Abstract
The diurnal variability of thunderstorm occurrence in Arizona is complex and related to terrain elevations. Generally, thunderstorms occur in the higher mountains during the afternoon with activity primarily of the nocturnal nature in the adjacent desert valleys, most noticeably the Phoenix area. Aircraft temperature probes have found cooling in cumulus areas. This cooling can frequently advect with the steering wind to destabilize the desert air mass and increase nighttime thunderstorms. The same destabilization process could contribute to nocturnal thunderstorms in the High Plains.