Hook Echo, Debris Ball, Bow Echo: What Meteorologists Mean By These Radar Terms

R​adar displays several visual cues to meteorologists when tracking severe weather and tornadoes. "Debris ball," "hook echo" and "bow echo" are just some of the terms you might have heard before on The Weather Channel or elsewhere.

W​e're here to give a little Meteorology 101 lesson on what these mean so that next time severe weather threatens, you can put this knowledge to use.

1. H​ook Echo

As its name implies, this refers to an appendage that appears as a hook on radar and usually comes out of the southwest (lower left) portion of some supercell thunderstorms. It's an indication the storm has a strong updraft and sometimes rotation. When tornadoes are spawned by supercells, they are located near the tip of the hook echo on radar. But a hook echo doesn't always mean a tornado is in progress.

The example above shows a supercell with a hook echo near Lubbock, Texas, that produced large hail and strong wind gusts but no tornado.

2. D​ebris Ball

N​ow that we know what a hook echo is, we can move on to this next radar signature that's sometimes seen within them.

The mention of a debris ball on radar is an indication that a damaging tornado is in progress. It means the radar is sensing an area of higher reflectivity in the hook echo, which is often associated with debris that has been lofted thousands of feet in the air.

Above is an example of a debris ball (purple shading in the hook echo) from a tornado that produced EF3 damage near Crossville, Illinois, on Feb. 28, 2017.

3. 'T​DS'

T​his is an acronym you might hear that stands for "tornadic debris signature." Like a debris ball, it means the radar has detected debris lofted into the air from a tornado in progress.

The upgrade of National Weather Service radars to dual polarization technology earlier this century allowed meteorologists to see a TDS and communicate that a tornado is in progress and causing damage, even if it happens at night or no spotters have seen it yet. It's often seen using what's called correlation coefficient (CC) radar data.

Airborne tornado debris consists of items that are vastly different sizes and shapes, falling to the ground much differently than precipitation, which is what the CC parameter detects. The example CC radar snapshot above from an EF4 tornado that hit Newnan, Georgia, on March 25, 2021, shows the debris it lofted as a blue dot amid the broader area of red echoes.

4. B​ow Echo

This name is given to radar echoes that bow outward from a larger line of thunderstorms (see arrows in the image above). It's an indication of a concentrated area of damaging straight-line winds in a line of thunderstorms.

T​he bow echo shows where the rain-cooled thunderstorm downdraft is pushing down to the Earth's surface and spreading out horizontally. Wind gusts in bow echoes are frequently 60 to 80 mph, sometimes higher.

One or more of these curved lines of thunderstorms can sometimes be long-lived enough to be called a derecho, which is a widespread wind damage event.

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Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.