On the afternoon of April 29, 2020, a single flash of lightning tore throughout the sky from East Texas to the Mississippi coast, holding collectively as one steady electrical discharge for 768 kilometres — roughly 477 miles, or the gap from New York Metropolis to Columbus, Ohio. It was up to now exterior the vary of what atmospheric scientists had beforehand measured that the World Meteorological Group licensed it because the longest single lightning flash ever recorded, and the invention compelled the sector to rethink what the higher restrict of a lightning bolt really is.
That document has since been damaged. However the 2020 megaflash is the one which modified the definition.
A bolt the size of a rustic
Most lightning flashes journey lower than 16 kilometres earlier than dissipating. The typical bolt lives for a couple of tenths of a second, forks via the sky in a slender vertical column, and grounds itself a couple of times earlier than the cost is spent. The April 2020 megaflash did none of that. It travelled horizontally, snaking alongside the underside of a sprawling thunderstorm complicated, and stayed alive lengthy sufficient for satellites to hint its full size throughout three states.
The occasion was documented by NOAA’s GOES-16 satellite tv for pc, whose Geostationary Lightning Mapper captures optical flashes throughout the Western Hemisphere at millisecond decision. Earlier than satellites like GOES-16 got here on-line, ground-based lightning detection networks would have registered the flash as many separate strikes, since no single sensor might see the entire thing. The satellite tv for pc view revealed it as one steady occasion.
Why the definition needed to change
Earlier than the 2020 flash, meteorologists working below the American Meteorological Society’s official glossary handled a lightning “flash” as an occasion lasting no multiple second. That framing had held for many years. It match the physics of unusual bolts, and it matched what ground-based sensors might resolve.
Then GOES-16 began returning knowledge that broke the definition. Flashes have been being noticed that lasted 5, seven, even ten seconds. Some spanned a whole lot of kilometres of horizontal cloud. The 768-kilometre Texas-to-Mississippi occasion was the tipping level. In its wake, the American Meteorological Society revised its glossary to take away the one-second time cap, and the World Meteorological Group added a brand new class to its official archive of climate extremes: the megaflash.
The phrase describes precisely what it feels like — a uncommon, large bolt of lightning that travels monumental distances via the weaker, outer areas of a really giant thunderstorm complicated. Michael Peterson, an utilized physicist with the Extreme Storms Analysis Heart at Georgia Tech, has defined that these flashes will not be born within the violent core of a storm. They kind within the flatter, spread-out anvil areas the place the cost buildings of the cloud can help a bolt propagating sideways for extraordinary distances, as Peterson described to WXIA-TV.
The storm that produced it
The April 2020 megaflash got here out of a mesoscale convective system, a class of storm that meteorologists shorthand as MCS. These are the large, generally state-sized clusters of thunderstorms that roll throughout the American Nice Plains and the Deep South in spring and summer season. They will span 500 kilometres finish to finish, generate torrential rain and hail, spawn tornadoes, and maintain collectively for a lot of hours after dusk.
The stratiform area — the flatter, quieter a part of an MCS that trails behind the storm’s forefront — is the place megaflashes are inclined to kind. The cost inside these clouds is organized in broad, layered sheets reasonably than the tight vertical columns of a typical thunderhead. When a bolt begins in that surroundings, it could journey horizontally via the sheet for so long as the cost holds collectively.
On April 29, 2020, the circumstances have been near-perfect. A big convective system was draped throughout the Gulf Coast states. The stratiform layer stretched from East Texas throughout Louisiana and into Mississippi. When the bolt fired, it had a steady freeway of charged cloud to run via.
The way you {photograph} a bolt from orbit
The Geostationary Lightning Mapper on GOES-16 sits roughly 36,000 kilometres above the equator and stares constantly on the Americas. It information the optical pulses of lightning at 500 frames per second throughout a wide-angle area of view. When a flash happens, the instrument logs the placement, brightness, and period of each illuminated pixel, then software program stitches these pixels collectively right into a single occasion in the event that they belong to the identical steady discharge.
The 2020 megaflash seems in that dataset as a vein-like inexperienced hint that meanders throughout the map for a whole lot of miles. Blue and crimson dots mark the place the bolt touched the bottom.
That satellite-based technique is what made the document potential. It’s also what has since produced the present record-holder — a flash initially missed in 2017 and solely discovered years later when the archived knowledge was reanalysed.
The document that broke the document
In 2025, the World Meteorological Group licensed a brand new longest-flash-ever: a bolt that stretched 829 kilometres, or 515 miles, from East Texas to close Kansas Metropolis on October 22, 2017. The occasion lasted 7.39 seconds and struck the bottom greater than 100 instances alongside its path, based on findings by Georgia Tech researchers supported by NASA.
The 2017 occasion beat the 2020 Texas-to-Mississippi flash by about 61 kilometres, or 38 miles. It had been sitting quietly within the GOES-16 archive for about eight years, undetected, due to how the unique satellite tv for pc knowledge was processed. When researchers went again and reanalysed the observations, the bolt emerged from the noise as one steady discharge.
A automotive would want eight to 9 hours to cowl the identical floor. A business jet would want at the least ninety minutes, because the WMO famous when the document was introduced. The bolt did it in 7.39 seconds.
The place megaflashes reside
The Nice Plains of america is among the few locations on Earth the place the atmospheric elements for megaflashes come along with any regularity. Heat, moist air from the Gulf of Mexico rides north and meets colder, drier air spilling east off the Rockies. The collision zone spawns the huge convective methods that present the anvil clouds during which megaflashes propagate. The opposite world hotspot is the La Plata Basin in southern South America, the place an identical collision of heat subtropical air and funky air off the Andes produces the identical class of storm.
The longest-duration lightning flash on document — a bolt that lasted 17.102 seconds — occurred over Uruguay and northern Argentina on June 18, 2020. The longest-distance flash lives within the American Plains. Between the 2 hemispheres, they outline the present edges of what a lightning bolt is thought to be able to.
Randall Cerveny, a professor of geographical sciences at Arizona State College who chairs the WMO’s committee on climate extremes, has mentioned it’s seemingly that even better extremes exist and can be noticed as extra high-quality lightning measurements accumulate. The higher sure, in different phrases, has not but been discovered.
What it looks like on the bottom
A megaflash overhead doesn’t appear to be a horror-movie sky-splitting bolt. From instantly beneath, the strike zones would seem as unusual cloud-to-ground lightning — brilliant flashes, thunderclaps, the same old weight of a thunderstorm. The extraordinary factor is that observers a whole lot of kilometres aside, from small cities in East Texas to communities on the Gulf Coast of Mississippi, have been watching items of the identical bolt.
Lightning kills about 20 folks every year in america and injures a whole lot extra, based on Nationwide Climate Service knowledge. Florida leads the nation in fatalities due to the frequency of its afternoon thunderstorms. The megaflashes themselves will not be the deadliest bolts — they discharge throughout big cloud volumes reasonably than concentrating their vitality in a single strike — however every one seeds dozens of floor contacts alongside its path, and any of these contacts could be deadly.
The devices that preserve wanting
GOES-16 has a sibling, GOES-18, watching the western Americas, and the 2 satellites collectively present steady lightning protection from the Atlantic to the Pacific. Europe’s MTG-I1 satellite tv for pc carries a comparable Lightning Imager over Africa and Europe. Between them, the world now has near-total optical protection of lightning exercise throughout the Americas, Europe, and Africa, at a temporal decision that may have appeared like science fiction to the meteorologists who wrote the one-second flash definition into the AMS glossary a long time in the past.
That protection is why the information preserve falling. Silicon Canals has tracked the April 2020 megaflash as one of many clearest instances of devices outrunning definitions — a phenomenon that had most likely been occurring within the sky for millennia was solely changing into seen as a result of the sensors lastly existed to see it.
Each megaflash document up to now has come from the identical GOES-16 dataset. Each new one has been longer than the final. The 2017 bolt from Texas to Kansas Metropolis was hiding within the knowledge for practically a decade, solely surfacing when scientists went again to look. There is no such thing as a cause to suppose it’s the greatest one in there.
Rewriting what a bolt could be
The April 2020 occasion mattered much less due to its size than due to what it did to the definition. Earlier than it, a lightning flash was, by consensus, an occasion of at most one second. After it, the American Meteorological Society up to date the glossary. The WMO created a brand new document class. The phrase megaflash entered the working vocabulary of atmospheric science.
Cloud-to-ground bolts are those that kill folks and begin wildfires. Megaflashes largely keep within the sky, working horizontally via the anvil areas of continental storm methods. They’re {the electrical} equal of ocean-basin-scale climate — monumental, slow-moving, and till not too long ago, basically invisible to the devices that have been purported to measure lightning.
Someplace over the Plains this summer season, or over the Río de la Plata, a bolt longer than 829 kilometres will hearth via the underside of a storm and race throughout a state or two earlier than it fades. It should final eight seconds, or ten, or fifteen. GOES-16 will see it. The archive will maintain it. And some years from now, when somebody reanalyses the information, the document will change once more.
