21-22

Collapses and Whumphs on NE Aspect 8000 feet in Hyalite

Hyalite - East Fork
Northern Gallatin
Code
AF-O
Elevation
8000
Aspect
NE
Latitude
45.45050
Longitude
-110.91900
Notes

From email obs: 12/12/21: "Shooting cracks and whoomphing in wind loaded areas. An approximately 15x30ft wind slab cracked along the bas of a rock band and settled at the base of P2 on high fidelity. Was triggered while traversing along the rock band to gain the second pitch, 1-2 inches of facets on the ground. Wind slab of 6-36in in the gullies."

(Second photo, believed to be from different group, sent on IG)

Number of slides
0
Number caught
0
Number buried
0
Trigger
Foot penetration
Bed Surface
O - Old snow
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

From obs: 12/12/21: "Shooting cracks and whoomphing in wind loaded areas. An approximately 15x30ft wind slab cracked along the base of a rock band and settled at the base of P2 on high fidelity. Was triggered while traversing along the rock band to gain the second pitch, 1-2 inches of facets on the ground. Wind slab of 6-36in in the gullies." Photo: M. Hearley

Northern Gallatin, 2021-12-12

At Lionhead Ridge, strong winds are drifting snow into unstable slabs. On steep rollovers, we observed shooting cracks and one large collapse, or "whumph." With more wind and snow in the forecast, expect conditions to get more dangerous before they improve. Photo: GNFAC

Lionhead Range, 2021-12-12

GNFAC Avalanche Forecast for Sun Dec 12, 2021

Snowpack and Avalanche Discussion

<p>The mountains near Cooke City received 2 feet of snow (equal to 2.3” snow water equivalent) since last Monday. Avalanches breaking below this snow are possible to trigger and could be large enough to bury a person, especially where recent snow has been drifted into slabs 1-3 feet thick. Strong wind will continue to grow these slabs today. Be extra cautious of steep, wind-loaded slopes. On Friday, skiers reported stability tests breaking below the recent snow (<strong><a href="https://www.mtavalanche.com/images/21/woody-ridge-profile-10-dec-2021">… profile</a></strong>) which shows the potential to trigger slides. Avalanches breaking deeper than the recent snow are unlikely, but we have found weak layers deeper in the snowpack that are worth digging to look for and evaluate before riding steep slopes (<a href="https://www.youtube.com/watch?v=1Nt5LOMI1PQ"><strong>video</strong></a&…;, <a href="https://youtu.be/O29XGDZBL8c"><strong>video</strong></a&gt;). Today, human triggered avalanches are possible and the avalanche danger is MODERATE.</p>

<p>Yesterday my partner and I skied at Mt. Blackmore in Hyalite and experienced constant 30-40+ mph winds (<strong><a href="https://www.youtube.com/watch?v=lyl9dBUt0u4&amp;list=PLXu5151nmAvT1nrM2…;) which occurred throughout the advisory area. In the mountains near Bozeman, Big Sky and West Yellowstone the strong south-southwest winds created fresh drifts of snow that a person could trigger today. These drifts might exist on any aspect, near ridgelines, across the middle of slopes, and locations where we don’t usually expect snow to be drifted into slabs. Look for cracking around your skis or sled as a sign the drifted snow is unstable. If you see these signs, stay off steep, wind-loaded slopes, especially where the consequences of getting caught in a slide involve being pushed over cliffs, or into rocks, trees, or gullies. Even without clear signs of instability, remain skeptical of wind-loaded slopes today (<a href="https://www.youtube.com/watch?v=065JmnekjVs&amp;list=PLXu5151nmAvT1nrM2… Hyalite gullies video</strong></a>).</p>

<p>On slopes that do not have fresh drifts the snowpack is generally stable. There are weak layers that have formed, but they are not much of a concern until we receive more snow (<a href="https://www.youtube.com/watch?v=8yJ1-BzM8Eg&amp;list=PLXu5151nmAvT1nrM2… video</strong></a>).</p>

<p>Today the avalanche danger is MODERATE on wind-loaded slopes and LOW on all other slopes.</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>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), 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.