noun

• The average temperature or excess temperature over a period multiplied by the number of days in the period; the sum over a month or other period of the amounts by which the mean temperature each day exceeds a particular base value.

  Thus if the average daily temperature during a week were successively 10°C, 12°C, 13°C, 16°C, 16°C, 15°C, 15°C, the accumulated temperature would be 97°C; with reference to a base temperature of 6°C, the excesses are 4, 6, 7, 10, 10, 9, 9, and the accumulated temperature is 4 + 6 + 7 + 10 + 10 + 9 + 9, i.e. 55 degrees.