Totals are from L. H. Seamon, who worked for the U.S. Weather Bureau and wrote an academically peer reviewed paper in Monthly Weather Review combined with total from tornado expert Thomas P. Grazulis. Grazulis rated significant tornadoes (F2+ or a fatality). So, any tornado with a rating was done by Grazulis and any tornado rated "FU" was not rated by Grazulis.
Laura V. Wolford (U.S. Office of Climatology); Frederick H. Mueller (Secretary of Commerce); F. W. Reichelderfer (Chief of U.S. Weather Bureau) (1960). "Tornado Occurrences in the United States"(PDF). Department of Commerce. pp. 22–25. Retrieved 22 April 2023.
