 There are numerous issues and limitations associated with the use of growing degree-days.First, the Winkler index and its classification of climate regions by growing degree-days only describe one aspect of an area's climate—mean daily temperature.Many other important factors which contribute to a region's suitability for viticulture (and its terroir) are excluded; among them sun exposure, latitude, precipitation, soil conditions, and the risk of extreme weather which might damage grapevines (e.g., winter freezes, spring and fall frosts, hail, etc.