17-18

<p>The southern Ranges have a layer of facets buried 1-2 feet deep (<a href="https://www.mtavalanche.com/images/17/weak-facets-are-under-new-snow"><…;, <a href="https://youtu.be/sZxO8CPCcTk"><strong>video</strong></a&gt;). In the mountains around Cooke City, this weak layer just got loaded by well over a foot of snow over the past two days totaling 1.7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). In the mountains around West Yellowstone, this layer of facets got loaded by a foot of snow totaling roughly 1” of SWE. This rapid and heavy load has created thick slabs that will be easy to trigger.</p>

<p>Yesterday, a skier around Cooke City experienced widespread cracking and collapsing. These are major red flags the snowpack is unstable. We have limited observations from the mountains around West Yellowstone, but given the weak snowpack I found in the Lionhead area last week (<a href="https://www.mtavalanche.com/images/17/ski-hill-lionhead-15-dec">snowpit…;), there’s little question the snow structure is prime for producing avalanches.</p>

<p>On slopes that have been wind loaded, the pack is still near&nbsp;its breaking point. Winds have calmed this morning, but are forecasted to pick back up this afternoon. It won’t take much wind loading to make natural avalanches likely on wind loaded slopes today. In non-wind loaded terrain, human triggered avalanches remain likely on all aspects and elevations. Keep in mind, avalanches have the potential to be triggered from a distance or from the bottom of the slope making terrain management critical for safe backcountry travel.</p>

<p>Today, the snowpack remains under a tremendous amount of stress and the avalanche danger is rated <strong>HIGH</strong> on wind loaded slopes. Non-wind loaded slopes have a <strong>CONSIDERABLE</strong> avalanche danger.</p>

<p>The 6” of low density snow that fell over the past 24 hours will elevate the avalanche danger, mainly in wind loaded terrain. West-northwest winds will make slopes facing the east half of the compass most likely to harbor wind slabs. These will be 1-2’ thick and will easily fail under the weight of a skier or rider.</p>

<p>On non-wind loaded slopes, small soft slabs and loose snow avalanches (sluffs) will be possible in steeper terrain. These problems will be more likely in areas where the new snow fell on a weak layer of near surface facets. The tricky about this layer is it does not exist on all slopes. We know can it can be found on the west side of the Bridgers and certain areas around Hyalite and Big Sky, but we did not find it on Mt Ellis two days ago (<a href="https://youtu.be/7RTIXnPxSDQ"><strong>video</strong></a&gt;, <a href="https://www.mtavalanche.com/images/17/mt-ellis-shoulder-pit-profile-19-… profile</strong></a>). It’s worth digging down a foot or more to assess the new snow-old snow interface.</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, 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 mountains around Cooke City have gotten at least 1’ of new snow measuring 1.1” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE). Additionally, it’s very windy and snow will continue. On Sunday, I found a weak layer of faceted (sugary) snow on all aspects and elevations (<a href="https://www.mtavalanche.com/images/17/weak-facets-are-under-new-snow"><…;, <a href="https://youtu.be/sZxO8CPCcTk"><strong>video</strong></a&gt;). It is now buried 12-18” deep and is our main layer of concern. It will create avalanches today. An inch of SWE in 24 hours is a high rate of loading and is creating dangerous avalanche conditions. More snow and wind will not help. Cracking or collapsing on low-angled slopes or road cuts is a warning sign to not venture into or underneath avalanche terrain. Be cautious today as the avalanche danger is rated <strong>HIGH</strong> on all wind-loaded slopes and <strong>CONSIDERABLE</strong> everywhere else.</p>

<p>Carrot Basin in the southern Madison Range and the mountains outside West Yellowstone have received 6” of new snow (.5” SWE) and strong winds out of the southwest. The snowpack is thin, weak and unstable and will be taxed with this storm. On Friday, Eric found the top 6” of the snowpack to be weak and faceted and sitting on an ice crust, making a recipe for avalanches when it snows…like today. Wind-loaded slopes may avalanche naturally, but even on slopes without a wind-load you could trigger a slide since snowfall and winds are not abating. For today, the avalanche danger is rated CONSIDERABLE on all slopes.</p>

<p>The mountains around Big Sky and Bozeman have strong southwest winds and 1-2” of new snow. Wind slabs avalanched on Monday, but were stubborn yesterday. Weak, faceted snow can be found 4-6” under the surface on some slopes (W. side of the Bridger Range; in Hyalite) but not on others (<a href="https://youtu.be/7RTIXnPxSDQ"><strong>video</strong></a&gt;). Yesterday, three of us went to Mount Ellis and did not find this layer. In fact, we found a stable 3’ deep snowpack which was a bit surprising since this area tends to be shallower and weaker than other areas (<strong><a href="https://www.mtavalanche.com/images/17/mt-ellis-shoulder-pit-profile-19-… profile</a></strong>, <strong><a href="https://youtu.be/j6JQ1ovVrzQ">video</a></strong&gt;). For today, the avalanche danger is rated <strong>MODERATE</strong>, but could rise to <strong>CONSIDERABLE </strong>on wind-loaded slopes with the approaching storm.</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>Strong wind yesterday in the northern mountains built wind slabs 1-2 feet thick that were triggered by ski patrols, and avalanched naturally on Mt. Blackmore (<strong><a href="https://www.mtavalanche.com/images/17/mt-blackmore-avalanche">photo</a>…;) and in Beehive Basin (<strong><a href="https://www.mtavalanche.com/images/17/natural-avalanches-beehivemiddle-…;). The slides were small and only involved the new, wind-drifted snow. Winds were variable in speed and direction and loaded slopes at the ridgeline and cross-loaded slopes in gullies mid-mountain (<strong><a href="https://www.mtavalanche.com/images/17/winds-both-scoured-and-loaded-slo…;). Today, more wind and new snow will make wind slabs easy to trigger.</p>

<p>Snowfall today will further bury and stress a weak layer of faceted snow buried 5-10” under the surface. This problematic layer formed during sunny weather a week ago and will begin to crack, collapse and possibly avalanche with more snow in the coming days, which Alex explains in a video he made up Hyalite (<a href="https://youtu.be/7RTIXnPxSDQ"><strong>video</strong></a&gt;).</p>

<p>Natural and human triggered slides on wind-loaded slopes yesterday, plus continued wind today, point to a <strong>CONSIDERABLE</strong> danger on all wind-loaded terrain and<strong> MODERATE</strong> on all other slopes.</p>

<p>&nbsp;</p>

<p>In the southern mountains the wind has not been very strong, but this may change with today’s storm. At Lionhead on Friday, Eric found a thin, weak and faceted snowpack (<strong><a href="https://www.mtavalanche.com/images/17/ski-hill-lionhead">snowpit profile</a></strong>) which will become unstable with more snow. Outside Cooke City the snowpack is 4-6’ deep and stable, but on Sunday I found a weak layer of sugary facets 4-6” under the surface that will produce avalanches when loaded with more snow or wind slabs (<a href="https://www.mtavalanche.com/images/17/weak-facets-are-under-new-snow"><…;, <a href="https://youtu.be/sZxO8CPCcTk"><strong>video</strong></a&gt;). For today the avalanche danger is rated <strong>MODERATE</strong>, but could rise to <strong>CONSIDERABLE</strong> with today’s storm. This means that the ability to trigger avalanches will rise from <em>possible</em> to <em>likely</em>.</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>