19-20

<p>The last significant snowstorm in the Lionhead, Madison, and Southern Gallatin Ranges was ten days ago and with it steep slopes avalanched naturally and under the weight of riders (<a href="https://www.mtavalanche.com/node/21249"><strong>avalanche activity</strong></a>). Last night 1-2” of snow fell with 6-10” possible by Christmas morning. As snow adds up today, the avalanche danger will increase. Yesterday in the Taylor Fork, Ian and I found a weak snowpack (<a href="https://www.youtube.com/watch?v=gxj7yMOxTsc"><strong>video</strong></a&…;). On Sunday, Alex and Doug observed similar weak structures in the Lionhead Ridge (<a href="https://www.youtube.com/watch?v=Fd3eKZDCkB4"><strong>video</strong></a&…;), and I found a series of crusts mixed with weak facets on a tour to Beehive (<a href="https://www.youtube.com/watch?v=LY8WFaaPJbw"><strong>video</strong></a&…;). The constant in the Madison, Southern Gallatin and Lionhead Ranges is a poor structure that will produce avalanches under the weight of new snow.</p>

<p>As it snows today, watch for signs such as new avalanches, cracking and collapsing of the snowpack as indicators of increasing danger. Carefully assess the snowpack and make conservative terrain choices by staying off and out from under steep slopes to manage this hazard. The danger is rated MODERATE and will rise as snow falls.&nbsp;&nbsp;</p>

<p>Ten days have passed since Cooke City received significant snowfall, but reports of avalanches are continuing to come in, including one large slide in the Hayden Creek Drainage three days ago (<a href="https://www.mtavalanche.com/avalanche-activity"><strong>avalanche activity</strong></a><strong> - </strong><a href="https://www.mtavalanche.com/images/19/large-natural-avalanche-near-cook…;, </strong><a href="https://www.mtavalanche.com/node/21218"><strong>2</strong></a><strong&gt;, </strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-crowns-near-coo…;). Doug, Ian, and Alex all visited Cooke City last week and found buried weak layers on many slopes. These layers were more prevalent in areas with a south facing component (<a href="https://www.mtavalanche.com/images/19/poor-snow-structure-near-cooke"><…;, <a href="https://www.youtube.com/watch?v=MOUWPWg2J4A&amp;list=PLXu5151nmAvSbcbVf…;). The forecasted 1-3” of new snow today will not significantly change the avalanche picture in Cooke City. Dig a snowpit to look for existing weak layers about halfway down in the snowpack and avoid steep slopes where you find them. Large, human triggered avalanches are possible, and the danger is MODERATE.</p>

<p>The snowpack in the mountains near Bozeman is generally stable. Without new snow, avalanches are unlikely. Winds hammered slopes through the weekend, leaving little untouched. Saturday, riders triggered fresh drifts of snow 3-5 feet deep in the Bridger and Northern Gallatin Ranges (<a href="https://www.mtavalanche.com/images/19/snowmobile-remote-triggered-avala…;, <a href="https://www.mtavalanche.com/images/19/rider-triggered-slide-heavily-win…;). On Sunday, climbers in Hyalite felt a hard wind slab collapse under their weight with a large “whumph” (<a href="https://www.mtavalanche.com/node/21321"><strong>activity</strong></a&gt;). Instabilities related to this weekend’s wind have stabilized but look for isolated areas where they may persist and choose a different slope if you find hard, wind packed snow that sounds or feels hollow. The avalanche danger is LOW in the Bridger and Northern Gallatin Ranges. Look for isolated areas of instability and assess the consequences of small avalanches.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>observat… form</strong></a>, email us (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

<p>Yesterday Doug and I went to Lionhead Ridge near West Yellowstone and found a snowpack capable of producing large avalanches (<strong><a href="https://www.youtube.com/watch?v=Fd3eKZDCkB4">video</a></strong&gt;). Sugary, weak snow near the ground below a foot of dense snow creates a poor snowpack structure (<strong><a href="https://www.mtavalanche.com/images/19/shallow-and-unstable-lionhead">ph…;). Dave was in Beehive Basin where he found a more stable, but weak snowpack (<strong><a href="https://www.youtube.com/watch?v=LY8WFaaPJbw">video</a></strong&gt;). The mountains have not received more than a couple inches of snow the last nine days, and the snowpack had time to gain stability. This means signs of instability such as recent avalanches and collapsing are scarce, but it is possible to trigger a large avalanche.</p>

<p>Yesterday below Lionhead Ridge we snowmobiled under a couple large avalanche paths. We stayed far away in&nbsp;the flats of the runout zone and exposed only one person a time. You don’t have to be on the steep part of a slope to trigger an avalanche. Today practice cautious route finding and conservative terrain selection. Avalanche danger is <strong>MODERATE</strong>.</p>

<p>In the mountains near Cooke City, avalanche activity from the past week shows a snowpack capable of producing large avalanches. Over the weekend, skiers south of Cooke City saw a large natural avalanche that broke on weak snow near the base of the snowpack (<strong><a href="https://www.mtavalanche.com/images/19/large-natural-avalanche-near-cook…;). A large natural avalanche last weekend was on a similar aspect and elevation (NE, 9,800’) (<strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-crowns-near-coo…;). Additionally, last weekend snowmobilers triggered several large slides that broke on weak snow a couple feet deep (<strong><a href="https://www.mtavalanche.com/node/21222">incident</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/images/19/avalanche-crown-butte">photo</a><…;). We visited Cooke City last week and found these buried weak layers on many slopes (<strong><a href="https://www.mtavalanche.com/images/19/poor-snow-structure-near-cooke">p…;, <strong><a href="https://www.youtube.com/watch?v=MOUWPWg2J4A&amp;list=PLXu5151nmAvSbcbVf…;). Study our <u><strong><a href="https://www.mtavalanche.com/forecast/cooke-city">Cooke City regional page</a></strong></u> to see types of terrain where these instabilities exist, and avoid slopes where you suspect buried weak layers. Today large human triggered avalanches are possible and danger is MODERATE.</p>

<p>Near Bozeman unstable snow is isolated to slopes where extreme southwest winds over the weekend built hard drifts on top of weak snow. On Saturday riders triggered two avalanches 3-5 feet deep on heavily wind loaded slopes (<u><strong><a href="https://www.mtavalanche.com/images/19/snowmobile-remote-triggered-avala…;, <u><strong><a href="https://www.mtavalanche.com/images/19/rider-triggered-slide-heavily-win…;). Yesterday Ice climbers in Hyalite had a freshly drifted hard slab collapse, crack and “whumph” on their approach (<strong><a href="https://www.mtavalanche.com/node/21321">activity</a></strong&gt;). These hard slabs will gain stability today, but deserve caution. Identify them as hard pillows of snow which may sound hollow or like a drum. Avalanches may be triggered on isolated slopes where hard slabs formed over weak snow. Otherwise the snowpack is generally stable and avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<u><strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong></u&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>