The temperature sensor is mounted in the front opening to the evap, the intercooler (if you have a turbo) and the radiator. So if you are sitting at a light or in stop and go traffic, don't be surprised if it reads VERY high.

Other instances where it will read high are, when it is very sunny, and temps just over the road, as the sensor is, are much higher then ambient. Also, after stopped for a bit, say to grab a coffee, being parked for a couple minutes will cause it to read high as well, as the heat exchanges have been emitting heat.