CHICAGO >> It’ll be a white Christmas for the northern Plains and some Western states, but it’s likely to cause troublesome travel.

Forecasters cautioned drivers to keep alternate routes in mind and prepare for possible delays.

A large swath of the Dakotas is under a blizzard warning Sunday and Monday, with the National Weather Service forecasting heavy snow and strong winds.

The Dakota Access pipeline protest encampment in southern North Dakota will be affected by the blizzard conditions. Morton County Sheriff’s Department spokesman Rob Keller says many left during a blizzard earlier this month, but added that there could be at least 500 people still at the camp.

To the east, parts of central Minnesota are under an ice storm warning.

Snow is also forecast for much of Idaho, Montana, Utah and northeast Colorado.

Air travel wasn’t yet impacted Saturday at the nation’s major airports. But snowy conditions Friday in Appleton, Wisconsin, caused the Minnesota Vikings’ team plane to slide off a runway.

The Storm Prediction Center cautioned that warm, humid air could cause severe weather in the lower Plains, Arkansas and Oklahoma on Sunday.