AUSTIN, TX – The World Meteorological Organization (WMO) has officially recognized a new record for the longest single lightning flash, a staggering "megaflash" that covered 515 miles across the central United States on October 22, 2017. The bolt of lightning stretched from eastern Texas all the way to near Kansas City, Missouri. This newly certified record shatters the previous mark of 477 miles set by a megaflash over the southern United States and the Gulf of Mexico in April 2020.

Lightning is often thought of as a localized danger, where safety advice suggests that if you can hear or see lightning, you're close enough to be at risk. However, these "megaflashes" challenge that idea. They are single, continuous flashes that can extend for hundreds of miles through clouds, initiating numerous cloud-to-ground (CG) strikes along their path. They can also occur in seemingly inactive storm systems, with long periods between flashes, and are known to produce significant effects like damaging high-current CG strokes and "sprites" (light shows above cloud tops).

The record-breaking megaflash originated within what is called a quasi-linear convective system (QLCS) – a type of organized thunderstorm complex – that moved through the central U.S. in October 2017. Researchers were able to identify this overlooked event thanks to new methods used to process data from satellites.

Documenting these extreme megaflashes is important for understanding the physics of lightning and for improving public safety guidelines. They reveal the maximum extent of lightning hazards from the most impactful individual flashes on Earth.

After a detailed review of imagery and data, the WMO committee unanimously recommended this flash as the new world record for lightning discharge distance. These megaflashes can occur far from areas of active lightning and even long after the last thunder has been heard, highlighting a poorly understood safety hazard.

While this megaflash set a new distance record, its duration of 7.391 seconds was well short of the current WMO record for the longest duration megaflash, which stands at 17.102 seconds for an event over Argentina and Uruguay in June 2020.

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