GNFAC Avalanche Forecast for Thu Nov 24, 2022
<p><span><span><span><span><span><span>The storm dropped 8-11" of snow around Bozeman, Big Sky, Cooke City and Taylor Fork, and 3-5” around West Yellowstone. In some areas this new snow fell onto a weak surface (facets). On slopes that were drifted by the wind it remains possible to trigger avalanches. Alex found this avalanche recipe (slab sitting a weak layer) in Bridger Bowl yesterday. He intentionally triggered a 20-foot wide, 6-8” deep, soft slab of wind blown snow. It ran 250 feet and broke on the faceted, old surface (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/26906"><span><span><span><strong><span… and photos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Additionally, on high elevation sloples, especially north facing, there could be weak snow at the ground. As evidence, a large avalanche on Hyalite Peak last Friday broke on this basal layer (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/26883"><span><span><span><strong><span… and details</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). We do not believe this deep instability to be widespread, but we will be hunting for it. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Our main avalanche concern is wind drifted snow. Shooting cracks are signs the snow is unstable, and any avalanche, no matter how small, is bullseye data to stay off steep terrain. Digging and testing the snow is fruitful since there are not many layers. With 2-3 feet of snow in the mountains, travel is getting easier which means our exposure to avalanche terrain is rising. Ice climbers and hunters need to be extra careful crossing wind-loaded gullies. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Today, triggering avalanches is possible and the avalanche danger is rated MODERATE.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Dave will issue the next forecast tomorrow morning. If you get out, please share avalanche, snowpack or weather observations via our </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/add/snow_obs"><span><span><span><stron…;, email (</span></span></span></span></span></span><a href="mailto:mtavalanche@gmail.com"><span><span><span><strong><span><u><span>…;), phone (406-587-6984), or Instagram (#gnfacobs).</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>About 2-3” fell in the mountains around Island Park. This new snow fell onto a surface of weaker snow (facets). On Monday a sledder had cracks propagating in wind drifted snow on Reas Peak which was a warning that some slopes were unstable (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/22/wind-slabs-cracking-reas-peak-isl…;). Digging and testing the snow is fruitful since there are not many layers (</span></span></span></span></span></span><a href="https://youtu.be/_Yw-PrBh6FU"><span><span><span><strong><span><u><span>…;). With 3-4 feet of snow in the mountains, travel is getting easier which means our exposure to avalanche terrain is rising. </span></span></span></span></span></span></p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Wind slabs cracking on Reas Peak
A snowmobiler noted cracking of the snow surface on the south face of Reas Peak out of Island Park. The wind crust was 3-4" thick and had facets underneath which aided the propagation.
A snowmobiler noted cracking of the snow surface on the south face of Reas Peak out of Island Park. The wind crust was 3-4" thick and had facets underneath which aided the propagation. Photo: Anonymous
Forecast link: GNFAC Avalanche Forecast for Thu Nov 24, 2022
Skier triggered wind slab at Bridger
At 1:30pm on 11/23 I intentionally triggered a fresh drift of snow in a narrow avalanche path along the edge of the north bowl at Bridger. Northeast aspect at 7,600’ elevation. The crown was 6-8” deep consisting of snow that fell today, 20’ wide and ran 250’ vertical. SS-ASc-R2-D1.5-I.
Wind was moderate, gusting strong out of the north and west and transporting snow. There were 3-4” on lower mountain and 7-8” new up high. Snowpack is 1-2’ deep. Prior to this storm, snow close to the surface had turned to small (1-1.5mm) facets during previous cold weather, capped by a thin crust (wind or sun) on many slopes.
At 1:30pm on 11/23 I intentionally triggered a fresh drift of snow in a narrow avalanche path along the edge of the north bowl at Bridger. Northeast aspect at 7,600’ elevation. The crown was 6-8” deep consisting of snow that fell today, 20’ wide and ran 250’ vertical. SS-ASc-R2-D1.5-I. Photo: GNFAC
Forecast link: GNFAC Avalanche Forecast for Thu Nov 24, 2022
At 1:30pm on 11/23 I intentionally triggered a fresh drift of snow in a narrow avalanche path along the edge of the north bowl at Bridger. Northeast aspect at 7,600’ elevation. The crown was 6-8” deep consisting of snow that fell today, 20’ wide and ran 250’ vertical. SS-ASc-R2-D1.5-I. Photo: GNFAC
Forecast link: GNFAC Avalanche Forecast for Thu Nov 24, 2022GNFAC Avalanche Forecast for Fri Nov 25, 2022
Skier triggered wind slab at Bridger
At 1:30pm on 11/23 I intentionally triggered a fresh drift of snow in a narrow avalanche path along the edge of the north bowl at Bridger. Northeast aspect at 7,600’ elevation. The crown was 6-8” deep consisting of snow that fell today, 20’ wide and ran 250’ vertical. SS-ASc-R2-D1.5-I.
Wind was moderate, gusting strong out of the north and west and transporting snow. There were 3-4” on lower mountain and 7-8” new up high. Snowpack is 1-2’ deep. Prior to this storm, snow close to the surface had turned to small (1-1.5mm) facets during previous cold weather, capped by a thin crust (wind or sun) on many slopes.
GNFAC Avalanche Forecast for Wed Nov 23, 2022
<p><span><span><span><span><span><span>Today avalanches are possible where drifts of new snow are created by moderate west-northwest wind. Skiers, snowmobilers, ice-climbers and hunters should be cautious of steep slopes that have dense drifts of snow. Watch for cracking across the snow surface as a clear sign that these drifts are unstable and should be avoided. Find alternate routes if you encounter terrain that has higher consequences of being caught in even a small slide, such as narrow gullies or steep slopes above cliffs or thick trees.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>The mountains have 1-3 feet of snow on the ground which fell in late October and early November. A few recent avalanches are evidence that weakness can be found deeper in the snowpack. A large avalanche on Hyalite peak last Friday broke a couple feet deep and 150 feet wide (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/26883"><span><span><span><strong><span… and details</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Yesterday, Big Sky ski patrol triggered avalanches with large explosives that broke 12” deep, above a crust that formed on top of late-October snow (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/26904"><span><span><span><strong><span… and details</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). Avoid buried persistent weak layers by digging to assess snowpack structure and stability before riding in steep terrain. We have not seen or had reports of widespread unstable buried weak layers which means assessment may be trickier. With a lack of clear unstable snowpack test results, remain cautious if you find buried weak layers that cause concern. Take a step back with today's storm and see which layers break in avalanches and snowpack tests after the added weight of new snow and drifts. </span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Today, avalanches are possible and avalanche danger is MODERATE.</span></span></span></span></span></span></p>
<p><span><span><span><span><span><span>Doug will issue the next forecast tomorrow morning. If you get out, please share avalanche, snowpack or weather observations via our </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/add/snow_obs"><span><span><span><stron…;, email (</span></span></span></span></span></span><a href="mailto:mtavalanche@gmail.com"><span><span><span><strong><span><u><span>…;), phone (406-587-6984), or Instagram (#gnfacobs). </span></span></span></span></span></span><a href="https://www.mtavalanche.com/snow-observations-list"><span><span><span><… Observations Page</span></span></u></span></strong></span></span></span></a><span><span><span><strong><span><span>, </span></span></strong></span></span></span><a href="https://www.mtavalanche.com/node/add/snow_obs"><span><span><span><stron… your observations</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>.</span></span></span></span></span></span></p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Explosive triggered hard slabs at Big Sky
Triggered with 4lbs, after they were not affected by 2lbs shots yesterday. The crowns were in the 12” range and hard slabs. The weak layer is subtle-trapped lower density (but still 4F) above the crust, with tiny facets mixed with rounds. The slides were not running directly on the crust, but just above, leaving 2-3 cm’s behind on top of the crust.