DES MOINES, Iowa – Snow and ice plastered a wide area of the Midwest on Saturday, disrupting campaigning by presidential hopefuls, making highways hazardous and closing Des Moines’ airport.

The National Weather Service posted winter storm and ice warnings across parts of Nebraska, Iowa, Minnesota, Wisconsin, the eastern Dakotas, Illinois and northern Michigan, although some warnings were lifted by midday. Six to 16 inches of snow was forecast in parts of Minnesota.

Much of Iowa was hit by snow, sleet and freezing rain.

Hundreds of flights were canceled at airports in Des Moines, Chicago and Milwaukee. Officials decided to close Des Moines International Airport for several hours after a United Airlines plane slid off a taxiway as it was heading to a runway for a flight to Chicago’s O’Hare, said airport spokesman Roy Criss. He said none of the 44 passengers was injured and the airport reopened by mid-afternoon.

At Dane County Regional Airport in Madison, Wis., an incoming Mesa Airlines regional jet flying for United Express slid off the pavement after failing to make a turn onto a taxiway, but no injuries were reported among the 25 passengers, said United Airlines spokesman Jeff Vick.

Madison was expecting three inches of snow and overnight wind gusts of up to 30 mph, an outlook so bleak that even meteorologists were postponing their own events. The University of Wisconsin-Madison’s Department of Atmospheric and Oceanic Sciences department postponed its annual Solstice Party, which was set for Saturday, until February.

“This is the most treacherous kind of weather that the weather can deliver,” said department chairman Jonathan Martin.

The storm also complicated plans for some presidential hopefuls drumming up support for the Jan. 3 caucuses that kick off the nomination process.

Republican Mitt Romney canceled three campaign stops planned Saturday in southern Iowa, and former President Clinton canceled a rally for his wife, Sen. Hillary Rodham Clinton, scheduled Saturday afternoon outside Des Moines.

Heavy ice accumulations on power lines blacked out more than 14,000 customers scattered around Iowa, said representatives of for Alliant Energy and MidAmerican Energy. Thousands more were without power near Galesburg, Ill., Ameren spokesman Leigh Morris said.

Numerous accidents were reported on Iowa highways, said Transportation Department spokeswoman Dena Gray-Fisher.

Many travelers checked into motels to wait out the storm in the northern Iowa city of Clear Lake, but Lake Country Inn manager Linda Lorenz said she was surprised by the numbers of vehicles that stayed on the highways.

“They’re still going,” Lorenz said. “I don’t know why they aren’t home, I’m not leaving.”

Freezing rain coated Illinois highways with ice, causing spinouts and accidents, weather officials said. Ice was about a quarter-inch thick in parts of central Illinois, said weather service meteorologist Dan Kelly.

More than 400 flights were canceled at O’Hare International Airport and 25 were reported at Midway International Airport, said Gregg Cunningham, a spokesman for Chicago’s Department of Aviation. Flights at O’Hare were delayed 40 to 60 minutes, with times expected to increase.

“The snow has turned over more to freezing rain, so the weather and low visibility is causing those delays,” Cunningham said.

Many parts of Minnesota reported difficult driving conditions by early afternoon, the state Department of Transportation reported. Snow mixed with sleet along the Interstate 90 corridor across the southern edge of the state and visibility was down a quarter-mile in places.

Snow with wind of 20 to 25 mph reduced visibility in southeastern South Dakota and brought cancellations of regular weekend activities such as YMCA basketball, church practices, high school athletics and community events. One Sioux Falls television station had posted 43 event cancellations and postponements on its Web site by noon.

In North Dakota, snowy conditions caused numerous accidents, among them a crash on Interstate 94 in Fargo that involved a dozen vehicles including a passenger bus, Highway Patrol Capt. Jim Prochniak said.

Vehicles are “bumping into one another like pingpong balls out there,” he said.

The weather also caused the search for two missing Illinois women to be called off after four hours of searching Saturday. More than 200 people scoured parts of Romeoville for Stacy Peterson, 23, who disappeared over a month ago from her Bolingbrook home, and 38-year-old Lisa Stebic, of Plainfield, who was reported missing in April.

Associated Press writers Ashley M. Heher and Sophia Tareen in Chicago contributed to this report.