Scientists now have a way to understand the fierce tornado that killed veteran stormchaser Tim Samaras in 2013 in El Reno, Oklahoma. The May 31 storm was the largest ever recorded, and one of the fastest.

For the first time, scientists can now actually see the “sub-vortex” that spun out of the tornado at 175 miles (280 kilometers) per hour, killing Samaras, his son Paul, and colleague Carl Young.

“That sub-vortex had a structure unlike anything we’ve ever seen, but now we're able to track it second by second—using footage from different perspectives—to see if we can learn more about how it formed,” says Anton Seimon, a tornado scientist at Appalachian State University who co-developed the new software tool with