22-23
Snowpits Lionhead Range
We sledded from Buttermilk to Ski Hill and dug a pit at 8000'. Snow depth was 80 cm, ECTN15 on E aspect–no NSFs or surface hoar at the pit.
While touring up Lionhead Ridge we triggered a whumpf with a noticeable crack on wind pillows at 8500’. At the whumpf snow depth was 83 cm on the NE aspect with ECTP11– failed on a layer of near surface facets.
As the terrain below the ridge (to the east) became steeper, we triggered a loud whumpf at 8600’. At the whumpf snow depth was 105 cm on NE aspect with 2x ECTP11. This was on a well-defined layer of 4mm surface hoar 35 cm from the surface. All ECTPs were on NE aspects with new snow and wind load atop the layer. This layer of near surface facets and surface hoar is our primary concern, and triggering a slide in steeper terrain with this weak layer seemed likely today.
GNFAC Avalanche Forecast for Tue Nov 29, 2022
<p>The mountains of Southwest Montana received 6 to 13” of snow last weekend. Strong winds on Sunday created unstable drifts on many slopes. Skiers in the Bridger and Northern Gallatin Ranges triggered avalanches breaking 6 to 12” deep on wind-loaded slopes, with one failing nearly 100’ wide (<a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>avalanche activity log</span></strong></a>). On Sunday, the Big Sky Ski Patrol triggered avalanches 12-18” deep on similarly loaded slopes within the ski area boundary during their morning work runs. Yesterday, my partner and I found a weak layer of feathery surface hoar and sugary facets buried one foot deep at Lionhead Ridge and triggered five loud “whumphs” on low-angle slopes, a sure sign of instability (<a href="https://www.youtube.com/watch?v=PVQkjFvFnnw&list=PLXu5151nmAvTi1DBS…;). We will assume this layer is widespread until proven otherwise. Slopes with this weak layer will stabilize more slowly than others.</p>
<p>Additionally, on Sunday, the BSSP triggered a large avalanche that broke two and a half feet deep on weak layers near the ground (<a href="https://www.mtavalanche.com/node/26966"><strong><span>details and photos</span></strong></a>). Similar avalanches on <a href="https://www.mtavalanche.com/node/26883"><strong><span>Hyalite Peak</span></strong></a> ten days ago and a natural avalanche <a href="https://www.mtavalanche.com/node/26938"><strong><span>earlier this week at Big Sky</span></strong></a> point to a trend of weaker snow on high-elevation north-facing slopes.</p>
<p>Today, carefully evaluate the snowpack for signs of instability such as “whumphs,” shooting cracks or, the big one, recent avalanches. Dig down and test for instabilities in the upper couple of feet of the snowpack. Remember that we gather this information to turn us around, NOT to prove stability and move us forward. Travel in terrain that avoids steep slopes or minimizes the consequences of mistakes.</p>
<p>Heightened avalanche danger continues as human-triggered avalanches are possible. The avalanche danger is rated MODERATE.</p>
<p>A major storm is set to impact the mountains around West Yellowstone and the southern portions of the advisory area starting tomorrow. The avalanche danger will rapidly increase if this storm comes to fruition. <span> </span></p>
<p><span>If you get out, please share avalanche, snowpack or weather observations via our </span><span><a href="https://www.mtavalanche.com/node/add/snow_obs"><strong><span><span>webs…;, email (</span></span><a href="mailto:mtavalanche@gmail.com"><strong><span>mtavalanche@gmail.com</span…;), phone (406-587-6984), or Instagram (#gnfacobs).</span></span></span></p>
<p>The mountains around Island Park received 13” of snow last weekend, with strong winds on Sunday loading slopes with unstable drifts. Avalanches breaking 6-18” deep on weak layers buried below the recent snow and drifts are possible. Watch yesterday’s <a href="https://www.youtube.com/watch?v=PVQkjFvFnnw&list=PLXu5151nmAvTi1DBS…; from nearby Lionhead Ridge for a further explanation of these conditions.</p>
<p>Carefully evaluate the snowpack for signs of instability such as “whumphs,” shooting cracks or recent avalanches. Dig down and test for instabilities in the upper couple of feet of the snowpack and travel in terrain that avoids steep slopes or minimizes the consequences of mistakes.</p>
<p>A large storm during the second half of the week will rapidly increase the avalanche danger.</p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
Tuesday, November 29, 6 p.m. Sidecountry Avalanche Awareness for Families (and Friends) at Story Mill Park. Free.
Kicking wind slabs on Blackmore Trail
Toured up to the NE shoulder on Mt. Blackmore yesterday. Winds were strong and variable, but mostly gusting from the S-SW. A lot of snow was moving around, skin tracks were filled in very quickly, and you could actively see small cornices starting to build on the lee side of the ridge.
On the descent, I intentionally triggered a small wind pocket in one of the chutes in the cliffs near the trail at 8700 ft. I included a video. It was D1 and about 5 inches deep at the crown. I think just a good reminder that even in the trees, the tops of those chutes get wind loaded and can definitely slide.
Toured up to the NE shoulder on Mt. Blackmore yesterday. Winds were strong and variable, but mostly gusting from the S-SW. A lot of snow was moving around, skin tracks were filled in very quickly, and you could actively see small cornices starting to build on the lee side of the ridge. Photo: H. Darby
On the descent, I intentionally triggered a small wind pocket in one of the chutes in the cliffs near the trail at 8700 ft. I included a video. It was D1 and about 5 inches deep at the crown. I think just a good reminder that even in the trees, the tops of those chutes get wind loaded and can definitely slide. Photo: H. Darby
Forecast link: GNFAC Avalanche Forecast for Fri Dec 2, 2022