"Station: Duluth, MN". U.S. Climate Normals 2020: U.S. Monthly Climate Normals (1991–2020). National Oceanic and Atmospheric Administration. Retrieved June 22, 2021.
Official records for Duluth were kept at downtown from August 1871 to May 1941, and at Duluth Int'l since June 1941. For more information, see ThreadEx.