A hook-shaped extension on the back side of a supercell’s radar echo, caused by precipitation wrapping around the rotating updraft. Tornadoes are often found near the tip of the hook.
A hook in reflectivity (left) and a tight green-beside-red couplet in velocity (right) at the same spot is the classic radar sign of a rotating storm that may be producing a tornado.
How to spot it
Seen only on radar, as a curved appendage at the south-west corner of a storm echo.
On radar
A clear hook in reflectivity; confirm with a velocity couplet in the same location.
Safety
Not every hook means a tornado, and not every tornado has a hook. Treat it as a warning sign.
