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  • Writer's pictureMeteorologist Beth Carpenter

New Strongest Recorded Tornado in History

STILL SHOT FROM REED TIMMER'S VIDEO OF THE GREENFIELD, IOWA TORNADO


May 21, 2024 –

 

THE STORM

During the afternoon hours on May 21, 2024, a strong area of low pressure moved across eastern Nebraska, western Iowa, and into Minnesota. Late in the morning and into midday, thunderstorms developed across eastern and southeastern Nebraska along the area of low pressure and trailing cold front. These storms then moved into Iowa during the early afternoon. Ahead of the front, the Storm Prediction Center (SPC) had already outlined portions of Iowa, northern Missouri, far southern Minnesota, and northwestern Illinois in a Moderate risk of severe weather, including a 15% probability of tornadoes, some potentially strong.



In Iowa, within the warm sector of the storm system, the atmosphere was significantly destabilizing as the morning rain and storms cleared out of the area. At 2 PM CDT, southwestern Iowa had 3000 J/kg of MLCAPE (Mixed Layer Convective Available Potential Energy). Strong winds from the surface up through the atmosphere created the necessary wind shear to support rotating thunderstorms and tornadoes. Given this volatile environment, the SPC issued a PDS (Particularly Dangerous Situation) Tornado Watch from 1:10 pm to 9 pm CDT.



A project out of the NWS Hazardous Weather Testbed called WOFS (Warn On Forecast) model gave forecasters a 75-minute lead time as it showed high confidence in strong, near-ground rotation near Greenfield, Iowa. The WOFS model relies not only on forecast model guidance, but also incorporates machine learning to aid in longer lead times for severe weather and tornadoes.



NATIONAL WEATHER SERVICE SURVEY

The National Weather Service (NWS) official storm survey concluded that the tornado was on the ground for over 46 minutes and traveled 44 miles. The maximum width was roughly 1000 yards, or 0.56 miles. Sadly, the Greenfield, Iowa tornado caused over 35 injuries and 5 deaths.

NWS damage surveys are used to determine the official rating of the tornado based on dozens of damage indicators- physical evidence of damage left behind. In order to be given a rating, the tornado must have caused observable damage and the level of damage to the object (tree, house, etc.) hit is recorded and analyzed by meteorologists and engineers. Based on their survey, the tornado was rated an EF-4 on the Enhanced Fujita Scale with estimated peak winds of 175-185mph.


NEW DATA

New data released from the Doppler on Wheels (DOW), a mobile radar network with sophisticated weather monitoring equipment led by nine scientists, indicates that the Greenfield, Iowa tornado from May 21st of this year may be the strongest tornado measured in recorded history. Preliminary data analysis from the team suggests maximum windspeeds of 308-319mph were observed in sub-vortices of the more than half-mile wide tornado. This is only the third time that DOW’s research group has measured over 300mph winds in tornadoes. The other two: Bridge Creek, Oklahoma on May 3, 1999 and El Reno, Oklahoma on May 31, 2013.

STRONGEST TORNADOES ON RECORD

Official tornado ratings DO NOT take into account readings from weather stations, estimated wind speeds on radar, or the like. Therefore, the new data provided by the DOW will not be taken into consideration for updating the tornado’s strength. One reason for this is because radar data measures wind speeds above ground level, and tornadoes are officially rated based on estimated wind speeds and related damage at the surface.


While the Greenfield, Iowa may lead unofficial records in strongest estimated maximum winds for a tornado, it won’t be placed at the top of official records.


You can stay ahead of incoming severe weather by receiving location-based NWS Alerts, lightning alerts, track incoming storms, and stay up to date on the forecast, all with the TDS Weather mobile app! Download it for FREE from the Apple App Store or the Google Play Store!

 




 

Thermodynamic Solutions (“TDS Weather”) provides professional weather consulting services to a variety of industries including: professional and minor league sports, snow removal and landscaping, golf courses and turf management, colleges and universities, and hospital networks. With nearly two decades of living and forecasting in the Ohio Valley region, our meteorologists provide custom, reliable forecasts that help clients SAVE and MAKE money in their daily operations. Our services include commercial and agricultural forecasting in the short and long ranges, lightning alerts and on-site hazardous weather monitoring, 24/7 on-call decision support services, forensic weather reporting, and more! For weather consulting inquiries, please contact us at info@tdsweather.com.




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