18-19

<p>Over the past two days, the Lionhead area near West Yellowstone picked up to 7-8” of snow totaling .7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;. The southern Madison and Gallatin Ranges were less favored, but still received 5-6” of snow totaling .5” of SWE. The snowpack in the southern ranges resembles a house of cards, which will be pushed close to its breaking point today (<u><strong><a href="https://www.youtube.com/watch?v=3Y_F3uaJKvI&amp;t=0s&amp;list=PLXu5151n…;

<p>A layer of surface hoar buried up to a foot deep and/or facets near the ground are both capable of producing avalanches (<u><strong><a href="https://www.mtavalanche.com/images/19/surface-hoar-teepee-basin">photo<…;). A large slide triggered by skiers in the southern Madison Range on Monday&nbsp;is a good example of what’s possible today. This slide occurred on a wind loaded slope, broke 2-3’ deep, 400’ wide and failed on facets near the ground (<u><strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-near-taylor-fork"…;, <u><strong><a href="https://www.mtavalanche.com/node/19716">details</a></strong></u&gt;). Today, all steep slopes, wind loaded or not are capable of producing avalanches. The best defense against a persistent weak layer problem is to avoid riding on or underneath slopes steeper than 35 degrees (<strong><a href="https://www.mtavalanche.com/images/19/snomobiler-triggered-skyline">pho…;).</p>

<p>Today, dangerous avalanche conditions exist and the avalanche danger is rated <strong>CONSIDERABLE</strong>.&nbsp;</p>

<p>The mountains near Cooke City squeezed out 6-7” of snow totaling .7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…; over the past two days. Normally, this would be a small to medium sized storm for Cooke City, but this year is different. Below average snowfall has left the snowpack shallow and weak on many slopes. The new snow will be adding stress to weak layers buried mid pack and near the ground. Slopes that have wind drifted snow and areas where the snowpack is less than 3’ deep will be the most unstable. Due to the high variability of the snowpack around Cooke City, it’s necessary to evaluate each slope carefully before committing to avalanche terrain.</p>

<p>Signs of instability such as cracking and collapsing or recent avalanches are Mother Nature’s bull horn alerting you to unstable conditions. Today, a snowpack under stress makes human triggered avalanches likely and the avalanche danger is rated <strong>CONSIDERABLE</strong>. &nbsp;&nbsp;&nbsp;</p>

<p>Someone burned a good pair of skis last night and got Ullr’s attention. Since midnight, the Bridger Range received 4-5” of new snow totaling .5” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;. The mountains around Big Sky picked up 4-6” since yesterday morning. New snow combined with west-northwest winds will create a touchy batch of wind slabs up to a foot thick. Fresh wind slabs will be most prevalent on upper elevation slopes loaded by west-northwest winds. Most slides will stay confined to the new snow, but there is the potential for slides to step down to weak layers buried deeper in the pack. Watch out for this problem on slopes with a weak and shallow snowpack (<u><strong><a href="https://www.youtube.com/watch?v=Ryd8fZKwVmo&amp;t=0s&amp;list=PLXu5151n…;, <u><strong><a href="https://www.youtube.com/watch?v=VnA2ZhT8vzY&amp;t=0s&amp;list=PLXu5151n…;, <u><strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-avalanche-mc…;).</p>

<p>Skiers or riders may also trigger dry loose avalanches or sluffs on steep slopes. This problem won’t create a significant hazard, but will be something to watch out for in steep terrain. &nbsp;</p>

<p>Today, human triggered avalanche are possible and the avalanche danger is rated&nbsp;<strong>MODERATE.&nbsp;</strong>&nbsp; &nbsp;</p>

<p>The mountains south of Big Sky to West Yellowstone have received 2-4” of snow in the last 36 hours. The snowpack here is weak and consists mostly of sugary facets. You do not need to dig a snowpit to find them, just step off your skis or sled and you’ll sink knee deep to the ground in them. On slopes where this layer is capped by a slab of cohesive snow, avalanches are still possible. In Taylor Fork, both skiers (<u><strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-near-taylor-fork"…;, <u><strong><a href="https://www.mtavalanche.com/node/19716">details</a></strong></u&gt;) and sledders (<u><strong><a href="https://www.mtavalanche.com/images/19/snomobiler-triggered-skyline">pho…;, <u><strong><a href="https://www.mtavalanche.com/node/19715">details</a></strong></u&gt;) triggered 2-3 foot deep avalanches on Sunday and Monday when wind slabs broke on these facets. I visited on Tuesday and found this same poor snow structure in my snowpits (<u><strong><a href="https://www.youtube.com/watch?v=3Y_F3uaJKvI&amp;t=0s&amp;list=PLXu5151n…;

<p>The new snow may not have added much weight to the snowpack, but it did bury a new weak layer of surface hoar. In Teepee Basin sledders found these feathery crystals on many slopes (<strong><a href="https://www.mtavalanche.com/images/19/surface-hoar-teepee-basin">photo<…;). In Taylor Fork the winds scoured high elevation slopes (<strong><a href="https://www.mtavalanche.com/images/19/sage-peak-wind-scoured">photo</a>…;), but I’m sure the surface hoar survived in some areas. We’ll be looking for it and tracking its locations since it may become a problem. For today, the avalanche danger is rated MODERATE.</p>

<p>The northern mountains and Cooke City area have slopes that are weak, but stable. Snowpacks less than 3 feet deep consist of weak facets, as Eric found north of Big Sky on Saturday (<u><strong><a href="https://www.youtube.com/watch?v=Ryd8fZKwVmo&amp;t=0s&amp;list=PLXu5151n…;) and Ian and Alex saw on Buck Ridge on Friday (<u><strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-avalanche-mc…;, <u><strong><a href="https://www.youtube.com/watch?v=VnA2ZhT8vzY&amp;t=0s&amp;list=PLXu5151n…;). Yet overall, it is difficult to trigger avalanches and these mountains are <em>mostly stable</em>. Until we get a substantial amount of new snow, triggering slides is unlikely. The words “<em>mostly stable</em>” are a qualifier since there is still lingering potential to trigger an avalanche. Skiers in Hyalite got a wind slab to break clean in a stability test and another group found a small wind slab had cracked. These signs of instability are isolated and small, similar to an avalanche a person may trigger. These conditions remind me of accidents when climbers or skiers have been swept off their feet by tiny slides (<strong><a href="https://www.mtavalanche.com/accident/15/04/15">Beehive Peak, 2015</a></strong>).</p>

<p>Eric toured into Frazier Basin in the northern Bridger Range yesterday and found stable snow and wind stripped terrain (<strong><a href="https://www.mtavalanche.com/images/19/low-tide-and-low-danger-northern-…;, <strong><a href="https://www.youtube.com/watch?v=rO33kOEG51g&amp;t=0s&amp;list=PLXu5151n…;). He also cautioned us to be on the lookout for instability. For today, avalanches are unlikely, but not impossible, and the danger is rated LOW.</p>

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