22-23

<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&amp;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>&nbsp;</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&amp;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>