GNFAC Avalanche Forecast for Mon Dec 13, 2021

Not the Current Forecast

Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Monday, December 13th at 7:00 a.m. This information is sponsored by Cooke City Super 8/Bearclaw Bob’s and Mystery Ranch. This forecast does not apply to operating ski areas.

Mountain Weather

This morning the mountains near West Yellowstone and Cooke City have 5-8” of new snow with no new snow elsewhere. Temperatures are high teens to high 20s F. Strong south-southwest wind has been steady at 20-40 mph with gusts of 40-80 mph. Today temperatures will be high 20s to low 30s F and strong southwest winds will continue at 20-40 mph. Heavy snowfall is expected near West Yellowstone today and tomorrow with snow elsewhere tomorrow. By tomorrow morning the mountains near Bozeman and Big Sky might get 1” of new snow with 1-3” near Cooke City, and 10-15” near West Yellowstone.

Snowpack and Avalanche Discussion

The mountains near West Yellowstone, southern Madison and southern Gallatin Range are in the direct path of the incoming storm. Snowfall is expected this morning and will continue into Wednesday. Avalanche danger will begin to increase today, especially on wind loaded slopes where continued strong winds will blow snow into thick drifts. Yesterday Dave and his partner rode into Lionhead Ridge and had a thick drift collapse and “whumph” beneath their skis (video). Skiers in the Taylor Fork sent this photo of a thick wind drift that broke on a small slope. Drifts of snow that formed from recent southerly winds overloaded weak layers and made the snowpack unstable. These drifts will continue to grow and become more unstable with new snow and strong wind today, and it will become likely for riders and skiers to trigger these drifts and cause avalanches on steep slopes. Be prepared to avoid steep, wind-loaded slopes today as they become more unstable.

Today, new snow and strong wind will increase the avalanche danger to CONSIDERABLE on wind-loaded slopes and MODERATE on all other slopes.

In the mountains near Bozeman, Big Sky and Cooke City recent strong southerly winds created unstable drifts that can avalanche under the weight of a person (video of strong wind). Yesterday multiple groups of climbers in Hyalite reported large drifts that cracked and “whumphed” under their feet (photo, photo). These drifts formed above weak, sugary snow which means they will remain possible to trigger for a couple days (photo of weak snow in Hyalite). The strong southerly winds formed drifts on many aspects, near ridgelines, across the middle of slopes, and locations where we don’t usually expect snow to be drifted into slabs. If you see cracking snow around your feet, stay off steep, wind-loaded slopes, especially where the consequences of getting caught in a slide involve being pushed into rocks, trees, gullies, or cliffs. Even without clear signs of instability, remain skeptical of wind-loaded slopes today (drifted Hyalite gullies video).

On slopes that are not wind-loaded the snowpack is generally stable. There are weak layers that are worth digging to look for and assess, but they are of little concern until we receive more snow (Bridgers video, Cooke City video 1, Cooke City video 2).

Today the avalanche danger is MODERATE on wind-loaded slopes and LOW on all other slopes.

If you get out, please send us your observations no matter how brief. You can submit them via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

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.

Wednesday, December 15, 6-7 p.m. FREE Sidecountry Avalanche Awareness for Families (and Friends). In partnership with Bozeman Parks and Recreation at Beall Park.  A 1-hr avalanche awareness talk with an emphasis on “Sidecountry Terrain and Snowpack.”

Every Saturday near Cooke City, 10a.m.-3p.m. FREE snowpack update and transceiver/rescue training. Stop by for 20 minutes or more. At the Round Lake Warming Hut.

Friends of GNFAC Powder Blast Fundraiser

The Friends of the Avalanche Center are hosting the Virtual Powder Blast fundraiser. With only $3,500 left to go, help us reach the $65,000 goal. Your donations support free and low-cost avalanche education, beacon checkers at trailheads, beacon parks, weather stations, and GNFAC programs!

The Last Word

Sadly, on Saturday a group of skiers were caught in an avalanche in the backcountry near Crystal Mtn., Washington and one person was killed. Link to Article. Our deepest condolences go out to those affected by this tragic event.


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