GNFAC Avalanche Forecast for Wed Dec 18, 2024

All Regions

Dangerous avalanche conditions exist across the advisory area. New and wind-drifted snow are adding weight to persistent weak layers buried 1-2.5 feet deep. The mountains have received snow for the last four days straight, with 1-2” in the last 24 hours. Today, strong winds gusting to 60 mph will transport recent snow, thicken slabs over weak layers, and build unstable drifts at all elevations.

Four-Day Storm Totals:

• Bridger Range, Cooke City, Island Park and Big Sky - 15-23” (1.4-2.1” SWE)
• West Yellowstone, Taylor Fork and Hyalite Canyon - 9-14” (0.8-1.4” SWE)

The threat of persistent slab avalanches is our primary concern, with human-triggered slides likely on steep slopes. Yesterday, Ian and his partners triggered an avalanche on a steep slope while they were still 200 feet away at Buck Ridge (details and media). In the Centennial Range, Mark traveled “really carefully, avoiding avalanche terrain” because of a weak layer of facets buried 1-2 feet deep throughout the range (video), and in Cooke City, I triggered whumphing collapses (video). Recent avalanches, whumphs, and shooting cracks communicate instability. Heed the message and minimize your exposure to steep terrain.

Wind slab avalanches failing 1-3 feet deep are likely. Their distribution will be widespread and atypical as strong winds rip through recent snow. Yesterday, we saw clear examples of wind-loaded terrain near Cooke City with large drifts at ridgelines and gullies. Similar images can be found across the advisory area (photo, photo 2). Beyond recent avalanche activity, shooting cracks and a stiffening of the snow surface indicate unstable wind slabs.

Notable Recent Avalanche Activity Since Sunday (More at Avalanche log):

• A remotely triggered avalanche at Buck Ridge slid on a steep slope 200 feet away from a group of riders (details and photos)
• Two recent avalanches in McAtee Basin (details and photos)
• An intentionally triggered slide that broke up to 2 feet deep near Ross Peak in the Bridger Range (details and photo)
• Many natural avalanches on Saddle Peak and in Argentina Bowl (details)
• Remotely triggered wind slab avalanche on Henderson (details, GNFAC video and ob)
• Small snowmobiler-triggered avalanche at Buck Ridge (details and photo)
• Persistent slab avalanche near Island Park (details)
• Collapsing, cracking, and a remotely triggered storm snow avalanche in Beehive (details, details)
• Skier triggered storm slab avalanche on The Throne (details)

Today, seek out smaller, lower-consequence terrain and slopes sheltered from the effects of the wind. Recreating in terrain less than 30 degrees without steeper terrain above largely eliminates the risk of avalanches. Safer travel in and around avalanche terrain requires careful route-finding and snowpack assessment. The avalanche danger is rated CONSIDERABLE.