Scientists used pre-storm conditions from an observed F4 tornado in South Dakota in 2003 to initialize a simulation that produces a severe supercell storm that produces a powerful tornado and terabytes of data. Data driven visualization components reveal the inner-workings of thesimulation. Interactively filtered streamtubes colored orange when risingand blue when sinking represent the path of air through the storm. A swirling mass of red spheres in the low pressure tornado vortex delineates the developing tornado. On the ground plane, tilting cones represent wind speed and direction. Colored by temperature, they show a surface boundary where warm and cold air interact at the tornado's base. This visualization represents one hour of storm evolution. Large scale thunderstorm simulations have only recently produced small scale tornadic features as seen here.