He is known for his scientific research in weather modification through cloud seeding, while working as an associate director at the Institute for Atmospheric Physics and a professor of meteorology at the University of Arizona in Tucson.

He served as a cryptographer in the United States Navy during World War II, and afterwards, married Betsy Hunt.

in meteorology from the Massachusetts Institute of Technology in 1945, where he completed the thesis titled Summer air mass instability and its synoptic representation under the supervision of Thomas F.

His PhD thesis was supervised by Joseph M. Keller and it has the title Radiation-Errors and Lag-Errors in the Measurement of Turbulent Temperature Fluctuations.

He examined physical factors influencing raindrop shape, identifying surface tension, hydrostatic pressure, and aerodynamic pressure as the primary contributors to deformation and revealed with high-speed photography the significant role of boundary-layer separation in shaping drops and influencing surface processes.

[12][13] McDonald's first detailed, public discussion of UFOs was in a lecture given before an American Meteorological Society assembly in Washington, D.C., on October 5, 1966.

[14] In his Statement on Unidentified Objects to the House Committee on Science and Astronautics, McDonald made the following remarks regarding types of UFO accounts.

Ufologist Jerome Clark called the lecture "one of the most powerful scientific defenses of UFO reality ever mounted".

During that testimony Congressman Silvio O. Conte of Massachusetts—whose district contained factories that would help build the SST—tried to discredit McDonald by referring to his UFO research.