The United States has experienced two major drought episodes during the 20th Century.  During the peak of the "Dust Bowl" decade of the 1930's, nearly two-thirds of the contiguous U.S. experienced severe to extreme drought (as measured by the Palmer Drought Index).  The 1950's major drought episode peaked at about half of the country with severe to extreme drought.  Other large-scale droughts since then include the 1960's Northeast drought, the 1976-77 drought, and the national drought of the late 1980's.

The last three decades of the 20th Century were characterized by large areas of unusual wetness, similar in extent to the wet 1940's.