High Quality Content by WIKIPEDIA articles! A tornado warning (SAME code: TOR) is an alert issued by government weather services to warn an area that a tornado may be imminent. It can be issued after either a tornado or funnel cloud has already been spotted, or if there are radar indications that a tornado may be possible. When this happens, the tornado sirens may start going off in that area, letting people know that a tornado was seen or is forming nearby.