Storm chasers catch tornado winds above 300 mph in rare ‘intercept’

The tornado ripped through southern Iowa at nearly 45 mph, destroying wind turbines like shredded cheese.

In the town of Greenfield, it overturned cars and ripped houses from their foundations, leaving a gash of destruction that can be seen from space. The tornado, which the National Weather Service later classified as EF4, killed five people on May 21, making it one of the deadliest so far this year, and injured 35.

More than a dozen tornadoes touched down in the state that day. While nearly everyone in the area was hunkered down in basements, a team of nine scientists – storm chasers – sought to get as close to the tornadoes as possible.

Just before 3pm, they saw their opportunity. When a tornado began appearing on radar screens, the group sprang into action. They took one of their radar trucks to a location about 10 miles west of Greenfield, a community of about 2,000 people in southwestern Iowa.

Another team rushed to deploy a suite of scientific instruments directly into the tornado’s path.

“There was debris falling on us,” said Jennifer Walton, a storm chaser and staff photographer.

A third truck passed through town, suddenly surrounded by trees and buildings that blocked the radar’s view of the tornado. They knew they were ahead of the storm; they didn’t know by how much.

“This is probably the most anxious time for all of us because we know a tornado is coming,” said Joshua Wurman, a research scientist at the University of Illinois. “We really don’t know if it will come in five minutes, three minutes or two minutes.”

It worked. The team achieved an “intercept,” as they call it, collecting data about the storm with the capsule and two mobile radar devices and giving scientists a rare, detailed, up-close look at one of the most powerful twisters ever recorded in this way.

The data collected marks only the third time scientists have calculated wind speeds that reached more than 300 mph inside a tornado. And because storm chasers took readings from multiple angles as the tornado tore through Greenfield, the findings now offer a grim look at the winds and internal dynamics of a vortex powerful enough to level homes.