19-20
GNFAC Avalanche Forecast for Thu Dec 19, 2019
Snowpack and Avalanche Discussion
<p>In the mountains around Big Sky to West Yellowstone the snowpack is weak. Sugary snow near the ground continues to show signs of instability. Karl and I rode into Lionhead on Tuesday and got large collapses on this layer. The snowpack was less than 3 feet deep and audibly “whumphed” under our body weight. Alex found similar structure in Taylor Fork (<strong><a href="https://youtu.be/GvpDqZDLTto">video</a></strong>) and riders reported avalanches over the weekend (<strong><a href="https://www.mtavalanche.com/node/21249">details</a></strong>). Dave had these facets break in stability tests during an avalanche class on Buck Ridge (<u><strong><a href="https://www.youtube.com/watch?v=F29K5DVfNgs&list=PLXu5151nmAvSbcbVf…;) and heard a third hand account of riders tiggering avalanches nearby slopes. Yesterday, the Big Sky Ski Patrol triggered an avalanche with explosives on this weak layer. <strong><a href="https://www.mtavalanche.com/avalanche-activity">Almost daily signs of instability</a></strong> and poor stability test scores can only be interpreted one way: avalanches are still possible and getting onto steep terrain requires a serious assessment. For today, the avalanche danger is rated MODERATE.</p>
<p>The mountains around Cooke City have not gotten snow in the last six days and avalanche activity has subsided since the weekend. There is still weakness lingering in the snowpack: weak snow (facets) on an ice crust is buried 2-3 feet deep on many slopes, seemingly south to east facing. On Monday, Ian and I investigated a large slide on Mt. Abundance that was triggered by a sledder who was unharmed, unlike his totaled sled (<u><strong><a href="https://www.mtavalanche.com/node/21222">photos and details</a></strong></u>, <strong><a href="https://www.youtube.com/watch?v=rg0OZvz7Qf4">video</a></strong>). We posted photos of many avalanches that occurred on Saturday, December 14. These slides on <strong><a href="https://www.mtavalanche.com/images/19/mount-fox-avalanche">Mt. Fox</a></strong>, <strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-republic-crk">R… Creek</a></strong>, the <strong><a href="https://www.mtavalanche.com/images/19/avalanche-mount-republic">Fin</a>…; and <strong><a href="https://www.mtavalanche.com/images/19/snowmobile-triggered-slide-crown-… Butte</a></strong> are reminders to not be complacent. Although slopes have become less sensitive to triggering, avalanches are still possible. Popular riding spots like the south face of Scotch Bonnet and south face of Mt. Abundance have this weak layer and are suspect. For today, the avalanche danger is MODERATE. Ride and ski with partners, watch each other, only go one at a time on steep slopes and carry rescue gear. <strong><a href="https://www.mtavalanche.com/images/19/bison-triggered-avalanche">And this advice goes for Bison too!</a></strong></p>
<p>In the Bridger and northern Gallatin Ranges the snowpack is generally stable. Yesterday, Ian skied into Divide Peak and found stable and similar conditions to Dave’s trip to Mt. Blackmore (<strong><a href="https://youtu.be/2AwTcIdcgVM">video</a></strong>). West to southwest wind has been blowing strong all week and drifting snow. During the day and evening on Tuesday natural avalanches released in the wind-drifted snow. A few smaller slides in Hyalite pulled off the ridgeline (<strong><a href="https://www.mtavalanche.com/node/21288">details</a></strong>) and a much larger slide broke in wind-loaded terrain on Saddle Peak (<strong><a href="https://www.mtavalanche.com/node/21283">details</a></strong>). There are still isolated pockets of windblown snow that could be triggered and it is worth doing a quick stability test before getting into avalanche terrain. For today, the avalanche danger is rated LOW.</p>
<p>If you get out, please send us your observations no matter how brief. You can fill out an <u><strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong></u>, email us (<u><strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong></u>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.
COOKE CITY
Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.
CHOTEAU
From Instagram: "Couple of small natural wind slabs around 10,200’ NE in Hyalite. Not sure exactly how recent. Played it conservative and chose to stay off a similar slope." B. Gill
Avalanche Details: Shallow wind slab avalanches in Hyalite
Forecast link: GNFAC Avalanche Forecast for Fri Dec 20, 2019
Northern Gallatin, 2019-12-19
Forecast link: GNFAC Avalanche Forecast for Fri Dec 20, 2019
Shallow wind slab avalanches in Hyalite
Maid of the Mist
Northern Gallatin
Code
SS-N
Aspect
E
Latitude
45.41640
Longitude
-110.97000
Notes
1. From an email: The wind sure moved snow around up Hyalite last night, and our party observed several small to medium-sized releases that occured on a heavily-loaded east aspect overnight. None stepped down in the snowpack, but they certainly could have taken a person for a ride. Overalll, stability seemed to be good, with the exception of isolated wind-loaded areas.
2. From IG: Couple of small natural wind slabs around 10,200’ NE in Hyalite. Not sure exactly how recent. Played it conservative and chose to stay off a similar slope.
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
Bison triggered Avalanche in YNP?
Out of Advisory Area
Code
SS-AW
Latitude
44.92680
Longitude
-110.45100
Notes
From an email:
Upper Elk Creek, E. aspect, 8,200 ft
Debris looked pretty fresh, Who knows, but could have been triggered either directly or remotely by bison. The disturbance to lookers left (at bench) is due to bison - they are not cryptic animals!
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Wildlife
Images
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
From an email:
"Upper Elk Creek, E. aspect, 8,200 ft
Debris looked pretty fresh, Who knows, but could have been triggered either directly or remotely by bison. The disturbance to lookers left (at bench) is due to bison - they are not cryptic animals!" Photo: J. Logan
From an email, "... our party observed several small to medium-sized releases that occured on a heavily-loaded east aspect overnight. None stepped down in the snowpack, but they certainly could have taken a person for a ride. Overalll, stability seemed to be good, with the exception of isolated wind-loaded areas." Photo S. Reinsel