Hook echo
A comma- or hook-shaped appendage on the rear edge of a supercell’s reflectivity, where the rear-flank downdraft wraps rain around the mesocyclone. It is the oldest tornado signature on radar, spotted in 1953, and it is still the shape people look for first.
A hook is a hint, not a verdict: plenty of hooks never produce a tornado, and plenty of tornadoes come from storms that never draw a tidy one. Read it alongside the velocity — a tight couplet in the same place is the real tell — and CC, which drops where debris is being lofted.
The longer story is where this app got its name.
Related
- Storm-relative velocity Velocity with the storm's own travel subtracted, so rotation stops hiding inside the storm's motion.
- TDS (tornado debris signature) High reflectivity, a velocity couplet, and a hole in CC in the same place: the radar seeing lofted debris.
- Reflectivity (Z) How much energy the echo sends back. Where the rain is.
See it on real storms: open the radar, or read reading the radar.