This paper presents the tropospheric conditions at Phoenix, Arizona which accompany the development of five radar reflectivity regimes during three summer seasons in central Arizona. The five reflectivity regimes include: the eastern mountain regime (EMR), the central and eastern mountain regime (CEMR), the central, eastern, and Phoenix (CEPR) regime, the widespread regime (WR), and the dry regime (DR). It describes 1) how characteristics of composite 12 UTC soundings at Phoenix relate to each reflectivity regime, 2) how surges from the Gulf of California and the position of the Arizona monsoon boundary relate to each reflectivity regime, and 3) how evolution of the planetary boundary layer between 12 UTC and 23 UTC at Phoenix indicates the importance of sustained low-to-mid-level moisture for storm development in Phoenix.

Previous studies, based primarily on low-resolution radar, lightning, and terrain data, show that elevated terrain influences the climatological diurnal precipitation cycle in central Arizona. Also, such studies show that summer precipitation in Arizona occurs intermittently as "bursts", or periods of widespread rainfall, and "breaks", or periods of little-to-no rainfall, owing to variations in the synoptic-scale pattern. In the present study, high resolution (1-km) WSR-88D Level II data and digital terrain data show that within a burst, storms may initiate over a variety of elevated terrain features and either evolve mostly over mountains in the afternoon, or evolve over the mountains in the afternoon and over Phoenix during the evening. Such variations in reflectivity regime appear related to the tropospheric moisture, wind shear, wind direction profiles at Phoenix, and lifting mechanisms available on a given day (e.g., diurnal heating, thunderstorm convergence lines, mountain-driven circulations, and synoptic-scale circulations).