If you were living near the U.S. Gulf Coast or Southwest in 2021, you were no stranger to lightning. Between an active monsoon and abnormally high number of tropical storms, streaks of energy raced through the atmosphere in record numbers. Newly released data shows that those regions experienced more lightning last year than in the previous five years on average.
“When you look at lightning counts, you get a feel for how stormy the year was, how much instability was there in the atmosphere, how much precipitation was there,” said Chris Vagasky, a meteorologist with the company Vaisala, which operates a network of lightning sensors in the U.S. for almost 40 years and globally for 10 years.
Lightning is a large natural spark of electricity, caused by an imbalance of electrical charges in the atmosphere. Most lightning is formed from thunderstorm clouds, which develop when warm, moist air rises into cold air, often during warmer seasons. A storm’s lightning flash rate is often related to a storm’s severity, or how deep the thunderstorm cloud is.
Vaisala sensors detected more than 194 million lightning events in 2021, about 24 million more than in 2020, which was an extremely low year. Despite the increased activity, the nation’s lightning in 2021 was below recent averages for the second year in a row. Thirty-two of the Lower 48 experienced lower-than-normal activity. But although the exceptions were few, they were grand.
“There’s a background level of lightning that you would expect, and then you have extreme events that take that up above the background level, or you have droughts, or high pressure systems in certain locations, that then takes things down below the average,” Vagasky said.
The United States also hit a record low for lightning deaths in 2021 at less than 12 fatalities, although the decrease also may be attributable to better awareness and more caution or potentially even people quarantining indoors because of the pandemic.
Vaisala data indicates that the United States experienced the second-highest lightning count worldwide — not necessarily surprising, given the country’s size and the fact it typically is one of the stormiest locations in the world because of extreme north-south temperature contrasts.
In 2021, the top two states to experience lightning were Texas and Florida. The two often take the top spots because of their relatively tropical and less stable atmospheres, which make thunderstorms more common than in other parts of the nation. Texas and Florida experienced the most lightning in 2020 as well.
In a somewhat unexpected shift, Louisiana experienced the third-highest lightning counts in the United States last year — topping traditional lightning powerhouses such as Oklahoma, Kansas and Missouri. The activity probably was tied to the active hurricane season, which was headlined by Category 4 Ida.
“There were several systems that tracked right along the Gulf Coast or made landfall right around the Louisiana area,” said meteorologist Elizabeth DiGangi. “A lot of lightning you may see in tropical systems is in the outer rain bands. Even something that made landfall in the Houston area would have ended up providing a good bit of rainfall and lightning to Louisiana as well.”
Meanwhile, the Southeast and Central Plains experienced a quieter-than-normal severe weather season in the spring. According to Vaisala’s data, Oklahoma experienced fewer than 10 million lightning events — about 1 to 2 million fewer than normal.
“Oklahoma, Kansas, and Missouri all moved down a spot this year. They were all lower than what you would normally expect to see for lightning, and there was less severe weather reported in these areas,” Vagasky said. “It’s kind of another down year for tornadoes up until December, unfortunately.”
On Dec. 10, a tornado outbreak ravaged the Southeast from Arkansas to Kentucky, where more than 70 people died. Then on Dec. 15, a line of violent thunderstorms and tornadoes, or a derecho, unleashed damage in seven states in the central United States.
Sensors detected more than 3 million lightning events in December 2021, a bit more than normal for the month, Vagasky said.
Most notable was that last year marked the return of an active monsoon season in the Southwest. After 2020’s “non-soon,” 2021 came back with a roar — and with lightning. Vaisala data showed Arizona experienced around 3.5 million lightning events — 2 million more than in the previous year. Southern California in the U.S.-Mexico border area experienced more than twice the average number of lightning events.
“In both 2019 and 2020, the monsoon basically failed to develop, for other large-scale atmospheric reasons. It was probably some much-needed relief this year for the area, but that did mean that there was more lightning for sure in that area than there was in previous years,” said DiGangi, a lightning researcher at Earth Networks.
Earth Networks operates a global network of lightning ground sensors that provide data to government entities, emergency management organizations, aviation companies and other private-sector entities. The company also detected a slight increase in lightning counts from 2020 to 2021 with their sensors.
In addition to lightning counts, DiGangi and her colleagues at Earth Networks count thunder days and thunder hours per year to measure the storminess of an area. A thunder day is one on which a person at a given location can hear thunder caused by a nearby storm.
Thunder is created when lightning travels through the atmosphere, heating the air to 50,000 degrees. When the air cools shortly after the lightning flash, the rapid expansion and contraction creates a sonic discharge, the rumble of thunder. The thunder day metric relies less on the number of lightning flashes detected and more on the convection present in a certain mile radius.
In 2021, Earth Networks counted more than 7,800 thunder days across the United States — a 4 percent increase from 2020. Similar to the Vaisala lightning data, Texas, Florida and Louisiana experienced the most thunder days. New Mexico, while not ranking in the top 10 for lightning counts, did have the ninth-highest number of thunder days in the nation last year.
“You can get a sense of what locations experience a lot of active convection versus places where it’s less common,” said DiGangi. “It tells you more about if the location experiences storms, which is our kind of primary concern in a lot of ways, because it’s the storm bringing the rain, it’s the storm bringing the wind, the severe events and, of course, the lightning.”
In addition to the Southwest, other states across the northern United States experienced anomalous amounts of lightning and thunder days. Michigan registered an unusually high number of lightning strikes for 2021, thanks to a slew of summer storms every couple of weeks.
“In 2020, Michigan had what we think was their biggest year, and then that was surpassed [in 2021],” Vagasky said.
Many northeastern states, such as Pennsylvania, New Jersey and Massachusetts, also experienced higher-than-normal numbers of lightning events. Vagasky cites abundant tropical storm activity as well as the multiple active weather patterns traveling from the Great Lakes region.
Although the nation’s overall lightning activity was below average again, researchers do not think the current lightning trends are necessarily tied to climate change — at least not in the United States. Vaisala data over 30 years shows that trends in the United States have been relatively consistent, with annual ups and downs based on weather patterns.
“In a broader sense, with the climate warming up, we would have more updrafts and we would have more thunderstorms,” said Rachel Albrecht, a professor and lightning researcher at the University of São Paulo. “But it is not homogeneous around the globe.”
This year, the Arctic experienced more lightning than it did from 2012-2020 combined, according to Vaisala data. Lightning in the Arctic is particularly concerning because it indicates an increase in warm and moist air intrusions into the high latitudes. Vagasky said background warming helps to drive some of these weather patterns.
“We know that climate is changing faster in the Arctic than anywhere else on the Earth,” Vagasky said. “Monitoring these trends really helps us get a good feel for exactly what’s happening up there.”