More than a foot of snow is expected in parts of Michigan and Wisconsin, forecasters said. Severe weather, with the possibility of tornadoes, will sweep states from Mississippi to the Carolinas.
The cancellations were felt most acutely in Chicago, where ice and snow briefly halted all flights on Tuesday afternoon. Airports elsewhere in the Midwest and the Northeast were also affected.
Four other students and an administrator were injured in the shooting at an Iowa school. The gunman, identified as a 17-year-old student, died from a self-inflicted gunshot, the authorities said.