Elsewhere, severe thunderstorms moving in from the Gulf of Mexico are expected to dump from 2 to 6 inches of rain over New Orleans, Louisiana, and Montgomery, Alabama, according to CNN's weather center, before rolling up toward Atlanta.
The torrential rains could lead to significant river flooding near the Gulf, as flood watches are still in effect from last week's heavy rains.
Heavy winds, hail and tornadoes are possible, the National Weather Service says. Downpours are expected to continue into Friday.
It was snowing Wednesday in Denver where almost a dozen inbound flights were canceled, according to the flight-tracking website FlightAware.com. More than 200 flights into or out of U.S. airports were canceled, the website said, with almost 175 already called off for Thursday.
Kansas City International Airport posted a statement on its website advising passengers to check their flight status before heading to the airport.
"There is potential for more cancelled or delayed flights as the storm continues," the statement said. Flight Aware reported that more than 100 flights were affected at that airport.