Megaflash: World record lightning bolt stretches 800km across three US states

This satellite image provided by the National Oceanic and Atmospheric Administration shows a thunderstorm complex. Photo / Supplied

A "megaflash" bolt of lightning that spanned nearly 800 kilometres across three US states has set the record for the most far-reaching.

The lightning was in the southern US in April 2020, extending 768km through Texas, Louisiana and Mississippi - around the distance between Auckland and Christchurch.

It beat the old 2018 record set in Brazil by almost 64km.

Ordinarily, lightning does not last for longer than a second or stretch further than 16km, Randall Cerveny at Arizona State University, told the New Scientist. This lightning - known as a megaflash because of its size - moved from cloud to cloud rather than to the ground.

The World Meteorological Organisation (WMO) also identified another lightning bolt over Uruguay and northern Argentina in 2020 that lasted 17.3 seconds - a record.

"We now have clear proof that single lightning events can last 17 seconds," said Cerveny.

"This is important to scientists because it improves our understanding of the dynamics of lightning – how, where and, importantly, why lightning occurs the way it does."

Both bolts were spotted in thunderstorm hotspots in the Great Plains of America and the Río de la Plata basin in South America.

Thunderstorms develop into massive events in the two areas, bringing huge lightning strikes, because they are prone to relatively large convective systems.

"We have had this type of lightning-detection and mapping equipment in orbit only for a handful of years – and through it, we are learning much more about megaflashes," said Cerveny.

The WMO confirmed the records after checking their validity via new satellite tracking technology.

That both records were set in 2020 could indicate that weather is becoming more extreme - but it is likely down to improved technology than climate change.