MINNEAPOLIS — The Upper Midwest is about to plunge into a deep freeze.

The National Weather Service says the wind chill factor could dip to 40 to 50 degrees below zero in parts of Wisconsin and Minnesota and to 30 to 35 below in the Dakotas starting Thursday night.

Such wind chills, which describe the combined effect of wind and cold temperatures on exposed skin, could cause frostbite within minutes.

The deep freeze caused organizers of the Winter Carnival in Minnesota to cancel several events, including Thursday night's parade through downtown St. Paul.

Sioux Falls, South Dakota, has closed its six outdoor skating rinks because of the cold weather.

Forecasters say the frigid weather is expected to stick around into next week.