The climatology of Iowa tornadoes, prepared to consolidate and update these data for effective public service use, research, and other applications to the State's economy, is based on the 667 reported incidences from 1916 through 1960. But some comparison with earlier record is made since many of the outstanding tornadoes and most of the heavy losses of life occurred from 1859 through 1918. The outstanding tornadoes are grouped in the following classes: (1) with path length 25 miles or longer, (2) property loss of a quarter million dollars or more, and (3) those with outstanding loss of life and property.

The Iowa tornado climatology agrees broadly with the characteristics of tornadoes in the United States as a whole. However, the areal, seasonal, and diurnal distributions for Iowa are refined, thereby increasing the useful knowledge for regional use.