As you can tell from this map from FlightAware and the tracking info, the plane diverted to Green Bay.
While landing in Green Bay, snow on the ground caused the aircraft to slide off the runway.
The plane took off from Madison but severe weather prompted another diversion, this time to Green Bay, where it skidded off the runway, United says, adding that no one was hurt. That's where the plane left the runway after landing.
A United flight diverted from the Twin Cities in Minnesota slid off an icy runway at Green Bay's Austin Straubel International Airport. They were taken to the terminal by bus where alternative transportation is being arranged. United says Flight 878 was first sent to Madison, Wisconsin due to severe weather in Minneapolis. "Customers were also provided meals and hotel accommodations". However, the airport confirmed that an investigation from the Federal Aviation Administration (FAA). It was diverted to Madison because of bad weather conditions. Here, a United plane is pictured sitting on the tarmac at San Francisco International Airport on June 10, 2015 in San Francisco, California.