Abstract
This paper identifies the spatial and temporal patterns in diurnal variations of Arizona's monsoon precipitation frequencies. Long-term (1948–83) hourly rainfall data reveal a strong nocturnal tendency in the Salt and Gila River basins of central Arizona. First harmonic phase angles suggest that storms tend to develop into the Phoenix area from all directions to ultimately produce a strong maximum frequency near midnight over the city. Other areas of the state appear to have the more normal daytime maximum in their monsoon precipitation. The practical and theoretical utility of the results are briefly discussed.
