A June 2007 storm in Oklahoma produced the longest lightning flash in the world.
A World Meteorological Organization committee determined the bolt covered 199.5 miles. NASA research scientist Timothy Lang measured the flash, which started near Tulsa and reached the panhandle.
"When these big — we call them mesoscale convective systems or squall lines — in these big systems, it's very common to see large lightning flashes, but this was extremely unusual," Lang said.
Lang measured the flash using the National Severe Storms Laboratory in Norman’s lightning mapping array.
"This is something that listens for radio static from lightning, and, using a lot of different detectors and the difference in the time of arrival of the lightning static at different sensors, it can basically map the lightning channel in three dimensions," Lang said.
WMO this week also confirmed a new record for longest lightning bolt in duration. A 2012 storm in southern France produced a single flash lasting 7.74 seconds. WMO warns the discovery could alter traditional thinking on when it's safe to go outside after a storm passes.
"We probably aren't going to change those recommendations, because the vast majority of lightning flashes do occur within 10 miles and 30 minutes of where thunder could be heard from a previous flash," said John Jensenius, the National Weather Service’s lightning safety expert.
The current guidelines are summed up as "when thunder roars, go indoors" — go inside when you hear thunder, and don't resume outdoor activities until 30 minutes after the last flash of lightning.