Official temperatures for the City of Phoenix that are mentioned on local news and radio weather reports are obtained from the National Weather Service in Phoenix, AZ. The ASOS (Automated Surface Observation System), pictured here, is the system used to determine the official readings for the temperature in Phoenix.
The National Weather Service operates and maintains three ASOS locations in the greater Phoenix area. They are at Deer Valley Airport, Scottsdale Airport, and Phoenix Sky Harbor Airport. The observations from these sites are automatically input into the weather data stream for the National Weather Service.
Other systems in the area collect weather data that is manually input into the system. These are the AWOS (Automated Weather Observation System) and LAWRS (Limited Aviation Weather Reporting System) locations in greater Phoenix: Chandler, Falcon Field in Mesa, Williams Field in Mesa, Gila Bend, Goodyear. Both AWOS and LAWRS are FAA maintained sites. The weather equipment located at Luke AFB in Litchfield Park is operated and maintained by the USAF.
Why is the temperature mentioned on the news different than what my outdoor thermometer reads?
Greater Phoenix covers a large area. Your location may be at a higher elevation or have more surrounding vegetation, for example. Official readings in Phoenix may be as much as five or ten degrees different than other parts of the Valley of the Sun (maybe hotter, maybe cooler) at any point in time.