On a stormy day in 2017, a single lightning flash stretched across five U.S. states — from northeast Texas all the way to Kansas City — racing 515 miles in just 7.4 seconds.
At the time, no one realized the scale of what had just happened. Years later, advances in lightning detection and data processing revealed the full story. In July, the World Meteorological Organization (WMO) certified the event as the longest lightning flash ever recorded.
We had the chance to talk with Dr. Michael Peterson, senior research scientist at the Georgia Tech Research Institute, whose team uncovered the discovery. Below, we explore highlights from our conversation — including how this record was revealed, why these “mega flashes” happen, and what scientists are still working to understand.
A lightning flash that defied expectations
Most lightning is over in milliseconds. A quick burst of energy that vanishes almost instantly. But this flash was different. It traveled nearly half the continental U.S. before dissipating.
In this clip, Dr. Peterson describes the extraordinary scale of the record-setting flash:
Mega flashes are rare, but when they happen, they can be dangerous in unexpected ways. Because these events cover hundreds of miles, lightning strikes can occur far from where storms seem to be.
In this clip, Dr. Peterson warns that mega flashes can “strike out of the gray,” posing hazards even when skies seem calm:
Mega flashes don’t form in ordinary thunderstorms. They require enormous, organized storm systems called mesoscale convective systems (MCSs for short).
These sprawling systems develop when multiple thunderstorm cells merge into a coordinated structure, sometimes stretching hundreds of miles. Within them, lightning can propagate horizontally through vast electrified cloud layers, allowing flashes to travel remarkable distances.
In isolated storms, lightning might cover 10 miles at most. MCSs, by contrast, create the conditions that make mega flashes possible. But even here, not every storm produces one. That unpredictability remains a key mystery researchers hope to solve.
Despite frequent severe storms across the U.S. and beyond, extreme mega flashes have only ever been recorded in two regions worldwide.
In this clip, Dr. Peterson identifies where these rare events have been observed:
Uncovering the full scale of the 2017 mega flash required the right combination of tools.
The Geostationary Lightning Mapper (GLM) on NOAA’s GOES satellites first detected the flash from space, providing a top-down view of the storm. But GLM detects only the optical flashes at the cloud tops. To understand more about what was happening inside the storm — and especially which strokes reached the ground — Dr. Peterson’s team turned to AEM's Earth Networks Total Lightning Network (ENTLN).
In this clip, Dr. Peterson explains how GLM captures the big picture and why ground-based data like ENTLN was critical to filling in the details:
The record-setting discovery is only the beginning. Dr. Peterson and his team are now working to understand why some storms produce mega flashes while others don't.
In this clip, he highlights one of the biggest unknowns researchers are still trying to solve:
These highlights only scratch the surface of what we discussed with Dr. Peterson. For the complete story, including what this discovery means for the future of lightning science and severe weather preparedness, watch the full episode of Talking with the Experts below.