World's longest 'megaflash' of lightning confirmed over US

The World Meteorological Organization (WMO) confirmed on Tuesday two "megaflashes" of lightning, which set new world records for both length and duration, in North and South America.

The record-breaking lightning bolt stretched 768 kilometers (477.2 miles) across parts of the southern US on April 29, 2020, the organization said in a statement.

It is equivalent to the distance between New York City and Columbus, Ohio in the US or between London and the German city of Hamburg.

The other record for the longest-duration lightning strike is 17.1 seconds, coming from the flash that developed continuously through a thunderstorm over Uruguay and northern Argentina on June 18, 2020.

"These are extraordinary records from single lightning flash events," said Randall Cerveny, the rapporteur of Weather and Climate Extremes for the WMO. "It is likely that even greater extremes still exist and that we will be able to observe them as lightning detection technology improves."

WMO Secretary-General Petteri Taalas also said that the findings highlight "important public lightning safety concerns for electrified clouds where flashes can travel extremely large distances."

Only lightning-safe locations are substantial buildings that have wiring and plumbing, and a fully enclosed metal-topped vehicle, said Ron Holle, a lightening specialist and committee member.

"If lightning is within 10 km (6.2 mi) as found with reliable lightning data, go to the lightning safe building or vehicle.

"As these extreme cases show, lightning can arrive within seconds over a long distance, but they are embedded within larger thunderstorms, so be aware," Holle warned.