The Dust Bowl heat wave reaches its peak, sending temperatures to 109 °F (43 °C) in Chicago and 104 °F (40 °C) in Milwaukee.

The Dust Bowl was a period of severe dust storms that greatly damaged the ecology and agriculture of the American and Canadian prairies during the 1930s. The phenomenon was caused by a combination of natural factors and human-made factors: a failure to apply dryland farming methods to prevent wind erosion, most notably the destruction of the natural topsoil by settlers in the region. The drought came in three waves: 1934, 1936, and 1939–1940, but some regions of the High Plains experienced drought conditions for as long as eight years. It exacerbated an already existing agricultural recession.

Chicago is the most populous city in the U.S. state of Illinois and in the Midwestern United States. Located on the western shore of Lake Michigan, it is the third-most populous city in the United States with a population of 2.74 million at the 2020 census, while the Chicago metropolitan area has 9.41 million residents and is the third-largest metropolitan area in the nation. Chicago is the seat of Cook County, the second-most populous county in the United States.

Milwaukee is the most populous city in the U.S. state of Wisconsin. Located on the western shore of Lake Michigan, it is the 31st-most populous city in the United States and fifth-most populous city in the Midwest with a population of 577,222 at the 2020 census, while the Milwaukee metropolitan area with over 1.57 million residents is the 40th-largest metropolitan area in the nation. It is the county seat of Milwaukee County.