Cooke City

Strong winds and over a foot of new snow caused avalanches yesterday. Winds will continue today making dangerous avalanche conditions on many slopes. Avalanches can break 2 feet deep but may break 3-5 feet deep in heavily wind loaded areas. The safest terrain option is slopes less than 30 degrees in steepness that aren’t steep enough to slide. Avoid being under steeper slopes in case an avalanche happens above you.

In the past week, there have been 38 avalanches recorded, 6 people caught, 4 partial burials, 2 full burials, and 1 tragic fatality (avalanche activity log). This activity was concentrated in the Island Park, Lionhead, Cooke City, and Southern Madison areas. Yesterday’s activity was near Cooke City which had winds like everywhere else but more snow.

What’s going on in the snowpack? It’s been an odd season for sure.

1. Dry weather in most of January and the first week of February created a widespread weak layer of faceted snow on the snow surface. 
2. A storm Feb 8th & 9th capped this layer, then 4 days of dry weather faceted/weakened that snow creating a second weak layer in some places.
3. Surface hoar formed on top of the snowpack  in many areas during those periods of dry weather as well. Most notably Dave found it buried everywhere in the Portal Creek area of the Northern Gallatin Range, but we have found it mixed in with other faceted layers in other places sporadically.
4. All these weak layers exist on southerly facing slopes but also have ice crusts in the mix.
5. Snow falling Feb 15-19th (strong winds on the 17th) built a slab on these weak layers with the most avalanches and most snowfall occurring near Island Park & West Yellowstone.
6. Yesterday more avalanches happened near Cooke City which got the most snow plus the winds that all areas received. View avalanches on Henderson1, Miller, Scotch Bonnet, and Henderson2.

As you can imagine, all this weather has created two overlapping avalanche problems - wind slabs and persistent slabs. The avalanche danger has varied across the forecast area based on snowfall and wind (more snow and/or more wind -> higher danger).

Where does that leave us today?

In the Southern Gallatin and Madison Ranges, near Cooke City, near Island Park, and in the Lionhead area near West Yellowstone; avalanche activity + snowfall + wind + widespread weak layers all add up to dangerous avalanche conditions and CONSIDERABLE danger. There aren’t too many slopes in these areas where you can do careful assessments and confidently get into steeper terrain. I’d simply ride slopes less than 30 degrees in steepness to have fun and not worry about avalanches. 

The Northern Gallatin and Madison Ranges have gotten less snow thus the danger has generally been less. Seeking sheltered slopes is a good start, but there are buried weak layers to worry about. Watch Ian’s video from Tuesday as he describes the riding options. At upper elevations the danger remains CONSIDERABLE due to winds, and MODERATE at lower elevations.

The Bridger Range has had only one possible persistent slab avalanche about 10 days ago that was small. In the Bridgers, the main strategy has been to avoid recently formed wind slabs. Yesterday,the Bridger Ski Patrol triggered many 4-6” deep wind slabs and pillows at the ridge level with a few up to 12” deep. The danger in the Bridger Range is MODERATE today at upper elevations.