Examining the May 20, 2013, tornado strike in Moore, Okla., which occurred two years after the worst tornado season on record, and whether improved radar and warning systems led to fewer deaths than in the May 22, 2011, tornado hit in Joplin, Mo. The installment also explores whether the warming atmosphere will cause more tornadoes in the future; features scientists who study extreme-weather events and storm survivors; and explains how people and communities can protect themselves.