21-22

Bear Basin old natural avalanche

Date
Activity
Skiing

We found two past avalanches on an E facing slope at 8400' near the bottom of Bear Basin after skiing of the Beehive/bear ridge. They appeared to be wet slabs that broke on the ground naturally during the warmup. ~100' wide with 3-4' crowns. Photos show new snow covering the paths and debris piles that could have buried a car. No signals in the debris.

Region
Northern Madison
Location (from list)
Bear Basin
Observer Name
Alden Sonnenfeldt

GNFAC Avalanche Forecast for Mon Apr 18, 2022

Snowpack and Avalanche Discussion

<p>Clear skies and above freezing temperatures today, and maybe later in the week, will quickly get the new snow wet and make avalanches easier to trigger (<strong><a href="https://www.youtube.com/watch?v=JqwSknw4e_E&amp;list=PLXu5151nmAvT1nrM2…;). Anticipate changing conditions and monitor the wetness of the snow surface. Plan to be off and out from underneath steep terrain that receives direct sunshine before it becomes unstable. If you see large pinwheels of snow on the surface or can make a snowball of moist snow, it is time to retreat to lower angle or shadier terrain.</p>

<p>Over the weekend recent new snow created dangerous avalanche conditions, especially where it was drifted into thicker, dense slabs by strong wind. We received reports of natural avalanches in the Bridger Range (<strong><a href="https://www.mtavalanche.com/images/22/natural-avalanches-northern-bridg…;) and Cooke City (<strong><a href="https://www.mtavalanche.com/images/22/natural-avalanche-fin">photo</a><…;) which broke during and immediately after the heaviest snow fell on late Saturday. On Saturday in East Rosebud Creek, outside our advisory area, five skiers from two separate groups were caught in a natural dry loose snow avalanche. Luckily, no one was injured. The avalanche became large as it entrained snow while it swept down the couloir they were climbing (<strong><a href="https://www.mtavalanche.com/node/26486">details</a></strong&gt;). Yesterday near Cooke City, skiers intentionally triggered a 4-16” deep slab of wind drifted snow (<strong><a href="https://www.mtavalanche.com/node/26494">photo and details</a></strong>) as they descended a slope.</p>

<p>This week similar avalanches are possible which will involve the recent snow or snow that falls later this week. Watch for signs of unstable, wind-drifted snow and avoid steep slopes where you suspect it exists. Be especially cautious in terrain where even a small slab or loose snow slide would be deadly due to higher consequences, like potentially pushing you into rocks, trees or over cliffs. Before skiing or riding in steep terrain, dig down a couple feet and assess the stability of snow that fell over the last week. Avalanches could break on hardness differences within the recent snow, or on a hard melt-freeze crust buried below the recent snow.&nbsp;In isolated, colder areas, avalanches could break on weak layers 1-3 feet below the new snow.</p>

<p>Always follow safe travel protocols by skiing and riding with a partner, carrying a beacon, shovel and probe and exposing only one person at a time to avalanche terrain.</p>

<p>We will issue spring snowpack and weather updates each Monday and Friday through April, or as needed, and we will share relevant avalanche and snowpack information on our website and social media. If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Announcements, Avalanche Education and Events

Bridger Bowl is closed, and backcountry conditions exist. There is no avalanche mitigation or ski patrol rescue. In case of emergency, call 911. Please stay clear of work areas, snowmobiles, chair lifts and other equipment. Without the daily avalanche mitigation efforts of the ski patrol, backcountry conditions now exist within the boundaries of Bridger Bowl (video).

Skier triggered avalanche in Sheep Creek

Sheep Creek
Cooke City
Code
SS-ASc-R2-D1.5-I
Elevation
9500
Aspect
NE
Latitude
45.03440
Longitude
-109.98400
Notes

"Ski cut on belay a SS avalanche out of the start zone of this N facing slope in Sheep Creek basin. The crown was 4-16" deep and broke into the rocks on skier's right, as well as skirted the bottom of the rock wall skier's left. Winds along the Mineral ridge were moderate gusting strong from the south with active transport observed."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
2
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness
12.0 inches
Vertical Fall
650ft
Slab Width
30.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From obs 4/17/22: "Ski cut on belay a SS avalanche out of the start zone of this N facing slope in Sheep Creek basin. The crown was 4-16" deep and broke into the rocks on skier's right, as well as skirted the bottom of the rock wall skier's left. Winds along the Mineral ridge were moderate gusting strong from the south with active transport observed."

Cooke City, 2022-04-17

Natural Avalanche Fin

The Fin
Cooke City
Code
SS-N-R2-D2
Elevation
9900
Aspect
E
Latitude
45.00460
Longitude
-109.95800
Notes

This avalanche failed naturally on the Fin early in the morning on April 17th. It was the result of new snow and strong winds. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Problem Type
Wind-Drifted Snow
Vertical Fall
400ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Natural large slabs on The Throne

The Throne
Bridger Range
Code
SS-N-R3-D2-I
Latitude
45.88220
Longitude
-110.95200
Number of slides
3
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
3
D size
2
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness
10.0 inches
Vertical Fall
600ft
Slab Width
60.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Chamonix Couloir Avalanche

Date
Activity
Skiing
Snowboarding

Yesterday a natural dry/loose avalanche ran in the Chamonix couloir in East Rosebud, partially burry all four people in my party and one person in a party above us. Four of the five of us were able dig ourselves out and there were no significant injuries.

We knew the area had received a lot of snow in the last week but there was only a four or five inches of fresh snow at the lake. At about 8,700 feet, when we transitioned to boot packing, there was roughly a foot of low density fresh snow that was bonded well to the existing snow. Skies were clear at sunrise, clouds moved in throughout the morning and it began snowing lightly around 11:30.

We didn't see the beginning of the avalanche, two members of the party above us said that a sluff that ran off one of the walls above them and was small enough when it ran past them that it didn't effect them. I don't know how high they were above the third member of their party but the third member was a few hundred feet above us. By the time the avalanche reached us it had grown substantially and was an over-head wall of snow. The two skiers who saw the avalanche start didn't see it step down to any deeper layers, it was just the new snow. Based on the data from my watch, we were carried about 750 vertical feet. We didn't take any photos of the slide.

The other party in the couloir may submit a report as well. Let me know if any additional details could be helpful.

Region
Out of Advisory Area
Observer Name
Zach Cohen