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How to read radar for tornadoes

Weather radar shows two basic things: how much precipitation is out there (reflectivity) and how it is moving toward or away from the radar (velocity). Chasers use both to find the part of a storm where a tornado is most likely to form.

Hook echo and velocity coupletLeft: a reflectivity image of a supercell with green light rain, yellow and red heavy rain, a pink hail core and a hook curling from the south-west corner. Right: the same area in Doppler velocity, with a bright green inbound patch directly beside a bright red outbound patch at the tip of the hook, marking rotation.HOOKREFLECTIVITYCOUPLETVELOCITY
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.

Reflectivity: where the rain and hail are

Reflectivity measures how much of the radar beam bounces back from precipitation. Greens are light rain, yellows and oranges are heavier, reds and magentas are very heavy rain or hail. A compact area of the highest values is the storm’s core.

The core is where the hail is. Chasers who drive through it are doing something called core punching, and it is dangerous. The safer view is usually on the clear, quieter side of the storm.

The hook echo

In a supercell, rain and hail can be wrapped around a rotating updraft, producing a hook-shaped extension on the southwest side of the main echo. A hook on the radar is a classic sign of strong rotation, and the tornado, if there is one, is usually near the tip of the hook.

Not every tornadic storm shows a clear hook, and not every hook produces a tornado. It is a clue, not a guarantee.

Velocity: how the air is moving

Doppler radar also measures motion along the beam. Green shows motion toward the radar and red shows motion away. When a bright green patch sits right next to a bright red one, the wind is blowing in opposite directions over a short distance — rotation. Forecasters call this a velocity couplet.

Putting it together

A forecaster looks for a hook in reflectivity and a tight couplet in velocity in the same place. Radar can also detect debris being lofted by a tornado, which is a strong sign one is on the ground and damaging.

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Last reviewed 2 November 2026