This small wind slab was triggered by skiers descending from Imp Peak in the southern Madison Range. Although small, this slide is bull's eye information that larger slides are possible on wind loaded slopes. Photo: S. Knowles
<p>Yesterday’s wind was perfect for moving snow at all elevations and aspects. It loaded snow onto slopes at a fast rate and avalanched both naturally and from skiers. The slides were confined to the new windblown snow, 12-18” thick at its deepest, but enough to bury a person or push them into deadly terrain. We received a few reports, all with pictures, that are detailed on our <strong><a href="https://www.mtavalanche.com/avalanche-activity">avalanche activity</a></strong> page. A recap:</p>
<ul>
<li><!--[if !supportLists]-->Alex made a <strong><a href="https://www.youtube.com/watch?v=bptnYmW5i9s&index=2&t=0s&li… video of wind-loading</a></strong> in the Bridger Range which is worth watching.</li>
<li><!--[if !supportLists]-->Skiers triggered a wind slab in Beehive Basin (<strong><a href="https://www.mtavalanche.com/node/19185">report</a></strong>).</li>
<li><!--[if !supportLists]-->Skiers triggered wind slabs in Maid of the Mist Cirque in Hyalite (<strong><a href="https://www.mtavalanche.com/node/19191">report</a></strong>).</li>
<li><!--[if !supportLists]-->Natural avalanches were seen in Divide Basin in Hyalite (<strong><a href="https://www.mtavalanche.com/node/19180">report</a></strong>).</li>
</ul>
<p>Winds are decreasing but drifting will still occur. There are many wind-loaded slopes and gullies that are ripe to be triggered by a passing skier, sledder or post-holing ice-climber. <em>Extra caution is advised for all ice climbers attending the Bozeman Ice Festival. The steep gullies up Hyalite need to be crossed and ascended with caution. Turn around at the first sign of cracking.</em> For today, the avalanche danger is rated CONSIDERABLE on all wind-loaded slopes and MODERATE on all others.</p>
<p>The Lionhead area has weak snow on the ground (faceted, sugary grains) that is a source of concern. I don’t trust that it will unconditionally support the new snow and wind-loading from the last 7 days. Alex visited last week and found a very weak snow structure (<u><strong><a href="https://youtu.be/hl5lygIF7s4">video</a></strong></u>). For today, the avalanche danger is rated <strong>MODERATE </strong>since it is possible to trigger avalanches, especially near the ridgelines where the snow is deepest.</p>
<p>The southern Madison, southern Gallatin and mountains outside Cooke City received wind-loading yesterday that is the primary concern today. Recently formed wind slabs could be triggered by a skier or snowmobiler. Because the snowpack around Cooke City is generally strong, I do not expect avalanches to break on deeper, older layers.</p>
<p>Eric and I rode into Taylor Fork yesterday and didn’t hit any rocks or get the sleds stuck. We were pleasantly surprised to find 2.5 feet of supportable snow. Our stability test showed a concern at the interface between the old snow (facets and an ice-crust) and newer snow that fell in the last 7 days. His <strong><a href="https://www.youtube.com/watch?v=L8OXT0t4Eak&list=PLXu5151nmAvRNl9ku…; outlines both the snowpack’s strength and weakness. For today the avalanche danger is rated MODERATE on wind-loaded slopes and LOW on all others.</p>
<p>Eric will issue the next advisory tomorrow morning by 7:30 a.m. 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 5, 1-hr Avalanche Awareness, 6-7 p.m. at REI, Bozeman.
December 6, 1-hr Avalanche Awareness and Beacon Practice, 6:30-8 p.m. at Story Mill Park.
From e-mail: "We bailed on plan A ( bigger couloir ) because of the visual signs of rapid wind loading. We proceeded to plan B and started getting shooting cracks on small convex rollers. We found a nice small test slope and remote triggered a decent fresh windslab. It was surprising the energy it ran with. We decided to bail on plan b and head home. Remote triggered another smaller wind slab turning around."
Wind loads were easy to trigger. This one was triggered on purpose up Maid of the Mist in Hyalite. Photo: A. Peterson
Wind slabs were easily triggered. Although small in size, they indicate that larger slopes would have larger avalanches. Photo: A. Peterson
Strong winds on Tuesday (12/4) drifted recent low density snow into thick slabs at ridgelines, and mid to lower elevations in the Bridger Range. Photo: GNFAC
Strong winds on Tuesday (12/4) drifted recent low density snow into thick slabs at ridgelines, and mid to lower elevations. Photo: GNFAC
From e-mail: "We encountered very localized loading that easily fractured and propagated uphill on a south aspect (photos) then bailed on the E/NE facing run we had hoped to ski, due to a 12-18" slab at the top, obvious wind loading throughout the whole thing (9900'-10300'), and the aforementioned obvious signs of instability. When we turned around, another similar-sized (4-8" by 10-20') slide had occurred on the same aspect as the one we had triggered. Neither ran more than 100' or so."
