Degree Days are a practical method for determining cumulative temperatures over the course of a season. Originally designed to evaluate energy demand and consumption, degree days are based on how far the average temperature departs from a human comfort level of 19 °C *. Simply put, each degree of temperature above 19 °C is counted as one Cooling Degree Day, and each degree of temperature below 19 °C is counted as one Heating Degree Day. For example, a day with an average temperature of 25 °C will have 6 cooling degree days.
Also known as the "heat summation method." A scale created by the University of California at Davis in the 1930s to determine the suitability for vineyards in any given climate. Modern instrumentation has largely supplanted this scale. The total accumulative number of degrees above 50F during the growing season. If the temperature for any given day rises to 70F that day would add 20 points to the summation. Over the 200 days of the California growing season the total would range from less than 2,500 degrees days for the coolest areas, classified as Region I, to region V with more than 4,000 degree days.
A measure of how cold (or hot) the weather has been (relative to a stated base temperature) measured over a regular monitoring interval, usually weekly or monthly.