20-21

<p>New snow favored the Bridger Range and Hyalite with 3-4” equal to 0.3-0.5” of snow water equivalent (SWE). Moderate west wind drifted this snow into fresh slabs which add weight to an unstable snowpack and create dangerous avalanche conditions. Weak, sugary snow that formed during recent months of cold, dry weather is buried 2-3 feet deep (<a href="https://www.mtavalanche.com/images/21/giant-depth-hoar-throne"><strong>… of crystals</strong></a>),&nbsp;produced large avalanches during the last couple weeks, and is not getting stronger (<strong><a href="https://www.mtavalanche.com/node/23678">Large skier triggered slide in Hyalite</a></strong>, <strong><a href="https://www.mtavalanche.com/node/23771">natural avalanches in Bridgers</a></strong>). In addition to avalanches breaking deep and wide on sugary weak layers, you can also trigger fresh drifts along ridgelines. Although relatively smaller, these wind slabs can be harmful, especially in terrain with higher consequences.&nbsp;They could also trigger deeper avalanches. Today the avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on non-wind loaded slopes.</p>

<p>In the Madison Range, southern Gallatin Range and Lionhead area near West Yellowstone we have documented many recent avalanches and signs of instability on sugary weak layers buried 2-3 feet deep (<strong><a href="https://www.mtavalanche.com/avalanche-activity">avalanche log</a></strong>, <strong><u><a href="https://youtu.be/Feyz2_4aNmU">video from Lionhead</a></u></strong>, <strong><u><a href="https://youtu.be/XzPIY1Q1cKo">video from Bacon Rind</a></u></strong>, <strong><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQDzKmH5K3ZS8Gg3DzwsZ3… videos</a></strong>). The mountains also now have a layer of feathery surface hoar buried 6-12” deep, below snow that fell Tuesday-Wednesday. It is worth digging to see if this layer exists prior to traveling on steep slopes, and to test if it will be a problem with more snow. On Thursday, Dave was in Taylor Fork and documented 10 avalanches which broke under the new snow (<a href="https://youtu.be/ZKzc9qpSNhs"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/node/23795"><strong>details and photos</strong></a>). Today&nbsp;two buried weak layers make avalanches possible to trigger. Careful snowpack evaluation and cautious route finding are essential. The avalanche danger is rated MODERATE.</p>

<p>In the mountains near Cooke City, sustained strong wind earlier this week stripped slopes of new snow and piled thick drifts on other slopes. Natural avalanches were triggered during this loading event (<strong><a href="https://www.mtavalanche.com/node/23788">photo and details</a></strong>, <strong><a href="https://www.mtavalanche.com/images/21/natural-avalanche-south-cooke">ph…;). These and skier triggered avalanches last week (<strong><a href="https://www.mtavalanche.com/node/23644">Fin avalanche</a></strong>, <strong><a href="https://www.mtavalanche.com/node/23731">ski-cut north of Cooke</a></strong>) are good reminders that some slopes have unstable buried weak layers. Our main concern is a layer of sugary facets buried 2-3’ deep. Now in addition, the recent snowfall buried a weak layer of surface hoar (<a href="https://www.mtavalanche.com/images/21/surface-hoar-henderson-bench"><st…;) that may avalanche with the next few storms. Skiers got this layer to break clean in their stability test on Thursday. These layers are not on all slopes, so it is a good idea to dig to look for them before riding steep slopes, and to track their location as they could avalanche with the next round of snow. Today, buried weak layers make avalanches possible to trigger and avalanche danger is MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

<p>On Wednesday the mountains got blasted by strong wind and snowfall which resulted in many natural avalanches throughout southwest Montana (8 entries in our <a href="https://www.mtavalanche.com/avalanche-activity"><strong><u>Avalanche Activity Log</u></strong></a>). No mountain range escaped the wind: stripping the snow to dirt on some slopes (<a href="https://www.mtavalanche.com/images/21/wind-stripped-slope-taylor-fork">…;) and making dense wind drifts on others. Surprisingly these drifts have bonded well and are not cracking or sliding. Dave was in Taylor Fork yesterday and documented 10 avalanches, most small-sized and breaking under the new snow (<a href="https://youtu.be/ZKzc9qpSNhs"><strong><u>video</u></strong></a&gt;, <a href="https://www.mtavalanche.com/node/23795"><strong><u>details and photos</u></strong></a>).&nbsp;</p>

<p>On Tuesday, a layer of feathery <a href="https://avalanche.org/avalanche-encyclopedia/surface-hoar/"><strong><u>… hoar</u></strong></a> crystals got buried and preserved. It might have been the weak layer under the new snow in the Taylor Fork avalanches. Regardless, we know it is in all ranges but not on all slopes. It is shallowly buried and easy to look for.&nbsp;</p>

<p>Other avalanches involve depth hoar, the large, weak, sugary grains at the ground (<a href="https://www.mtavalanche.com/images/21/giant-depth-hoar-throne"><strong>… of crystals</u></strong></a>). We have recorded these in almost all of our snowpits and videos. I investigated slides on this layer in Lionhead (<a href="https://youtu.be/Feyz2_4aNmU"><strong><u>video</u></strong></a&gt;), while others saw cracking, collapsing and/or avalanche activity in the <a href="https://www.mtavalanche.com/node/23789"><strong><u>S. Gallatin</u></strong></a>, <a href="https://www.mtavalanche.com/node/23770"><strong><u>Madison</u></strong>…; and <a href="https://www.mtavalanche.com/node/23771"><strong><u>Bridger Ranges</u></strong></a> on it. Dave and his partner backed off skiing avalanche terrain in Bacon Rind on Tuesday (<a href="https://youtu.be/XzPIY1Q1cKo"><strong><u>video</u></strong></a&gt;) after finding this persistent weak layer.&nbsp;</p>

<p>There are now 2 layers in the snowpack to investigate: surface hoar near the top and depth hoar at the bottom. Follow our advice and dig, test and be conservative like Dave was in Bacon Rind. There have been many recent avalanches and triggering more is very possible. For today the avalanche danger is rated MODERATE on all slopes.</p>

<p>On Wednesday, the mountains outside Cooke City got blustery wind, snowfall, and avalanche activity up Hayden Creek (<a href="https://www.mtavalanche.com/images/21/natural-avalanche-south-cooke"><s…;) and off the highway (<a href="https://www.mtavalanche.com/node/23788"><strong><u>photos</u></strong><…;). Wind drifted snow was not reactive yesterday, which is good news. However, the snowfall buried a new weak layer of feathery surface hoar (<a href="https://www.mtavalanche.com/images/21/surface-hoar-henderson-bench"><st…;) that has our full attention because it may avalanche with the next few snowstorms. Yesterday, skiers got it to break clean in their stability test. Additionally, sprinkled throughout Cooke City is a layer of weak snow buried 2-3 feet deep that is responsible for recent avalanches. We are not done looking for this layer or trusting it. Two weak layers sporadically distributed makes stability assessment complicated. Digging and searching for these weak layers is the most prudent thing to do. Skipping this step leaves you with only one viable option: avoiding avalanche terrain. For today, triggering avalanches is possible on one of these layers which points to a MODERATE avalanche danger.&nbsp;</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>