John A. Day (May 24, 1913, Salina, Kansas – June 21, 2008, McMinnville, Oregon) was an American meteorologist, educator, and sky-watching evangelist. He charted new Pan American Airways air routes throughout the Asia Pacific region in the era before weather satellites and computer-generated instant data. A photographer of nature and atmospheric phenomenon, he published numerous books, articles, atlases and cloud charts that explained the importance of weather. Popularly known as “The Cloudman” during his decades as both a college professor and lay advocate for cloud appreciation.