DES MOINES — The first widespread snowstorm of the season crawled across the Midwest on Thursday, with whiteout conditions stranding holiday travelers and sending drivers sliding across slick roads — including into a fatal 25-vehicle pileup in Iowa.

The storm, which dumped a foot of snow in parts of Iowa and Wisconsin, was part of a system that began in the Rockies this week before trekking into the Midwest. It was expected to move across the Great Lakes overnight before moving into Canada.