- Location: Near Lake Dinah, west of Seeley Lake
- State: Montana
- Date: 2020/01/01
- Summary Description: 3 snowmobilers caught, 2 buried and killed, 1 partially buried
- Primary Activity: Snowmobiler
- Primary Travel Mode: Snowmobile
- Location Setting: Backcountry
- Caught: 3
- Partially Buried, Non-Critical: 1
- Partially Buried, Critical: 0
- Fully Buried: 2
- Injured: 0
- Killed: 2
- Type: SS
- Trigger: AM - Snowmobile
- Trigger (subcode): u - An unintentional release
- Size - Relative to Path: R3
- Size - Destructive Force: D2.5
- Sliding Surface: O - Within Old Snow
- Slope Aspect: E
- Site Elevation: 6740 ft
- Slope Angle: 35 °
- Slope Characteristic: --
This avalanche was a soft slab avalanche triggered on an east-facing slope at 6740 feet in elevation. The average slope angle is 35 degrees and 38 degrees at the crown. A pit profile was dug on the day of the avalanche in the southern Missions at a similar elevation and aspect. The weak layer was surface hoar and near surface facets. The avalanche length measured 560 feet from the crown to the deposition zone. The crown width is 100 feet and depth averages 3 feet deep. The deposition averaged 6 feet in depth. This avalanche is classified as: SS-AMu-R3-D2.5-O
The Seeley Lake area in west central Montana has become a destination for snowmobiling. The Lake Dinah area accessed from the Westside Trailhead parking area is increasingly popular for motorized users. Snowmobile use has dramatically increased, and several near misses have occurred in recent years.
The area around Lake Dinah has open terrain with access to larger bowls. Most avalanche paths in this area end in terrain traps (trees and rocks). There is abundant steep and open terrain pocketed with tree cover.
On January 02, 2020, two volunteers who assisted in the recovery and the West Central Montana Avalanche Center Director, Travis Craft, visited the avalanche site. We were not able to visit the crown of the avalanche due to weather conditions and exposure to avalanche hazard.
Snowfall and temperature data for this incident was collected from the North Fork of the Jocko SNOTEL. This SNOTEL is located 1.5 miles to the northwest of the avalanche site and at an elevation of 6330 feet. From Dec 29-Jan 1, the average temperature ranged from 15 to 31
degrees. It was 31 degrees at 1400 hours on the date of the accident. 3.5 inches of SWE was recorded from Dec 30-Jan 1. Wind Speed data was collected from the Point Six Raws station at 7920 feet, located 19.6 miles southwest of the avalanche site. Winds were from the west and averaged 27 mph and gusted 30-35 mph.
The southern Missions Mountains where the incident occurred had a relatively shallow snowpack in November and December. On December 29, 2019, a layer of surface hoar was preserved from a freezing fog crust, and near-surface facets developed. A significant storm system entered the forecast area on December 30, 2019. By January 01, 2020 at the time of the accident, 3.5 inches of SWE snow water equivalent or approximately 3 feet of new snow had fallen on a weak snowpack. This rapid load produced several natural and rider triggered avalanches throughout the advisory area on January 01, 2020.
Due to the dangerous avalanche conditions, The West Central Montana Avalanche Center (WCMAC) issued an Avalanche Warning on January 01, 2020.
Events Leading to the Avalanche
The group of 3 snowmobilers departed the Westside Trailhead parking area at approximately 0900 hours. The group traveled together to the Drift Riders Warming Hut. The plan was to ride in the trees. Rider #1 was the most familiar with the area and was the strongest rider in the group. They rode nearby terrain, played in trees, and decided to explore an area near Lake Dinah. No one in the group was familiar with this new area near Lake Dinah. No one in the group read the avalanche forecast posted that morning. All 3 riders were equipped with an avalanche airbag, shovel, and probe. Riders #2 and #3 also had transceivers. Rider #1 did not carry a transceiver. The 3 riders had little formal avalanche training.
At approximately 1400 hours, while riding on an open slope, rider #1 rode partway up the 30-35 degree slope and got his snowmobile stuck. Rider #2 rode up to help dig out the stuck snowmobile, and was followed by rider #3. As rider #3 parked downhill of his partners, an avalanche released, sweeping all 3 riders downslope.
Rider #3 was partially buried while riders #1 and #2 were fully buried. Rider #3 was able to self-rescue and immediately called 911 (SAR was mobilized at 1415 hours). He initiated a transceiver search and quickly located rider #2, who was buried 165cm (5’5”) deep. He was able to extract rider #2 in approximately 30 minutes and immediately began preforming CPR.
Volunteer members of the public arrived on the scene and took over care of rider #2 at approximately 1600 hours. They continued to search
for rider #1, and continued CPR on rider #2. Rider #1, despite not having a transceiver, was found by a volunteer on his first probe strike. Rider #1 was located in a likely spot next to a tree downslope from his last seen location. He was buried 240cm (7.5’) deep. Rider #1 was uncovered at approximately 1615 hours and was found with his avalanche airbag deployed.
Both rider #1 and #2 perished at the scene, while rider #3 was not injured. Search and Rescue teams were assisted by regional agency personnel and, brought all machines and people back to the Fawn Creek parking lot by 2215 hours. The Drift Rider Hut was used as a staging area for the rescue. Incident command was established at the Westside Trailhead parking lot.
All of the fatal avalanche accidents we investigate are tragic events. We do our best to describe each one to help both the people involved and the community as a whole better understand them. We offer these comments in the hope that it will help people avoid future avalanche accidents. We do not intend to place blame on any of the involved parties or imply that any particular action or decision would have prevented this tragic event.
Avalanche Forecast: WCMAC issued an Avalanche warning on January 01, 2020. Rider #3 informed us that his group did not read the forecast. Reading the forecast is the first step to making informed decisions on terrain choices and forming a trip plan when choosing to recreate in the winter backcountry.
Group Travel: 3 riders were on the same slope when the avalanche released. When traveling through or recreating on avalanche terrain it is advisable to expose only one person at a time.
Avalanche Education: The riders had little formal avalanche education. Level 1 avalanche training helps guide people with a decision-making format and avalanche hazard assessment given expected and current avalanche conditions.
Companion Rescue: Multiple burial companion rescue is a challenging scenario. Rider #1 did not have a transceiver making the chances of a successful companion rescue significantly less likely.
Rescue Equipment: While avalanche air bags are intended to help people stay near the surface when caught in an avalanche, they are not as effective when a terrain trap is involved. Rider #1’s, air bag was deployed, however he was pinned up against a tree under several feet of snow. Trees are terrain traps which increase the consequences of being caught in a slide by burying you deeper. Also, rider #1 did not have a beacon, slowing his recovery. Rider #2 had an air bag that was not deployed, but he was not buried as deep because he did not get caught in a terrain trap. Always carry a beacon, shovel and probe and practice using these tools.
Historical Myths: Common phrases such as “That slope never slides” or “just a freak accident” are common misconceptions. On the day of the accident the WCMAC observed 3 natural slides in the Seeley Lake area. A slope is steep enough to slide if it falls within the range of 30-50 degrees. An average slope steepness of 35 degrees is prime avalanche terrain.
Travis Craft and Jeff Carty of the West Central Montana Avalanche Center obtained information during the recovery from rescuers. Travis Craft interviewed rider #3 on the night of January 01, 2020.