An official air temperature is a surprisingly specific claim. To count, it must be measured in shade, with free airflow, roughly 4 to 6 feet above the ground, over natural surface, away from buildings and pavement. The sensor sits inside a radiation shield, a white louvered housing that blocks direct sun while letting air move through freely.
Every one of those conditions exists to isolate one thing: the temperature of the air itself, not the temperature of an object sitting in the sun.
Why your car reads higher
A vehicle's sensor typically sits near the front bumper, inches above asphalt that has been absorbing sunlight all day. Asphalt in summer sun can exceed 140°F, and it radiates that heat upward. Sitting still at a light, a car thermometer is partly reading the road.
It isn't broken. It's honestly reporting a genuinely hotter microclimate that you will also experience while standing on that pavement, which is worth knowing. It just isn't the air temperature.
A thermometer on a sunny porch reads high. One under a tree in a damp yard reads low. A backyard station above a driveway reads high all summer. Siting is the difference between a measurement and an anecdote.
Urban heat is real, though
Cities genuinely run warmer than surrounding countryside, often several degrees, and much more at night, because concrete and asphalt release stored heat for hours after sunset. That's a real phenomenon, not a siting error, and it means a downtown block can legitimately be hotter than the airport across town.
Which is the honest argument for showing you where your reading came from. A properly measured temperature from a station nine miles away tells you what the air mass is doing. Your street may run a couple of degrees warmer. Both facts are useful, and only one of them can be measured to a standard.
Celsius under the hood
Airport observations report temperature in whole degrees Celsius, which is why converted Fahrenheit readings sometimes seem to jump by two degrees at once. A change from 26°C to 27°C is 78.8°F to 80.6°F. Nothing glitched, the source data simply has one-degree Celsius resolution.