The science behind the EF-4 tornado that devastated Iowa

Satellite view of tornado damage in Greenfield, Iowa, captured on May 25, 2024, by the Operational Land Imager on Landsat 8.

During one of the most active tornado seasons in the US, a powerful EF-4 tornado ripped through Greenfield, Iowa with 185 mph winds. The destructive tornado destroyed homes, downed wind turbines and power lines, snapped trees and shredded roofs.

It was one of the busiest US tornado seasons in recent years. As of May 28, National Weather Service meteorologists have confirmed 875 tornadoes. One of the strongest and most destructive was a powerful twister that formed in southwest Iowa on May 21, 2024. The tornado traced a line of destruction nearly 44 miles across the town of Greenfield, Iowa.

The tornado was one of a twister outbreak that formed when a cold front produced a line of strong thunderstorms that swept across the Midwest. A particularly large and tall storm with rotating updrafts (a supercell) produced an EF-4 tornado that struck Greenfield with peak winds of 185 miles (300 kilometers) per hour.

Assessment of damages

The damage path through Greenfield is visible in the image above, acquired on May 25, 2024, with the OLI (Operational Land Imager) on Landsat 8. According to storm reports posted by NOAAStorm Prediction Center, the deadly twister destroyed homes, downed wind turbines and power lines, snapped trees and crushed roofs.

Satellite images of the storm system that preceded the tornado offered subtle hints of the destruction to come. The brightness temperature data below obtained with MODIS (Moderate Resolution Imaging Spectroradiometer) on GODMOTHERAqua’s satellite was collected about an hour before the tornado hit Greenfield. White and light purple cloud tops are cooler than dark purple and yellow surfaces.

Brightness temperature data captured on May 21, 2024 by the Moderate Resolution Imaging Spectroradiometer on NASA’s Aqua satellite.

Meaning of cloud formations

Notice the cooler (whiter) areas of cloud surfaces. These are surmounted by cloud tops – dome-shaped protrusions from storm clouds that are driven by convective air currents. These cloud tops can rise beyond the tropopause and the anvil portion of a storm cloud, sometimes striking the lower stratosphere.

According to Kristopher Bedka, an atmospheric scientist at NASA’s Langley Research Center, the overpass southwest of Greenfield was the coldest and largest in Iowa at the time. “This means a well-organized storm with a strong updraft,” Bedka said. “When this type of updraft ingests a highly unstable air mass with high vertical wind shear, catastrophic tornadoes and large hail are often the result.”

Advances in Storm Prediction

Researchers watch closely for passing clouds and other features that herald tornadoes, destructive hail and extreme lightning strikes. Bedka and other NASA scientists have developed automated and innovative techniques for quickly identifying such features in satellite images.

“We applied these techniques to long-term geostationary data records to quantify the frequency and risk of severe storms,” ​​Bedka added. “This has made it possible for us to provide the reinsurance industry with new and highly detailed information on severe storm activity and risks, which is particularly valuable in developing countries without weather radar coverage.”

NASA Earth Observatory imagery by Michala Garrison, using Landsat data from the US Geological Survey and MODIS data from NASA EOSDIS LANCE and GIBS/Worldview.