A weather system that blew in from California is leaving air travelers stranded and dumping steady snow on the Denver area Monday in what is expected to be the first big snowstorm of the season.

About a third of the flights at the city's airport were canceled before the snow picked up around midday. Up to about a foot of powder could fall along Colorado's heavily populated Front Range region by the time the storm moves out Tuesday and across the Plains.

Forecasters warned that the evening commute in the Denver area could be difficult and street conditions could worsen, but roads mainly were open around Colorado. Between 3 to 4 feet of snow is possible in the state's southwestern mountains, which typically get slammed by storms moving out of the Pacific.

Snow also was falling in parts of Wyoming, New Mexico and Arizona, and it's expected to spread into Iowa after voters have gathered for the state's leadoff presidential caucuses.

Possible blizzard conditions could complicate candidates' plans to leave Tuesday, when snow was likely in Nebraska, South Dakota, Minnesota and Wisconsin. The forecast prompted Nebraska state lawmakers to cancel hearings and debates, and some schools in Minnesota and Wisconsin announced closures for Tuesday.

Colorado's mountains have gotten plenty of snow so far this winter, which some experts believe is the result of the El Nino weather pattern, the natural warming in the Pacific Ocean that interacts with the atmosphere.

Denver and other communities just east of the mountains haven't gotten as much. But this storm will pack winds that are forecast to shift and blow up against the east side of the mountains, producing much more snow in populated areas.

"This is our first bigger storm," said Kari Bowen, a forecaster with the National Weather Service in Boulder.

The same system also brought about a foot of record-breaking snow to Lake Tahoe-area ski resorts, along with rain and cool weather to other parts of Nevada. It caused a pileup on Interstate 80 on Sunday near the Nevada-California line.

In Utah, about a foot of snow has fallen in the southern part of the state and on the ski resorts in the mountains east of Salt Lake City.

In California on Sunday, strong winds toppled power poles and trees, including one that killed a driver in San Diego County, and ripped off rooftops and even some solar panels.