21-22
Upper portion of the fatal avalanche on Scotch Bonnet. 12/28/21
Photo: GNFAC
Crown of the fatal avalanche on Scotch Bonnet. 12/28/21.
Photo: GNFAC
GNFAC Forecasters Ian Hoyer and Doug Chabot at the crown of the fatal avalanche on Scotch Bonnet. 12/28/21
Photo: GNFAC
GNFAC Avalanche Forecast for Wed Dec 29, 2021
<p>In the last 7 days Cooke City and the southern ranges, including West Yellowstone, have gotten 4 feet of snow and wind making unstable conditions on wind-loaded slopes. The avalanche on Scotch Bonnet outside Cooke City could have occurred in any of the southern ranges since the snow structure and instability are similar. Snow was blown and packed into dense drifts that are poorly supported by weak, sugary facets 12-18” off the ground. Ian and I found this combination at the crown of the avalanche (<a href="http://www.mtavalanche.com/images/21/ian-crown-avalanche-killed-2-snowm…;). In the last 48-hours skiers saw a slide on Henderson Bench (<a href="http://www.mtavalanche.com/images/21/natural-slide-henderson-wind-loade…;) and riders triggered two small avalanches on Mt Abundance (<a href="http://www.mtavalanche.com/images/21/human-triggered-avalanche-mount-ab…;). </p>
<p>Our recent field investigations in Lionhead (<a href="https://www.youtube.com/watch?v=qumV6n73pTs&list=PLXu5151nmAvT1nrM2…;) and Taylor Fork (<a href="https://www.youtube.com/watch?v=rdVk9B7UbtQ&list=PLXu5151nmAvT1nrM2…;) illustrate the likelihood of triggering slides on wind-loaded terrain. It is best to avoid these slopes. They will be found near ridgelines, above treeline and in gullies. The wind is still loading slopes and it is likely a skier or rider could trigger a large avalanche. For today, the danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.</p>
<p>The mountains around Bozeman and Big Sky have gotten snow over the last 5 days: 12+” in the Bridgers, a foot in Hyalite and 6-8” in Big Sky. Skiing and riding has improved and folks are sending us observations. The snowpack is generally stable, but like most things in life there’s an exception: wind-loaded slopes could avalanche. These will not be deep or widespread, but triggering them is a possibility. Evidence of wind-loading are cornices, smooth pillows of dense snow and shooting cracks, a bullseye sign of instability. </p>
<p>With a trend toward stability signs of danger may not be prominent (avalanche activity, whumphing, etc). Weak, faceted snow near the ground is widespread and should be looked at and tested before diving into avalanche terrain. We must hunt for instability because it’s much better to be the hunter than the hunted. We do not like surprises which is why we dig. Our field videos last week should be a starting point for your stability assessment: <a href="https://www.youtube.com/watch?v=_MhpDHnH8So"><strong><u>Saddle Peak</u></strong></a>, <a href="https://youtu.be/cf-qqv2Ssjw"><strong><u>Buck Ridge</u></strong></a> and <a href="https://youtu.be/ePMCJs3qAs0"><strong><u>Beehive Basin</u></strong></a>. For today, it remains possible to trigger slides on wind-loaded slopes which have a MODERATE danger. On all other slopes avalanches are unlikely and the danger is rated LOW. </p>
<p>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><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Upcoming Education Opportunities:
Get your avalanche brain ready for the season at one of the many classes listed on our education calendar, and list of upcoming events below.
Every Saturday near Cooke City, 10 a.m.-3 p.m. FREE snowpack update and transceiver/rescue training. Stop by for 20 minutes or more at the Round Lake Warming Hut.
Snowmobiled up to 9000ft, skinned up West face of Comet to 10K ft and skied low angle trees back to sled. Heavy windload with cross loading common on this slope. Dug a pit at 9200 ft, W aspect, 28 degree slope. Height of snow was 110 cm, about 3 and a half feet deep. Photo shows hand hardness profile in snowpit with faceted weak layers of concern in mid and lower snowpack. Extended column test had propagation on 18 (ECTP 18) on large facets (see photo) around a crust about 40 cm up from ground. No cracking or collapsing observed on tour.