In Wisconsin, Gov. Scott Walker declared a state of emergency, put the National Guard and state patrol on standby and closed state offices to the public in 20 counties most likely to be affected by the storm. Employees were still expected to report for work.
As much as 7 inches was already on the ground Thursday morning in parts of southern Wisconsin, with as much as another foot on the way during the storm's predicted Thursday afternoon peak.
The Wisconsin State Patrol and National Weather Service urged people to avoid traveling.
Blizzard warnings were up Thursday for portions of Nebraska, Missouri, Minnesota, Illinois and Wisconsin and virtually all of Iowa. Winter storm warnings extended further into Missouri, Illinois and Wisconsin, as well as into Michigan and Indiana.
Most airports were operating normally, the Federal Aviation Administration reported. One major exception was O'Hare International Airport in Chicago, where incoming flights were running nearly two hours behind because of high winds, the FAA said. Airlines canceled more than 200 flights at O'Hare Wednesday.
Southwest Airlines has canceled all flights out of Chicago's Midway starting at 4:30 p.m. Wednesday. Southwest has between 200 and 220 flights there on normal days.
The storm is expected to slide over New England by Friday.