17-18

<p>Spring weather can be highly variable and create a mix of avalanche problems to watch out for. Snow conditions and stability can change drastically from day to day or hour to hour. Anticipate rapid change and plan accordingly. Abundant snowfall over the winter (<strong><a href="https://www.mtavalanche.com/images/18/swe-snotel-sites-gnfac-area">grap…;) with more spring snow to come will make avalanches possible well into summer.</p>

<p><u>NEW SNOW AND WIND LOADED SLOPES</u></p>

<p>Spring storms are notorious for depositing heavy amounts of snow in the mountains. Even with a deep and generally stable snowpack throughout the advisory area, heavy and rapid loads of new snow will decrease stability. The main problems to look out for are avalanches breaking within the new snow, wind slabs, and loose snow avalanches. The likelihood of triggering an avalanche spikes during and immediately after snowstorms. New snow instabilities tend to stabilize quickly, but it’s a good idea to give new snow a day to adjust before hitting big terrain. New snow instabilities can be difficult to assess, and spring storms bond to old snow differently across aspects and elevations. Conservative terrain selection is essential during and immediately following storms. Wind loaded slopes and slopes steeper than 35 degrees should be avoided for 24-48 hours after new snow and wind.</p>

<p>New snow can quickly change from dry to wet on a spring day, and stability can decrease rapidly with above freezing temperatures or brief sunshine. New snow may bond well early in the morning, and then easily slide later. Wet loose slides are likely during the first above freezing temperatures or sunshine immediately after a storm. Anticipate changes in snow stability as you change aspect or elevation, and over the course of the day. An early start is always an advantage. Be ready to change plans or move to safer terrain at the first signs of decreasing stability.</p>

<p><u>WET SNOW AVALANCHES</u></p>

<p>Spring and wet snow avalanches go hand-in-hand. Above freezing temperatures, rain, and/or intense sunshine cause the snow to become wet and weak, and make wet avalanches easy to trigger or release naturally. Conditions tend to become most unstable when temperatures stay above freezing for multiple days and nights in a row. Avoid steep terrain, and be aware of potential for natural wet avalanches in steep terrain above you, if you see:</p>

<ul>
<li>Heavy rain,</li>
<li>Above freezing temperatures for more than 24 hours,</li>
<li>Natural wet avalanches,</li>
<li>Roller balls or pin wheels indicating a moist or wet snow surface,</li>
<li>Or if you sink to your boot top in wet snow.</li>
</ul>

<p>In general, if the snow surface freezes solid overnight, the snowpack will be stable in the morning and stability will decrease through the day as snow warms up. The snow surface hardness, rate of warming, duration of sunshine, aspect and elevation determine how fast stability will decrease through the day. Be aware that sunny aspects may have a wet snow avalanche danger while shadier slopes still have a dry snow avalanche danger. Getting off of steep slopes should be considered when, or before, the above signs of instability&nbsp;are present. Wet snow avalanches, whether loose snow or slabs, can be powerful, destructive and very dangerous. Conservative terrain choices, starting early in the day, and careful observations can keep you safe. See Eric’s recent <strong><a href="https://youtu.be/Bm9pfuscLMU">video</a>,</strong&gt; and this <a href="https://www.mtavalanche.com/blog/transitions-spring-snow-avalanche-prob…; for more spring travel advice.</p>

<p><u>CORNICES</u></p>

<p>Cornices along ridgelines are massive and can break under the weight of a person (<a href="https://www.mtavalanche.com/images/18/behemouth-cornices"><strong>photo…;). Prolonged above freezing temperatures and rain make them weaker and possible to break naturally. They can break off suddenly and farther back than one might expect. Cornice falls can also entrain large amounts of loose snow or trigger slab avalanches. Stay far back from the edge of ridgelines and minimize exposure to slopes directly below cornices. Regardless of whether a cornice triggers a slide or not, a falling cornice is dangerous to anyone in its path.</p>

<p><u>DISCLAIMER</u></p>

<p>It does not matter if new snow falls or not, avalanches will continue to occur until the existing snowpack is mostly gone. Always assess the slope you plan to ride with diligence and safety in mind. Do not let your guard down. Travel with a partner, carry rescue gear and only expose one person at a time in avalanche terrain.</p>

<p>Have a safe and enjoyable spring and summer!</p>

<p>Doug, Eric, and Alex</p>

<h3><strong>Share your observations with us on Instagram! #gnfacobs</strong></h3>

<p>Posting your snowpack and avalanche observations on Instagram (#gnfacobs) is a great way to share avalanche and weather information with us and everyone else this spring.</p>

<p>You can also drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt; or email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;) and we will share pertinent avalanche, weather and snowpack info as timely as possible.</p>

<p>A fast, wet storm last night blanketed the advisory area with 3-4” of snow equal to .4-.6” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). This storm began as rain and quickly changed to snow. The snowpack is 8-12 feet deep and generally stable below the recent snow, and deeper avalanches are not likely. Today, dry or wet loose avalanches of new snow are possible, and fresh wind slabs could be easy to trigger.</p>

<p>Above freezing temperatures yesterday, and brief sunshine in some locations, created a wet snow surface that probably froze as the storm moved in last night. Today’s new snow may slide easily on the firm, old snow surface. Assess how new snow bonds to old snow on small test slopes before riding in bigger terrain. Anticipate wet loose avalanches if temperatures get above freezing or if the sun shines.</p>

<p>Moderate westerly wind drifted the new snow into slabs 6-12” thick. These slabs are mostly confined to ridgelines, but could be easy to trigger. Avoid steep, wind loaded slopes if you see cracking of fresh drifts on test slopes or lower angle terrain. Even small slides are extremely hazardous in more consequential terrain. Evaluate snow and terrain carefully today. Avoid freshly wind loaded slopes, and avoid steep slopes if new snow easily slides.</p>

<p>New snow and moderate wind make fresh wind slabs likely and loose snow avalanches possible today. Avalanche danger is rated <strong>CONSIDERABLE</strong> on wind loaded slopes and <strong>MODERATE</strong> on non-wind loaded slopes.</p>

<p>The mountains got 2-3 feet of snow over the last week. Though not likely, avalanches can break within this recent snow where the snow was less affected by above freezing temperatures yesterday (e.g., higher elevation, shady slopes). On Thursday, Eric and his partner remotely triggered an avalanche on the Throne in the northern Bridger Range. It broke above an ice crust 18-20” deep, 200’ wide and ran 5-600’ vertical (<a href="https://youtu.be/Ge8XVqQb5Os"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/images/18/remotely-triggered-slide-northern…;). Dig a couple feet to assess the recent snow before committing to steeper terrain.</p>

<p>If you get out and have any avalanche or snowpack observations to share, drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt;, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

<p>Recent heavy snowfall and today’s forecast for wind, rain, and above freezing temperatures make various types of avalanches possible. Anticipate changing conditions and plan accordingly. Conservative route choices are recommended today.</p>

<p><u>WET AVALANCHES</u></p>

<p>Above freezing temperatures and rain this afternoon will decrease the strength of the snowpack and make wet snow avalanches possible. Small precipitation amounts are expected, but enough rain is possible for recent snow to become wet and non-cohesive. Mostly cloudy skies this morning will delay the onset of wet snow hazard, but any sunshine will decrease stability. Wet snow avalanches could entrain large amounts of snow and travel far distances. Avoid steep terrain and be aware of avalanche terrain above you if you see: Heavy rain, natural wet avalanches, roller balls or pin wheels indicating a moist or wet snow surface, sinking to your boot top in wet snow.</p>

<p><u>RECENT NEW SNOW AND WIND LOADED SLOPES</u></p>

<p>Avalanches breaking 1-2’ deep in the recent snow are possible to trigger. The mountains got 1-2 feet of snow on Wednesday and Thursday equal to 1-2” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). On Thursday, Eric and his partner remotely triggered an avalanche on the Throne in the northern Bridger Range. It broke above an ice crust 18-20” deep, 200’ wide and ran 5-600’ vertical (<a href="https://youtu.be/Ge8XVqQb5Os"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/images/18/remotely-triggered-slide-northern…;). They were surprised after not seeing any red flags and getting stable results in stability tests.The snowpack lacks buried weak layers and deeper avalanches are unlikely. Dig a couple feet and test the new snow to see how it is bonding to the old surface. If the new snow is sitting on an ice crust it may slide more easily. Fresh drifts near ridgelines from moderate south-west wind today are possible to trigger. Slopes loaded from various wind directions yesterday have drifts that are less reactive today, but still deserve caution. Carefully assess terrain and snowpack today, and be cautious of wind loaded slopes.</p>

<p><u>CORNICES</u></p>

<p>Cornices along ridgelines are massive and can break under the weight of a person (<a href="https://www.mtavalanche.com/images/18/behemouth-cornices"><strong>photo…;). Warm temperatures and rain today will make them weaker and possible to break naturally, as Doug discussed in his <a href="https://www.youtube.com/watch?v=QNEryYa2nKI"><strong>video</strong></a>…; </strong>from Wednesday in the Taylor Fork. Stay far back from the edge of ridgelines and minimize exposure to slopes directly below cornices.</p>

<p>A mix&nbsp;of spring weather today makes various avalanche types possible and avalanche danger is <strong>MODERATE</strong>.</p>

<p>If you get out and have any avalanche or snowpack observations to share, drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt;, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

<p>It has snowed every day for the last 10 in the Bridger Range with the last 48 hours getting 15” of dense snow (15%) measuring 2.1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>. Eric visited <a href="///H:/ADVISORIES/Throne%20in%20the%20Bridger%20Range">the Throne</a> in the Bridger Range, north of the ski area and said, “It’s important to remember that rapid and heavy loads create unstable conditions no matter how strong the snowpack.” He should know, because he unexpectedly triggered a large avalanche from 30’ away, aka “remote trigger”. It failed on an ice crust on a SE facing slope. It broke 18-20” deep and ran 200’ wide and 5-600’ vertical distance. It surprised him. He and his partner saw no signs of instability in his snowpit tests nor any other red flags as they skied. Although rare, this happens, which is why we travel one a time, go with partners and carry rescue gear. Sometimes we assess incorrectly and our safety protocols are the only thing separating a good story from a tragedy. Here is his <strong><a href="https://youtu.be/Ge8XVqQb5Os">video</a></strong&gt; and a <strong><a href="https://www.mtavalanche.com/images/18/remotely-triggered-slide-northern…; from the slide.</p>

<p>Instabilities will likely remain in the new snow, especially if it is snow is piled on top of an ice crust.</p>

<ul>
<li>Recent snow? Yup.</li>
<li>Winds? Yup.</li>
<li>Avalanches? Yup.</li>
</ul>

<p>New snow, strong winds at all elevations and directions, and recent avalanches point to a <strong>CONSIDERABLE</strong> avalanche danger on all slopes today.</p>

<p>In the last 48 hours 6-11” of snow has fallen from Bozeman to West Yellowstone and Cooke City roughly amounting to 1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>. Winds are blowing moderate out of the W-SW, loading slopes and creating instability. This new, windblown snow is our main avalanche concern. I rode into Carrot Basin on Wednesday and found wind-loaded slopes and cornices had my attention (<a href="https://www.youtube.com/watch?v=QNEryYa2nKI"><strong>video</strong></a>…;, </strong><a href="https://www.mtavalanche.com/images/18/behemouth-cornices"><strong>photo…;). The snowpack lacks buried weak layers and deep avalanches are unlikely, but as Eric found out yesterday sometimes the snowpack can surprise us. I recommend avoiding wind-loaded terrain. Today, winds will shift easterly and wind-loading patterns will shift with it. Dig a couple feet deep and test the new snow to see how it is bonding to the old surface. If the new snow is sitting on an ice crust its ability to slide may be enhanced. For today, the avalanche danger is rated <strong>CONSIDERABLE</strong> on all wind-loaded slopes and <strong>MODERATE</strong> on slopes without a wind-load.</p>

<p>If you get out and have any avalanche or snowpack observations to share, drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt;, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>