17-18

<p>The current storm has heavily favored the mountains around West Yellowstone and Cooke City, which have picked up over a foot of high density snow totaling 1.5 to 2” of SWE (<a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>). This rapid and heavy load will be applying significant stress to any weakness in the snowpack. Stress will be especially concentrated on wind loaded slopes, which will likely produce human triggered avalanches today. Natural avalanches will also be possible, so carefully evaluate terrain and avoid traveling underneath large, steep slopes.</p>

<p>Winds have blown predominately out of the west-southwest, making slopes facing the east half of the compass most susceptible to heavy wind loading. However, all slopes have the potential to hold wind drifted snow, especially at higher elevations. Obvious signs of instability such as cracking and collapsing are obvious clues the snowpack is unstable. Also, keep an eye out for large cornices along the ridgelines. These are key indicators heavy wind loading has taking place. Yesterday, skiers up Beehive Basin near Big Sky observed a natural cornice failure that triggered as small slab avalanche on the slope below (<strong><a href="https://www.mtavalanche.com/images/17/cornice-triggered-avalanche-beehi…;). Today, I expect cornices and slopes below cornices to remain highly sensitive to human triggers.</p>

<p>Outside of wind loaded slopes, the snowpack has a few lingering instabilities. The main concern is the interface between the old snow surface (Sept.- Oct. snow) and the 2-4’ that has fallen over the past few weeks. On Wednesday, Alex and I got multiple ECT’s to propagate on this interface at higher elevations in the northern Bridgers (<strong><a href="https://www.youtube.com/watch?v=omz-G0veivc&amp;list=PLXu5151nmAvQSYtIf…;). A large natural avalanche outside of Cooke City a week ago is a good example of what’s possible when slides fail on layers deeper in the pack (<strong><a href="https://www.mtavalanche.com/images/17/crown-butte-avalanche">photo</a><…;). This interface isn’t unstable on all slopes, so it’s worth digging a snowpit and doing a stability test to assess the relationship between all layers in the snowpack.</p>

<p>We are still collecting snowpack data from around the advisory area and will begin&nbsp;issuing danger ratings when we start daily advisories a week from today.</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>