A handful of Oklahoma schools have preemptively canceled classes Tuesday in light of an ominous forecast that's predicting dangerous tornadoes and giant hail for parts of the Great Plains.

Mid-Del Public Schools in the Oklahoma City suburb of Midwest City called off classes, saying that the safety and security of students and staff was the top priority. That district, along with others across Oklahoma, implemented new tornado safety plans following the 2013 twister that killed seven schoolchildren in Moore.

The Storm Prediction Center says much of the central U.S. is at risk for severe weather Tuesday, including tornadoes and grapefruit-sized hail. In all, nearly 37 million people are at a slight risk or higher for severe weather Tuesday.