I am amazed at this weather event and would never have expected such an event to occur around Phoenix.
I have been to Phoenix in the heat of summer of June 2002 and the city is laid out across a desert environment. Glendale is a suburb of Phoenix. It is a very dry environment. There are mountains to the north of the city but further south and west, the Sonoran Desert takes over. Rainfall is low (Apparently the range is from 2.82 inches recorded in 2002 to as high as 19.73 inches recorded in 1905). Temperatures as high as 45C are common especially during the summer months. Phoenix is regarded as the third hottest major city in the USA during July and the 11th hottest city in the USA based on average annual temperatures (Christopher C Burt, Extreme Weather 2007, Page 15 and 279).
The city appears to average 10 to 30 thunderstorm days per year decreasing to the south west but increasing to the north east toward the mountains.
Harley Pearman