An avalanche in southern Montana buried three snowmobilers from North Dakota, killing a 33-year-old man.

The Park County Sheriff's Office says two riders were able to dig themselves out Saturday from the slide north of Cooke City on the Montana-Wyoming line. The victim and his companions have not been identified.

The Gallatin National Forest Avalanche Center is warning people in the backcountry about dangerous conditions.

Officials said Sunday that continuing snowfall and strong winds have made the snowpack unstable and natural and human-triggered snow slides are likely.

The warnings cover the mountains near Cooke City, the Madison Range, the Gallatin Range, the Lionhead area near West Yellowstone and the Bridger Range.