Daily Archives: September 28, 2026

Climate normals are 30-year averages for various climate observations such as temperature, precipitation and snowfall. A 30-year period smooths out weather variability while getting a good representation of our current climate. The current 30-year normal covers the period 1991-2020. This averaging provides a baseline for comparisons and assessing whether a particular day or month is warmer or cooler than normal, or if it is wetter or drier than normal.

The World Meteorological Organization (WMO) recommends 30 years as the reference for current average conditions, and member nations follow that recommendation. For the United States, NOAA’s National Center for Environmental Information (NCEI) is the official source of the country’s climate normals. The computation is nontrivial and more complicated than one might initially anticipate. Climate scientists employ complex statistical calculations to ensure the observations accurately represent the full 30-year climate period. The determination of normal must account for the occasional missing data, change in station location and instrument upgrades. Continue reading →