The storm has caused severe air travel disruptions. According to FlightAware, more than 1,800 flights in and out of the U.S. have been canceled so far, including nearly 500 at Reagan National and more than 250 at Chicago's O'Hare International Airport, which issued a temporary ground stop earlier Monday due to snow and ice.

The National Weather Service has issued a Winter Storm Watch that goes into effect starting Sunday morning for Butler, Champaign, Clark, Clinton, Darke, Greene, Logan, Mercer, Miami, Montgomery, Preble, Shelby, and Warren counties in Ohio through Monday evening. It also includes Randolph, Union, and Wayne counties in Indiana.

Millions were under weather advisories as the storm stretched from southern Illinois to Washington, D.C. Snow could fall at 1-2 inches per hour.