Alexander George McAdie (August 4, 1863 – November 1, 1943) was an American meteorologist. While in college he joined the Army Signal Service, the predecessor of the U.S. Weather Bureau. He graduated from Harvard University in 1885. From 1903 until 1913 he ran the U.S. Weather Bureau in San Francisco. He was also the vice president of the Sierra Club, starting in 1904, and continuing until 1913. In 1913 he became Professor of meteorology at Harvard, and remained there until 1931. During the same period he also served as the director of the Blue Hill Observatory.