This 640 x 200 pixel image shows how the signature of a tornado may be detected by Doppler radar up to 20 minutes before touchdown. Winds in the clouds changing abruptly across a short distance may signal a potential or actual vortex, as for a tornado (top) in Hanston, Kan., observed by the author on May 16. A mesocyclone, in which tornadoes are usually embedded, appears on conventional radar as a hook-shaped appendage to the southwest side of the thunderstorm. The curl in the radar hook (bottom) for the storm in Hanston reveals the tornado as well.
