All of our GPS devices feature the ability to give a temperature reading (+/- 2°C). Sometimes though, the device might give you a different reading than what your local weather man or the app on your phone tells you.
When you get the temperature for your city, on any given day, it's the temperature measured in a specific location in a specific way. The most important thing to remember is that a weather station measures temperature in open shade, which is an obvious distinction from most of us who ride with the sun beating down on us, and more importantly, beating down on the device. We try to adjust for this, but adjusting for it too much would cause the opposite problem (and may to an extent do so anyway).
Also, anyone who's ever ridden over a river or into a canyon can tell you that there's often a change in temperature influenced by topography. These pockets of cold or warm air present additional challenges, and it can take time for the device to adjust. The device isn't a mercury-filled glass tube, so when it really comes down to it, it isn't the most ideal device to give a temperature reading. They will however give you a relatively accurate estimation (again +/- 2°C).