In this video excerpt from NOVA: “Deadliest Tornadoes,” examine how the climate phenomenon of La Niña may help set up conditions conducive to large tornado outbreaks. Thermal images show a region of unusually cold sea-surface temperatures in the eastern Pacific Ocean, off the coast of Peru. This deviation from normal sea-surface temperatures, called La Niña, impacts ocean processes and global weather. Scientist Roger Pielke, Sr. explains how during a La Niña event, the combination of a strong jet stream and moist air in the southeastern United States may provide prime conditions for a particularly dangerous tornado season in 2011. (Pielke was correct, as an unusually high number of tornadoes were reported across the United States in 2011.)
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