On May 4, 2021 the NOAA National Center for Environmental Information (NCEI) released updated climate normals, reflecting observed data for the 1991-2020 period. These updates occur every 10 years, in accordance with established practices by the World Meteorological Organization, and reflect the most recent three decade period. Climate normals provide a benchmark to compare daily weather to and are broadly utilized by industry, media, and researchers.

Climate normals are produced for a number of meteorological variables including temperatures, precipitation, growing season length, etc. In producing the newest set of Climate Normals, the years of 1981-1990 were replaced with the years 2011-2020 before passing through NCEI (National Centers for Environmental Information) data quality checks.

The uses for climate normal are many. For example, planners use climate normal to prepare for flooding and drought, farmers use climate normal to decide what and when to plant and energy companies use climate normals to meet demand.

The U.S. Climate Normals collection has 10 versions: 1901-1930, 1911-1940, and so on through 1991-2020. Places where the annual temperature during a given Normals era was colder than the 20th-century average are blue; places where the temperature was warmer than average are red.

The earliest map in the series has the most widespread and darkest blues, and the most recent map has the most widespread and darkest reds. Temperatures across the U.S. have been steadily warming through the 20th and early 21st century.