Excessive precipitation produced severe flooding in a nine-State area in the upper Mississippi River Basin during spring and summer 1993. Following a spring that was wetter than average, weather patterns that persisted from early June through July caused the upper Midwest to be deluged with an unusually large amount of rainfall. Monthly precipitation data were examined at 10 weather-station locations in the flood-affected region to illustrate precipitation patterns and amounts in the flood-affected area. In 1993, all 10 of the selected locations received greater than the normal rainfall for January through June 1961-90, 8 of the 10 locations received more than 200 percent of the normal rainfall for July 1961-90, and 3 received more than 400 percent of the normal rainfall for July. (The average rainfall for any given 30-year period is termed the 'normal' rainfall for the given period.) May through July 1993 was the wettest or nearly the wettest such period on record at many locations in the flooded area. Of the 10 locations, 6 received more rainfall in the first 7 months of 1993 than generally is received in a year.
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USGS Numbered Series
Precipitation in the upper Mississippi River basin, January 1 through July 31, 1993