What is the explanation for the following sentence being written as it is:
The newborn baby was discovered by passing cyclists on a day when temperatures surpassed 40 degrees Celsius.
The singular temperature sounds much better to me while temperatures sounds a little odd. There is only one temperature - it can be either high or low, rising to 30, 40, 50 degrees or decreasing to -20, -30, etc. In which context should one use temperatures?