temperature extremes

The highest and lowest values of temperatures attained at a specified location during a given time interval, for example, daily, monthly, or seasonal.

In climatology, if this is the whole period for which observations are available, it is called the "absolute extreme."

Any function of time f(t) is periodic with period t if f(t) = f(t + τ) for all times t, where τ is the smallest number for which this equality holds.