Travelers planning to head Friday from Minnesota through Iowa or to Chicago will likely encounter difficulties as the region digs out from a blizzard that was expected to dump 12 to 20 inches of snow across Wisconsin and 6 to 9 inches in the Chicago area.

The National Weather Service said travel on the first day of winter would be "extremely difficult." Winds up to 50 miles per hour are expected to reduce visibility and make it difficult for plows to keep roadways clear.

In Minnesota, heavy snow closed schools and highways across the state's southeast corner Thursday. And in Iowa, two people were killed in a 25-vehicle pileup on Interstate 35 about 60 miles north of Des Moines, where drivers blinded by blowing snow didn't see vehicles that had slowed or stopped on the highway. The highway was closed from Ames to Albert Lea, Minn., a stretch of 120 miles.

Blizzard warnings were in effect for much of the day Thursday across southeast Minnesota, eastern Iowa, southern Wisconsin and northern Illinois. State offices across Iowa were closed Thursday.

By midafternoon Thursday, 12 inches had fallen at Foster, Wis., along Interstate 94 south of Eau Claire. Spring Valley, Minn., southeast of Rochester, reported 8 inches.

In Chicago, high winds and rain -- which was expected to turn to the season's first measurable snow overnight -- grounded hundreds of flights at the city's two major airports, as well as at Kansas City and Detroit. At Minneapolis-St. Paul International Airport, spokesman Patrick Hogan said about two dozen flights to Chicago were canceled Thursday. But he expected some improvement Friday. Travelers should check their flight's status with their airline.

Shanna Tinsley, 17, and Nicole Latimer, 20, were headed from Milwaukee to the Kansas City area to see their families for the holiday when their flight Thursday morning was canceled. Neither cared about a white Christmas.

"It would be cool I guess, but I'd rather be there than stuck without family with a white Christmas," Latimer said.

Eight jackknifed semitrailer trucks were reported on a section of Interstate 80 east of Des Moines. The storm also closed part of Interstate 29 in northern Missouri and part of Interstate 80 in Nebraska. Iowa and Wisconsin activated National Guard troops to help rescue stranded drivers. At the University of Wisconsin in Madison, in-person final exams were called off Thursday.

Armories in cities across the state were opened as emergency shelters and warming areas. National Guard soldiers were on call to respond to stranded motorists and help in closing roads.

The owner of the Norske Nook restaurant and bakery in Osseo, along Interstate 94 in west-central Wisconsin, where 10 inches of snow had fallen by Thursday morning, said that "blizzardy" conditions were not unusual for the area and that the weather would not upset her business.

"It's our policy to stay open for the customers," Jean Zingshiem said. "In case someone is stranded they'll have somewhere to go."

Star Tribune staff writers Bill McAuliffe and Paul Walsh contributed to this report.