What are general conditions for tornado formation in the United States?
The exact process of tornado formation is still in doubt, but in general this is how it works in the central area of the United States: A layer of cool, dry air moving high in the sky from the west or northwest rides over warm, moist surface air coming from the south. The warm air, sometimes a few thousand feet deep, is thus constrained from its natural tendency to rise by the lid of cold air pushing down on it. This sets up a condition of imbalance that is adjusted by a breakthrough, occurring most likely where the potential energy is greatest. At this breakthrough, the warm lower air forces its way upward and the heavier cool airdrops down. When this movement is accompanied by strong winds blowing in from the sides, a rotary flow of air is created that may form into a tornado vortex.
