Photo of the snowmobile triggered slide that fully buried a rider on February 7th, 2019.
<p>Another 7-8” of new snow last night bring three day snow totals to around a foot (~1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>) in the southern ranges. Strong and shifting winds (from southeast to west) built thick drifts on a wide variety of slopes, multiplying the load on a weak snowpack. With the wind shift and continued snowfall, identify and avoiding windloaded slopes will be more challenging than usual. Avalanche can break on weak layers buried 2-4’ deep, either mid-pack or near the ground. There were a number of avalanches on these weak layers in the middle of last week (<strong><a href="https://www.mtavalanche.com/images/19/avalanches-lionhead-ridge">photo<…;, <strong><a href="https://www.youtube.com/watch?v=xlsoevxJbKc&index=2&list=PLXu51…;, <strong><a href="https://www.mtavalanche.com/node/20024">details</a></strong>). This new load will wake them back up and triggering an avalanche is likely today.</p>
<p>Yesterday, a snowmobiler triggered a large avalanche in the Gravellys (<strong><a href="https://www.mtavalanche.com/node/20054">details</a></strong>) and on Saturday a rider was buried by an avalanche in the Centennials (<strong><a href="https://www.mtavalanche.com/node/20032">link to video</a></strong>). While both these incidents were outside our advisory area, the snowpacks are similar and they serve as good reminders of the sort of high consequence slide you can trigger today. The avalanche danger is CONSIDERABLE.</p>
<p>The lower snowpack is generally stronger in the northern ranges and near Cooke City, and less new snow has accumulated. However, another couple inches of snow last night (generally 2-4”, 6” on the Bridger ridge) accompanied by strong west winds have built fresh drifts. These new drifts will mostly be thin, but be wary of areas where they have piled up more deeply and high consequence terrain where taking a small ride would be a big problem. Watch out for and steer around these wind drifts.</p>
<p>Triggering avalanches on weak snow deeper in the pack also remains a lingering concern. Avalanches triggered on Saturday near Cooke City and in Hyalite broke 1-2.5’ deep and several hundred feet wide (<strong><a href="https://www.mtavalanche.com/node/20037">details and photos</a></strong>, <strong><a href="https://www.mtavalanche.com/node/20042">details</a></strong>). I also found these mid-pack weak layers yesterday on Buck Ridge and they were still producing unstable test results (<strong><a href="https://www.youtube.com/watch?v=6pL0K8aaJjI">video</a></strong>). Dig down 3-4 feet to look for these weak layers and assess their stability before committing to steep slopes.</p>
<p>On wind loaded slopes, the avalanche danger is MODERATE. On non-windloaded slopes, avalanches are unlikely and the avalanche danger is LOW.</p>
<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a>, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
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Stop by the public beacon park at the Bozeman Parks North Recreation Center at Story Mill on Rouse St. It is operational from 8:30 a.m. to 5:00 p.m. 7 days a week. Here’s a fun video outlining how to use the park: https://www.facebook.com/friendsgnfac/videos/279522799401278/
A large snowmobile triggered avalanche in the Gravelly Range (Outside of advisory area) on February 10th, 2019.
From email: "One rider was involved in the incident and was fortunate to be on the upper left side of the bowl when he saw the slide start. ... the crown was about 325 wide and varied in depth from 1 to 4 or 5 feet. The ridge line was wind loaded and this was an issue we had discussed as a group and wanted to avoid. We had read the reports for the day and knew that wind loading as well as a persistent week layer were both concerns. .... The rider involved entered the area from around where the road switchbacked and did not realize what was above him due to reduced visibility."
A large snowmobile triggered avalanche in the Gravelly Range (Outside of advisory area) on February 10th, 2019.
This slide was triggered by a snowmobiler near Daisy Pass last weekend (2/2/19).
This slide was triggered by a snowmobiler near Daisy Pass last weekend (2/2/19).
Riders reported cutting across this slope and then an hour later a different snowmobiler triggered it. It was a couple hundred feet wide and debris stopped just above groomed trail. The rider that triggered it was caught and deployed his airbag and able to escape, but his sled was towed back to town.
