Using information gathered from 4,775 US weather sites, in the early 2000s, the U.S. Department of Energy’s Pacific Northwest National Laboratory created a simplified map separating North America into 8 general climate zones based primarily on temperature. It was then divided into three moisture categories designated A, B, and C. Zone A being humid, Zone B being dry, and zone C Marine, where the warmest months don’t exceed 72 °F and winter temperatures range between 27 and 65 °F.