A method for classifying wine climate regions that was developed in the 1930s at the UNIVERSITY OF CALIFORNIA, DAVIS by Professors A. J. Winkler and Maynard Amerine. This system is referred to variously as degree days, heat summation method, Winkler Scale, and Regions I –V. The method is based on the theory that no vine shoot growth occurs below 50°F and that each degree a day averages above 50°F is considered a degree day. For example, if during a 24-hour period the temperature ranges from 57 to 81°F, the average is 69°F, which is equivalent to 19 degree days (69 minus 50). The heat summation (sum of all the degree days between April 1 and October 31) of a growing region determines its classification, which is described in total degree days. There are five climate region classifications, which suggests that California has growing environments that are comparable to the various traditional winemaking regions throughout the world. Climate Region I (up to 2,500 degree days) is the coolest and is similiar to regions like CHAMPAGNE and CÔTE D’OR in France and the RHINE in Germany. It includes portions of the following areas: ANDERSON VALLEY, CARNEROS, EDNA VALLEY, Marin, MENDOCINO, MONTEREY, NAPA, RUSSIAN RIVER VALLEY, SANTA CLARA, SANTA CRUZ MOUNTAINS, and SONOMA. Suggested varieties for Region I include CABERNET SAUVIGNON, CHARDONNAY, PINOT NOIR, RIESLING, and SAUVIGNON BLANC. Climate Region II (from 2,500 to 3,000 degree days) is similiar to France’s BORDEAUX region and includes portions of the following areas: ALEXANDER VALLEY, Anderson Valley, CHALK HILL, Edna Valley, Mendocino, Monterey, Napa, POTTER VALLEY, Russian River Valley, Santa Clara, and Sonoma. Suggested varieties include those for Region I plus MERLOT. Climate Region III (from 3,000 to 3,500 degree days) is equivalent to France’s RHÔNE region and includes portions of the following areas: ALAMEDA, Alexander Valley, CONTRA COSTA, EL DORADO, KNIGHT’S VALLEY, LAKE, MCDOWELL VALLEY, Mendocino, Monterey, Napa, PASO ROBLES, PLACER, REDWOOD VALLEY, RIVERSIDE, SAN BENITO, Santa Clara, and Sonoma. Suggested varieties include CARIGNAN, RUBY CABERNET, Sauvignon Blanc, SÉMILLON, and ZINFANDEL. Climate Region IV (3,500 to 4,000 degree days) is similar to southern Spain and includes portions of the following areas: AMADOR, CALVERAS, El Dorado, Fresno, MERCED, Riverside, SACRAMENTO, San Diego, SAN JOAQUIN, and YOLO. Suggested varieties include BARBERA, EMERALD RIESLING, Ruby Cabernet, and those used for PORT-style wines. Climate Region V (more than 4,000 degree days) is the hottest region and is similar to North Africa. It includes portions of the following areas: Amador, Calveras, Fresno, Kern, MADERA, Merced, Sacramento, San Bernardino, San Diego, San Joaquin, Stanislaus, and Tulare. Suggested varieties include SOUZÃO, TINTA MADERA, and VERDELHO. The authors of this approach have acknowledged that within these broader regions there are MESOCLIMATES capable of growing other varieties. Other states, such as OREGON and WASHINGTON, also use this method to classify their regions.