In which year was the first official tornado forecast and warning issued in the United States?

The first official tornado forecast and tornado warning was made by United States Air Force Captain (later Colonel) Robert C. Miller and Major Ernest Fawbush, on March 25,1948. The first such forecast came as a result of events that occurred 5 days earlier on March 20th.

Miller was a California native who was stationed at the Tinker Air Force Base located in Oklahoma County. He was assigned to work the late shift as a forecaster for the base's Air Weather Service office that evening. As he examined and analyzed the U.S. Weather Bureau surface maps and upper-air charts, he noticed that the air charts failed to note atmospheric instability and moisture content present over the state of Oklahoma. This condition would be suitable for producing thunderstorm activity.

In fact, thunderstorms developed producing 92 miles per hour (148 km/h) wind gusts and a tornado touched down in the area crossing the Air Force Base grounds, damaging several military aircraft, estimated at $10 million (USD). Following an inquiry by military personnel, Miller and Fawbush were tasked with studying methods to forecast tornado thunderstorms.

As a result of their work, their forecasts were distributed to the American Red Cross and Oklahoma Highway Patrol as well as the local U.S. Weather Bureau's Oklahoma City office.