23-24

Surface Hoar and Instability in Lionhead

Date
Activity
Skiing

From email: 12/13: "Many slopes had half-inch to inch-sized surface hoar crystals on the surface, some of the largest I've ever seen! 

Wind was light out of the north on the ridgeline. We noticed 2 natural avalanches on the east-facing slopes below Bald Peak. I lost count, but we experienced well over 30+ collapses while walking on the ridgeline. Many of these collapses were very large and we were able to watch the slopes 'sink' by upwards of an inch which made our hair stand on end.

We dug a pit near the saddle below Lionhead Peak at 9300' on an east-facing slope (HS ~85cm). We performed an ECT and our results indicated poor stability (ECTP 14 @ 50cm)." 

Region
Lionhead Range
Location (from list)
Lionhead Ridge
Observer Name
Robby Parsons

GNFAC Avalanche Forecast for Thu Dec 14, 2023

Snowpack and Avalanche Discussion

<p><span>Dangerous avalanche conditions resulting from persistent weak layers require patience from those looking to travel in steep terrain. Stability is slowly improving, with fewer signs of instability warning of the lurking danger, but human-triggered avalanches remain likely.</span></p>

<p>Recent evidence of the avalanche danger has been plentiful. Yesterday, Ian rode into Tepee Basin and explained that recent avalanches, whumphing collapses, and poor snowpack structure were enough to keep them off steep slopes (<a href="https://youtu.be/4-uZDC6UnqA"><strong><span>video</span></strong></a&gt;). Skiers in the Bridger Range heard the snowpack collapse on some slopes (<a href="https://www.mtavalanche.com/node/29518"><strong><span>observation</span…;), and a group south of Livingston, outside the advisory area, heard frequent whumphs as they traveled and observed a couple of recent avalanches (<a href="https://www.mtavalanche.com/node/29522"><strong><span>observation</span…;). Tuesday, a skier triggered a dangerous slide on Mt. Blackmore in the northern Gallatin Range. Thankfully, quick moves and luck were on his side (<a href="https://www.mtavalanche.com/node/29503"><strong><span>observation and video</span></strong></a>). Ian and Doug assessed the backcountry snowpack at Bridger Bowl and observed a loud collapse in the Fingers Meadow with very unstable snowpit results (<a href="https://www.mtavalanche.com/node/29503"><strong><span>photo, snowpit, and video</span></strong></a>). During an Avalanche Fundamentals Course in the Lionhead Ridge area, our group heard a large whumph (<a href="https://www.mtavalanche.com/node/29513"><strong><span>observation</span…;).</p>

<p>The extended period of high pressure will further weaken the snowpack from the top down and the bottom up. Yesterday, Ian saw “the largest feathers of surface hoar” in his life in Tepee Basin (<a href="https://www.mtavalanche.com/node/29519"><strong><span>observation</span…;), and riders at Buck Ridge saw blankets of these feathery crystals (<a href="https://www.mtavalanche.com/node/29525"><strong><span>observation</span…;). Stability will continue to improve as the snowpack finds equilibrium in its current state, but mentally prepare yourself for significant and extended periods of instability when snow returns.</p>

<p>Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential. The avalanche danger is rated CONSIDERABLE on all slopes.</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.

TODAY, Thursday, December 14th, 6:30 p.m., Community Partnership Series @ MAP Brewing, featuring Wiley Miller’s “RUN” and Q&A with Miller and GNFAC forecaster Alex Marienthal.

Surface Hoar at Buck Ridge

Date
Activity
Snowmobiling

From email: "Over the last couple days, I’ve been seeing very large surface hoar formations on most of the snowpack from ~7000 ft+. They continue to grow day to day, I’ve measured crystals over 5mm tall. Hopefully the warm temperatures over the next week will melt these before our next storm cycle, but only time will tell."

Region
Northern Madison
Location (from list)
Buck Ridge
Observer Name
Sebastian Gralla

Absaroka Obs

Date
Activity
Skiing

From email: "Skinned up to about 8600ft in Mill Creek area near Arrastra drainage. Frequent collapses heard/felt once above about 8k, where snow totals seemed to average 12-24 inches on E to N aspects, more up higher. Sparse/discontinuous snowpack below 8k. Lots of 1cm surface hoar in protected areas.

Saw a couple recent (<48 hours old) large crowns up higher in the E facing bowls around 9800ft, one of which appeared to be triggered by a cornice fall (not pictured).  Lots of ridge top wind transport a few days ago in this area, none seen this morning"

Region
Out of Advisory Area
Location (from list)
Arrastra Creek
Observer Name
Tim Benson

Poor Structure in Tepee Basin

Date
Activity
Snowmobiling

We rode into Tepee Basin to look at an avalanche that was triggered by riders on Saturday (12/9) from the flats below the slope. On the way in we saw widespread and large surface hoar on the snow surface. We dug a snowpit next to the avalanche and we saw ECTN results (ECTN 13) on weak-faceted snow under early December snow. This was the same layer that the avalanche failed on. Recent avalanche activity and poor structure were more than enough to keep us from riding steep slopes. 

Region
Southern Madison
Location (from list)
Tepee Basin
Observer Name
Zach Peterson
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