WMO certifies two mega flash lightning records

The World Meteorological Organization (WMO) has established two new world records for mega flashes of lightning in notorious hotspots in North and South America.

WMO's Committee on Weather and Climate Extremes, which maintains official records of global, hemispheric and regional extremes recognized the longest single flash that covered a horizontal distance of 768 ± 8 km (477.2 ± 5 miles) across parts of the southern US on April 29, 2020.

This is equivalent to the distance between New York City and Columbus Ohio in the US or between London and the German city of Hamburg.

Similarly, other record was for the greatest duration for a single lightning flash of 17.102 ± 0.002 seconds was from the flash that developed continuously through a thunderstorm over Uruguay and northern Argentina on June 18, 2020.

The new record for the longest detected mega flash distance is 60 kilometres more than the previous record, with a distance of 709 ± 8 km (440.6 ± 5 mi) across parts of southern Brazil on October 31, 2018.

Both the previous and new record used the same maximum great circle distance methodology to measure flash extent while the previous longest duration mega flash record was of 16.73 seconds, which was derived from a flash that developed continuously over northern Argentina on March 4, 2019, 0.37 seconds shorter than the new record, the WMO said in a release.

The findings were published in the Bulletin of the American Meteorological Society.

"These are extraordinary records from single lightning flash events. Environmental extremes are living measurements of the power of nature, as well as scientific progress in being able to make such assessments. It is likely that even greater extremes still exist, and that we will be able to observe them as lightning detection technology improves," said Professor Randall Cerveny, rapporteur of Weather and Climate Extremes for WMO.

"Lightning is a major hazard that claims many lives every year. The findings highlight important public lightning safety concerns for electrified clouds where flashes can travel extremely large distances," said WMO Secretary-General Professor Petteri Taalas.

The new record strikes occurred in hotspots for Mesoscale Convective System (MCS) thunderstorms, whose dynamics permit extraordinary mega flashes to occur - namely, the Great Plains in North America, and the La Plata basin in South America.

Many lightning scientists acknowledged that there are upper limits for the scale of lightning that could be observed by any existing LMA. Identifying mega flashes beyond these extremes would require a lightning mapping technology with a larger observation domain.