The World Meteorological Organization has certified that two lightning flashes that occurred in 2020 have broken historical records in length and duration. A lightning bolt in April 2020 spanned 477 miles across the southern United States. Two months later, a flash across the Uruguay-Argentina border lasted an incredible 17 seconds. Neither lightning bolt hit the ground. From New Scientist:
"We now have clear proof that single lightning events can last 17 seconds," says Randall Cerveny at Arizona State University. "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."
The flashes were seen in thunderstorm hotspots, in the Great Plains of North America and the Río de la Plata basin in South America, respectively. The geography of the areas makes them prone to relatively large convective systems, which can cause individual thunderstorms to combine into massive weather systems that trigger extreme lightning strikes.
The flash that spanned the southern US would have been difficult to measure with conventional ground-based equipment, so meteorologists turned to lightning mappers on geostationary satellites, which have a far wider field of view.
(Thanks, Bob Pescovitz!)