‘Megaflash’ lightning bolt traveled over 500 miles, setting a new record, study says

Lightning is a familiar sight in stormy skies, but a new report has revealed just how far some bolts can travel — in one case, more than 500 miles.

That astonishing bolt sparked to life in eastern Texas and stretched all the way to Kansas City, Missouri, traveling 515 miles in seconds. It struck during a thunderstorm in October 2017, but the bolt’s exact distance was finally verified in the study, published Thursday in the Bulletin of the American Meteorological Society.

“We call it megaflash lightning and we’re just now figuring out the mechanics of how and why it occurs,” said Randy Cerveny, one of the study’s authors and a professor of geographical sciences at Arizona State University.

Researchers discovered the record-breaking megaflash while re-evaluating satellite data with new computational methods. The data from the satellites also provided much greater detail than previous observations, letting scientists determine individual megaflashes in these past storms.

“Flashes at this extreme scale always existed, and are now becoming identifiable as our detection capabilities and data processing methods improve,” the paper says.

It’s helping scientists and forecasters better understand what lightning is capable of and the dangers it poses.

What causes a megaflash?

All lightning is an electric discharge — much like a static shock, just on a larger scale.

Inside a thunderstorm, ice and water particles collide and exchange electrons, creating a buildup of electric charge. Lightning occurs when that charge becomes too strong for the atmosphere to hold onto and discharges it in the form of a bolt either through the cloud or down to the ground.

Most lightning stays within 10 miles of the storm where it originated. When it travels more than 60 miles, it’s considered a megaflash.

Michael Peterson, the report’s lead author and a senior scientist at Georgia Institute of Technology’s Severe Storms Research Center, said megaflashes tend to form in the weaker, outer parts of a storm system — not the intense core most people associate with lightning — and often after the storm has moved on.

The record-breaking 2017 flash followed that same pattern, creeping through the broad cloud layers that trailed a cold front across the southern Plains. Flat, sheet-like clouds stretching from Texas to Kansas City formed a shallow layer that could easily conduct electricity — creating ideal conditions for lightning to travel horizontally for hundreds of miles.

As the megaflash travels through the clouds, it can shoot off multiple ground-striking bolts. “You might have an entire thunderstorm’s worth of lightning, cloud to ground strokes, in one flash,” Peterson noted.

Megaflashes are rare: Fewer than 1% of thunderstorms produce them, according to satellite data analyzed by Peterson in the study. The storms that do are also generally long-lived and massive, covering thousands of square miles.

That expansiveness is key, Peterson said, and is likely “the primary driver” of megaflashes, as smaller storms can’t support as much horizontal travel.

“But the thing is that we don’t actually know exactly what sets of conditions actually allow these flashes to occur at these scales,” Peterson added.

A lightning record — for now

The 2017 megaflash may be the longest ever verified, now beating out a bolt of 477 miles in April 2020, but scientists don’t expect it to hold that title for long.

“Oh, we’ll find more,” Cerveny said. “We are still in the process of evaluating data.”

The satellite-based lightning mappers that made this discovery possible have only been operation for about 10 years — a short window in climate science terms — and there’s a lot more data to analyze.

The tools used to track extreme events like the Texas-to-Missouri bolt are opening new frontiers in lightning research, said Chris Vagasky, a meteorologist with the National Lightning Safety Council who was not involved in the study.

“What I’m looking forward to is seeing how does the location of where lightning occurs change?” Vagasky said. “It is going to be really useful from having all of these datasets, ground-based or satellite- based, to help us really understand what is going on with lightning and thunderstorms.”

A worst-case lightning scenario

While megaflashes are rare, their risks are very real.

Peterson said they represent a kind of worst-case lightning scenario: Powerful discharges capable of sparking wildfires or causing damage far from a storm’s core.

“You don’t see where they come from. You only see where they strike,” Peterson said. “The extent of the hazard and then the fact that it’s unexpected both contribute to why it’s important to understand for public safety.”

Many lightning injuries happen because people underestimate how far a bolt can actually travel from a storm and how long the danger can linger.

Cerveny, too, emphasized the importance of correcting the misconception that lightning can strike “out of the blue.”

“These megaflashes really point out one of the severe problems that is associated with thunderstorms,” said Cerveny. “A lightning flash can start in a thunderstorm very far away, and travel, as we’ve just shown, 500 miles before it ends.”

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