A
hook echo is a pendant or hook shaped
weather radar signature as part of some
supercell thunderstorms. It is found in the lower portions of a storm as air and precipitation flow into a
mesocyclone resulting in a curved feature of
reflectivity. The echo is produced by rain, hail, or even debris being wrapped around the supercell. It is one of the classic hallmarks of
tornado-producing supercells. The
National Weather Service may consider the presence of a hook echo as sufficient to justify issuing a
tornado warning.