20-21
Sietz
Date
Activity
Skiing
This morning we toured up the Sietz Slidepath to check out the new snow. The last few days of sun baked the top of the snow event from Sunday/ Monday, and created a new crust layer. On East and North East aspects, this failed easily. Multiple hand pits on the ascent revealed a Q1 shear with minimum effort approximately 20cm deep in the snow (photo). A quick snow pit on a Northeast aspect dug to 1m, yielded ECTN11 @ 5cm, ECTN23 @ 20cm, and ECTN27 @ 30cm. Photo is of pit, with a shear conducted on remaining block with a Q1 shear at 20cm. On Southern aspects this crust layer was much more solid and we observed no failures. On due north aspects, and isolated areas that were very protected by tree cover, we did not observe this crust.
Region
Bridger Range
Location (from list)
Northern Bridgers
Observer Name
Erich Schreier
GNFAC Avalanche Forecast for Fri Apr 23, 2021
Snowpack and Avalanche Discussion
<p>The <em>amount </em>and <em>type</em> of precipitation will drive our avalanche concerns this weekend. Rain and above freezing temperatures are likely at lower elevations and will increase in the wet snow avalanche danger. Alarm bells should go off if you observe an unsupportable wet snowpack or if you sink into wet snow deeper than mid-boot (<a href="https://www.youtube.com/watch?v=YIajdl9hhyo"><strong><u>wet loose vs wet slab video</u></strong></a>). Colder temperatures will freeze the surface of the snowpack at higher elevations limiting avalanches to the new snow (<a href="https://mtavalanche.com/images/21/new-snow-sluffing-outside-advisory-ar… snow avalanches outside the advisory area</u></strong></a>). Look for a supportable crust below the fresh snow and assess how the new snow is bonding before committing to any steep terrain. Expect variations in snowpack stability as <em>temperatures fluctuate</em> throughout the day and at <em>different elevations</em> and <em>aspects</em>. Increasing winds on Sunday will drift recent snow into unstable slabs that will avalanche under the weight of a skier or rider. </p>
<p>Ask yourself these questions before entering avalanche terrain this weekend:</p>
<ol>
<li>Is it raining on the snowpack? Avoid steep terrain and go watch a movie, it’s raining.</li>
<li>Is the snowpack frozen with a crust? A solid crust will minimize the potential for deeper avalanches.</li>
<li>If there is a crust, how is the new snow bonding to it and how much new snow is there? Manage this hazard by avoiding areas with terrain traps.</li>
<li>Is wind drifting the snow and increasing the danger? Avoid these drifts in steep terrain.</li>
</ol>
<p>Deep-slab avalanches are unlikely, but skiers near Big Sky recently observed the weak, sugary snow at the base of the snowpack on colder, shady slopes (<a href="https://www.mtavalanche.com/images/21/depth-hoar-n-madison"><strong><u>…;). A large spring storm or the rapid addition of liquid water to the snowpack would increase the deep-slab danger. Our <a href="https://www.youtube.com/watch?v=1PFmB3aoeNI&list=PLXu5151nmAvQDzKmH… snowpack summary video</u></strong></a> highlights the poor snowpack structure that could still large avalanches. See our website for additional general spring snowpack and travel advice.</p>
<p>We will issue spring snowpack and weather updates each Monday and Friday through April, or as needed, and we will share relevant avalanche and snowpack information on our website and social media. 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><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Announcements, Avalanche Education and Events
Bridger Bowl is closed, and backcountry conditions exist (video). There is no avalanche mitigation or ski patrol rescue. Please stay clear of work areas, snowmobiles, chair lifts and other equipment.
See our education calendar for an up-to-date list of all local classes.
Loose snow avalanches run readily on top of the crust in the Absaroka Range south of Livingston on Tuesday 4/20. Photo: E. Schreier
Forecast link: GNFAC Avalanche Forecast for Fri Apr 23, 2021
Mission Creek
Date
Activity
Skiing
This morning we toured up an unnamed peak in the Mission Creek drainage to ski a North facing couloir. New snow from Monday was recorded at 25cm at about 2400m elevation, and 35cm at 2650m. Significant wind loading in this particular area was not widespread, and only observed at the very top of the ridge on N - NW aspects. A large cornice on a NW slope was observed in an adjacent basin (photo). The new snow was readily sluffing on top of the existing crust layer (photo). Cloud cover and temperatures below freezing prevented the snow from heating up, and dry sluff remained our greatest concern today. Had temperatures climbed much higher today, we likely would have backed off of this slope to avoid potential wet loose or slab hazards.
Region
Out of Advisory Area
Observer Name
Erich Schreier