Lightning flashes during a monsoon storm in the US
Edward Mitchell/World Meteorological Organization (WMO)
A lightning “mega-flash” over the US Great Plains region stretching 829 kilometres, or around 515 miles, has been identified as the longest on record. The flash spanned five states, ranging from eastern Texas to Missouri.
Such mega-flashes – extremely long-lasting or long-distance lighting discharges – occur within the huge clusters of thunderstorms that regularly form over the US Great Plains and other lightning hotspots. But it remains an open question as to why some of these storms generate mega-flashes and others do not. “We don’t know exactly why this happens,” says Michael Peterson at the Georgia Institute of Technology.
The lightning occurred in October 2017 and lasted just over 7 seconds. But it was too long to be fully mapped by ground-based lightning sensors at the time.
Zigzagging branches of the longest flash of lightning on record
Michael Peterson, GTRI
To see its full extent, Peterson and his colleagues revisited data from a geostationary satellite equipped with cameras that continuously monitor lightning. They used newly-developed software to comb through millions of separate light pulses and traced the lightning as it zigzagged and branched through the storm.
“Each time we see a new pulse, we get an impression of how that flash is growing over time,” says Peterson. “By playing connect-the-dots, we can essentially map out the entire structure.”
They found the most distant points of the flash, when measured along a straight line, spanned 829 kilometres, give or take 8 kilometers. That is roughly the distance between London and Zurich. The total length tracing along the lightning bolt itself would stretch well beyond 1000 kilometres. “A mega-flash can go a mega-metre,” says Peterson.
The World Meteorological Organization, which keeps records of weather extremes, certified the flash as the longest on record, surpassing the previous record holder from 2020 by about 61 kilometres.
“We were able to see over 100 cloud-to-ground strokes from this single flash,” says Peterson. “Even though these mega-flashes are very rare, they individually are extremely impactful.”
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