On radar, high reflectivity from tornado-lofted debris is colloquially called a debris ball.
A debris ball is the radar appearance of a tornadic debris signature, or TDS. When a tornado lifts pieces of buildings, trees, vehicles, and other objects, those targets reflect radar energy and appear as a compact, rounded area of unusually high reflectivity. The signature is especially useful when rain obscures the tornado from ground observers.
Modern dual-polarization radar adds confirmation. Debris has irregular shapes and tumbles through the air, typically producing a low correlation coefficient and differential reflectivity near or below 0 decibels. Meteorologists therefore examine reflectivity, velocity, and polarimetric data together rather than treating one bright spot as conclusive proof.
A debris ball is not guaranteed with every tornado. It depends on the tornado’s strength, the availability of debris, the radar’s distance and viewing angle, and whether the debris reaches the radar beam. A hook echo indicates storm structure, while a dry slot is a region of relatively dry air.