23-24

Collapsing and Poor Test Score in the Centennials

Date
Activity
Snowmobiling

The snowpack at low elevations is thin (<1 foot). Off-trail riding looked questionable, and we let the sleds stay in one piece for another day or two. We went a  cornice line at 9000.’ We walked over to our pit site on a NE facing slope, triggered a large collapse, and got an ECTP13 in a snowpack that resembled what Dave saw at Lionhead and Ian and Alex saw in Cooke City. There was 8” of new snow with 1” of SWE with a total snow height of just over 105cm.

Across the way, we dug on a SW-facing slope and found a similar snowpack structure although there were a few more ice crusts mixed into the 90cm deep snowpack (ECTP14).

We rode up a bit farther to get a view of the Jefferson Bowl and saw one, small natural avalanche that occurred within the storm snow.

There was no real way to navigate avalanche terrain without rolling the dice with the persistent weak layer that makes up the foundation of the snowpack. Avoidance is key.

Region
Island Park
Location (from list)
Sawtelle Peak
Observer Name
David Zinn

Skier triggered pocket at Bridger Bowl

Bridger Bowl
Bridger Range
Code
ASu-R0-D1
Elevation
8500
Aspect
NE
Latitude
45.81560
Longitude
-110.92300
Notes

From IG: Pocket I set off between finger 2 and 3 at Bridger Bowl just above the road. Finger 1 had someone ski it while we were hiking and they got a face wide crack.

Number of slides
1
Number caught
0
Number buried
0
Trigger
Skier
Trigger Modifier
u-An unintentional release
R size
0
D size
1
Problem Type
New Snow
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Skier triggered pocket at Bridger Bowl

Date
Activity
Skiing

From IG: Pocket I set off between finger 2 and 3 at Bridger Bowl just above the road. Finger 1 had someone ski it while we were hiking and they got a face wide crack.

Region
Bridger Range
Location (from list)
Bridger Bowl

The Gullies Are Dangerous

Date
Activity
Ice Climbing

8" of snow fell in 3 hours this morning. We inspected the snowpack in the gully above Silken Falls for the Bozeman Ice Festival. New snow and wind are increasing the avalanche danger. Be careful crossing gullies, especially the one above the Sceptor, the one below Responsible Family Man, Avalanche Gulch and Silken Falls. Triggering an avalanche in these is a very real possibility as they continue to get wind-loaded.

Region
Northern Gallatin
Location (from list)
Hyalite - main fork
Observer Name
Doug Chabot

GNFAC Avalanche Forecast for Thu Dec 7, 2023

Snowpack and Avalanche Discussion

<p>Dangerous avalanche conditions exist in the southern portions of the advisory area where a slab of cohesive snow sits on top of a weak foundation of sugary facets. Snowfall throughout the day will make conditions more dangerous. Slopes with wind-drifted snow are most likely to avalanche, but all are suspect.</p>

<p>In the past week, evidence of the danger included human-triggered and natural avalanches, shooting cracks, and whumphing collapses. On Sunday near West Yellowstone, a splitboarder had a close call on Lionhead Ridge while I made a video outlining the instability (<a href="https://www.mtavalanche.com/node/29358"><strong><span>avalanche details</span></strong></a>, <a href="https://youtu.be/ChZK6ex_f7k"><strong><span>video</span></strong></a&gt;). Sledders from nearby in Island Park sent observations of natural avalanches and shooting cracks in Black Canyon (<a href="https://www.mtavalanche.com/node/29376"><strong><span>details</span></s…;, <a href="https://www.mtavalanche.com/node/29377"><strong><span>details 2</span></strong></a>). On Monday, riders in the Taylor Fork observed several avalanches and triggered two slides from one hundred feet away (<a href="https://www.mtavalanche.com/node/29373"><strong><span>details and photo</span></strong></a>). In Cooke City, the weak foundation of faceted snow couldn’t support last weekend’s storm avalanching naturally on some slopes (<a href="https://www.mtavalanche.com/node/29381"><strong><span>details and photos 1</span></strong></a>, <a href="https://www.mtavalanche.com/node/29354"><strong><span>2</span></strong>…;). On Tuesday, Alex and Ian triggered loud whumphs that told them conditions remained unstable (<a href="https://youtu.be/tCIhNk8uJoM"><strong><span>video</span></strong></a&gt;).</p>

<p>Do not let the thin snow cover fool you. There is enough snow to avalanche, bury and injure skiers, riders and climbers. Avoid slopes steeper than 30 degrees as human-triggered avalanches are likely. The danger is rated CONSIDERABLE.</p>

<p>Human-triggered avalanches large enough to bury or injure climbers, skiers or riders are possible in the northern portions of the advisory area. Today, new and wind-drifted snow will further prime slopes with a weak foundation for avalanches.<span>&nbsp; </span></p>

<p>Groups will swarm to the gullies of Hyalite Canyon for this weekend’s Bozeman Ice Fest. Consider the locations of parties uphill and downhill of your group. On Monday, a climber in the Dribbles area observed cracking across the slope (<a href="https://www.mtavalanche.com/node/29362"><strong><span>observation and photo</span></strong></a>). Gullies funnel small avalanches into concentrated blasts that can knock people off their feet in consequential terrain.</p>

<p>In Big Sky, Alex made a <a href="https://www.youtube.com/watch?v=khUlf_rurog"><strong><span>video</span>…; </strong>showing a weak snowpack last week. Big Sky Ski Patrol’s snow safety team notes that the area’s snowpack is still weakening. During avalanche mitigation work on wind-loaded slopes, they have triggered several hard slab avalanches (<a href="https://www.mtavalanche.com/images/23/ski-patrol-triggered-hardslab-big…;).</p>

<p>Before considering steeper terrain, assess the snowpack for instability. Watch for signs of recent avalanches, shooting cracks or collapsing, and dig a snowpit to test for less obvious instability. Remember the adage, “If you are on a slope with enough snow to ski or ride, there is enough snow to slide.” The avalanche danger is rated MODERATE.</p>

<p>Dangerous avalanche conditions exist in Island Park where a slab of cohesive snow sits on top of a weak foundation of sugary facets. Snowfall throughout the day will make conditions more dangerous. Slopes with wind-drifted snow are most likely to avalanche, but all are suspect. Avoid slopes steeper than 30 degrees, as human-triggered avalanches are likely.</p>

<p>The avalanche danger is CONSIDERABLE.</p>

Upcoming Avalanche Education and Events

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

We rode up Daisy Pass road... saw a couple 8-10" deep natural avalanches on the steep slopes above Miller Creek that probably ran in the last 24-48hours. We had multiple collapses on the NE facing slope where we ski toured to dig our second pit. Photo: GNFAC

Cooke City, 2023-12-06