23-24

Toured into Horse Creek Divide up Jardine, observed several natural avalanches on North facing slopes. Avalanches had broke in the last week. Most avalanche activity was on North slopes between 9300 and 9800 ft. From a distance looks like they broke 2-3 feet deep and ran 300-600 feet. Opted to stick to low angle terrain, but had big shooting cracks and large whumpfs, especially above 9000 ft. Snowpack in Jardine closely resembles what I have seen South of Cooke City this year.

Region

Out of Advisory Area

Location (from list)

Jardine

Observer Name

Oscar Dalling

Weak Snow, Improving Stability

Date

Sun, 12/31/2023 - 11:55

Activity

Skiing

Snowmobiling

We rode north of Cooke City today. The first stop was Scotch Bonnet, and just stepping off the snowmachines we were sinking through the upper portion of the snowpack. Here we transitioned to skis and started ascending, much of the tour was on a supportable crust with faceted weak snow below. Using a ski pole to probe during the accent we didn't find evidence of a cohesive slab below our feet. At 10000' on the SW side of the mountain, we dug and did not have propagating results in stability tests (HS: 74, ECTN 28, below the early December storm). We continued and wrapped around to the SE side of the mountain and dug again. This slope had been previously wind-loaded and had more of a cohesive slab above weak snow. Again, we had no propagation in stability tests, ECTN 21, but the poor structure and the presence of a cohesive slab were enough for us to retreat to a different ski run where no slab could be found.

North of Sheep Mountain we dug again on a north-facing slope at 9600' and saw similarly poor structure and stability test results as we did on the southeast side of Scotch Bonnet. While this slope wasn't wind-loaded it likely received more snow during the previous storm cycles, and was the deepest snow we saw today, 106 cm.

On every slope, we found surface hoar, even at ridgelines.

Region

Cooke City

Location (from list)

COOKE CITY

Observer Name

Zach Peterson

GNFAC Avalanche Forecast for Sun Dec 31, 2023

Snowpack and Avalanche Discussion

The snowpack is shallow with an abundance of weak, sugary snow on most slopes. Ian and Doug discuss this in their <a href="https://www.youtube.com/watch?v=YSYlarbuzJQ&list=PLXu5151nmAvSH326z…; from Taylor Fork last week. A person can trigger an avalanche where the weak snow is capped with a supportable, cohesive slab. Slopes with this poor snow structure are mostly confined to where last week’s strong winds drifted snow into thicker slabs, or where more snow accumulated with the most recent storm over a week ago.

On Thursday in the Bridger Range, Dave and Ian saw an avalanche that broke earlier in the week on a wind-loaded slope (<a href="https://www.youtube.com/watch?v=Rd_XSNJjLYs&list=PLXu5151nmAvSH326z…;, <a href="https://www.mtavalanche.com/images/23/natural-avalanche-throne"><…;). Over the last two days, skiers reported collapsing of the snowpack in Hyalite (<a href="https://www.mtavalanche.com/node/29714"><span… 1</a>, <a href="https://www.mtavalanche.com/node/29723"><span… 2</a>), Beehive (<a href="https://www.mtavalanche.com/node/29715"><span…;) and near Cooke City (<a href="https://www.mtavalanche.com/node/29716"><span…;), a sign of poor snow structure and the potential to trigger an avalanche on steeper slopes. The likelihood of triggering an avalanche has decreased as each day passes without snow, but large slides remain possible in specific areas.

Before riding or crossing steep slopes assess the snowpack for instability. If you find a stiff slab of snow that supports you on a sled or skis, stop to look for weak snow underneath. Avoid steep terrain where you find this poor snow structure, or if you see obvious signs of instability like collapsing and cracking. The thin snowpack requires only a few minutes to dig and do a stability test before getting into avalanche terrain.

Human-triggered avalanches are possible and the avalanche danger is MODERATE in the mountains around Bozeman, Big Sky, West Yellowstone, Island Park and Cooke City.

Read more about GNFAC Avalanche Forecast for Sun Dec 31, 2023

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 31, 2023

Read more about Weather and Avalanche Log for Sun Dec 31, 2023

Cracking and collapsing in Hyalite

Hyalite - main fork

Northern Gallatin

12/30/2023

Code

Elevation

8500

Aspect

Latitude

45.40340

Longitude

-110.96100

Notes

Skiers in Hyalite experienced a large collapse and cracking while approaching. From obs: While descending "the slope in front of me collapsed, with shooting cracks about 25ft in length. Both my partner and I experienced collapses the entire way down the slope while skiing."

Number of slides

Number caught

Number buried

Problem Type

Persistent Weak Layer