Greenfield, Iowa tornado rated EF-4 — strongest U.S. tornado of 2024

On May 21, 2024, a powerful EF-4 tornado with winds reaching up to 298 km/h (185 mph) devastated Greenfield, Iowa, resulting in at least five fatalities and significant property damage.

• In terms of wind speed, this is now the strongest tornado in the U.S. this year.
• It is also the third EF-4 tornado reported in 2024, with the other two occurring in Oklahoma during the spring.

Multiple rounds of thunderstorms brought torrential rainfall, damaging winds, hail, and destructive tornadoes to Iowa on May 21.

These thunderstorms were the result of a low pressure system that lifted north into the area on the night of May 20 (LT), producing slow-moving storms that dropped 50 to 100 mm (2 to 4 inches) of rainfall, which resulted in flash flooding over portions of northern and central Iowa through the morning of May 21.

Following the heavy rainfall through the morning, skies cleared out ahead of an approaching cold front. By the afternoon hours of May 21, this cold front produced a line of strong thunderstorms which produced multiple strong tornadoes throughout the state, including one that led to significant damage in the town of Greenfield, IA, among other locations. This line of storms also produced damaging winds, leading to widespread tree damage and power outages throughout the forecast area.

Initial storm surveys have confirmed EF-4 damage in Greenfield, Iowa, EF-3 Damage in NW Adams County, and EF-2 damage in Polk into Story County. Additional damage assessment evaluation will continue over the next several days and results are subject to change.

The Greenfield tornado caused significant devastation during its 71 km (44 miles) path through southwestern and central Iowa. At least five people were killed, and dozens of homes were destroyed. It was initially rated as EF-3 but later bumped up to EF-4.

“We got together with the structural engineers and experts in the field and discussed the damage that occurred within Greenfield and along the entire path,” NWS said. “Some of the significant damage that occurred in Greenfield after further evaluation of structures, we decided to bump the rating.”

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An EF-4 tornado features wind speeds of 267 – 322 km/h (166 – 200 mph), meaning the Greenfield tornado was close to the threshold for an EF-5. The last EF-5 tornado in the United States struck Moore, Oklahoma, on May 20, 2013, causing 24 fatalities and hundreds of injuries.

Before the Greenfield tornado, the strongest tornado in 2024 was an EF-4 that hit Barnsdall, Oklahoma, on May 6. This tornado had wind speeds exceeding 290 km/h (180 mph) and resulted in two fatalities. Barnsdall, located approximately 64 km (40 miles) from Tulsa, has about half the population of Greenfield.

Tornadoes are rated on the Enhanced Fujita (EF) Scale, which ranges from EF-0 to EF-5 based on wind speeds and the resulting damage. Most tornadoes in the United States are rated as EF-0 or EF-1, accounting for the majority of the approximately 1 300 tornadoes recorded annually.

The Greenfield tornado is the third EF-4 tornado reported in 2024, with the other two occurring in Oklahoma during the spring.

References:

¹ Event Summary May 21, 2024 Tornadoes, Winds and Flash Flooding – NWS – May 23, 2024

² Deadly Greenfield tornado rated EF-4 with highest winds of 2024 yet – FOX Weather – May 23, 2024

Featured image credit: Live Storms Media (stilshot)