On May 3, 1999, one of the most powerful tornadoes ever recorded carved a path of complete destruction near Oklahoma City. To scientists, the supertwister held sobering lessons about the future for rapidly expanding cities in tornado-threatened areas. Most tornadoes form suddenly and with little warning. But now meteorologists are on the verge of a breakthrough that may solve the puzzle of how these killer storms spawn and where they are likely to strike. NOVA follows stormchasers as they probe the tornado's deadly secrets. The program features noted researchers Joshua Wurman of the Center for Severe Weather Research in Boulder, Colorado, and Howard Bluestein of the University of Oklahoma--fellow stormchasers who have perfected the art of tracking down tornadoes with instrument-laden vehicles designed to gather data from as close to the churning vortex as possible. Also included is Lou Wicker of the National Severe Storms Laboratory, who is creating computer models in collaboration with scientists at the National Center for Supercomputing Applications (NCSA)/University of Illinois, that provide exciting insights into the intricate sequence of steps that goes into spawning a twister. NOVA goes supertwister hunting with Wurman and Bluestein on a day that threatens tornadoes all across the Texas Panhandle. Wurman heads north and captures the first twin tornadoes ever recorded on radar. Meanwhile, Bluestein stays in the southern Panhandle and eventually bags his own treasure-trove of twister data. Not to be outdone, computer modeler Lou Wicker captures the biggest prize of all: a supertwister in the process of formation in the equations of his program. Having input data on an F4 storm that devastated Manchester, South Dakota, on June 24, 2003, he sees a supertwister take shape with uncanny similarity to the real thing.