PIERRE, S.D. - Millions of people will feel the effects - to varying degrees - of the first significant wintry storm of the season, which is forecast to bring up to a foot of snow to parts of the Midwest.

Iowa and northern Illinois are bracing for some of the largest snow totals, but several states are under a winter storm warning or watch, the National Weather Service said Friday.

The storm system is moving east and will last through Saturday evening when it tails through Michigan, according to Richard Otto, lead forecaster at the National Oceanic and Atmospheric Administration's Weather Prediction Center.

The snowfall is "right on track" for the season, Otto said. But don't look for it to be the picturesque light, fluffy snow that often occurs in the dead of winter, he said - much of it will be wet and heavy.

Already, southern South Dakota saw significant snowfall and poor traveling conditions Friday morning, with a foot or more of snow expected by the time it tapers off. Tractor-trailers pulled off slow-moving interstates to park for the day, said Bret Brown, a cashier at Roadway Express truck stop in Sioux Falls.

"A lot of people complaining about it, nobody wants to be out in it," he said. "Interstates are down to 10 miles per hour, the side streets are blocked and there's a lot of cars in ditches everywhere."

In central and eastern Iowa, road conditions were deteriorating around the state Friday evening as they became covered in snow or ice. Six to 10 inches of snow was expected.

Meanwhile, northern Illinois was under a winter storm warning, with six to 10 inches expected. The weather service said it'll start off as rain and snow early Friday night, but turn into wet snow through Saturday afternoon.

The weather service also issued a winter storm watch for northern Indiana, saying snow accumulations of 4 to 7 inches are possible. The Indiana Toll Road in the northern part of the state is banning triple-trailer trucks from 7 a.m. Saturday to 1 a.m. Sunday because of dangerous conditions.