This photo was taken up Hyalite from Divide Peak. Variable winds both scoured and loaded many slopes at all elevations. In this photo a NW facing slope was scoured to the ground while the lee side was loaded with wind slabs and cornice growth. Photo: G. Antonioli
Winds have been strong and moved snow into drifts at the ridge lines and cross-loaded mid-elevation slopes. A skier saw this natural avalanche get triggered by a falling cornice on the ridge between Beehive and Middle Basins. Photo: S. Casper.
A skier wrote the following email with the picture. The red line marks the crown. Wind-loading was the likely trigger.
<p>In the mountains near Bozeman and Big Sky, strong wind yesterday morning drifted new snow into slabs 2-3 feet thick. Skiers in the Bridger Range and Hyalite easily triggered these wind slabs near ridgelines, on steep rollovers, and along the edges of cliffs (<strong><a href="https://www.mtavalanche.com/images/17/wind-slab-ridge-north-bridger">ph…;). These slabs are possible to trigger today, and large enough to carry or bury a person. Strong wind today will continue to grow wind slabs. Wind was from the northwest yesterday and changed to southwest overnight, so fresh slabs may be found in different locations than yesterday.</p>
<p>On non-wind loaded slopes, dry loose avalanches and storm slabs are possible to trigger and could run far and wide where the underlying snow is weak (<strong><a href="https://youtu.be/7RTIXnPxSDQ">video</a></strong>). These avalanches will likely be small, but could knock a person over or carry them into undesirable terrain.</p>
<p>Be extra cautious of wind loaded terrain today, and assess the consequences of being caught in even a small slide, such as being dragged through trees or over cliffs. Fresh wind slabs and recent snow make avalanches possible, and the avalanche danger today is <strong>MODERATE</strong>.</p>
<p>Near Cooke City and West Yellowstone 3-5” of low density snow fell over the weekend, and a couple inches are expected today. Strong wind will drift this snow into slabs 1-2 feet thick near ridgelines. Be cautious of these drifts, and completely avoid them where the consequences of a small slide could be a nasty ride through trees or over cliffs.</p>
<p>On some slopes, weak facets that formed during recent high pressure are now buried by the new snow (<a href="https://www.mtavalanche.com/images/17/small-faceted-grains"><strong>pho…;). Doug was in Cooke City yesterday and found this sugary weak layer below the new snow on all aspects (<strong><a href="https://www.mtavalanche.com/images/17/weak-facets-are-under-new-snow">p…;, <strong><a href="https://youtu.be/sZxO8CPCcTk">video</a></strong>). This layer is not a major problem at the moment, but will produce avalanches when loaded with more snow or wind slabs.</p>
<p>Today, fresh wind slabs are possible and the avalanche danger is <strong>MODERATE</strong> on wind loaded slopes. On non-wind loaded slopes, avalanches are not likely until more snow falls and the avalanche danger today is <strong>LOW</strong>.</p>
<p>If you get out and have any avalanche or snowpack observations to share, drop a line 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>
BOZEMAN
Dec. 21, Avalanche Awareness, 6-7:30 P.m. at Play It Again Sports, Bozeman
Jan. 12 and 13, Companion Rescue Clinic, Info and Register
Fresh wind slabs 2-3 feet thick were easily triggered near ridgelines in the Bridger and northern Gallatin Range yesterday (12/17). Photo: GNFAC
Riding around Cooke City on all aspects we found a weak layer of near-surface facets buried under the new snow. This layer may persist for a while and with additional weight (new snow or wind-loading) it could avalanche in the coming weeks. This picture shows the top 80 cm of the snowpack. Photo: GNFAC
