An Atlas V rocket carrying the Defense Meteorological Satellite Program-19 spacecraft blasted off from Vandenberg Air Force Base at 2016 IST (1446 GMT) today, headed for a polar orbit.
United Launch Alliance webcast commentator Matt Donovan says the satellite later successfully separated from the rocket's upper stage.
The Air Force says the programme's satellites have been the primary provider of terrestrial and space weather information to the US military for 50 years. The satellite was built by Lockheed Martin.