The busiest travel weekend of the year got a bit busier in the Midwest.

Blizzard-like conditions in Kansas, Missouri and Illinois caused a flurry of cancellations and delays on Sunday and Monday at Kansas City International Airport and O’Hare International Airport in Chicago, creating a Thanksgiving weekend travel nightmare. The storm dumped more than a foot of snow in an area stretching from northern Kansas through Iowa and into Illinois.

“As a city, we are used to snow, but it is the first of the season,” Mayor Rahm Emanuel of Chicago said at a Sunday evening news conference. “It is an all-hands-on-deck effort for the city.”

Mr. Emanuel said he was rallying resources to streamline Monday morning’s commute for Chicagoans. Gov. Jeff Colyer of Kansas declared a state of disaster emergency, enabling state resources to be used for the response to the snowstorm.

Over 600 flights have been canceled at O’Hare, and over 120 flights have been canceled at Midway Airport in Chicago, according to the flight tracking website FlightAware.com. More than a dozen flights departing from Kansas City were canceled on Monday morning. At O’Hare on Monday, a handful of departure flights were delayed, while many were still scheduled to leave on time.