22-23 | Gallatin National Forest Avalanche Center

There was 6" of new snow in Hyalite Canyon with increasing winds throughout the day. Our primary concern is avalanches within the new and wind-drifted snow. Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Tue Dec 6, 2022

Northern Gallatin, 2022-12-05

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Unstable in Pioneers

Date

Sat, 12/03/2022 - 16:10

Activity

Skiing

Early season snow recon outside of Maverick Mountain Ski Area boundary. Cracking of surface slab on easterly aspect at 8000 ft (see pics). Well developed weak layer about mid-pack that formed during November. Several storms the first week of December put down a 1-2 foot slab on top of this weak layer. Cohesiveness of slab varies by aspect and elevation. Wind and sun exposed slopes more reactive due to higher slab density. Areas protected from wind were not as reactive with no cracking experienced. Spatial variability is high with a shallow snowpack. See picture of quick pit showing major layering on north facing aspect at 8400 ft. Height of snow between 65-75 cm. Notable results were CTM 11 with a sudden collapse fracture character at 35cm up from the ground at November/December snow interface. ECTN 11 on same layer. The slab was not stiff enough in this protected location to propagate however this pit is representative of poor structure that is widespread.

Also, snowmobilers reported avalanches on some of the steep roadcuts on the Pioneer Scenic Byway.

Region

Dillon Area

Location (from list)

West Pioneer Mountains

Observer Name

Alex Dunn

GNFAC Avalanche Forecast for Mon Dec 5, 2022

Snowpack and Avalanche Discussion

Today’s 6-10” of new snow equals 0.8-1.1” of snow water equivalent (SWE) and creates dangerous avalanche conditions. Southwest wind will increase through the day and drift the new snow into thicker, heavier slabs. The weight of new snow and drifts will stress weak layers deeper in the snowpack and could cause avalanches breaking 2-4 feet deep. Fresh drifts could break naturally, will easily avalanche under the weight of a person, and could trigger a deeper slide.

During and after the storm that dropped two feet of snow last Thursday and Friday there were large natural and human triggered avalanches near Cooke City (<a href="https://www.mtavalanche.com/images/22/large-natural-sheep">… Mountain</a>, <a href="https://www.mtavalanche.com/images/22/large-natural-fox"><s… Mountain</a>, <a href="http://www.mtavalanche.com/node/27060">…;) and Lionhead (<a href="https://www.mtavalanche.com/node/27046"><span… Bowl</a>, <a href="https://www.mtavalanche.com/node/27021"><span… Ridge</a>). Many of these avalanches likely broke on weak layers buried deeper in the snowpack. I was in Cooke City last week and found weak layers buried below the new snow (<a href="https://www.youtube.com/watch?v=p4oOrj6x7oU&list=PLXu5151nmAvTi1DBS… from Friday</a>, <a href="http://www.mtavalanche.com/images/22/new-snow-and-ectp-scotch-bonnet"><…;), and earlier last week Dave was in Lionhead and found weak layers that are now buried 3-4’ deep (<a href="https://www.youtube.com/watch?v=PVQkjFvFnnw&list=PLXu5151nmAvTi1DBS…;, photo). Over the weekend, skiers at Bacon Rind in the southern Madison Range saw recent natural avalanches, and had collapsing and unstable snowpack test scores on weak snow buried 1-2 feet deep (<a href="https://www.mtavalanche.com/node/27037"><span… Rind observation</a>).

New snow, wind and buried weak layers make large, human triggered avalanches likely and natural avalanches possible today. Avalanche danger is CONSIDERABLE. Cautious route finding and conservative terrain selection is essential.

Today’s 6-8” of new snow is equal to 0.8” of snow water equivalent and will be drifted by strong wind into fresh drifts that will be easy to trigger. Avalanches of new and wind-drifted snow will be large enough to bury or injure a person and could break deeper, on weak layers buried below last Thursday’s 6-8” of snow. Today’s new snow and increasing southwest wind create dangerous avalanche conditions and avalanche danger is CONSIDERABLE. Avoid steep, wind-loaded slopes and choose your terrain and objectives carefully.

Big Sky and Hyalite received 5-8” of snow equal to 0.4-0.6” of snow water equivalent. This snow will be drifted into thicker slabs by increasing southwest wind this afternoon. These slabs are possible for a person to trigger, and could break 1-2 feet deeper on buried weak layers. Today, Be cautious of fresh drifts on steep slopes and dig down to check for buried weak layers before riding any steep slopes. Human-triggered avalanches are possible and the avalanche danger is MODERATE.

If you get out, please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs">…; website</a>, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Read more about GNFAC Avalanche Forecast for Mon Dec 5, 2022

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Divide Peak

Date

Sun, 12/04/2022 - 13:30

Activity

Skiing

Snow pack of 108cm on a 25 NE facing slope at 9,625'

Observed CT11 Q2 at new/old interface, 93cm, as well as an ECTN13 Q2 on what we believe to be a buried layer of surface hoar at 26cm. Also had some warming of the surface.

With the poor pit performance we decided to not ascend to the ridge and ski the intermediate terrain in the cirque, then out the drainage.

Region

Northern Gallatin

Location (from list)

Divide Cirque

Observer Name

Shep