One maybe two distinct seemingly natural large natural slab avalanches on small slope directly next to bridger canyon drive. One on the lookers left was likely cornice triggered, but on the right it's unclear to me if it propagated or released naturally.
<p>In the Bridger and Northern Madison Ranges, four to 6” of snow since Sunday night is being blown into drifts by 20 to 30 mph winds. Human-triggered avalanches are likely on freshly wind-loaded slopes. High-elevation terrain near ridgelines, gullies loaded by spindrift and other slopes with fresh drifts are all suspect. Avoid slopes with of recent or ongoing wind loading or signs of instability, such as recent avalanches, shooting cracks, and collapsing.</p>
<p>Persistent weak layers buried in the upper few feet of the snowpack and near the ground make deeper avalanches possible on both wind-loaded and non-wind-loaded terrain. Ian described these weak layers in his <a href="https://www.youtube.com/watch?v=ITX7Ic3eFYM&list=PLXu5151nmAvTi1DBS…; from the Bridger Range, as did Alex in his <a href="https://www.youtube.com/watch?v=LZ9aWLM7J2A&list=PLXu5151nmAvTi1DBS…; from the Northern Gallatin Range last week.</p>
<p>Avoid wind-loaded slopes where the danger is CONSIDERABLE. Dig and test for weak layers in the upper 3 feet of the snowpack before considering travel in non-wind-load avalanche terrain where the danger is MODERATE.</p>
<p>Since Sunday night, four to 7” of snow fell in the mountains near Big Sky, West Yellowstone and Cooke City. Persistent weak layers of feathery surface hoar and sugary facets exist in the upper three feet of the snowpack on most slopes across the area. Slopes with more recent snow or drifts of wind-loaded snow are the most dangerous today.</p>
<p>Recently, Alex uncovered the concerning weak layers in the top three feet of the snowpack in Beehive Basin near Big Sky (<a href="https://www.youtube.com/watch?v=6zNtBZuvEWw&list=PLXu5151nmAvTi1DBS…;) and north of Cooke City (<a href="https://www.youtube.com/watch?v=XhCVFXtNsKg&list=PLXu5151nmAvTi1DBS… video</span></strong></a>). Go back a full week with our <strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvTi1DBS5B4DBCruL1ULhkt…; and we describe similar conditions in all regions of the advisory area. Recent avalanches are the clearest indicators of potential instability. Yesterday, riders triggered a 30’ wide avalanche on Sheep Mountain near Cooke City that broke up to two feet deep (<a href="https://www.mtavalanche.com/node/28021"><strong><span>photo and details</span></strong></a>). On Thursday and Friday of last week, skiers triggered two avalanches in the backcountry outside Big Sky Ski Resort, with one skier caught and carried (<a href="https://www.mtavalanche.com/node/27963"><strong><span>details 1</span></strong></a>, <a href="https://www.mtavalanche.com/node/27980"><strong><span>details 2</span></strong></a>). A rider captured some spooky point-of-view footage when he was carried in a small avalanche near Buck Ridge at night (<a href="https://www.mtavalanche.com/node/28009"><strong><span>details and video</span></strong></a>), a skier was buried to their waist on Fisher Mountain (<a href="https://www.mtavalanche.com/node/27986"><strong><span>details</span></s…;) and a rider triggered a small slide on Mount Abundance near Cooke City (<a href="https://www.mtavalanche.com/node/27978"><strong><span>details</span></s…;).</p>
<p>If you are considering steeper terrain, dig down and test for instability related to weak layers in the upper three feet of the snowpack. The avalanche danger is rated MODERATE.</p>
<p><span>Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs"><span> </span></a><a href="https://www.mtavalanche.com/node/add/snow_obs"><strong><span>website</s…;, email (<strong>mtavalanche@gmail.com</strong>), phone (406-587-6984), or Instagram (#gnfacobs). <span><span> </span></span></span></p>
<p>The mountains in Island Park received up to 7” of new snow since Sunday night. Avalanches are possible in thicker drifts near ridgelines and on slopes with buried weak layers in the top three feet of the snowpack. Avoid slopes where pillows of drifted snow show signs of instability, such as shooting cracks and dig to perform an extended column test to investigate potential instability related to weak layers before riding steep slopes.</p>
<p>Yesterday, Doug and I rode in the Centennials and found weak layers in the upper three feet of the snowpack. They were not propagating failure in our stability tests. This is a good sign, but we are not ready to trust them. Today, we will continue hunting for instability in Island Park (<a href="https://www.youtube.com/watch?v=1izHP8-z8gY&lc=UgwTk8WVKJoymJc7HyN4…;
Thank you and great work to everyone who participated in this year’s King and Queen of the Ridge event. This year we set a fund-raising record of $31,626! We greatly appreciate the support from everyone who hiked, donated, and raised money for The Friends of GNFAC. The King of the Ridge for the second year in a row is Casey Bloomer, with a record 34 hikes, and Queen is Rachel Topf, with 23 hikes!
We rode north of Round Lake this morning (2/6/23)....
There was a small snowmobiler triggered slide on a convex bench between Sheep Mtn. and Round Lake that was triggered this afternoon. It was 1.5-2' deep, 30' wide, and looked to have broke on a weak layer below last week's snow, on a freshly wind-loaded slope. In a relatively shallow, rocky area (photo attached).
On 2/6/23 there was a small snowmobiler triggered slide on a convex bench between Sheep Mtn. and Round Lake that was triggered this afternoon. It was 1.5-2' deep, 30' wide, and looked to have broke on a weak layer below last week's snow, on a freshly wind-loaded slope. In a relatively shallow, rocky area. Photo: GNFAC
We rode north of Round Lake this morning (2/6/23). Near Long lake we measured 9" of new snow = 0.55" snow water equivalent. Near the Goose Lake wilderness boundary we measured 10" new snow = 0.65" SWE. In places there were 1mm facets below the new snow.
Wind was moderate-strong at the ridgelines, but calm around the lakes.
There was a small snowmobiler triggered slide on a convex bench between Sheep Mtn. and Round Lake that was triggered this afternoon. It was 1.5-2' deep, 30' wide, and looked to have broke on a weak layer below last week's snow, on a freshly wind-loaded slope. In a relatively shallow, rocky area (photo attached).
We rode up Yale Creek to across from Arange Peak, then back into Yale Creek. We dug 3 snowpits looking for weak layers and found them a foot or two under the surface. Feathery surface hoar mixed with small, sugary facets were found in all. This layer was not propagating in our tests, but we know that nearby in Lionhead they avalanched. We are not completely trusting of these layers, especially at higher elevations where wind drifts would be adding even more weight to these layers.
Dave Zinn measures snow water equivalent to see how much weight was added to the snowpack from the recent storm in Island Park. Photo: GNFAC
We rode down a narrow gully to get into the head of Yale Creek in Island Park. We descended one at a time, just in case our assessment was wrong. There was older debris in the gully. Photo: GNFAC
