We found unstable stability test scores (ECTP 11) in this pit. And this drift collapsed with an audible "whumph" and cracks 30 feet wide. A buried layer of surface hoar and facets collapsed under a hard slab that formed from strong winds last night. Photo: GNFAC
Crack in a drift that collapsed 30 feet wide, accompanied by an audible "whumph", as we skinned over it. 12/15/18 West side of Bridger Range. Recent strong winds formed hard slabs over weak surface hoar and facets. Photo: GNFAC
This drift collapsed and cracked 30 feet wide, accompanied by an audible "whumph", as we skinned over it. 12/15/18 West side of Bridger Range. Recent strong winds formed hard slabs over weak surface hoar and facets. Photo: GNFAC
A skier in Hyalite observed several day-old wind slab avalanche near the top of Flanders, and noted "small rolls above the glade and up to ridgeline were still cracking under the weight of a skier." Another reminder that recently wind-loaded pockets are reactive throughout the advisory area. Photo: G. Antonioli
Big Sky Ski Patrol saw two natural wind slab avalanches during control this morning that had released after being loaded by strong winds last night. From BSSP: "We observed the evidence of 2 small naturals this am in the upper cirque where the strong winds had managed to deposit some snow very low below cliff bands. We did not see this loading pattern anywhere else on the hill." Photo: BSSP
This wind slab failed as a snowbiker rode by on the road immediately below the road cut. While this slope was not particularly dangerous, these isolated wind slabs can pose a serious threat in the wrong terrain. Photo: C. Matthees
This wind slab failed as a snowbiker rode by on the road immediately below the road cut. While this slope was not particularly dangerous, this is a good indicator of heavier loading on larger slopes up high. Photo: C. Matthees
<p>The snowpack situation in Lionhead is different than all other areas. A persistent weak layer of sugary facets makes up the foundation of the pack here (<u><strong><a href="https://www.youtube.com/watch?v=kqiXL3X2coU&t=0s&list=PLXu5151n…;, <u><strong><a href="https://www.mtavalanche.com/images/18/poor-snowpack-structure-lionhead-…;). This problematic layer is slow to gain strength – as a result will become a major problem once more snow falls. For now, it’s only a problem on slopes that are wind loaded.</p>
<p>In these wind loaded areas, the recipe for an avalanche exists. Be extra cautious on any slope where a cohesive slab of wind drifted snow rests over weak facets near the ground. Slopes loaded by west-southwest winds will be most prone to unstable conditions, but be aware that swirling winds have formed slabs on all aspects. </p>
<p>Today, human triggered avalanches 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><strong>PRIMARY PROBLEM: </strong>Persistent weak-layer</p>
<p>Over the past few day’s strong winds have hammered slopes on all aspects and elevations. There’s still soft snow to be found in protected areas, but fresh lines are rapidly disappearing and conditions are becoming adventurous in the backcountry. Yesterday, skiers up Flanders in Hyalite found generally “obnoxious” conditions with lots of breakable crust. Skiers north of Bridger Bowl also found wind affected snow and triggered a small wind slab near the ridgeline (<strong><a href="https://www.mtavalanche.com/images/18/small-wind-slab-bridger-range">ph…;).</p>
<p>Today, wind loading remains the primary avalanche concern. There’s not much snow available for transport, but strong winds continue to form slabs in isolated areas. These slabs will be firm and stubborn, but could still fracture under the weight of a skier or rider. Be especially cognizant of wind drifted snow near ridgelines, cross-loaded gullies and rock bands.</p>
<p>In some areas wind slabs rest over a layer of small grained facets or surface hoar that formed early December. I found this layer in the northern Bridgers on Thursday (<u><strong><a href="https://www.youtube.com/watch?v=MAWIffJc_nA&list=PLXu5151nmAvRNl9ku…; and Alex found it in the Taylor Fork yesterday (<strong><a href="https://www.youtube.com/watch?v=MY_ES6Wo1q8&t=0s&index=2&li…;). This layer is not highly reactive, but is something to look for and assess before committing to steeper terrain.</p>
<p>Today, heightened avalanche conditions exist on steep 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, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
COOKE CITY
Every Friday and Saturday, Rescue Training and Snowpack Update. Friday 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.
