Interesting find.
I don't recall that 'normal' as a fixed number was a term widely bandied about in the statistics I was exposed to in college and medical school. It's a
range when the parameters of a person's blood work, etc. are evaluated in the laboratory or office. Here's the NWS's definition of a climate 'normal':
In the strictest sense, a "normal" of a particular variable (e.g., temperature) is defined as the 30-year average. For example, the minimum temperature normal in January for a station in Chicago, Illinois, would be computed by taking the average of the 30 January values of monthly averaged minimum temperatures from 1981 to 2010. Each of the 30 monthly values was in turn derived from averaging the daily observations of minimum temperature for the station. In practice, however, much more goes into NCEI's Climate Normals product than simple 30-year averages. Procedures are put in place to deal with missing and suspect data values. In addition, Climate Normals include quantities other than averages such as degree days, probabilities, standard deviations, etc. Climate Normals are a large suite of data products that provide users with many tools to understand typical climate conditions for thousands of locations across the United States.
They are talking about averages and then stating that they're 'normal'. This implies that any deviation from these averages is 'abnormal'. This leads to apocolyptic interpretations of weather trends, and isn't very helpful. Defining a range of 'normal' would be much more useful.
