Within seconds, branches of the largest lightning “megaflash” ever observed shot through clouds stretching from Texas to Mississippi in 2020. Several of these branches spanned parts of Pearl River County.
Last Wednesday, the World Meteorological Organization announced that it had certified two new world records for mega-lightning events. One was for the longest duration, 17.1 seconds, for a mega-flash in South America in 2020. The other was for the longest horizontal distance for a mega-flash. This continuously interconnected web of lightning along the northwestern and north central Gulf Coasts spread across an oval area 477 miles long on April 29, 2020. (See images of the megaflash by searching “WMO press release megaflash” online.)
Mega flashes are not ordinary flashes. While mega-lightning can generate offshoots from cloud to ground, they are electrical discharges within a broad cloud shield that span distances of at least 50 miles and last longer than five seconds.
Interestingly, these titans of the lightning world do not typically form in the intense portions of severe thunderstorms, but in the extensive cloud decks that produce light rain behind the strongest thunderstorm clusters or lines.
That was the case in the record-breaking Gulf Coast event in 2020. A series of severe thunderstorms swept through Texas, Louisiana and Mississippi ahead of a cold front, then bumped into the coast. The megaflash occurred in the thick cloud layer behind the main line of storms.
Just a few years ago, the technology for observing these rare mega-flashes was very limited. Ground-based lightning detector arrays would occasionally catch a glimpse of something big, but they’re better suited for collecting cloud-to-ground lightning data.
Then, in 2016, a new lightning detection sensor was launched on NOAA and NASA’s sixteenth Geostationary Operational Environmental Satellite (GOES-16). Another Geostationary Lightning Mapper (GLM) was launched in 2018 aboard GOES-17.
From their perches 22,000 miles above the Earth, the GLMs overlook the non-polar regions of the Americas and most of the Atlantic and Pacific Oceans. In the past five years, for the first time, meteorologists and other atmospheric researchers have been able to accurately map mega-lightning events and measure their duration.
Scientists analyzing the record-breaking 2020 Gulf Coast megaflash used data from GLMs GOES-16 and GOES-17, as well as from a Houston-based ground-based flash detection system.
Last Thursday, the GLMs didn’t spot any mega-lightning events, but they certainly spotted plenty of lightning over Pearl River County. Thunderstorms have dumped so much rain that everyone in our county has had either a flash flood warning or a flood advisory at some point. Total rainfall for the Wednesday through Friday period varied widely across the county, from three to eight inches.
We don’t have to worry about lightning or rain for the next week. A cold, dry mass of air followed the cold front that caused Thursday’s storms. This air, which was over northern Canada just five days ago, will give us a very chilly weekend and start into the work week. Forecasters are predicting a slow warming trend mid and late in the week.