Recent changes in the diurnal cycle of precipitation over the United States

Hourly precipitation data from 1963 to 1993 of the contiguous United States were analyzed for secular trends in the diurnal cycle of precipitation. Du ring the period the winter daytime and nighttime precipitation frequencies and the diurnal amplitude of precipitation frequency increased by similar t o 30-47% over the Southwest, while the winter precipitation frequencies and the diurnal amplitude of precipitation intensity decreased by similar amou nts over the Northwest. During this period, summer afternoon precipitation frequency increased by similar to 30-60% in the Southwest and decreased by similar to 15-30% in the Southeast.