We use the plural form when we are thinking of more than one temperature.
The temperatures in Paris and Berlin reached record heights yesterday.
Temperatures were in the 90s (Fahrenheit) yesterday.
The children had temperatures ranging between 29 and 40.5 degrees.
The atmosphere in the Commons was tense yesterday, and temperatures/the temperature rose as anti-monarchist Fred Bloggs began to question the Prince's personal habits.
It is possible to use temperature as an uncountable, noun meaning 'degree/amount/intensity of heat', in the first two examples. When we use it countably, we think more of individual figures
In the last example, we can think of the temperatures of individual MPs, or the temperature in the debating chamber.