Classic appearing tornado hook echo on bottom of thunderstorm in lower left quadrant of scope. Apparently a storm in eastern Colorado or southwest Nebraska as Storm Data shows tornadoes only in that area on given date. June 12, 1983. The hook echo is one of the classical hallmarks of tornado-producing supercell thunderstorms as seen on a weather radar. The echo is produced by rain, hail, or even debris being wrapped around the supercell. The National Weather Service considers the presence of a hook echo as sufficient to justify issuing a tornado warning.