GNFAC Avalanche Advisory for Thu Dec 7, 2017

Not the Current Advisory

Good Morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Thursday, December 7th at 6:45 a.m. Today’s advisory is sponsored Yellowstone Arctic Yamaha and Yamaha Motor Corp in partnership with the Friends of the Avalanche Center. This advisory does not apply to operating ski areas.

Mountain Weather

Overnight the mountains around Cooke City picked up 2” of new snow while the mountains around West Yellowstone picked up a trace to 1”. At 5 a.m. temps range from the teens to low 20’s F and winds are blowing 10-25 mph out of the W-NW. Today, skies will be mostly clear and temps will warm into the mid to upper 20’s F. Winds will continue to blow 10-25 mph out of the W-NW. A strong ridge of high pressure builds over the area starting today producing clear skies and dry weather for the extended forecast.

Snowpack and Avalanche Discussion

Wind slabs in the Bridger Range remain a problem on all aspects and elevations. Yesterday, the Bridger Bowl Ski Patrol triggered numerous slides during control work, all of which occurred on wind loaded slopes. The most significant slide broke 4’ deep and 100’ wide near the south boundary of the ski resort. Other slides breaking 12- 20” deep occurred across the mountain. These slides are bull’s eye information the snowpack has not yet adjusted to the heavy snow and wind from the past few days. Slides have been running on the Thanksgiving ice crust and have not broken into deeper layers. In general, the old snow underneath this crust is strong and stable (video).

Today, wind loaded slopes will remain sensitive to human triggers. For this reason, the avalanche danger is rated CONSIDERABLE on all wind-loaded slopes and MODERATE on all others.

The mountains around Big Sky, West Yellowstone and Cooke City including Hyalite have been mostly spared from the strong winds that nuked the Bridgers over the past few days. As a result, wind loading has been light with the exception of some transport occurring along the ridgelines (photo). Today, upper elevation slopes leeward to west-northwest winds could harbor the occasional wind slab. I don’t expect these to be overly sensitive to human triggers, but it’s worth assessing wind loaded slopes carefully before committing to serious terrain. If wind drifts present signs of instability such as shooting cracks or collapsing, it will be best to avoid these areas and seek terrain that is less wind loaded.

Aside from wind loaded slopes, the snowpack is mostly stable. Yesterday, I rode in Tepee Basin in the southern Madison Range and found stable snow in multiple snowpits. This is consistent with what Doug found on Buck Ridge on Tuesday (snowpits, video of Buck Ridge). It’s also similar to what skiers and riders are finding around Cook City.

For today, the avalanche danger is rated MODERATE on wind-loaded slopes and LOW on all other slopes.

If you get out and have any avalanche or snowpack observations to share, drop a line via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Upcoming Avalanche Education and Events

Events and Education Calendar

BOZEMAN

TONIGHT: Dec. 7, Avalanche Awareness and Beacon Practice, 6-8 p.m. at Beall Park, Bozeman

Dec. 13, Avalanche Awareness, 6:30-8 p.m. at Gallatin Valley Snowmobile Association, 4-Corners

Jan. 12 and 13, Companion Rescue Clinic, Info and Register

Jan. 17, 18 and 20 or 21, Introduction to Avalanches w/ Field Day, Info and Register Here

Jan. 24, 25 and 27, Advanced Avalanche Workshop w. Field Day, Info and Register Here

Feb. 9 and 10, Companion Rescue Clinic, Info and Register

HELENA

TONIGHT: Dec. 7, Avalanche Awareness, 6-7:30 p.m. at Basecamp, Helena

WEST YELLOWSTONE

Dec. 14 and 15, Snowmobiler Introduction to Avalanches with Field Course, Info and Register Here

COOKE CITY

8 and 9 December, Current Conditions and Avalanche Rescue, 6:30-7:30 p.m. Friday @ the Super 8, and anytime between 10-2 on Saturday @ Lulu Pass road.

 
The Last Word

Check out this 2-minute video on the snowpack. Great graphics illustrate the process of sintering and faceting. Thanks to SINTR Visual Communications!


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