Climatological normal

[3] Climatological normals are used as an average or baseline to evaluate climate events and provide context for year-to-year variability.

[1] Climatological standard normals are overlapping periods updated every decade: 1971–2000, 1981–2010, 1991–2020, etc.

The term "normal" first appeared in the literature by Heinrich Wilhelm Dove in 1840 and the concept was formalized by the International Meteorological Committee in 1872.

[5] The continued use of 30 year normals has increasingly been called into question due to substantial evidence that the stationarity of climate statistics can no longer be taken for granted due to climate change.

[4][6] This has led to alternative definitions such as "Optimal Climate Normal" and the "Hinge Fit" approach to supplement the standard 30 year normals which are still commonly used.