17-18

<p>The northern mountains and Cooke City got a healthy shot of snow out of the latest storm system. The mountains around Bozeman and Big Sky picked up 8-10” of snow totaling .7-1.1” of SWE (snow water equivalent) since Tuesday. A reliable observer around Cooke City said Fisher Creek Snotel site under reported and the upper elevations around that area picked up close to a foot.</p>

<p>Today, fresh snow combined with moderate to strong winds out of the west-northwest will produce touchy wind slabs. Watch for wind loaded slopes below ridgelines, cross loaded gullies and steep convex terrain features (<a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche"><strong>phot…;). Fresh wind slabs will be most prominent in upper elevation terrain, but could also be encountered on mid to low elevation slopes. On Tuesday, I observed blowing and drifting snow on all aspects and elevations in the Bridger Range (<a href="https://youtu.be/HlPWDeqNgZY"><strong>video</strong></a><strong&gt;, </strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-bridger-range">…;). Today, the story is similar to the past few days – avoid wind loaded slopes and you’ll likely avoid avalanches.</p>

<p>Cornices also pose a serious threat. These can break farther back than you might expect along the ridgelines and can trigger avalanches below (<strong><a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche-debri…;).</p>

<p>Today, fresh snow and wind is creating unstable conditions and a <strong>CONSIDERABLE</strong> avalanche danger on all wind loaded slopes. Slopes without a wind-load have a <strong>MODERATE</strong> danger.</p>

<p>A northwest flow has not favored the mountains near West Yellowstone including the southern Madison Range. These areas only picked up a few inches of snow over the past few days, which will limit the size and distribution of fresh wind slabs. With that said, wind loaded slopes are the main concern and still hold the potential to produce avalanches.</p>

<p>Watch for and avoid thick wind drifts near upper elevations ridgelines and cross loaded terrain features. Wind slabs won’t be hair trigger today, but do hold the potential to fail under the weight of a skier or rider. In addition to wind loaded slopes, cornices are a significant problem. Last Saturday, a cornice failed naturally and triggered a large slide in the Lionhead area (<a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche"><str…;). This is great example of the threat that cornices pose, both on and below the ridgelines.</p>

<p>Today, human triggered slides are possible on wind loaded slopes which have a <strong>MODERATE</strong> avalanche danger. Non-wind loaded slopes have a <strong>LOW</strong> avalanche danger.</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>The Bridger Range has 4” of snow and stronger wind than elsewhere. Gusts of 70 mph were recorded at Bridger Bowl yesterday and there were many avalanches on wind-loaded slopes, both naturally occurring (<strong><a href="https://www.mtavalanche.com/images/18/natural-avalanche-bridger-range">…;) and also easily triggered from the ridgelines by the ski patrol. The wind slabs were 1.5’ thick and ran far distances. Eric went into the northern Bridger Range near Fairy Lake and had to notch back his plans when he was confronted with natural avalanches, shooting cracks under his feet, strong winds and active loading (<strong><a href="https://youtu.be/HlPWDeqNgZY">video</a></strong&gt;).</p>

<p>Alex took a big tour in Hyalite yesterday and noted isolated wind slabs were breaking near the ridgelines and some higher elevation gullies. Cornices also recently broke with the wind-loading (<strong><a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche-debri…;, <strong><a href="https://www.mtavalanche.com/images/18/cornice-fall-mt-blackmore">photo2…;) and pose a serious threat. He reported at least 4” of new snow by late afternoon and SNOTEL shows another 4-5” (.4-.5” snow water equivalent) last night, including similar amounts in Big Sky, to West Yellowstone, and Cooke City. Winds are moderate with strong gusts (40 mph) and I expect wind-loaded slopes could be easily triggered in all our ranges today. Recent avalanches outside Cooke City (<strong><a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche">photo</a></s…;) and Lionhead (<strong><a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche">phot…;) illustrate this instability. On slopes without a wind-load the main concern is checking to see if the new snow is sticking to the older snow. A quick stability test in the upper couple feet is a good idea since avalanches are more likely during and immediately after a storm.</p>

<p>As Eric said in his video, “If you avoid wind-loaded slopes you’ll avoid avalanches.” This is true again today. New snow this morning and continued wind is creating unstable conditions and a <strong>CONSIDERABLE</strong> avalanche danger on all wind loaded slopes. Slopes without a wind-load have a <strong>MODERATE</strong> danger.</p>

<h3>WET AVALANCHES</h3>

<p>If the sun comes out today the new snow will wet and avalanche. Most slides will be loose avalanches; not very large, but numerous. Snow conditions and stability change quickly in the spring. Pinwheels and sluffing of the surface snow are classic signs the wet avalanche danger is increasing.</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>Starting yesterday afternoon wind speeds in the northern mountains increased into the 30s and 40s and loaded slopes at all elevations (<strong><a href="https://www.mtavalanche.com/images/18/wind-loading-ridgeline">photo</a>…;). Skiers in <a href="https://www.google.com/maps/d/edit?mid=18gJmy0S6HyEAGjuEHTcI38bRD94&amp… Basin</a> saw avalanche debris from the weekend and wind slabs building in the afternoon. I expect a few natural avalanches on wind-loaded slopes this morning (<a href="https://www.mtavalanche.com/images/18/wind-slab-avalanches-saddle-peak"…;). Cornices are also growing and will be extra touchy. Wind-loaded slopes, found along ridgelines, under cornices, and in low elevation gullies should be avoided since triggering slides is likely. On slopes sheltered from the wind the main avalanche concern will be sun warming the snow surface creating loose avalanches. Alex’s videos from <strong><a href="https://youtu.be/GgZtfI4E2DQ">Beehive Basin</a></strong> (Fri) and <strong><a href="https://youtu.be/ZnWFDXZ444o">Buck Ridge</a></strong> (Sat) explain these concerns. For today the avalanche danger is rated <strong>CONSIDERABLE </strong>on all wind-loaded terrain and <strong>MODERATE</strong> elsewhere.</p>

<p>The southern mountains are less windy than its northern neighbors with west winds blowing 10-25 mph. Wind-loaded slopes, along with touchy cornices, are the main avalanche concern. A snowmobiler saw a large avalanche triggered by a cornice fall near West Yellowstone on Lionhead ridge that broke late Saturday (<strong><a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche">phot…;). Yesterday, south of Cooke City, a skier saw a natural avalanche on a wind-loaded slope in Republic Creek (<strong><a href="https://www.mtavalanche.com/images/18/wind-slab-avalanche">photo</a></s…;). Both are evidence that triggering wind-loaded slopes are possible today given the recent snow and wind. Eric rode into Teepee Basin on Saturday, got stuck, and nonchalantly made a<a href="https://youtu.be/iaHHEql8ZwU"&gt; <strong>video</strong></a> outlining these avalanche concerns, which remain today. Approach wind-loaded slopes cautiously and be extra careful of cornices, both triggering them from the ridgelines and also playing on slopes underneath. Slopes without a wind-load are generally safe, but given the rapidly changing spring conditions, a shot of sun warming the snow surface could create loose snow avalanches. On Sunday, skiers near Cooke City triggered a 16” deep soft slab avalanche which remains possible on other slopes. For today, the avalanche danger is rated <strong>MODERATE</strong> on all slopes.</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>