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 debris being wrapped around the supercell.[1] It is one of the classic hallmarks of tornado-producing supercells.[2] The National Weather Service may consider the presence of a hook echo coinciding with a tornado vortex signature as sufficient to justify issuing a tornado warning.[3][4]