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Wyoming-Montana Water Science Center
Flood of August 1, 1985, Cheyenne, Wyoming
The August 1, 1985, flood in Cheyenne was one of the most devastating historic floods in Wyoming. The flood was the result of unusually severe thunderstorms that were centered over Cheyenne and that covered an area of about 50 square miles. There were 12 storm-related deaths, numerous injuries, and an estimated $61.1 million in damage (in 1985 dollars).
How Large Was The Flood?
Streamflow in Crow Creek that night ranged from 2,300 to 8,260 cubic feet per second (cfs) and in Dry Creek ranged from 3,820 to 5,880 cfs. The average flow on August 1 for the last 22 years at the USGS streamgage at 19th Street is around 4 cfs.
How Did It Happen?
Several thunderstorms passing over the city combined to produce 6.06 inches of rain and hail between 6:20 and 9:45 p.m. at the National Weather Service recording station at the Cheyenne airport. The maximum 1-hour precipitation was 3.51 inches between 8 and 9 p.m. One of the storm cells became stationary over the Dry Creek area in the northwest part of the city and by 7:45 p.m. had reached an altitude of more than 60,000 feet above sea level according to the National Weather Service. Another storm cell over central Cheyenne continued to increase in intensity until about 9:30 p.m., causing torrential rain, severe hail, and winds of as much as 70 miles per hour.
Was This Flood Unique?
Large floods are not uncommon in the Crow Creek and Dry Creek drainages and in the Cheyenne area; however, because the area along Crow Creek (since 1867) was urbanized earlier than that of Dry Creek (since about 1950) and because of Crow Creek's larger drainage area, more historical flood information is available for Crow Creek. Prior to August 1, 1985 flood, the largest known floods in Crow Creek occurred in 1904 and 1929, each having a maximum streamflow comparable to the 1985 flood. In addition, information provided by area residents indicates that significant floods also occurred in Crow Creek in 1883 and 1896.
Is There More Flood Information?
What Are Today's Streamflows?
Who Can Answer Questions?
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