The U.S. Climate Normals are computed every ten years for the most recent 30-year period. These provide a basis for comparisons of temperature, precipitation, snowfall, and other variables to today’s observations. The normals themselves do not assess long-term climate trends, but comparisons of normals between different 30-year periods can show trends in climate.
The normals give the public, meteorologists and climatologists, and businesses a standard way to compare today’s weather to what has occurred over the past 30 years. These comparisons can be related to other changes, such crop development, energy usage, water supply, retail activity, and many others.
For more information on the utility of climate normals see this link on the NCEI web site: NOAA Delivers New U.S. Climate Normals