However, it has been found that simple growing season temperature parameters can be used effectively to define spatial variations in varietal potential and growing season climates . For example, Amerine and Winkler (1944) developed a heat summation index for California (growing degree days from April–October in the Northern Hemisphere with a base of 10 ◦C) to place a region into one of five climate types capable of adequately ripening certain grape vari- eties. In addition, Jones (2005a) showed that grape growing climates can be ordered into cool, intermediate, warm, and hot groupings based on average growing season temperatures (April–October in the Northern Hemisphere) and varietal ripening potential. Since warmer growing seasons have been related to longer growing sea- sons