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Read more about Thin Snowpack in Black Canyon

The snow depth was 60-70 cm (2-2.5 feet) at the upper elevations of the Big Springs Loop around the Black Canyon area in Island Park. Photo: GNFAC

Island Park, 2024-12-09

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Read more about Buried Surface Hoar in Island Park

Surface hoar and near surface facets are now capped by this weekend's snow. The layers are buried 2-4" deep in the Black Canyon area of Island Park. Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Tue Dec 10, 2024

Island Park, 2024-12-09

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Weak Layers Buried in Island Park

Date

Mon, 12/09/2024 - 13:00

Activity

Snowmobiling

The snowpack remains thin in Island Park. We rode the Big Springs Loop around the Black Canyon area in Island Park. We dug two pits near the top of the loop in the area where one crosses the Canyon. One was on a southwest facing slope and the other on a north-facing slope. Both near 8100' elevation.

The snow depth was 60-70 cm (2-2.5 feet). Surface hoar and near surface facets are now capped by this weekend's snow. The layers are buried 2-4" deep. These are not a concern currently but certainly will become so with the next significant storm (or incremental loading). ECTN2-4 on these layer for now. Winds were calm and avalanches in non-wind-loaded terrain are unlikely. Small areas of isolated instability are possible in higher elevation wind-loaded terrain.

Region

Island Park

Location (from list)

Black Canyon

Observer Name

Dave Zinn

Weak Layers Buried in Island Park - 9 December 2024

Read more about Weak Layers Buried in Island Park - 9 December 2024

GNFAC Avalanche Forecast for Mon Dec 9, 2024

Snowpack and Avalanche Discussion

The mountains south of Bozeman in the Northern Gallatin Range received more snow than the rest of the forecast area, with 10” falling in the last 24 hours and storm totals likely reaching 12” today (1” of SWE). This storm is loading weak layers of faceted snow and wind is drifting snow into unstable wind slabs, making human-triggered avalanches likely on steep slopes.

Wind-slab avalanches could break 1-2 feet deep and are today's primary danger. Avoid steep slopes with active wind-loading or signs of fresh drifts, such as shooting cracks, collapsing (whumphs), or stiffening of the snow surface. Recent avalanche activity is the number one sign of instability. Wind slab instability will likely be confined to upper-elevation slopes near ridgelines and gullies. Ice climbers in town for the <a href="https://bozemanicefest.com/home">Bozeman Ice Festival</a> should note spindrift and wind-loading in gullies and avoid these areas.

The fresh snow fell on a thin snowpack with persistent weak layers throughout. Look for indicators of persistent slab instability, including avalanches and collapsing. Maintain a high index of suspicion for instability as the snowpack gets its first real test.

Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential for a safe day in and around avalanche terrain. The danger is CONSIDERABLE.

In the mountains north of Bozeman and near Big Sky, West Yellowstone, Island Park, and Cooke City, human-triggered avalanches are possible on wind-loaded slopes near ridgelines and in steep gullies. Storm totals range from 2-4.” Continued snowfall near Bozeman and Big Sky will add 1-2 inches today, potentially increasing avalanche size if snow exceeds predictions.

0800 UPDATE: It is snowing hard in the Bridger Range. Since publishing the forecast 1 hour ago, 2-3" of light snow fell. Stay heads up for evolving conditions if intense snowfall continues.

New snow is falling on weak layers formed during high pressure, making fresh drifts unstable (recent videos from <a href="https://www.youtube.com/watch?v=mknP2-CIWHA&list=PLXu5151nmAvToI_ir…;, <a href="https://www.youtube.com/watch?v=NjaZDAmyhvU&list=PLXu5151nmAvToI_ir… Ridge</a>, <a href="https://www.youtube.com/watch?v=jCM-9E88N5c&list=PLXu5151nmAvToI_ir… Fork</a> and <a href="https://www.youtube.com/watch?v=HFn7MC-Sy64&list=PLXu5151nmAvToI_ir… City</a>). Wind slab avalanches are today's primary concern and could break 4-8” deep on steep slopes. Indicators of instability include shooting cracks and recent avalanche activity. A small avalanche can cause significant problems on steep or technical slopes for a skier or rider who impacts trees, gullies, cliffs, and rocks.

Seek out slopes sheltered from recent wind-loading where human-triggered avalanches are unlikely. Carry rescue equipment, assess for instability related to buried weak layers before committing to steep slopes, and travel one at a time with someone in a safe position for rescue.

The avalanche danger is MODERATE on wind-loaded slopes and LOW on non-wind-loaded slopes.

Read more about GNFAC Avalanche Forecast for Mon Dec 9, 2024

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar

Tuesday, December 10, 9 a.m.-3 p.m., West Yellowstone Avalanche Fundamentals: Motorized Guide Cert Course, Pre-registration required.

Taylor Forking

Date

Tue, 12/03/2024 - 10:00

Activity

Skiing

This was a nice walk to stretch the legs in the Taylor Fork. My observations largely aligned with what GNFAC fxers observed in the same drainage on the same day.

Deep temperature inversion was present, it was 3 F when I left the car at 10 in the morning, and I eventually climbed out of the cold pool of air around 8,200'. I stopped and dug a few roadside handpits on the drive in from 191, it was impressive how much additional faceting was occurring below the level of the inversion. Here, the snowpack consisted mostly of 20-30cm of facets (DH near ground), with a decomposing 4F ambient temp crust in the mid-pack. I had no stability concerns down low today, but this very weak lower-elevation snow will create problems with additional loading. With enough load I would expect to see frequent, long-running collapses as well as the potential for remotely triggering slides from long distances in valley bottom locations. Many low elevation slopes facing SSE-S-SW-WSW had lost much of their snow cover, but solar margins and anything tilted a bit away from the sun were holding snow.

Above the level of the inversion and continuing up into the alpine the snowpack looked a bit better, but not great. Faceting was less pronounced and I was unable to get ECTs to propagate in a pit dug in a relatively flat meadow at ~8,600' (which felt like a decent proxy for shaded slopes based on structure). However, shortly after leaving this pit I initiated a large collapse that traveled across an entire large meadow; the collapse was audible for over a second as it propagated. This collapse and the weak layer of concern in my pit is the widespread basal weak layer, buried beginning in mid-November. This was the only direct instability feedback from the snowpack I experienced this day.

In the alpine, snow surfaces were weathered and highly variable, presenting as a mish-mash of facets, crusts, thin wind skins, and stiffer, denser hard slabs from recent snowfall. None of these surfaces looked terrible, but I'd expect a quick load of snow+wind to find plenty of locations with collapsible weak layers capable of producing avalanches. I looked around for a place to dig and look at basal weakness but was unable to find anything of value due to this high degree of variability. There was a thin but widespread rime/humidity crust in the upper few cms of the snowpack that was present as high as I observed (11,000' +). I observed some cracking that had occurred previously in steep, heavily wind-loaded north-facing terrain. It was not perfectly clear if this cracking involved the weak layer near the ground or just the thinner, wind-drifted hard slab near the surface, but it seemed like it was more of a surficial problem.

Region

Southern Madison

Location (from list)

Imp Peak

Observer Name

Ben VandenBos

Weather and Avalanche Log for Mon Dec 9, 2024

Read more about Weather and Avalanche Log for Mon Dec 9, 2024

GNFAC Avalanche Forecast for Sun Dec 8, 2024

Snowpack and Avalanche Discussion

New snow will be drifted into fresh slabs along ridgelines and below rollovers and avalanche danger will slowly rise through the day. Wind slab avalanches are the primary problem and will probably be less than 6-8 inches deep and relatively small. However, fresh drifts will be deposited on weak layers making them easy for a person to trigger.

On many slopes the snow surface became weak during the past week of high pressure. See our recent videos from <a href="https://www.youtube.com/watch?v=mknP2-CIWHA&list=PLXu5151nmAvToI_ir…;, <a href="https://www.youtube.com/watch?v=NjaZDAmyhvU&list=PLXu5151nmAvToI_ir… Ridge</a>, <a href="https://www.youtube.com/watch?v=jCM-9E88N5c&list=PLXu5151nmAvToI_ir… Fork</a>, <a href="https://www.youtube.com/watch?v=HFn7MC-Sy64&list=PLXu5151nmAvToI_ir… City</a> for a look at what lies on the ground. Expect fresh drifts to be unstable today. Cracking across the snow surface or natural avalanches are a clear sign that you can trigger an avalanche. Even a small slab can easily carry you, so be especially cautious in terrain with higher consequences.

If you are skiing or riding slopes steeper than 30 degrees, or ice-climbing in steep gullies, steer clear of fresh drifts, and keep in mind the increased risk of even a small slide due to thin snow cover, or being pushed over cliffs or into rocks or trees.

On slopes without fresh drifts avalanches are unlikely. Weak layers are buried near the bottom of a 1-2 foot deep snowpack, but probably need more than the weight of today’s new snow before they are a potential or more widespread problem. Quickly dig to assess for buried weak layers before committing to a steep slope, carry proper rescue gear, and travel one at a time across steep slopes.

Fresh wind slabs will grow today and the avalanche danger is MODERATE on wind-loaded slopes and LOW on non-wind loaded slopes.

In the Bridger Range and Hyalite snowfall is forecast to begin later, and without fresh snow avalanches are unlikely today. Quickly dig to assess for buried weak layers before committing to a steep slope, carry proper rescue gear, and travel one at a time across steep slopes. If snowfall begins earlier than expected, or if you are out after dark, watch for fresh wind slabs to form and expect them to be easy to trigger. Avalanche danger is LOW.

Read more about GNFAC Avalanche Forecast for Sun Dec 8, 2024

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar

Weather and Avalanche Log for Sun Dec 8, 2024

Read more about Weather and Avalanche Log for Sun Dec 8, 2024

@0600

GNFAC Avalanche Forecast for Sat Dec 7, 2024

Snowpack and Avalanche Discussion

Avalanches are unlikely today and the snowpack is generally stable. Weak layers are buried near the bottom of a 1-2 foot deep snowpack on some slopes and many weak layers have formed on the surface, but without new snow over the past week you are unlikely to find an unstable slab that could avalanche.

Above freezing temperatures may soften the snow surface this afternoon, but wet avalanches will be inhibited by cloud cover and a snow surface that has been through several melt-freeze cycles which is more resistant to falling apart. Watch for isolated small wet slides on sunny slopes around rock outcrops.

Despite a low likelihood for avalanches, an isolated unstable slope might be found somewhere in our large forecast area. If you are skiing or riding slopes steeper than 30 degrees be aware of the lingering chance to trigger an avalanche, and keep in mind the increased risk of even a small slide due to thin snow cover.

The shallow snowpack means you can quickly dig to assess for buried weak layers before committing to a steep slope. Watch for signs of instability (cracking and collapsing, rollerballs or a sticky snow surface), carry proper rescue gear (beacon, shovel and probe), and travel one at a time across steep slopes. The avalanche danger is LOW.

The new snow tonight and tomorrow will fall on weak layers that formed on the surface of the snowpack over the last week and danger will probably increase. Make sure to check the forecast for updates, and see our recent videos from <a href="https://www.youtube.com/watch?v=mknP2-CIWHA&list=PLXu5151nmAvToI_ir…;, <a href="https://www.youtube.com/watch?v=NjaZDAmyhvU&list=PLXu5151nmAvToI_ir… Ridge</a>, <a href="https://www.youtube.com/watch?v=jCM-9E88N5c&list=PLXu5151nmAvToI_ir… Fork</a>, <a href="https://www.youtube.com/watch?v=HFn7MC-Sy64&list=PLXu5151nmAvToI_ir… City</a> and the <a href="https://www.youtube.com/watch?v=tJcHZcSB454&list=PLXu5151nmAvToI_ir…; for a look at what lies on the ground throughout our forecast area.

Read more about GNFAC Avalanche Forecast for Sat Dec 7, 2024

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar

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