24-25

<p><span><span><span><span><span><span>Natural and human triggered avalanches are likely today. Heavy snowfall continued yesterday near Island Park and West Yellowstone. Snow totals were a little less in Cooke City yesterday, but heavy snowfall will continue there today. 3-4 ft of new snow have fallen since last Thursday. Large, natural avalanches have been breaking and will continue to break today. Yesterday, Dave saw many large natural avalanches along Lionhead ridge (<a href="https://www.youtube.com/watch?v=vE7BvsmgjQc">video</a>).&nbsp;</span></…;

<p><span><span><span><span><span><span>Very strong winds have drifted snow at all elevations. Strong winds will pick back up again this morning, drifting the snow that fell since the last round of intense winds on Sunday night.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Storm Slab, Wind Slab and Persistent Slab avalanches could all break today, but the specific weak layers and types of avalanches don’t matter - any of them will be large enough to kill or seriously injure a rider or skier. </span></span></strong></span></span></span><span><span><span><span><span><span>Even non-windloaded slopes without persistent weak layers have the potential for deadly slides.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Avoidance is the only safe option. This means avoiding travel on slopes steeper than 30 degrees and also on lower-angle terrain in the runout zones beneath avalanche paths.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>The avalanche danger is HIGH.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Human triggered avalanches are likely today in the Bridger, Southern Madison and Southern Gallatin Ranges. </span></span></span></span></span></span><span><span><span><strong><span><span>Wind Slab and Storm Slab avalanches are the primary concerns today.&nbsp; Persistent Slab avalanches are also possible near West Yellowstone.</span></span></strong></span></span></span><span><span><span><span><span><span>&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Avalanches are most likely to break on slopes where the new snow has been drifted into even deeper and stiffer slabs, but Storm Slab avalanches could also break on slopes without wind effect. A number of natural avalanches were reported yesterday in the northern Bridger Range (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34645"><span><span><span><strong><span…;).</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Persistent Slab avalanches breaking 3-5 ft deep on the weak layers buried in late January provide an additional reason to avoid steep slopes in the West Yellowstone area. There has only been one avalanche on these weak lakers in the last couple weeks (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34610"><span><span><span><strong><span…, photo and obs</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>), but the load from recent new snow and wind will make it easier to trigger these slides, so it wouldn’t be surprising to see more of them today.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Avalanche conditions are dangerous and cautious route finding is required today. The avalanche danger is CONSIDERABLE.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Wind slab avalanches </span></span></strong></span></span></span><span><span><span><span><span><span>breaking 1-2 feet deep are the primary concern today. Look out for visual clues of wind drifting and avoid wind drifts. Cracks shooting out from your skis or sled mean you’ve found an unstable drift and should retreat to lower angled or non-wind effected terrain.</span></span></span></span></span></span></p>

<p><span><span><span><strong><span><span>Loose snow avalanches</span></span></strong></span></span></span><span><span><span><span><span><span> are also possible on slopes that haven’t been wind effected and can run long distances on crusts below the recent snow.&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Seek out slopes sheltered from the wind that will have better snow and safer avalanche conditions. The avalanche danger is MODERATE.</span></span></span></span></span></span></p>

<p>Very dangerous avalanche conditions exist in the mountains of Island Park, West Yellowstone and Cooke City. Natural and human-triggered avalanches are likely. Avoid slopes steeper than 30 degrees and lower-angle terrain in the runout zones of avalanche paths.</p>

<p>Slides will fail within the new and wind-drifted snow as <strong>wind slab </strong><span>and</span><strong> storm slab avalanches. </strong>Since Thursday, the mountains in Island Park have received 40” of snow, equal to 4.1” <a href="https://avalanche.org/avalanche-encyclopedia/#snow-water-equivalent-swe… water equivalent (SWE)</span></a>. During the same period, the Lionhead area received 30” of snow and Cooke City received 24” of snow. Yesterday, hurricane-force gusts up to 100 mph transported snow into unstable slabs at all elevations (the strongest gusts were recorded on Lionhead Ridge).</p>

<p>In the Lionhead area, <strong>persistent slab avalanches </strong>breaking 3-5 feet deep on the weak snow buried in late January are possible. Slides on buried weak layers tapered off a couple of weeks ago, but heavy loading from recent snow could wake these layers up, resulting in large avalanches failing deep within the snowpack.</p>

<p>The specifics of weak layers and types of avalanches are irrelevant today. All can be large enough to injure or kill riders and skiers. Avoidance is critical.</p>

<p><span>The avalanche danger is HIGH on all slopes.<span>&nbsp;&nbsp; </span></span></p>

<p>Dangerous avalanche conditions exist in the Bridger, Southern Madison and Southern Gallatin Ranges, where 20-24” of snow has fallen since Thursday, and strong winds built unstable slabs of drifted snow. Human-triggered <strong>wind slab avalanches</strong> breaking 2-3 feet deep are likely. Yesterday, Alex and I avoided the steep terrain in Tepee Basin, where we measured two feet of recent snow and saw failures within and below the new snow (<a href="https://www.youtube.com/watch?v=VpFFY3Gug0w"><strong><span>video</span>…;). A warming trend yesterday is likely to result in increased instability within layers of the storm snow and <strong>storm slab avalanches</strong>.</p>

<p><strong>Persistent slab avalanches</strong> breaking 3-5 feet deep on the weak snow buried in late January are possible in the Southern Gallatin and Southern Madison Ranges. On Friday, a snowmobiler triggered a 2-3 foot deep hard slab on a steep slope with a relatively shallow snowpack in the Taylor Fork (<a href="https://www.mtavalanche.com/node/34610"><strong><span>video, photo and obs</span></strong></a>). With the heavy loading from recent snow, we could see an increase in larger avalanches.</p>

<p><span>To enjoy a safe day in the mountains, cautious route-finding that largely avoids steep slopes and runout zones is essential. The avalanche danger is CONSIDERABLE on all slopes.<span>&nbsp; </span></span></p>

<p>Since Thursday, the Northern Madison and Northern Gallatin Ranges have received 11-19” of snow (0.8-1.1” SWE). Strong winds scoured some slopes and loaded others, where <strong>wind slab avalanches </strong>breaking 1-2 feet deep are the primary concern. Yesterday, Mark and his partner triggered small drifts on test slopes (<a href="https://www.mtavalanche.com/node/34624"><strong><span>photos and details</span></strong></a>). Seek out slopes sheltered from the wind for better snow and safer avalanche conditions.</p>

<p>On non-wind-loaded slopes, <strong>loose snow avalanches</strong> are possible. While relatively harmless in open terrain, they can be dangerous above cliffs, rocks, or trees.</p>

<p><span>Identify and avoid unstable wind-loaded terrain by watching for a textured or pillowy snow surface, cracking or a stiffening of the snow surface. The avalanche danger is MODERATE. </span></p>