A tornado warning will tell you specifically what prompted it to be issued. Many are issued based on radar showing rotation, ...

Follow your tornado drill protocol and make your way to the designated tornado shelter area. Maintain a safe distance from windows and avoid seeking refuge in large open rooms like cafeterias ...

meaning a violent tornado has touched down in the area. The website uses the phrases "be prepared," "take action" and "seek shelter immediately" to summarize the three alerts. Sirens are tested on ...