17-18

<p>The Lionhead area outside West Yellowstone received a foot of dense snow measuring 1.2” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE) in the last 12 hours. This is a heavy and rapid load that fell onto a weak and unstable snowpack. Two days ago skiers reported widespread collapsing and cracking, and yesterday Eric and I got poor test results in our snowpits (<strong><a href="https://youtu.be/e9OACzfb7pQ">video</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/18/poor-snowpack-structure-lionhead"…;). Today’s snowfall has created dangerous avalanche conditions on all slopes for all users: skiers, snowmobilers, snow shoers, the avalanches do not care. People will easily trigger avalanches from the <u>bottom</u> of slopes on <u>flat </u>terrain. <em>You do not need to be on the slope to trigger it.</em> Many people have died in similar conditions, so to be safe, give all slopes a wide berth. The avalanche danger is rated <strong>HIGH</strong> and traveling in the backcountry is serious and risky.</p>

<p>This morning it is still snowing and the winds are blowing SW-W at the ridgelines. I am unclear on the exact amount of snow that has fallen because above freezing temperatures at some lower elevation SNOTEL sites are recording lots of water, but not much snow. For example, Brackett Creek in the Bridger Range has 1.3” of SWE but reading only 5” of snow. I can only assume the higher elevations have a lot more snow and elevated avalanche danger.</p>

<p>Today is a day to be conservative. Most avalanches occur during and immediately after a storm, and today is no exception. An inch or more of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…; in 12 hours is a lot of weight and the snowpack will struggle to handle it. Some avalanches will occur at the interface of yesterday’s snow surface, others may break 2-4’ deep on a layer of facets. My advice is to be wary of avalanche terrain and be especially mindful traveling underneath ridgelines where wind-loaded slopes could avalanche naturally. The avalanche danger is rated <strong>HIGH</strong> on all wind-loaded slopes and <strong>CONSIDERABLE</strong> on all other terrain.</p>

<p>The SNOTEL at <a href="https://www.mtavalanche.com/weather/stations/shower-falls-snotel-site">… Falls</a> in Hyalite is showing 2” of new snow (.2” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2…;) with wind gusting to 40 mph out of the west on Flanders Mountain. The avalanche concern is with this new wind-blown snow since these drifts will be easy to trigger. The underlying snowpack is generally stable and although higher elevations may have 4+” of new snow I do not expect avalanches to break into older layers. For today, the avalanche danger is rated <strong>CONSIDERABLE</strong> on all wind-loaded terrain and <strong>MODERATE</strong> on all other 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>

<p>From Big Sky to West Yellowstone and Cooke City the snowpack is gaining strength at different rates. Yesterday, snowmobile guides found instability in their tests in Teepee Creek in the southern Madison Range when faceted snow broke clean 2’ deep (<strong><a href="https://www.mtavalanche.com/images/18/instability-teepee-basin">photo</…;). In the northern Madison Range we have reports of stable snow, most notably in Beehive Basin, yet on Sunday on Buck Ridge, Alex had a mixed bag with one pit stable and another not (<strong><a href="https://youtu.be/k_zQen8dMqI">video</a></strong&gt;), while nearby, a skier on Cinnamon Mountain had collapses in a shallow snowpack. Cooke City has the deepest snow and largest avalanches last week, some 4’ deep (<strong><a href="https://www.mtavalanche.com/images/18/snowmobile-triggered-avalanche-co…;). Skiers were still getting collapses there on Saturday and it’s not out of the question to get another today. Think of collapses as avalanches on flat terrain; these are major red flags.</p>

<p>The Lionhead area near West Yellowstone has the weakest and thinnest snowpack in our advisory area and will not withstand a punishing storm. Just a little weight, such as 1"of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>, could tip the scales and create dangerous avalanche conditions. A week ago I had lots of collapsing, cracking and poor stability test scores above Hebgen Lake on a layer of facets 2’ deep (<strong><a href="https://youtu.be/5yXaQvWxJZI">video</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/18/trapper-creek-pit-profile-2-jan">… profile</a></strong>). I expect today will not be as reactive, but I know better than to trust the poor structure holding the weight of much new snow. Eric and I are headed to Lionhead today since this area concerns us the most with the approaching storm.</p>

<p>For today, stay out of avalanche terrain if you get collapsing, cracking or poor test scores. Avalanches are still possible and the danger is rated <strong>MODERATE</strong>. If the storm arrives as predicted, around West Yellowstone the avalanche danger will rise with new snow and wind.</p>

<p>Skiers and climbers are reporting good conditions which is similar Alex’s assessment from Saturday on Mount Blackmore (<strong><a href="https://youtu.be/DsWaaQxR2Qs">video</a></strong&gt;). Although avalanches are unlikely, they are not impossible on slopes that are shallower. For example, on Sunday, skiers on Divide Peak backed off a thinly covered slope when they got facets breaking under an ice crust 1.5’ deep in their stability test. I love hearing stories like this, because digging saves lives. For today, avalanches are unlikely and the danger is rated <strong>LOW</strong>.</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>Avalanches breaking 2-4’ deep on weak facets are difficult to trigger compared to a week ago, but continued signs of instability show they are possible. Yesterday, skiers near Divide Peak in Hyalite had propagation in their stability tests&nbsp;and decided to not ski a steep slope. Over the weekend, skiers near Cooke City had many unstable stability test results and one large collapse in low angle terrain. I rode near Buck Ridge yesterday and skied in Hyalite Saturday. In both places I found stable slopes, and unstable slopes (<strong><a href="https://youtu.be/k_zQen8dMqI">video</a></strong&gt;, <a href="https://youtu.be/DsWaaQxR2Qs"><strong>video</strong></a&gt;).</p>

<p>Today, travel in avalanche terrain requires thorough snowpack assessment. Review our <a href="https://www.mtavalanche.com/photos"><strong>photos</strong></a&gt; and <a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQSYtIfyQP-gMYrlfja6Ls…; </strong>to learn the general character and distribution of unstable slopes. Recent signs of instability and many avalanches last week were observed on slopes where the snowpack is relatively shallow, less than 3-4 feet deep. These unstable slopes are common on southerly aspects and low elevations, but possible on any aspect or elevation. You have to dig to know exactly what is under your feet. Otherwise, avoid avalanche terrain altogether.</p>

<p>Dig a couple pits on terrain similar to what you plan to ride for the day. Avoid steep slopes if stability tests break clean, or if you find sugary, weak facets buried 2-4’ deep (<a href="https://youtu.be/5yXaQvWxJZI"><strong>video</strong></a&gt;). In addition, be cautious of wind slabs 6-12" thick near ridgelines. These slabs are difficult to trigger, but will hurt if they catch you above cliffs or trees. Carefully assess the terrain for consequences of even small slides, and expose only one person at a time to steep slopes.</p>

<p>Today, large avalanches are possible to trigger and the avalanche danger is <strong>MODERATE</strong>.</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>