CHICAGO (AP) — A winter storm blanketed much of the central Midwest with snow on Sunday at the end of the Thanksgiving weekend, bringing blizzard-like conditions that grounded hundreds of flights and forced the closure of major highways on one of the busiest travel days of the year.

"It's going to be messy," said Todd Kluber, a meteorologist for the National Weather Service who is based in suburban Chicago.

With much of the central Plains and Great Lakes region under blizzard or winter storm warnings, around 1,200 flights headed to or from the U.S. had been canceled as of 6 p.m. Sunday, accord...