mountains got 6-8” of new snow equal to 0.6” of snow water equivalent. Yesterday, moderate south-southwest wind formed fresh drifts that are possible to trigger. These slabs can break deeper and wider on a weak layer of surface hoar or facets buried 18-24” deep. Doug was in Cooke City on Monday and found this layer in his snowpits and in the crown of a snowmobile triggered avalanche (<a href="https://youtu.be/Ui1wdUHE56E"><strong>video</strong></a&gt;, <strong><a href="https://www.mtavalanche.com/images/21/2-avalanches-sheep-mtn">photo of avalanches</a></strong>). Be cautious of steep wind-loaded slopes and avoid steep slopes where you suspect buried weak layers exist. Large avalanches are possible to trigger and the avalanche danger is MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>