When was the first geostationary weather satellite launched?

ATS-1 was launched on 6 December 1966 and became the first satellite placed in a geostationary orbit for weather observation. Because it stayed fixed over one region of Earth, it could continuously monitor cloud systems and storm development. That made it especially valuable for tracking rapidly changing weather over the Pacific. Geostationary weather satellites later became a backbone of modern forecasting around the world.