20-21

<p>The mountains near West Yellowstone, Big Sky, and Bozeman received 4-8” of snow equal to 0.4-0.7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>-SWE in the last 48-hours. In his <a href="https://www.youtube.com/watch?v=gPWSDAr-K1Q"><strong>video</strong></a&…; from the Northern Bridgers, Ian provides a good discussion of how to responsibly explore more adventurous terrain in a year defined by deeply buried persistent weak layers. He suggests taking “baby steps” rather than going all-in on big objectives in complex or exposed terrain, evaluating the snowpack to minimize surprises, and rigorously following safe travel protocols by exposing <em>only one person at a time</em> to potential avalanche hazards. As he said, “It may be unlikely, but if you trigger a slide, it could be catastrophic.” Recently, groups in Hyalite and near Hebgen Lake followed this travel model, found areas of unstable snow, and pulled the plug on skiing steep terrain. This is precisely how it should work in periods of low danger. Search for isolated instabilities and adjust your plans if you find them.</p>

<p>The last human-triggered avalanches we know of occurred ten days ago in the Madison Range (<a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><strong>avalanche… log</strong></a>). Without significant new loading, deep-slab avalanches are unlikely, but the weak facets near the ground and the fundamental nature of the snowpack haven’t changed (<a href="https://www.youtube.com/watch?v=H8RLSPzsCtc"><strong>video</strong></a&…; from the Throne, <a href="https://www.youtube.com/watch?v=jHcGBFkyLbk&amp;list=PLXu5151nmAvQDzKmH…; from Maid of the Mist).</p>

<p>Today, follow Ian’s travel advice and pay attention to instabilities within the new snow. Storm snow avalanches will be relatively small but they can be hazardous in the context of steeper or more technical terrain. The avalanche danger is LOW.</p>

<p>The mountains around Cooke City received 6-10” of new snow equal to 0.6” of SWE. Yesterday, skiers observed several small storm slab avalanches (<a href="https://mtavalanche.com/images/21/storm-slab-cooke-city"><strong>photo<…;). Slides like this are dangerous in the context of steep and technical terrain if they tumble us into trees or off cliffs. Stay heads up for areas where yesterday’s wind may have drifted snow and enhanced potential avalanches’ size. Minimize time spent under behemoth cornices that overhang slopes this time of year. A cornice collapse on a small slope west of Cooke City is a good indicator of what a fall would be like where they are larger (<a href="https://mtavalanche.com/images/21/cornice-drop-west-cooke"><strong>phot…;). Watch for areas of isolated instability like the wind-loaded slope a rider triggered east of Cooke City on Friday (<a href="https://mtavalanche.com/node/24583"><strong>photos and details</strong></a><strong>: EVENT DATE CORRECTED</strong>), carry rescue gear, and expose only one person at a time to avalanche terrain. The avalanche danger is LOW.</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>

<p>The mountains south of Big Sky through West Yellowstone picked up 4-6” of fresh snow equal to 0.4-0.5” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>-SWE with 2-3” (0.2” SWE) in the Bridger Range through Big Sky. The depth will be greater in areas of drifted snow. As I explain in my <a href="https://www.youtube.com/watch?v=H8RLSPzsCtc"><strong>video</strong></a&…; from the Throne, the snowpack structure remains poor, but without significant snowfall, avalanches breaking on deeply buried weak layers are unlikely. The last human-triggered slab avalanches we know of occurred in the Madison Range nine days ago (<a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><strong>avalanche… log</strong></a>). On Sunday, Alex and I went into the Maid of the Mist Basin to look at one of these old, deep-slab avalanches (<a href="https://www.youtube.com/watch?v=jHcGBFkyLbk&amp;list=PLXu5151nmAvQDzKmH…;, </strong><a href="https://www.mtavalanche.com/images/21/deep-slab-arden-crown"><strong>ph…;). A skier or rider getting unlucky and hitting the trigger-point of one of these giant slides is a sobering thought.&nbsp;</p>

<p>Yesterday, skiers north of West Yellowstone dug two snowpits, got unstable results, and subsequently decided to stay in low-angle terrain. In Hyalite, a group ascending a steep chute noticed the snow depth change dramatically from their first pit, got unstable results in a second, and decided to pull the plug. These examples demonstrate how we should use snowpack assessment tools to find isolated areas of instability and adjust plans accordingly.</p>

<p>Today, human-triggered avalanches are possible in wind-loaded terrain. These slides will most likely be small, but be wary of the chance that a small slide or cornice collapse could trigger a larger avalanche. The avalanche danger is MODERATE on wind-loaded terrain and LOW on non-wind-loaded terrain.&nbsp;</p>

<p>The mountains around Cooke City received 3” of new snow equal to 0.3” of SWE. The snowpack lacks widespread buried weak layers and large slab avalanches are unlikely. Yesterday, riders east of Cooke City triggered a small, wind-loaded slope after cutting across it a couple of times (<a href="https://mtavalanche.com/node/24583"><strong>photos and details</strong></a>) and skiers west of Cooke City saw a large cornice collapse on a small slope (<a href="https://mtavalanche.com/images/21/cornice-drop-west-cooke"><strong>phot…;). These are good examples of how riders and skiers may still find isolated instability on low danger days and why safe travel protocols are vital on <em>all</em> days spent in avalanche terrain. Everyone should carry and be familiar with avalanche rescue gear and expose only one person at a time to avalanche hazards. Today, manage small slabs and loose snow avalanches by avoiding terrain that may elevate a slide’s consequences. The danger is LOW in the mountains near Cooke City.</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>