The North American Drought of 1988 ranks among the worst episodes of drought in the United States. This multi-year drought began in most areas in 1988 and continued into 1989. The drought caused $60 billion (1988 United States dollars) in damage ($120 billion in 2014 United States dollars, adjusting for inflation). The drought occasioned some of the worst blowing-dust events since 1977 or the 1930s in many locations in the Midwestern United States, including a protracted dust storm, which closed schools in South Dakota in late February 1988. During the spring, several weather stations set records for lowest monthly total precipitation and longest interval between measurable precipitation, for example, 55 days in a row without precipitation in Milwaukee. During the summer, two record-setting heat waves developed, similar to those of 1934 and 1936. The concurrent heat waves killed 4,800 to 17,000 people in the United States. During the summer of 1988, the drought led to many wildfires in forested western North America, including the Yellowstone fires of 1988. At its peak, the drought covered 45% of the United States. Despite the lesser areal coverage of drought than 70% during the Dust Bowl, the drought of 1988 ranks as not only the costliest drought in United States history but also the costliest natural disaster in United States history before Hurricane Katrina.