23-24

Read more about Skier triggered Wet slide on the fin

On 5/4/24 Skiers triggered large wet loose slides on the Fin near Cooke City

Avalanche Details: Skier triggered large Wet loose on the fin

Cooke City, 2024-05-05

Access other image sizes:

Wet loose on the fin

Date

Sat, 05/04/2024 - 12:00

Activity

Skiing

Snowboarding

Our party (3) triggered a significant wet loose slide on the fin today. I, the first skier dropped in next to existing tracks from earlier in the morning. I made a couple of small turns in unskied snow to test it and decided that not much was moving. As I continued down the wet surface snow started to slide and accumulate. My partner called me on the radio to tell me a lot of snow was moving behind me and I cut left. I traversed hard to lower angle terrain until I felt I could safely descend the rest of the slope. My partners descended the bed surface until they could traverse out.

We made several key mistakes today. We knew it would be warm and that we should be up and down early. We left later than planned, moved slower than expected and failed to adjust our plan. We mistook lack of wet loose activity on similar aspects and elevations on features we could see as sign of stability. We failed to make a plan B or establish a turnaround time. We interpreted a party ahead of us that skied the slope as a go ahead. Another party approaching behind us added pressure to go. They also skied the slope after us in similar style to my partners.

In our favor, we communicated well, radios were key, stayed calm and we managed ourselves through the situation. I feel humbled and lucky to have gotten away with a free lesson. One that I didn't think I should have needed.

Region

Cooke City

Location (from list)

Republic Mountain

North side of Wolverine

Date

Thu, 05/02/2024 - 13:50

Activity

Skiing

Snowmobiling

Wind load on old crust, probably from Wednesday.

Region

Cooke City

Location (from list)

Wolverine Peak

Read more about Skier triggered slab at Bridger

From email 5/2/24: "Triggered in the virtues this evening. 40' wide, 4-12" deep, failed as a dense, wind-packed slab on the rain/sun/heat crust underneath the most recent snow. I had marginal visibility but it looked like there were similar small-ish wind pockets that had failed in a few spots. Good skiing up high, fun first day up there."

Avalanche Details: Skier triggered slab at Bridger

Bridger Range, 2024-05-03

Access other image sizes:

GNFAC Avalanche Forecast for Thu May 2, 2024

Snowpack and Avalanche Discussion

NEW SNOW AND WIND LOADED SLOPES

Spring storms are notorious for depositing heavy amounts of snow in the mountains. Even with a generally stable snowpack throughout the advisory area, heavy and rapid loads of new snow will decrease stability. The main problems to look out for are avalanches breaking within the new snow, wind slabs, and loose snow avalanches. The likelihood of triggering an avalanche spikes during and immediately after snowstorms. New snow instabilities tend to stabilize quickly, but it’s a good idea to give fresh snow a day to adjust before traveling on steep slopes. New snow instabilities can be challenging to assess, and spring storms bond to old snow differently across aspects and elevations. Conservative terrain selection is essential during and immediately following storms. Avoid wind-loaded slopes and slopes steeper than 35 degrees for 24-48 hours after new snow and wind.

New snow can quickly change from dry to wet on a spring day, and stability can decrease rapidly with above freezing temperatures or brief sunshine. New snow may bond well early in the morning and then easily slide later. Wet loose slides are likely during the first above freezing temperatures or sunshine after a storm. Anticipate changes in snow stability as you change aspect or elevation and over the course of the day. An early start is always an advantage. Be ready to change plans or move to safer terrain at the first signs of decreasing stability.

WET SNOW AVALANCHES

Spring and wet snow avalanches go hand-in-hand. Above freezing temperatures, rain, and/or intense sunshine cause the snow to become wet and weak, and wet avalanches become easy to trigger or release naturally. Conditions tend to become most unstable when temperatures stay above freezing for multiple days and nights in a row. Avoid steep terrain, and be aware of the potential for natural wet avalanches in steep terrain above you, if you see:

<ul>
<li>Heavy rain,</li>
<li>Above freezing temperatures for more than 24 hours,</li>
<li>Natural wet avalanches,</li>
<li>Rollerballs or pinwheels indicating a moist or wet snow surface,</li>
<li>Or if you sink to your boot top in wet snow.</li>
</ul>

In general, if the snow surface freezes solid overnight, the snowpack will be stable in the morning and stability will decrease through the day as snow warms up. The snow surface hardness, rate of warming, duration of sunshine, aspect and elevation determine how fast stability will decrease through the day. Be aware that sunny aspects may have a wet snow avalanche danger while shadier slopes still have a dry snow avalanche danger. Getting off of steep slopes should be considered when, or before, the above signs of instability are present. Wet snow avalanches, whether loose snow or slabs, can be powerful, destructive and very dangerous. Conservative terrain choices, starting early in the day, and careful observations can keep you safe.

CORNICES

Cornices along ridgelines are massive and can break under the weight of a person. Prolonged above freezing temperatures and rain make them weaker and possibly break naturally. They can break off suddenly and farther back than one might expect. Cornice falls can also entrain large amounts of loose snow or trigger slab avalanches. Stay far back from the edge of ridgelines and minimize exposure to slopes directly below cornices. Regardless of whether a cornice triggers a slide or not, a falling cornice is dangerous to anyone in its path.

DISCLAIMER

It does not matter if new snow falls or not, avalanches will continue to occur until the existing snowpack is mostly gone. Always assess the slope you plan to ride with diligence and safety in mind. Do not let your guard down. Travel with a partner, carry rescue gear and only expose one person at a time in avalanche terrain.

Have a safe and enjoyable spring and summer!

Doug, Alex, Ian and Dave

For more spring travel advice see this <a href="https://www.mtavalanche.com/blog/transitions-spring-snow-avalanche-prob… our GNFAC forecaster blog.

Read more about GNFAC Avalanche Forecast for Thu May 2, 2024

Upcoming Avalanche Education and Events

Hyalite Road Closure: Hyalite road is closed to ALL MOTORIZED VEHICLES until the morning of May 16. This is a regular annual road closure to reduce road damage during the spring thaw. Bicycle and foot traffic are allowed. Contact the Bozeman FS Ranger District for more info.

Read more about North side of Wolverine

From obs 5/2/24: "Wind load on old crust, probably from Wednesday."

Avalanche Details: Natural wind slab North side of Wolverine

Cooke City, 2024-05-02

Access other image sizes:

Rider/skier triggered avalanche

Sheep Mountain

Cooke City

5/1/2024

Code

SS-ASu-R2-D1.5-I

Elevation

9500

Aspect

Latitude

45.07220

Longitude

-109.92800

Notes

From email 5/1/24: "Hi crew. I triggered a soft slab avalanche on the North side of Sheep Mountain today. D1.5 200’ wide ran 200’. Crown was 6-12’’ deep. I was able to ride out of it and anchor in a safe spot.

It broke on our 7th lap and we had seen no signs of instability prior to the avalanche but wind loading was occurring and obvious. The avalanche broke and on a dirty crust that formed during a rain event last week."

Number of slides

Number caught

Number buried

Avalanche Type

Soft slab avalanche

Trigger

Skier

Trigger Modifier

u-An unintentional release

R size

D size

1.5