From IG Message: Wind slab avalanche on “east facing slope in hyalite”
Widespread SH had formed over the past couple of days in areas on the approach that were out in the open but shaded from the wind. We observed cornices in the back of the basin (NE/E facing) and a small wind slab had broken off underneath them. Wind-blown snow had filled in the skin track and ski lines from yesterday in maiden bowl. The sun was baking the southern facing slopes for most of the day today, and when we skied out, the snow in the direct sunlight was wet.
On Jan 27 we saw a cornice fall on a very big steep slope up Republic Creek which did not trigger anything large or deeper, but entrained some snow and ran over a thousand feet vertical. Photo: GNFAC
On Jan 27 We saw one old, but very large persistent slab avalanche further up Republic Creek (pictured). It was on similar aspect and elevation as a somewhat more recent persistent slab in nearby Hayden Creek, North-northeast, 10,000'. It appeared to be 6'+ deep and 500'+ wide. The bed surface and crown had been partially drifted in, so it seemed it was probably at least a week old...? Photo: GNFAC
We skied up west Woody Ridge and skied down into Hayden Creek about 500 feet, then back up and over, and out Republic Creek.
Skies were clear with calm winds and a light breeze at the ridgetop. Temperatures were still mostly cold, single digits down low and teens up high in the morning. The sun felt hot mid-day, snow bombs were falling off trees and there were some small rollerballs around steep rocks on southerly facing slopes.
We saw one old, but very large persistent slab avalanche further up Republic Creek (pictured). It was on similar aspect and elevation as a somewhat more recent persistent slab in nearby Hayden Creek, North-northeast, 10,000'. It appeared to be 6'+ deep and 500'+ wide. The bed surface and crown had been partially drifted in, so it seemed it was probably at least a week old...?
There was also a recent cornice fall on a very big steep slope up Republic Creek (picture) which did not trigger anything large or deeper, but entrained some snow and ran over a thousand feet vertical.
We dug a pit at 9,900' on a west aspect. Snow depth was 150cm (5 feet). We had an ECTN11 below 3 inches of snow on top of small sugary facets near the surface. There were soft (4f+) sugary facets at the bottom of the snowpack, but they did not break in an ECT or with extra force. Snow depth above 9,000' was ~4 feet average based on a few places we probed as we toured up.
There were signs of a lot of previous wind up high. It has been a few days without wind, but there are probably some isolated instabilities of small stiff wind slabs sitting on facets which could be triggered.
<p>In the mountains around Bozeman and Big Sky, the wind is transporting recent snow into unstable drifts at many elevations. <strong>Wind slab avalanches </strong>are the primary concern.</p>
<p>Skiers north of Bridger Bowl triggered an avalanche on a wind-loaded slope that broke a foot deep and twenty feet wide (<a href="https://www.mtavalanche.com/node/33857"><strong><span>observation</span…;), while others noted cracks in wind-drifted snow shooting from their ski tips (<a href="https://www.mtavalanche.com/node/33851"><strong><span>observation</span…;). Local Ski Patrols triggered <strong>wind slab avalanches </strong>that broke 6-18” deep during routine mitigation work. On many slopes, recent snow and wind slabs sit on weak layers of surface hoar and facets, slowing stabilization (Buck Ridge <a href="https://www.mtavalanche.com/node/33832"><span>observation</span></a>, Divide Basin (<a href="https://www.mtavalanche.com/node/33810"><span>observation</span></a>, Beehive Basin <a href="https://www.mtavalanche.com/node/33824"><span>observation</span></a>).</p>
<p>Avoid steep wind-loaded terrain, opting for sheltered slopes, where the surface conditions will be better, and avalanche conditions will be safer. Visual clues, a stiffening snow surface, and signs of instability, including avalanche activity and shooting cracks, can help us identify concerning terrain features.</p>
<p>In non-wind-loaded terrain, assess the upper few feet of the snowpack for instability before considering steeper slopes. Follow safe travel protocols, carry avalanche safety equipment and carefully evaluate terrain to consider the consequences of potential slides.</p>
<p><strong>*** Ice climbers</strong> in steep, confined gullies should watch for roller balls and wet loose avalanches coming from rocky areas above during the heat of the day. Shady aspects will have lower wet snow hazard.</p>
<p><span>The avalanche danger is MODERATE.</span></p>
<p>Time and the absence of significant loading allowed the snowpack to adjust and stabilize in the mountains of Island Park, West Yellowstone, and Cooke City, as well as in the Southern Gallatin and Southern Madison Ranges. While avalanches are unlikely, they are not impossible, and a very large slide south of Cooke City last week demonstrates their potential (<a href="https://www.mtavalanche.com/node/33847"><strong><span>photo</span></str…;).</p>
<p>We are encouraged by minimal avalanche activity, the generally small size of slides, the lack of signs of instability and unremarkable test results (<a href="https://youtube.com/shorts/wYfXLeIfQ38"><strong><span>Lionhead video</span></strong></a><strong>, </strong><a href="https://youtube.com/shorts/zUjqH2ol3u8"><strong><span>Cooke City video</span></strong></a>). As Mark stated in the Lionhead video, “The weak layers are dormant, not dead.” <strong>Persistent slab avalanches</strong> remain the primary concern, and conditions will become more dangerous again when it snows. For now, generally safe avalanche conditions exist.</p>
<p>Isolated <strong>wind slab avalanches </strong>breaking within recent drifts are a secondary concern. This is especially true in steep and technical terrain, where a small avalanche can have significant consequences.</p>
<p><strong>Travel Advice:</strong> Just because the danger dropped to low <strong><em>doesn’t</em></strong><em> mean you should shred all avalanche terrain on day one. </em>Avoid the highest-consequence slopes—very steep and large faces and avalanche paths with terrain traps such as cliffs, trees, and gullies where isolated instability would be fatal. If you elect to travel in avalanche terrain, look for signs of isolated instability, follow safe travel protocols, expose only one person at a time to potential risk, and ensure everyone carries avalanche safety gear.</p>
<p><span>The avalanche danger is rated LOW. </span></p>
Do you like to hike? Do you like to ski/ride? Then the King & Queen of the Ridge on 2/1 is for you. Hike, ride and raise money for the Friends of the Avalanche Center at Bridger Bowl this year! Join this fun event to promote and support avalanche safety and awareness! Fundraising prizes for the top 5 individuals who raise over $500. No racing is necessary to compete for the fundraising prizes.
Strong wind at all elevations in the Bridger Range
From obs: "We skied north from Texas Meadows to the Playground. Strong southerly winds were actively building wind slabs up to 25 cm deep in immediate lees at treeline. We experienced a few instances of cracking in this wind slab, propagating 2 or 3 meters from our ski tips."
