In April 2011, the worst tornado outbreak in decades left a trail of destruction across the U.S., killing more than 360 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, get a look at the science behind the last year's outbreak, meeting those affected and the scientists striving to understand the forces behind the outbreak. Could their work improve tornado prediction in the future? Learn how we all can protect ourselves and our communities in the future.