Dashcam video from the scene shows a tractor-trailer losing control on Interstate 41 in Washington County and slamming into a snowplow before overturning in the low-visibility weather.
"Just kind of slalomed my way through that, worried about the stuff in the middle of the road, but at that point, there's nothing I can do," Bill Van Aacken, who recorded the video, told WDJT-TV.
The Washington County Sheriff's Office said the pileup on I-41 involved a total of 48 vehicles and that 38 were damaged.
A 37-year-old woman from Tennessee died in the pileup, the station reported. Authorities said six motorists were taken to local hospitals and treated for various degrees of injuries, while another 26 people were treated at the scene.
"Near white-out snow conditions will likely be a contributing factor in the investigations," the sheriff’s office said.
The Washington County Sheriff’s Office, Wisconsin State Patrol and Slinger Police Department are investigating the 20 different crashes that occurred on I-41.