515-mile-long lightning bolt that spanned 5 states is the longest on record

A lightning bolt that spanned five states in the Great Plains has set a new record for the longest lightning bolt ever recorded, the World Meteorological Organization has confirmed.

The "megaflash" zipped across 515 miles (829 kilometers) from eastern Texas through Oklahoma, Arkansas, Kansas to near Kansas City, Missouri, in seven seconds, beating the previous record of 477 miles (768 km).

The flash occurred on Oct. 22, 2017, but it was too long to be fully measured by ground-based sensors at the time. Now, a new study that used data from a geostationary satellite has finally documented the massive scope of the bolt. The researchers published their findings Thursday (July 31) in the Bulletin of the American Meteorological Society.

"It is likely that even greater extremes still exist, and that we will be able to observe them as additional high-quality lightning measurements accumulate over time," study senior author Randall Cerveny, a professor of geographical sciences at Arizona State University, said in a statement.

Exactly how lightning gets its initial spark is still contested. But scientists know it arises when electrons pool in one region of a storm cloud, thus creating an ionized path in the air between which the electrons can flow from regions of negative to positive charge.

In some storm clouds, particularly the huge clusters that form over hotspots such as the Great Plains, understudied dynamics within the clouds can lead to discharges that stretch beyond 60 miles (100 km) — earning them the title of "megaflashes."

Related: Lightning on Earth is sparked by a powerful chain reaction from outer space, simulations show

In the study, the scientists reconstructed the flash's length by analyzing data from the National Oceanic and Atmospheric Administration's GOES-16 satellite — one of four of the agency's satellites with mappers that continuously monitor the ground for zaps of lightning. Using new algorithms, the scientists separated the bolt from millions of other light flashes to reveal its full extent.

"Our weather satellites carry very exacting lightning detection equipment that we can use to document the millisecond when a lightning flash starts and how far it travels," Cerveny said.

Experts say that, beyond highlighting the impressive advancements in new weather-monitoring technologies, the discovery is an important reminder that lightning can strike far from the storm cells where it was initially generated.

"It illustrates the threat of the newly recognized 'bolt from the gray,'" analogous to the 'bolt from the blue' from isolated cells, but one that can travel many hundreds of kilometers from the main charge generating region," co-author Walt Lyons, president of FMA Research, a forensic meteorology investigation firm in Fort Collins, Colorado, said in a statement.

"If lightning is within 10 km [6.2 miles] as found with reliable lightning data, go to the lightning safe building or vehicle," he added. "As these extreme cases show, lightning can arrive within seconds over a long distance, but they are embedded within larger thunderstorms, so be aware."