UW-Madison researcher creates tornado computer simulation

MADISON - As clouds billowed like smoke rising from a forest fire, a twirling white funnel suddenly snaked downward.

The supercell storm was strong. Most are. But most don't spawn tornadoes. On May 24, 2011, near El Reno, Okla., the F-5 tornado birthed by the supercell remained on the ground for nearly two hours, leaving a path of destruction and death that stretched for 63 miles.

Leigh Orf wasn't there. But he has watched the 2011 El Reno tornado on his computer more times than he can count. That's because he re-created the entire tornado through a computer simulation.

"This is a very, very high-resolution model of a single storm. This is only recently possible because of advances in computer technology," Orf said in his office on the University of Wisconsin-Madison campus as the simulation ran on his computer.

"This storm here doesn't have a tornado. But now it does," said Orf, as he watched a finger-sized image push down from a huge cloud.

Orf is a scientist with the Cooperative Institute for Meteorological Studies at UW-Madison who leads a team of researchers using computer models to unlock the mysteries of tornadoes. As tornado season gets underway, scientists like Orf are working to peel back the layers of twisters to determine how and why they form.

The recipe always includes wind shear, instability and lots of moisture plus a trigger to move the air up, which can be a difference in temperature or moisture. But what vexes researchers is that storms that have all of those ingredients often don't form tornadoes.

Unlocking the tornado code could help forecasters better predict them and give people in their path more time to seek shelter.

"My dream, and maybe in my lifetime it will happen, is we can predict a scenario where in a 1 square kilometer region we can say a tornado will hit and we can do that well in advance of the storm," said Orf.

The problem is that unlike a hurricane or snowstorm that can take days to arrive, supercell storms and tornadoes often form quickly. Issuing a tornado watch or warning too soon might mean people ignore it, too late and it's not enough time to find a safe spot. Plus tornadoes are incredibly unpredictable — they can last a minute or hours, travel in a straight line or hopscotch drunkenly through neighborhoods. They can obliterate buildings while leaving homes right next door untouched. They can also peter out only to reform a few minutes or miles away.

Running computer simulations of many tornadoes will help build a database for  accurately predicting twisters. That would be a much safer alternative to storm chasers' usual tactics: putting themselves in harm's way to set up instruments to measure tornadoes. Two years after the 2011 El Reno tornado, four storm chasers were killed by a twister in the same area.

Orf chose the 2011 El Reno tornado because good data was available from sensors near that storm. He used the atmospheric sounding — a vertical profile of temperature, air pressure, wind speed and moisture — to input into an existing meteorological computer model, which he tweaked by writing additional code.

"We said 'OK, we're going to grow a cloud with our data,' " said Orf. "It wasn't easy and we didn't even know we'd get a tornado out of it."

Work began on the computer simulation a few years ago, but Orf has worked on the problem for a decade. Now that the research has been published, Orf is getting more grants to reproduce tornadoes that devastated Joplin, Mo., and Tuscaloosa, Ala., as well as others.

Before Orf earned his undergraduate and graduate degrees in meteorology at UW-Madison, he was a kid growing up in Connecticut, where his home was struck by lightning two years before it was hit by a tornado. Orf vividly recalls what was dubbed the Windsor Locks Tornado, an F4 twister that killed three people and injured 500 on Oct. 3, 1979. Then 11, Orf watched the tornado knock down trees before disintegrating over his house.

"Early on I was impacted by severe weather," said Orf, who credits his career choice to that tornado. "Let's just say, I have a lot of respect for it."