Skiers in Hyalite observed several wind slabs release in addition to this slab collapsing under the weight of a skier. Photo: G. Antonioli
<p>Eric was in Lionhead yesterday and found the snowpack to be wanting. It’s shallow (under 2 feet deep), weak (the bottom half are sugary facets), and unstable on anything wind-loaded (stability tests all propagated). Seeing is believing and his <strong><a href="https://www.youtube.com/watch?v=kqiXL3X2coU&t=0s&list=PLXu5151n…; and <strong><a href="https://www.mtavalanche.com/images/18/poor-snowpack-structure-lionhead-…; illustrate the terrible snowpack structure. Last night’s 4” of snow (.2” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>) and west winds will create dangerous avalanche conditions. Cracking and collapsing of the snowpack as you ride or ski are signs of unstable snow. Avalanches may run on the ground and break wide across the slope. Today the avalanche danger is rated CONSIDERABLE on all wind-loaded slopes and MODERATE on all others.</p>
<p>Yesterday’s 4” of new snow was blown onto many slopes and into gullies. I toured into Mt. Blackmore in Hyalite and was able to watch the wind-loading trigger a couple avalanches off the ridge and on the east face (<strong><a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche-blackmore1">p… 1</a></strong>,<strong> <a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche-blackmore2">p… 2</a></strong>, <strong><a href="https://www.youtube.com/watch?v=eIscuLfDH8c&list=PLXu5151nmAvRNl9ku…;, <strong><a href="https://www.mtavalanche.com/node/19244">report</a></strong>). Nearby, ice climbers reported heavy drifting in the gullies that scared them off. South of Cooke City a skier triggered a small (6” x 20’) wind slab (<strong><a href="https://www.mtavalanche.com/node/19250">report</a></strong>) and ski patrols reported touchy wind slabs that did not propagate far.</p>
<p>The wind will be strong today, but without new snow there is not much left to blow around. Slopes with a wind-load should be approached cautiously. I did not venture onto anything steep and wind-loaded yesterday, nor would I today. Rethink your travel plans if you get shooting cracks or collapsing. For today, the avalanche danger is rated MODERATE on all wind-loaded terrain since avalanches are possible. On slopes without a wind-load, the danger is LOW.</p>
<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
BOZEMAN
TONIGHT! December 12, 1-hr Avalanche Awareness for Snowmobilers, 6-7 p.m. at Yellowstone Motorsports, Bozeman.
December 13, 1-hr Avalanche Awareness, 7-8 p.m. at Play It Again Sports, Bozeman.
From an email:
The Lionhead area near West Yellowstone has the shallowest and weakest snowpack in our forecast region. The bottom half of the pack consists of weak, sugary facets. This well developed weak layer produced unstable results in stability tests on any slope that had wind drifted snow. With more snow and wind in the forecast, this area will experience increasingly unstable conditions. Photo GNFAC
Two obvious avalanches released naturally in the late morning while we were in the bowl. Upwards of 8" of new snow fell with winds gusting 30-40 mph from the west.
This avalanche originated from the ridgetop and ran down the east face of Mt Blackmore. Winds were loading slopes quickly. This avalanche occurred in the morning right after we arrived in the bowl. Photo: G. Antonioli
