21-22

Airplane Bowl natural avalanche

Lionhead Ridge
Lionhead Range
Code
SS-N-R2-D2-O
Elevation
9400
Aspect
SE
Latitude
44.71450
Longitude
-111.31800
Notes

This natural avalanche likely released after the large storm ended Wednesday, December 15. This slope is SE facing and the crown is about 9,400 feet. Faceted snow at/near the ground was the likely weak layer that avalanched.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Located off Lionhead Ridge outside West Yellowstone, this natural avalanche likely released after the large storm ended Wednesday, December 15. This slope is SE facing and the crown is about 9,400 feet. Faceted snow at/near the ground was the likely weak layer that avalanched. Photo: GNFAC

Lionhead Range, 2021-12-20

GNFAC Avalanche Forecast for Mon Dec 20, 2021

Snowpack and Avalanche Discussion

<p>The mountains around Cooke City received 7” of snow overnight equal to 0.6” of <a href="https://missoulaavalanche.org/2021/01/what-is-swe-snow-water-equivalent… water equivalent</u></a> (SWE). Continued heavy snowfall through the morning in conjunction with increasing winds today will create dangerous avalanche conditions in wind-loaded terrain where human-triggered avalanches are likely. Yesterday, my partner and I observed generally stable conditions, but, today, will be carefully assessing for signs of increased instability and testing weak layers in the mid and lower snowpack now that they are loaded by new snow (<a href="https://www.youtube.com/watch?v=4GrVPi-1FC8&amp;list=PLXu5151nmAvT1nrM2…;). Avoid steep wind-loaded slopes and carefully evaluate terrain and snowpack conditions before entering avalanche terrain.&nbsp;</p>

<p>The avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all others.</p>

<p>The Bridger, Madison, and Southern Gallatin Ranges received 4-6” of snow equal to 0.4-0.6” of SWE in the last 24-hours. Southwest winds are transporting the new snow into drifts on wind-loaded slopes where instabilities will be the most evident. Recent avalanches in the Bridger Range on Thursday (<a href="https://www.mtavalanche.com/node/25164"><strong><u>photos and details</u></strong></a>) and the Taylor Fork (<a href="https://www.youtube.com/watch?v=PPHZEgnv4lM"><strong><u>video</u></stro…;) and Bacon Rind (<a href="https://mtavalanche.com/images/21/avalanche-bacon-rind-photo-15-dec-202…;) on Wednesday are indicators of the types of avalanches we are concerned about. Evaluate snowpack stability, paying special attention to wind-loaded slopes, and assess terrain for features such as cliffs, rocks, trees, and gullies that amplify the consequences of even a small avalanche prior to entering steep terrain.&nbsp;</p>

<p>Areas south of Big Sky received nearly 3’ of snow within the last week, avalanches failing 1-3’ deep under last week’s storm snow less likely but remain a possibility.&nbsp;</p>

<p>Human-triggered avalanches are possible and the danger is rated MODERATE.</p>

<p>The northern Gallatin Range received 1” of snow in the last 24 hours while the Lionhead area remained dry. Wind from the southwest is creating fresh drifts of snow where avalanches are most likely to fail today. Similar to recent avalanches in the Southern Madison Range, these slides could be relatively small to 1-3’ deep breaking under last week’s snow (<a href="https://www.youtube.com/watch?v=PPHZEgnv4lM"><strong><u>video</u></stro…;, <a href="https://mtavalanche.com/images/21/avalanche-bacon-rind-photo-15-dec-202…;). Yesterday, groups of skiers testing the snowpack in Hyalite found both stable and unstable conditions illustrating the importance of assessing the specific terrain you are considering. Today, avoid freshly wind-loaded slopes where the danger is the greatest and assess the snowpack stability before traveling in steep terrain. Human-triggered avalanches are possible and the danger is rated MODERATE.&nbsp;</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Education Opportunities:

Get your avalanche brain ready for the season at one of the many classes listed on our education calendar, and list of upcoming events below. Don’t delay preparing and inspecting your avalanche gear. Get some tips from Dave Zinn in this Pre-Season gear check video.

Cornices that formed mid-slope, indicating recent heavy wind-loading in the Bridger Range. Strong southwest wind between 12/18 and 12/19/21 drifted recent snow into hard, pillowy drifts. We avoided these drifts on steep slopes to give them a day or two to stabilize. Photo: GNFAC

Bridger Range, 2021-12-19

These pillowy, hard drifts formed from strong southwest wind overnight between 12/18 and 12/19/21 in the Bridger Range. We saw minimal signs of instability, lke whumphing or cracking in these drifts, but avoided these features on steep slopes until they have more time to gain stability. Photo: GNFAC

Bridger Range, 2021-12-19