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SC tornadoes are common in spring, but Monday's deadly twisters stood out

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Borg Warner plant (copy)

BorgWarner plant employees survey damage to the plant in Seneca on Monday, April 13, 2020, after a tornado struck the area in the early morning hours. The National Weather Service later confirmed the twister could have reached 160-mph wind speed, a remarkably strong tornado for South Carolina. Bart Boatwright/Special to The Post and Courier

The line of destructive tornadoes that descended on South Carolina Monday was a sucker punch: Amid a pandemic that kept many confined to their houses, a violent wave of storms left at least 200 people suddenly homeless. 

The twisters spun off a fast-moving wave of severe weather that rolled over two days from Louisiana to North Carolina. In South Carolina, at least nine people died. The total number of tornadoes has not been finalized but the National Weather Service has confirmed nine so far, stretching from the Upstate to the coast.

The number of tornadoes will likely rise in the coming days because no twister has yet been confirmed in the coastal area covered by the Weather Service's Charleston office. Employees of the forecasting service can pick out potential rotation in radar but have to take observations on the ground to make it official. 

While a few of the tornadoes Monday were exceptional, their presence this time of year is not. Spring is prime time for the destructive phenomenon in South Carolina. The state is most likely to get hit, according to historical trends, in April and May. 

The front that moved in a nightmarish wave across the Southeast followed a common springtime pattern: A cold front colliding with warm moist air out of the Gulf of Mexico spurred the rolling tempest. 

As early as last week, forecasters with the Weather Service warned a dangerous front was brewing; that signal only got clearer as Sunday approached. In a few cases, the twisters that spun off were more like the long-range powerhouses that tear through the Midwest's Tornado Alley.

Richard Okulski, a meteorologist at the Weather Service's Columbia office, said the severe weather event was the most significant in South Carolina since 2008 in a post-storm media briefing Monday evening. 

The longer tracks of some of the tornadoes, he added, are "a very rare situation that I've only faced working in different parts of the country."

One EF3 — estimated to reach a wind speed of 140 mph — tore a 31-mile path through Barnwell, Orangeburg and Calhoun counties shortly before 6 a.m. It's been blamed for at least two deaths and injuries to seven other people, according to a Weather Service assessment from the Columbia office. 

With a shorter track, another EF3 twister ripped 16 miles through Seneca. Damage on the ground indicated winds could have reached 160 mph, the Weather Service reported

A tornado with an intensity of EF2 also spun around Murrells Inlet and off the coast, happening to pass over or near a weather-recording station that clocked winds at 114 mph. 

"For it to pass right over a center like that is pretty unique, but it definitely gives a good picture for how strong winds can be in a tornado," said Michael Kochasic, a meteorologist with the Weather Service in Wilmington, N.C. 

Though far afield of the Great Plains corridor that's most famous for twisters, tornadoes have long been a threat in South Carolina and have been recorded touching down in every county of the state. In 1879, one tracking from Walterboro to approximately Givhans Ferry leveled more than 100 homes and churches and injured about 60, according to a S.C. State Climate Office timeline of historic severe weather

That office conducted an analysis of tornado trends in 2017 showing that in the 67 years prior, the state averaged about 14 twisters a year. The more intense ones have tended to hew to the Midlands and farther north, but the coast is not immune, particularly because hurricanes can also spur tornadoes.

But the occurrence of tornadoes varies wildly from year to year, which can challenge researchers trying to pick out long-term trends. It's still a hot topic of debate how climate change, or the steady increase in temperatures around the world, will affect tornadoes in the United States. 

Because the warming planet has started to alter the Jet Stream — an atmospheric river that flows west to east across the country— there's an expectation that the regions and seasons in which tornadoes occur will change, said Michael Mann, director of the Earth System Science Center at Pennsylvania State University. 

There's still some disagreement, however, about whether the data are showing any differences yet, Mann said. 

Some investigators have picked up early signals. Zoe Schroder, a doctoral candidate at Florida State University, has found an increase in "bulk shear" in the lower atmosphere, or changing winds that can lead to rotation.

Her professor, James Elsner, also found an increased incidence in wintertime tornadoes in the Southeast in a 2018 study.

But the connections to climate aren't yet clear.

"It's definitely difficult to say these current changes or these current results we’re seeing are direct results of climate change," Schroder said.

Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.

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