NOAA's National Climatic Data Center (NCDC) is responsible for producing official climate normals of numerous climatological variables, including mean temperature. A climate normal is traditionally defined as a simple average over 3 decades, i.e. a 30-year average produced once every 10 years. NOAA's official climate normals were last produced for the 1971-2000 period.

Climate normals are calculated retrospectively, but utilized prospectively. However, mounting evidence suggests that global climate statistics are non-stationary, calling into question the predictive skill of traditional climate normals. To complicate matters, NOAA's official climate normals are only released every 10 years, a frequency which is problematic for many users given the rapid rate of warming since the mid-1970s. For instance, an energy regulator setting utility rates in 2009 may be reliant upon official climate normals that were released almost a decade ago, which in most instances are too cool for today's climate.

There is a clear need to compute new climate normals that (1) are representative of the current state of the climate at the time they are reported and/or (2) explicitly accommodate the prospect of a changing climate. NCDC scientists are currently developing a new suite of experimental products called ‘Optimal Normals' that attempt to address these two needs. The various techniques include simply updating the 30-year climate normals annually, as well as more rigorous techniques involving time series filtering theory, the estimation of optimal empirical weights, and the use of downscaled climate model projections for improved estimates of current and future climate normals.