About Climate Normal Difference Maps
These maps compare the normals of temperature, precipitation, snow, HDD, CDD, and GDD for the different climate normals periods.
Climate normals are an arithmetic average of a variable such as temperature over a prescribed 30-year period. This base period changes every 10 years to reflect the previous 30 years of data.
For more information on climate normals, view the National Centers for Environmental Information's U.S. Climate Normals page.