Hourly precipitation data from 1963 to 1993 for the United States (from Higgins et al., 1996) were analyzed for changes in the diurnal cycle. Several variables, including the amplitude and phase of the diurnal cycle of precipitation frequency and intensity, the daytime, nighttime and afternoon precipitation frequency and intensity, were examined. During the summer, afternoon precipitation is often associated with moist convection and thunderstorms over the Rocky Mountains and the Southeast. Therefore, the precipitation results should also have implications for the changes in summer moist convectivity over the United States. Detailed results will be presented at the AMS meeting