…is why Phoenix doesn't get rain. This is a perfect illustration of the heat bubble that rises over the city during the otherwise wet, monsoon months of summer. And why does this happen? Because the entire valley is paved over. The pavement absorbs the heat during the day, and then re-radiates it all night (which is also why we seldom drop below 90F in July/August). Storms approach, but dissipate or just split and go around this heat bubble, leaving the city dry.
Tucson to the south of us on the other hand, has retained its natural character and isn't paved over nearly as much, allowing it to get those beautiful summer monsoon storms.