Some confusion exists by print and broadcast media in reporting on weather conditions involving the true high temperature, finds Grumpy Editor.
During the past few days, as the usual muggy July weather grips parts of the nation, heat index readings are being used in some weather stories rather than thermometer only.
Combining temperature and high humidity results in readings above the real high.
An example from a lead in a Washington Post weather story on July 23 notes the “mercury rose above 100 degrees in Washington for the second consecutive day Saturday, setting a record for the date…”
The next paragraph makes it unclear if that was the true temperature or the heat index.
The second paragraph mentions, “Reports of a decline in the heat index, a joint measure of heat and humidity, seemed to offer little comfort.”
Nevertheless, according to the National Weather Service, Saturday’s official high temperature in Washington reached 97 degrees (not "above 100"). The relative humidity ranged from 40 percent at 5 p.m. to 70 percent at 11 p.m.
Temperature with humidity --- the so-called heat index --- usually gives a different reading than thermometer-only.
As the National Weather Service describes it: “The heat index or the ‘apparent temperature’ is an accurate measure of how hot it really feels when the relative humidity is added to the actual air temperature.”
In drier parts of the country, using the heat index gives a lower combined reading. For example, in Las Vegas, when the humidity is 20 percent (considered high because for much of the summer it is below 10 percent in the desert area), and the thermometer registers 102 degrees, the heat index is an even 100 degrees --- or two degrees cooler.
Of course, going to a Celsius (or Centigrade) reading, used in many foreign countries, sends the numbers down even more. One hundred degrees Fahrenheit becomes 38 degrees C.
But U.S. media won’t be going for that “cooling” effect --- not yet.
Grumpy Editor illustrates all this because he gets “hot under the collar” when the heart index wrongly is used as the high temperature in news stories.
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