The National Oceanic and Atmospheric Administration (NOAA) has just published the “new normal” temperature for the U.S. Every ten years NOAA calculates the average high and low temperatures for a 30-year period and this is used as the “normal” temperature baseline.
The new normal temperature will be about 0.5 F warmer than the old normal temperature because the period 1998-2008 was warmer than mid-20th Century norms. See graph below.
Notice than the 1920s and 1930s were as warm as 1998-2008. This was followed by a cooler period from 1940 to about 1978. The warm period of 1998 to 2008 is attributed to a super El Niño in 1998. It appears that the average temperatures have cooled since 2009. It remains to be seen whether this cooling will persist as some predict based on total solar irradiance and sunspot observations (see articles below).
The “normal” temperature baselines have some value to farmers in judging when to plant crops. Energy utilities also use these baselines to help predict energy demand. The “normal” temperature is just a mathematical construct. By choosing longer or shorter periods, the “normal” temperature would be different.