The record-long lightning bolt was spotted over Oklahoma on June 20, 2007, and traveled 199.5 miles, about three-quarters the length of the state. That’s almost the distance from New York City to Washington, D.C. And the world’s longest-lasting lightning flash lasted for 7.74 seconds on Aug 30, 2012, over Provence-Alpes-Côte d’Azur, France. A report about the records has been accepted for publication in the Bulletin of the American Meteorological Society. The lightning strikes were detected using extremely sensitive radio receivers, Cerveny said, likening it to how AM radio sounds during a thunderstorm, when the static of the lightning discharge can be heard.
http://www.usatoday.com/story/weather/2016/09/15/world-lightning-strike-records/90418046/
