"It's snowing sideways," said Kathleen Kelly, a ranger at Rocky Mountain National Park about 60 miles northwest of Denver. She said more than 5 inches of new snow had fallen at Bear Lake on top of 17 inches already on the ground.
The combination of zero visibility and closed roads forced drivers to pull off the roadway or find a different route. Slippery surfaces in some areas sent other cars spinning off roads.
The storm could drop more than 20 inches of snow before moving onto the Eastern Plains.
Winds gusted to 66 mph in Longmont, about 25 miles north of Denver, National Weather Service meteorologist Scott Entrekin said. Gusts of 60 mph were reported in Fort Collins, about 50 miles north of Denver.
Highway officials closed I-70 for nearly 60 miles between Georgetown and Vail for about eight hours, beginning about 30 miles west of Denver. U.S. 6 over Loveland Pass was also closed.
U.S. Highway 285 was shutdown between Fairplay and Kenosha Pass because of blowing snow, the state transportation department said.
Much of the central mountains were under a winter storm warning, and the entire eastern half of the state was under a high-wind warning. Transportation officials advised against driving high-profile vehicles on Interstate 25 north of Fort Collins.
Some ski resorts — with ski season starting to heat up — were expected to get another foot of snow.
In contrast, the city of Denver Tuesday was experiencing temperatures of nearly 50 degrees and some sun. Weather officials there say they expect rain later in the day with the possibility of light snow.
The Associated Press contributed to this report.