The Latest on severe weather predicted in the central and eastern U.S. (all times local):

6:15 a.m.

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.

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1:20 a.m.

School districts and authorities are bracing for the possibility of a severe weather outbreak that could bring powerful, long-track tornadoes and large hail to the Great Plains.

The weather on Tuesday could include heavy winds, tornadoes and hail as large as baseballs or softballs. The Storm Prediction Center in Norman, Oklahoma, says the most dangerous weather will likely take aim at an approximately 70,000-square-mile area stretching from southern Oklahoma to southern Nebraska.

In all, nearly 37 million people from the Rio Grande River in South Texas to Omaha, Nebraska, and the western regions of Missouri, Arkansas and Iowa are at a slight risk or higher of experiencing severe weather Tuesday.

In the east, a separate storm system could bring thunderstorms, strong winds and hail to Philadelphia, Baltimore and Washington, D.C., but the risk of severe outbreaks is low.