Ask Tom: Why do weathermen reporting temperatures above or below 'average'?

Tom Skilling sorts out the difference between an “average” and a “normal” temperature.

Dear Tom,

There is a trend toward weathermen reporting temperatures above or below "average" rather than above or below "normal." Why?

— Jerry Pinzino, Homewood

Dear Jerry,

It might be because weathermen, especially those in the broadcast media, are beginning to adhere to the precise meteorological definitions of those terms. In meteorology and other atmospheric sciences, the definitions of "normal" and "average" differ somewhat from their popular usage.

An average temperature is just what you would expect: the sum of individual temperatures divided by the number of summed values. A normal temperature, however, is the specific average temperature calculated over the 30-year period, 1981-2010. Most cited average temperatures are ordinary averages, not normals.

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