CHICAGO — An arctic air mass moved across the upper Midwest on Sunday, freezing water pipes in Minnesota and leading Chicago officials to ask residents to check on neighbors.

Due to El Niño, winter got off to a mild start. But a blast of dangerous cold moved east across the Northern Plains and Great Lakes over the weekend.

Temperatures bottomed out at 36 degrees below in Fosston in northwest Minnesota. More than 800 miles to the southeast, wind chills in Indianapolis were expected to plummet to 20 degrees below zero.

Parts of Illinois were in the single digits.