By Skip Rigney

In a matter of seconds in 2020, branches of the largest lightning “megaflash” ever observed shot through clouds stretching from Texas to Mississippi. Several of those branches spread over portions of Pearl River County.

This past Wednesday the World Meteorological Organization announced that it had certified two new world records for lightning megaflashes. One was for the longest time duration, 17.1 seconds, for a megaflash in South America in 2020. The other was for the longest horizontal distance for a megaflash. This continuously interconnected web of lightning along the northwest and north central Gulf Coast on April 29, 2020, spread over an oval-shaped area 477 miles long. (See images of the megaflash by searching online for “WMO press release megaflash”.)

Megaflashes are not your everyday lightning bolts. Although they can produce offshoot cloud-to-ground bolts, megaflashes are electrical discharges within a broad cloud shield that extend over distances of at least 50 miles and last longer than five seconds.

Interestingly, these titans of the lightning world aren’t usually produced within the intense portions of severe thunderstorms, but instead in the expansive deck of clouds producing light rain behind the most vigorous thunderstorm clusters or lines.

That was the case in the Gulf Coast’s record-setting event in 2020. A line of potent thunderstorms ahead of a cold front swept through Texas, Louisiana, and Mississippi and then pushed offshore. The megaflash occurred in the thick layer of clouds behind the main line of storms.

Just a few years ago, the technology to observe these rare megaflashes was very limited. Ground-based lightning detector arrays would occasionally get a glimpse of something big, but they are better suited for collecting data about cloud-to-ground lightning.

Then in 2016 a new lightning detection sensor was launched on NOAA’s and NASA’s sixteenth Geostationary Operational Environmental Satellite (GOES-16). Another Geostationary Lightning Mapper (GLM) was launched onboard GOES-17 in 2018.

From their perches 22,000 miles above the earth, the GLMs stare down at the non-polar regions of the Americas, and most of the Atlantic and Pacific Oceans. These past five years have been the first time that meteorologists and other atmospheric scientists have been able to accurately map megaflashes and measure how long they last.

Scientists who analyzed the 2020 record-setting Gulf Coast megaflash used data from the GOES-16 and GOES-17 GLMs and from a ground-based lightning detection system centered in Houston.

This past Thursday the GLMs didn’t detect any megaflashes, but they certainly detected a lot of lightning over Pearl River County. Thunderstorms dumped so much rain that everyone in our county was under either a flash flood warning or flood advisory at some point.

Total rainfall for the period Wednesday through Friday varied wildly across the county from three to eight inches.

We won’t have to worry about lightning or rain for the next week. A cold, dry air mass followed the cold front that caused Thursday’s storms. That air, which just five days ago was over northern Canada, will give us a very chilly weekend and start to the work week.

Forecasters predict a slow warming trend by the middle and latter part of the week.