During the approach of the most powerful storm in decades, university professor Dr. Jo Harding (Helen Hunt) and an underfunded team of students prepare the prototype for Dorothy, a ground-breaking tornado data-gathering device conceived by her estranged husband, Bill (Bill Paxton). When Harding tells Bill that Dorothy is ready for testing — and that their privately funded rival Dr. Jonas Miller (Cary Elwes) has stolen the idea and built his own — Bill rejoins the team for one last mission.