Tornadic supercell thunderstorm. A supercell thunderstorm is a severe long-lived storm in which the wind speed and direction changes with height. It comprises a strong rotating updraft of warm air, known as a mesocyclone, and a separate downdraft of cold air. When a tornado forms in the mesocyclone, the storm is classified as a tornadic supercell thunderstorm. The greenish color in the sky is caused by very large hailstones. Photographed in Nebraska, USA.
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