In 1961, 18-year-old Ross enlisted in the United States Air Force and was put into service as a medical records technician.  He rose to the rank of master sergeant and served as the first sergeant of the clinic at Eielson Air Force Base in Alaska, where he first saw the snow and mountains that later appear as recurring themes in his paintings. He developed his quick painting technique during brief daily work breaks.

From this wiki page, his style was built out of necessity, where he could only paint on a break, in effect he was one of the first speedpainters to become widely known (pulling that out of my ass because art history is something I know <1 about(slightly more than nothing).)