In 2011, the worst tornado season in decades left a trail of destruction across the U.S., killing more than 550 people. Why was there such an extreme outbreak? How do such outbreaks form? With modern warning systems, why did so many die? Is our weather getting more extreme - and if so how bad will it get? In this NOVA special, we meet scientists striving to understand the forces at work behind last year's outbreak. Could their work improve tornado prediction in the future? We also meet people whose lives have been upended by these extreme weather events and and learn how we all can protect ourselves and our communities for the future.