Climatological standard normals
From Glossary of Meteorology
climatological standard normals
Averages of climatological data calculated for the following consecutive 30-yr periods, established by international agreement: 1 January 1901 to 31 December 1930; 1 January 1931 to 31 December 1960; 1 January 1961 to 31 December 1990; 1 January 1991 to 31 December 2020; etc.
See normal.