This avalanche failed naturally sometime between Feb 13-15 after recent wind and storm loading. SE aspect, 9400 ft elevation, 2-4' deep. Photo: B. Fredlund
Skiers reported intentionally triggering multiple avalanches failing up to a foot deep at the Throne. From the email: "We dug a pit above the top of the throne (ENE aspect, 8400’, 28°) and got an ECTP17. The pit broke below 55cm of new snow, on top of an old wind slab. Bailed on our objective (the ruler) and skied the main ESE chutes on the throne. Ski cut the top of all 3 chutes and got them all to break out 8-12” deep, 100-200’ wide and they all ran 500-700’ into the trees at the bottom of the gullies.
Skiers reported intentionally triggering multiple avalanches failing up to a foot deep at the Throne. From the email: "We dug a pit above the top of the throne (ENE aspect, 8400’, 28°) and got an ECTP17. The pit broke below 55cm of new snow, on top of an old wind slab. Bailed on our objective (the ruler) and skied the main ESE chutes on the throne. Ski cut the top of all 3 chutes and got them all to break out 8-12” deep, 100-200’ wide and they all ran 500-700’ into the trees at the bottom of the gullies.
We saw this crown at 1545 on 2/15/19 after viewing this slope at least twice earlier in the day. We went to the avalanche on 2/16. It appeared to be triggered by a cornice fall and broke 4-8' deep. Photo: GNFAC
We saw this crown at 1545 on 2/15/19 after viewing this slope at least twice earlier in the day. We went to the avalanche on 2/16. It appeared to be triggered by a cornice fall and broke 4-8' deep. Photo: GNFAC
Saw natural slabs in the cliffs on Mineral peak south of Silver Gate and triggered a few small test slopes. 6-12" deep. 10-30' wide.
Forecaster Note: We saw this crown at 1545 on 2/15/19 after viewing this slope at least twice earlier in the day. We went to the avalanche on 2/16. It appeared to be triggered by a cornice fall and broke 4-8' deep.
This large deep slab avalanche broke on Mt. Henderson on the afternoon of 2/15/19 during strong winds. New snow and strong wind this past week has formed fresh drifts that are easy to trigger. This heavy, steady wind loading pushed deep weak layers to break. With more heavy loading from new snow and wind we will see more large avalanches like this. Photo: GNFAC
New snow and strong wind this week created fresh drifts that are easy to trigger. This small slide we triggered is a sign that drifts on larger, dangerous slopes are ready to avalanche. Photo: GNFAC
<p>The avalanche warning has expired, but dangerous avalanche conditions remain. Over the past three days, the southern mountains picked up over two feet of snow totaling 1.5-2” of SWE (<u><strong><a href="https://www.youtube.com/watch?v=JoXitoUtXfo&index=2&t=0s&li…;). Today, natural and human triggered avalanches are likely on all wind loaded slopes. Areas loaded by west-southwest winds will be the most susceptible to holding wind drifted snow.</p>
<p>Human triggered avalanches are also likely on non-wind loaded slopes. Slides breaking 1-3’ deep on density changes in the new snow will be easy to trigger. Slides could also break 3-5’ deep on weak layers near the ground (<strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-gravelly-ran…;). During these conditions, avoiding steep slopes and avalanche run out zones is essential. This includes staying off small steep slopes like road cuts and creek beds that may seem harmless during more stable conditions.</p>
<p>Today, very dangerous avalanche conditions exist on wind loaded slopes which have a <strong>HIGH</strong> avalanche danger. Non-wind loaded slopes have a <strong>CONSIDERABLE</strong> avalanche danger. </p>
<p>Storm totals over the past three days for the Cooke City area are 1.5-2’ of snow totaling roughly 2” of SWE. The snowpack around Cooke City is stronger than the pack around West Yellowstone (<strong><a href="https://www.mtavalanche.com/images/19/more-it">photo</a></strong>), but this heavy load is enough to create unstable conditions. Wind loaded slopes will be the most likely to produce human triggered avalanches today. Watch for and avoid areas of wind drifted snow in terrain loaded by west-southwest winds. Cracking/collapsing and recent avalanches are obvious signs the snowpack is unstable. Slides will likely stay confined to new and wind-blown snow, but the possibility remains for slides to break on weak layers buried mid pack and near the ground. This scenario is most likely in areas with a shallower and weaker snowpack. Today, careful snowpack evaluation and conservative decision making are essential.</p>
<p>As the snowpack works to adjust, human triggered avalanches are likely and the avalanche danger is rated <strong>CONSIDERABLE</strong>.</p>
<p>The mountains around Big Sky picked up 6” of snow overnight while the Bridger Range and northern Gallatin Range received 2-4”. This shot of snow isn’t enough to create widespread instability, but it will bump up the danger on wind loaded slopes. Temps are on the warm side, which will make fresh wind slabs denser and potentially harder to trigger. Watch for and avoid this problem on mid to upper elevations slopes loaded by west-southwest winds. Fresh wind slabs won’t produce large and destructive avalanches, but they will pack enough punch to carry and potentially burry a skier or rider (<strong><a href="https://www.mtavalanche.com/images/19/small-natural-avalanche">photo</a…;). Be especially cognizant of this problem when skiing or riding in higher consequence terrain. Fortunately, weak layers near the ground are gaining strength (<u><strong><a href="https://www.youtube.com/watch?v=xuXLoZvikoM&t=0s&index=3&li…;), which should keep slides confined to new and wind drifted snow.</p>
<p>Today, human triggered avalanches are likely on wind loaded slopes which have a <strong>CONSIDERABLE </strong>avalanche danger. Non-wind loaded slopes have a <strong>MODERATE</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.
BOZEMAN
February 22 and 23, Women’s Companion Rescue Clinic, 6-8 p.m. Friday at REI, 10-4 Saturday in the field. More Info and Register.
