May 9
- 1876 – An F3 tornado moved through downtown Chicago and onto Lake Michigan, killing two people. A newspaper reporter wrote a detailed description of the tornado's multiple-vortex structure, including the presence of a downdraft at the center, a century before such mechanics were documented scientifically.
- 1927 – The third and most violent day of a three-day tornado outbreak resulted in 212 fatalities in the southern and Midwestern United States. An F4 tornado killed 98 people after destroying 31 blocks of Poplar Bluff, Missouri. Other tornadoes had large death tolls in Strong, Arkansas, Nevada, Texas, and Garland, Texas.