GNFAC Avalanche Forecast for Tue Jan 24, 2023
<p>A weak layer of surface hoar buried six inches to two feet deep and drifting snow make human-triggered avalanches possible in the mountains around Big Sky, West Yellowstone and Cooke City. Persistent weak layers within the snowpack are our principal drivers of decision-making today. Yesterday, after thoroughly assessing the hazard presented by a feathery layer of buried surface hoar (<a href="https://www.mtavalanche.com/images/23/surface-hoar-bacon-rind-0"><stron…;), weak snow near the bottom of the snowpack caused us to reconsider our terrain choices at Bacon Rind (<a href="https://youtu.be/AbyeCAAcpGI"><strong><span>video</span></strong></a>). A group of riders near Two Top outside West Yellowstone excluded avalanche terrain from their travel plan after finding three stripes of surface hoar in the upper 20” of their snowpits (<a href="https://www.mtavalanche.com/node/27785"><strong><span>observation</span…;). Skiers in Cooke City recognized the same issue on Henderson Mountain (<a href="https://www.mtavalanche.com/node/27787"><strong><span>observation</span…;). Either thoroughly assess snowpack for instability related to weak layers or take a cue from the riders at Two Top and avoid slopes steeper than 30 degrees altogether (<a href="https://youtu.be/TV7IXE41Skg"><strong><span>Ian’s Hebgen Lake Video</span></strong></a>).</p>
<p>The mountains around Big Sky received up to five inches of snow in the last two days, and winds gusting to 40 mph are drifting this fresh snow into slabs that will avalanche in steep terrain. On Saturday, a skier outside the boundary of Big Sky Resort triggered a wind-loaded slope that broke 150’ wide (<a href="https://www.mtavalanche.com/node/27771"><strong><span>details and photo</span></strong></a>). Even without the new snow, riders north of West Yellowstone reported the formation of isolated drifts (<a href="https://www.mtavalanche.com/node/27789"><strong><span>observation</span…;). Do not underestimate the power of a small avalanche and avoid wind-loaded slopes, especially when terrain traps are present.</p>
<p><span>Today, human-triggered avalanches are possible, and the danger is MODERATE. </span></p>
<p>The mountains near Bozeman received 2-5” of low-density snow in the last two days. Skiers in the Bridger and Northern Madison Ranges reported wind drifts and loose snow avalanches (<a href="https://www.mtavalanche.com/node/27792"><strong><span>observations 1</span></strong></a><strong>, </strong><a href="https://www.mtavalanche.com/node/27786"><strong><span>2</span></strong>…;). Since noon yesterday, winds averaging 15-35 mph are transporting any fresh snow into drifts that can avalanche today. Do not underestimate these slabs of drifted snow, especially in terrain where cliffs, trees or rocks increase the consequences of getting swept down the hillside. Alex, Ian, and I all noted drifting snow as our primary concern in the Bridger Range this weekend (<a href="https://youtu.be/TV4GadWjnaA"><strong><span>Texas Meadows video</span></strong></a>). In larger scale terrain, the concern is correspondingly bigger (<a href="https://www.youtube.com/watch?v=1VdaJ49vISg&list=PLXu5151nmAvTi1DBS… Peak video</span></strong></a>).</p>
<p>New snow has added minimal weight to the snowpack, and avalanches breaking on sugary layers of facets within the snowpack remain unlikely. However, as snow adds up this week, they may “wake up” and produce avalanches.</p>
<p>Watch for instabilities related to new and wind-loaded snow, such as avalanches, cracking or drifts. Avoid slopes where these are present and perform a test to assess weak layers within the snowpack.</p>
<p>The avalanche danger is MODERATE.</p>
<p>Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs"><span> </span></a><a href="https://www.mtavalanche.com/node/add/snow_obs"><strong><span>website</s…;, email (<strong>mtavalanche@gmail.com</strong>), phone (406-587-6984), or Instagram (#gnfacobs). <span><span> </span></span></p>
<p><span>A weak layer of surface hoar buried 1-2 feet deep and drifting snow make human-triggered avalanches possible today. Persistent weak layers are our primary cause for concern and should be the principal driver of your decision-making. Thoroughly assess the snowpack and refrain from entering avalanche terrain if there are signs of instability related to weak layers or wind-drifted snow. Or choose to avoid slopes steeper than 30 degrees altogether.</span></p>
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Loose Snow Avalanches near Blackmore
Skiers near Mt. Blackmore noted easy-to-trigger loose snow avalanches sliding up to 8" deep.
Skiers near Mt Blackmore noted loose snow avalanches with ski cuts. This one slid for about 50 feet on a 34 degree slope. This location did not present any signs of significant wind loading. Photo: E. Schreier
Forecast link: GNFAC Avalanche Forecast for Tue Jan 24, 2023
Loose Snow Avalanches, Alex Lowe basin
From Obs: "Dug on a sheltered N aspect at 9,000 feet below Alex Lowe Peak. Performed an ECT with results of ECTN 12 at 30cm deep and ECTP 21 near the ground.
We also observed widespread sluffing of the new, low-density snow throughout the day and increasing wind transport in the afternoon."
Bacon Rind, Skillet
We toured up to the Skillet today. We dug 7 pits on our way up. We found surface hoar buried 6-10” below the surface in all of our pits. This layer failed (ECTN 11 and 12s), but it did not propagate. At this point we were thinking about skiing the Skillet. We dug a pit at the top of the chute at 8,900’. The buried surface hoar was present in this pit, but it did not fail in the ECT. We had an ECTP 22 in facets 2.5’ below the surface of the snow. Because of this result and the terrain traps in the Skillet, we changed our plan and took a more conservative route down. Looking ahead, the buried surface hoar is the primary concern in this area. When we get more snow on top of this layer, instability will increase.
Alex Lowe basin
Dug on a sheltered N aspect at 9,000 feet below Alex Lowe Peak. Performed an ECT with results of ECTN 12 at 30cm deep and ECTP 21 near the ground.
We also observed widespread sluffing of the new, low-density snow throughout the day, as well as increasing wind transport in the afternoon.
Surface hoar can often be seen as a grey stripe on the wall of your snowpit as was the case at Bacon Rind in the Southern Madison Range on 1/23. Photo: GNFAC