The latest Aon Weekly Cat report warns that the substantial severe weather outbreak in July, which affected the Midwest and resulted in additional storms impacting the eastern US, could rank near or among the top 10 costliest severe weather events in US history.
According to the broker, the outbreak will likely cause total economic and insured losses in the low-to-mid single-digit billions USD. The damage was caused by extensive wind, hail, and tornadoes seen in eastern Wisconsin and northern Illinois.
The broker said that the most notable event was a devastating EF-3 tornado that struck the Fox Cities region of Wisconsin, while the Chicagoland metro experienced very intense wind and hail impacts. Both areas saw extensive property and infrastructure damage, and hundreds of thousands of power outages.
The strong and destructive severe weather event occurred in the Midwest on July 27-28, with most impacts occurring on 27 July. In Wisconsin and Illinois, many of the storms produced intense and widespread wind, hail, and rainfall. Multiple northern Wisconsin counties, including Kewaunee, Door, and Shawano, saw hailstones over 3 inches wide, while other counties further north saw particularly strong wind gusts.
The storms moved through the Chicago metro area, which saw hurricane-force wind gusts and hail larger than 2 inches in diameter which impacted large swaths of Cook, Lake, DuPage, and Will counties.
Localised flooding was also observed as much of Chicago and the south and southwest suburbs recorded over 76 mm of rain in just a few hours. NWS damage surveys also confirmed 7 tornadoes in northern Illinois, including two EF-1 twisters in the southern Chicago suburbs. Additional, but less severe, impacts from tornadoes, wind, and hail were seen in Indiana, explained Aon.
According to Aon, the top five most costly severe weather events in US history includes: Midwest Derecho of August 2020 which caused insured losses of USD 11 billion, followed by Super Outbreak (Tuscaloosa) in April 2011 with losses of USD 11.3 billion, Joplin Tornado Outbreak of May 2011 with losses of USD 10.4 billion, and Eastern U.S. SCS Outbreak of March 2025 with losses of USD 8.3 billion, and Central/East U.S. SCS Outbreak of May 2025 with losses of USD 6.3 billion.
The other five are: Central U.S. Tornado Outbreak of May 2003 with losses of USD 6 billion, South/Ohio Valley SCS Outbreak of May 2024 with losses of USD 5.5 billion, South/Tenn. Valley SCS Outbreak of March 2023 with losses of USD 5.4 billion, Midwest SCS Outbreak of April 2026 with losses of USD 5.2 billion, and Central U.S. SCS Outbreak of March 2024 with losses of USD 4.9 billion.
All of the figures for the top 10 events in the US are insured losses only.
