The hook echo is one of the classical hallmarks of tornado-producing supercell thunderstorms as seen on 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.

presence of a hook echo as sufficient to justify issuing a tornado warning.

The hook echo has been recognized as a sign of tornado development for most of weather radar's existence. The first documented tracking of a hook echo was on April 9, 1953 by the Illinois State Water Survey, during preparations for an early test of radar's ability to measure rainfall rates.