Lightning ‘megaflash’ the length of three US states sets world record

The World Meteorological Organisation has certified two new world records for megaflashes in North and South America.

With the aid of sophisticated satellite technology, the organisation's Committee on Weather and Climate Extremes – which maintains official records of global, hemispheric and regional extremes – made some fascinating observations.

On 20 April 2020, across a Southern area of the United States, the world’s longest single flash of lightning was recorded, which had an incredible horizontal distance of 768km – surpassing the previous record by almost 60km.

This distance is the equivalent of going from New York City to Columbus, Ohio in the US, or London to Hamburg in Germany. The previous record had been set across southern Brazil back in October 2018, which was registered as being 709km across.

The WMO also revealed a new record for the longest duration of a single lightning flash, which was clocked at 17.102 seconds in the midst of a thunderstorm over Uruguay and parts of northern Argentina on 18 June 2020.

“These are extraordinary records from single lightning flash events. 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,” WMO Secretary-General Prof Petteri Taalas adds.

The new record strikes occurred in hotspots for Mesoscale Convective System (MCS) thunderstorms, whose characteristics permit extraordinary megaflashes to occur – namely in and around the Great Plains of North America, and the La Plata basin in South America.

Noted lightning specialist and committee member Ron Holle states: “these extremely large and long-duration lightning events were not isolated but happened during active thunderstorms. Any time there is thunder heard it is time to reach a lightning-safe place.”

“The only lightning-safe locations are substantial buildings that have wiring and plumbing; not structures such as at a beach or bus stop. The second reliably safe location is inside a fully enclosed metal-topped vehicle; not dune buggies or motorcycles.

“If lightning is within 10 km as found with reliable lightning data, go to the lightning safe building or vehicle. As these extreme cases show, lightning can arrive within seconds over a long distance, but they are embedded within larger thunderstorms, so be aware,” he concludes.