These ingredients are present elsewhere, such as South America, southeastern China, Bangladesh, and on the Tibetan Plateau, notes Paul Markowski, an associate professor of meteorology at Pennsylvania State University in State College. "But no place do these conditions occur on as vast a scale as the Great Plains of the United States," he says.
The Gulf of Mexico supplies warm, moisture-laden air that moves north near ground level. Winds flowing eastward over the Rocky Mountains provide an overlying layer of cold air. The initial lift can come from daytime heating, from wind deflected up as it blows across uneven terrain, or from a cold front moving east.
As the warm air rises and cools, water vapor in the air condenses, releasing back the heat that turned Gulf of Mexico seawater into a gas in the first place. This newly introduced heat source warms the surrounding air, giving the air parcel additional lift. If the surrounding air continues to get colder with altitude, the relentless flow of moisture-laden air into the updraft forms a sprawling, anvil-shaped thunderhead.
Meanwhile, wind shear at mid-levels sets up a rolling pin-like circulation of air drawn into the updraft, imparting rotation to the core of the storm.