The science behind the longest lightning bolt ever recorded

For 7.391 s in the wee hours of Oct. 22, 2017, a “megaflash” of lightning lit up 515 miles (829 km) of sky from Fort Worth, Texas, to Kansas City, Missouri, in a single brilliant stroke.Analysis of satellite data with new computational techniques has shown that the megaflash, which connected with 116 places on the ground, is currently the longest on record (Bull. Am. Meteorol. Soc. 2025, DOI: 10.1175/BAMS-D-25-0037.1). The previous record was a 2020 megaflash that spanned 477 miles (768 km) from Texas to Louisiana.But the factors that cause such megaflashes, which are defined as lightning that has traveled more than 100 km, are still unclear. In fact, “why lightning happens has been a mystery for the longest time,” Michael Peterson of the Georgia Institute of Technology, who led the satellite data analysis, told C&EN in an email.At its core, lightning occurs when opposing electrical charges build up in the skies and then recombine, either through lightning bolts in the clouds or strikes to the ground, as Benjamin Franklin demonstrated almost 300 years ago by flying a kite in a thunderstorm. Charge separation can occur when atmospheric particles collide in a brewing thunderstorm. For instance, small ice particles can lose electrons to larger soft hail pellets and then get carried upward quickly, leaving the heavier hail pellets behind, Peterson says. But to make a megaflash, electrical charges need to separate steadily for miles and miles without recombining. “If there was a recent prior flash, then there might not be