Peering Into the Deadliest, Most Destructive Tornadoes with Supercomputers

Leigh Orf became obsessed with storms after a close brush with a tornado when he was a little boy, and now, as a scientist, he uses supercomputers to study the deadliest and most destructive tornadoes on Earth.

"My family's house was hit by lightning when I was five years old, and a few years later a F4 tornado came very close to our house," Orf told Newsweek. "These events left an enduring impression."

The scientist uses supercomputers to look inside the strongest supercells and tornadoes, which register EF4 or EF5 on the Enhanced Fujita scale. Since 1950, 59 EF5 storms have hit the U.S., with Missouri's 2011 Joplin tornado being the deadliest, causing 158 fatalities.

The 2022 tornado season has started very strongly, with 420 already confirmed in the U.S. this year. A record-breaking number of tornadoes hit the country in March, while April has seen widespread destruction across several states.

Scientists have become much better at predicting when and where supercell tornadoes are going to hit. Christopher Weiss, professor of atmospheric science at Texas Tech University, previously told Newsweek: "[These are the] parent storms that produce the most violent tornadoes. These supercell storms feature strong rotation on the scale of the storm itself—called a mesocyclone, about five miles across, on average.

"However, the linkage between the mesocyclone and the actual production of a tornado remains elusive. Not even the majority of supercells produce tornadoes."

'Huge Rotating Updraft'

A supercell is a long-lived thunderstorm characterized by a huge rotating updraft.

"They occur under specific atmospheric conditions," Orf, from the University of Wisconsin-Madison, said. "They require lots of moisture, atmospheric instability, and wind shear. Supercells produce the most violent tornadoes compared to all other thunderstorm types. A recent example of a violent supercell is the storm that hit Mayfield, Kentucky, in December of 2021."

Orf's work involves simulating these huge tornadoes to find out what causes them to form and what happens once they have fully developed. He said the most violent tornadoes tend to form when weak, non-tornadic vortices "pile up in one spot underneath a very strong updraft."

In a video showing a simulation of a tornado forming, Orf explains "it's a vortex party and everyone's invited."

"It seems that timing of events occurring within the storm, as well as the spatial juxtaposition of specific storm features, is key to getting a tornado to form," he told Newsweek. "There need to be vertical vortices present in the vicinity of the updraft, and this needs to occur during a time when the updraft is very strong—this helps consolidate pre-existing clusters of weak rotation into a tornado.

"And the factors that go into making the updraft very strong have to do with the 'flavor of the air' that the storm's updraft is ingesting—it has to be cool, but not too cold, and it has to contain significant horizontal rotation, which is partly a function of the environment in which the storm formed, as well as the local environment formed by the storm itself."

An intensely strong updraft that continues ingesting the right sort of air allows the tornado to strengthen, he said. A tornado will dissipate when it moves too deeply into the rainy, cool air the storm has generated, as it loses its connection to the strong updraft that was powering it.

Orf's simulations show tornadoes forming, with different colors showing different streams of air being pulled upwards and into the storm. One formed, the animation shows the tornado tearing across the ground.

In real life, while experts have become adept at predicting where tornado-producing storms might hit, they aren't yet able to determine the path they will take or how strong they will get once formed. A general path can be estimated once the tornado has been spotted on the ground.

"Forecasting supercell and tornado behavior one to two hours in advance is a significant focus," Orf said. "There are significant challenges. Our weather models require good observational data to initialize them. Unfortunately, the technology for sampling large volumes of the atmosphere with high accuracy is still inadequate to provide our models with the accuracy they need to make extremely accurate forecasts.

"Currently tornado path forecasts pretty much only occur after a tornado has been spotted/detected. Once a tornado forms, we can look at the storm's motion vector to estimate the general path of the tornado.

"But tornadoes do not always follow expected paths."