A major winter storm is moving across the U.S., bringing snow from Denver to Chicago and ice to the South -- before heading to the Northeast.
Six inches to 1 foot of snow is possible, along with sleet and freezing rain, from St. Louis to Indianapolis and Detroit to Cleveland.
Thousands of flights have been canceled from Chicago to Denver.
MORE: Winter storms: How to prepare and everything else you need to knowA winter storm warning has been issued in Chicago where 5 to 10 inches of snow is expected.
Illinois Gov. JB Pritzker has issued a "disaster proclamation" and activated at least 100 National Guard members.
The Illinois Department of Transportation tweeted: "Two words of advice: Stay home."
A winter storm warning was also issued in Denver where up to 6 inches of additional snow is forecast.
Denver schools are closed Wednesday due to the storm.
In Missouri, Gov. Mike Parson has issued a state of emergency.
The storm has backed up lanes in both directions on Missouri's Interstate 70.
Further south, an ice storm warning was issued from Memphis to Louisville. By Thursday morning the ice could be as thick as half an inch, sending trees toppling onto power lines and making roads very dangerous.
A winter storm warning was also issued for Dallas, where residents could see a wintry mix of 1 to 3 inches of snow and sleet, as well as freezing rain.
By Thursday morning the heavy snow will stretch from Texas to St. Louis to Indianapolis to Cleveland to Buffalo. On Thursday very icy conditions are expected across Texas and Arkansas and up through Cincinnati and Pittsburgh.
Flooding is also a threat from northern Mississippi to West Virginia due to heavy rain on Thursday.
The storm will then move into the Northeast Thursday night into Friday morning, bringing snow, sleet and freezing rain.
Over 1 foot of snow is possible in western Pennsylvania, upstate New York and parts of New England.
A winter storm watch has been issued for Boston, where residents still digging out from last weekend's massive snowstorm could see an additional 6 inches of snow on Friday.
MORE: How to stay safe in coldDangerous ice accumulation is possible from Washington, D.C., to Philadelphia to New York City to Boston.
New York City will see rain on Thursday which will then change to freezing rain and some sleet on Friday morning. The National Weather Service warns that New York City Tristate region should be prepared for dangerous travel conditions on Friday.