Preliminary Report of Lake Dinah Avalanche Accident 

On January 01, 2020, at approximately 1400hrs, three snowmobilers were involved in an avalanche approximately 1 mile NW of Lake Dinah, 12 miles NW of Seeley Lake, MT. 

The riders were caught and carried a short distance, two were fully buried, and one extricated himself after being separated from his snowmobile.

While playing on a small open slope, rider #1 rode partway up the 30-35 degree slope and got stuck. Rider #2 rode up to help dig out the stuck snowmobile, followed by rider #3. As rider #3 parked next to his partners, an avalanche released, sweeping all 3 riders downslope, partially burying rider #3 and fully burying riders #1 and #2. 

Rider #3 was able to self-rescue and immediately called 911. He then began a transceiver search and quickly located rider #2, who was buried 165cm (5.5’). He performed CPR for several minutes.

Search teams arrived on the scene, at approximately 1600hrs, began searching for rider #1 and continued CPR on rider #2.

Rider #1 did not have a transceiver but was quickly found by a volunteer member of the public assisting in the rescue who probed a likely spot next to a tree downslope from rider #1’s last seen location. He was buried 240cm (7.5’) deep.  He did not have a transceiver but was wearing an avalanche airbag pack that was deployed.

Both rider #1 and #2 perished at the scene. Rider #3 was not injured.

This was a soft slab avalanche triggered on an east-facing slope at 6740 feet in elevation. The average slope angle is 35 degrees, 38 degrees at the crown. 

The bed surface is a layer of buried surface hoar and near-surface facets. The avalanche length measured 560 feet from the crown to the deposition zone. The crown width is 100’ and depth averages 3’ deep. The deposition averaged 6’ in-depth.

The West Central Montana Avalanche Center (WCMAC) issued an Avalanche Warning on New Years Day after a significant storm deposited up to 3.5” of snow water equivalent (SWE) on an already unstable snowpack.

Here is a video of the site.(video)

We will issue a more detailed report in the next few days.

Our condolences go out to friends and families for their losses.

Our thanks to the multiple agencies and volunteers who responded to this incident on what is usually a happy holiday.