AUSTIN, Texas—A major winter storm with millions of Americans in its path brought a mix of rain, freezing rain, and snow to the middle section of the United States on Wednesday as airlines canceled hundreds of flights, governors urged residents to stay off roads and schools closed campuses. The blast of frigid weather, which began arriving Tuesday night, put a long stretch of states from New Mexico and Colorado to Maine under winter storm warnings and watches. On Wednesday morning, Oklahoma, Kansas, Missouri, Illinois, Indiana, and Michigan saw freezing rain, sleet, and snow. The storm had already dropped heavy snow over much of Kansas and parts of Missouri by early Wednesday, with weather forecasters warning that the snow was only expected to intensify throughout the day. More than a foot of snow was expected in parts of central Missouri and Michigan, and up to a foot of snow could fall …