The Longest Lightning Flash

Of the naturally occurring phenomena, one of the most visceral is lightning. Few things can fill us with wonder and a sense of immense, dangerous power like a bolt from the sky.

So, it’s no surprise that we’ve studied lightning during this project over the years. We’ve seen it show up in the most likely spots, accompanying tornadic, supercell storms. It can come with snow. Lightning can team up with volcanoes or nuclear bombs. The flashes can take the form of fantastical creatures, such as sprites, elves, trolls, pixies, ghosts, and gnomes, or roll in like a ball. We can even see it fossilized.

But regular lightning can be spectacular, too, and new technology is illuminating just how monumental these electrical arcs can be.

Meteorologists have long employed arrays to map lightning strikes. Sensors placed in various locations can transmit data about signals to a central hub, allowing scientists to count and measure lightning incidents during a storm.

Like earthquake arrays, the different physical locations of the arrays can pinpoint a flash and create a three-dimensional look at its slithering strings.

These systems have allowed us to garner incredible insight into lightning, but they have one major downside: an array is only as good as its coverage.

A collection of sensors that covers a state the size of Oklahoma, for example, should be sufficient to map the flashes in the Sooner State, right?

In most instances, the answer is yes. But what happens if a lightning flash is even bigger than this massive area? Is a bolt that size even possible?

Astoundingly, yes.

Technology on a global scale has uncovered a phenomenon called megaflashes, bolts sometimes so big that land-based arrays can’t map their full extents.

The American Meteorological Society clarifies a megaflash as “a continuous mesoscale lightning flash with a horizontal path length of approximately 100 km (62 miles) or greater.”

While 62 miles is indeed a lengthy bolt, the Oklahoma array, for example, would have no problem handling it. But what if the megaflash stretched from northern Texas to central Missouri?

To map something of that scale, we need a different type of technology. Enter the satellites!

The National Oceanic and Atmospheric Administration has satellites that watch stormy hotspots with omniscience. GOES-16 – Geostationary Operational Environmental Satellites – sits over the Great Plains, monitoring 16 spectral bands.

And this viewpoint has revealed that storms can spark electricity on scales we previously found unimaginable.

On October 22, 2017, a massive storm produced a megaflash that spanned 515 miles!

Producing 116 subsidiary strikes, the event lasted seven seconds.

This flash surpassed the previous record of 477 miles from a 2020 storm. How can a 2017 event defeat something that transpired three years later? The science of mapping megaflashes is in its infancy. Satellites have gathered raw data on storms for years, but researchers have just started to sort through the information. So, even though the 2017 strike is the current holder, a longer flash might already have occurred.

Or it could be surpassed by a new megaflash at any point. Since this type of mapping is new, we don’t have much of a concept about how outlandish this record-breaker is. The 2017 flash might be one for the ages, or maybe it’s nowhere near the upper bounds, and it’s been beaten by dozens of strikes in the distant past.

Check the following video for an animation of the megaflash.

These types of mammoth bolts have, so far, only been detected in two spots: the Great Plains and the Río de la Plata Basin of South America. Megaflashes come from mesoscale thunderstorms, the same monsters that create tornadoes.

These supercell systems can stretch the requisite distances to cast such long lightning bolts. Despite the inherent danger of lightning, one that seems baked into human DNA, megaflashes can be ironically dangerous. We associate strikes with the gnarliest parts of storms, but megaflashes are so long that they can emanate from parts of the systems that do not appear to be so bad. If the big, bad head of a storm is 500 miles away, you might not ever suspect you could experience lightning, yet the megaflash could still impact your area.

Fortunately, only about 1% of all thunderstorms create megaflashes. And, of those supercells, 40% spawn only one during their life spans. So, the bolts are quite rare.

As satellite technology continues to improve, we can expect to learn more about megaflashes and see new lengths enter the record books.

BONUS FACT: The 2017 megaflash is the longest bolt ever recorded, but the word “longest” could mean something else. The 515-mile bolt transpired over seven seconds. Megaflashes tend to last longer than normal lightning, as you might expect. But the 2017 flash is not the longest lightning bolt in terms of duration. In 2020, a flash in Uruguay and Argentina unfolded over 17.1 seconds!