James E. McDonald was an American atmospheric physicist at the University of Arizona and, in the late 1960s, one of the most outspoken scientists arguing that unexplained UFO reports deserved serious study. He reviewed Air Force case files, interviewed witnesses, testified before a House committee in 1968 and became a leading scientific critic of the Air Force-funded Condon study. He passed away in 1971.

Born in Duluth, Minnesota, in 1920, McDonald earned a chemistry degree from the University of Omaha in 1942, a master's in meteorology from the Massachusetts Institute of Technology in 1945 and a doctorate in physics from Iowa State University in 1951. After teaching at the Naval Aerology School and Iowa State and spending a year at the University of Chicago, he helped start a meteorology program at the University of Arizona in 1953 and became associate director of its Institute of Atmospheric Physics in 1954, later serving as a professor there. His research covered cloud physics, the shape and behavior of raindrops, rain scavenging of airborne particles and weather modification, and in 1963 he joined a National Academy of Sciences panel on weather and climate modification.

His university papers show him following sightings from 1958, and in October 1966 he gave his first detailed public talk on the subject, "The Problem of UFOs," to an American Meteorological Society meeting in Washington. In 1967 he examined the Project Blue Book files at Wright-Patterson Air Force Base and concluded that the Air Force was mishandling the evidence. That year he spoke to the United Nations Outer Space Affairs Group, travelled to Australia and New Zealand, and said there was "no sensible alternative" to the hypothesis that UFOs were extraterrestrial probes.

At the 1968 Congressional UFO Symposium, held by the House Committee on Science and Astronautics on July 29, his statement argued that scientists had been "casually ignoring" a problem of major importance. He had sought a place on the Condon Committee and was turned down, and after its 1969 report concluded that further study was unwarranted he wrote detailed critiques, noting that the report itself left more than 30 percent of its cases unexplained. His lecture "Science in Default," given at the 1969 American Association for the Advancement of Science symposium, was later published in UFO's: A Scientific Debate (1972), edited by Carl Sagan and Thornton Page. When he testified to Congress that the supersonic transport could damage the ozone layer, Representative Silvio Conte questioned his credibility by citing his UFO research.

McDonald's papers, including about 580 Blue Book reports, most of them from pilots, are held by the University of Arizona, and Ann Druffel told his story in the 2003 biography Firestorm. In 2026 a long online documentary on science and UFOs revisited his clash with Condon, the researcher Richard Dolan included him among the candidates for the field's greatest investigator, and a reader of Druffel's book went looking for a Hynek article that the Blue Book chief Hector Quintanilla had reportedly described to McDonald. He remains the clearest example of an established physical scientist who staked his professional standing on the claim that some UFO reports were unsolved scientific problems.