A severe winter storm was driving across the upper Midwest on Sunday, dumping up to 15 inches of snow and causing white-out conditions in spots from the Dakotas through Minnesota and into Wisconsin.

State officials warned against travel in most of South Dakota where roads were not already closed, most southern Minnesota roads were slick and snow-covered with limited driver visibility and airlines canceled hundreds of flights.

In Seattle some flights were canceled due to the conditions in the Midwest. Click here for Sea-Tac Airport flight info.

The National Weather Service said travel will be very difficult at times due to ice and snow in southern Wisconsin, where a mass protest against changes to collective bargaining laws was expected to continue at the state capital in Madison.

Forecasters expect up to four inches of snow in southern Wisconsin with some sleet and freezing rain leading to ice accumulations in some areas.

The storm was expected to dump up to 15 inches of snow in Minnesota from Sunday to midday on Monday and nearly a foot of snow across central to northeast Wisconsin, the National Weather Service said. Earlier forecasts had aimed for snow accumulations of up to 18 inches in parts of Minnesota.

The National Weather Service on Sunday afternoon forecast 10 to 14 inches of snow for the Twin Cities overall by the time the storm ends on Monday, said Tony Zaleski, a meteorologist with the National Weather Service in Minnesota.

"The biggest snow amounts have been basically across south central Minnesota," Zaleski said.

Blizzard conditions were developing west and south of Minneapolis where up to 8 inches of snow were reported in New Ulm and Lester Prairie, the National Weather Service said.

South suburbs to Minneapolis and St. Paul had already reported snow falls of 5 to 7 inches on Sunday afternoon, Zaleski said.

"There is a lot of blowing snow out there, it's real tough to measure when you have the snow blowing at 20 to 30 miles per hour," Zaleski said.

Most flights were canceled out of Minneapolis-St. Paul International Airport on Sunday from the storm that brought high winds that reduced operations, airport spokeswoman Melissa Scovronski said.

Delta Air Lines canceled hundreds of flights at the airport Sunday and expects more flight cuts on Monday across its route system, particularly in the midwest and northeast United States, spokesman Anthony Black said.

Heavy snows in December and at other points already had pushed snowfall totals to more than 61 inches in the Twin Cities before the latest storm, making it the fifth snowiest on record, according to National Weather Service statistics.

A 10-inch snowfall would make it the second snowiest winter behind only 1981-82 when 76.9 inches of snow were recorded.

Blizzard conditions crossed much of South Dakota with more than a foot of snow and wind gusts of up to 40 miles per hour in a band from Pierre to Watertown, forecasters said.

South Dakota closed Interstate 29 from Sioux Falls north to the North Dakota border on the eastern side of the state and closed a 150 mile stretch of Interstate 90 from Wall to Chamberlain on the south central part of the state.