A winter storm pummeled parts of the Midwest on Saturday, turning roads into a snowy and slushy mess that has contributed to the deaths of at least nine people, including a state trooper in Illinois, the authorities said.

The storm was expected to head toward the Mid-Atlantic States, with several inches of snow forecast for Washington, D.C., and much of Virginia. In Missouri, up to 17 inches of snow had fallen in the central part of the state, the National Weather Service said.

Winter storm warnings extended across a widespread portion of the United States: from central Kansas, across areas of the Midwest and into southwestern Ohio, the Weather Service said. The warnings also stretched from the central and southern Appalachians to eastern Virginia. As the storm moved east, some in Washington sought to stock their shelves in preparation for its arrival.

As of Saturday afternoon, the Missouri State Highway Patrol reported more than 800 vehicle crashes and four fatalities. It also responded to almost 1,800 stranded drivers. Officials warned drivers to stay off the road, citing heavy snowfall and freezing rain in some places.