Doppler radar is a useful in finding the rotating winds of mesocyclones. A mesocyclone is a column of spinning air 5 to 10 kilometers across and a precursor to the development of a tornado.
Roughly 95 percent of all mesocyclones produce severe weather while approximately 30 percent result in tornadoes. Mesocyclones have a distinct signature on Doppler radar images, for example in the panel above. This image displays a mesocyclone associated with the tornadic supercell that moved through Ogden, Illinois around 9:00 PM CDT on April 19th.
The mesocyclone is shown here as the abrupt change in pixel color from red to blue, indicating a sharp change in wind direction over a very short distance. If a tornado develops out of a particular mesocyclone, the time between the initial mesocyclone identification and a tornado touchdown is roughly 20 minutes.