Archive for Wednesday, July 28, 2010

Summer sauna

July 28, 2010

With another brutal string of days with oppressive heat, people have been hearing more and more warnings and certain terms related to the throes of summertime. But what do those terms mean? The National Weather Service, which issues weather warnings, offers these answers.

Q: What is a heat advisory?

A: A heat advisory is issued within 12 hours of the onset of the following conditions: heat index of at least 105 degrees F. but less than 115 degrees F. for less than three hours per day, or nighttime lows above 80 degrees F. for two consecutive days.

Q: How is that different than an excessive heat warning?

A: It narrows the definition a bit. An excessive heat warning is issued within 12 hours of the onset of the following criteria: heat index of at least 105 degrees F. for more than three hours per day for two consecutive days, or heat index more than 115 degrees F. for any period of time.

Q: Just what is the heat index?

A: 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.

Q: What is the definition of humidity?

A: Generally, humidity is a measure of the water vapor content of the air. Popularly, it is used synonymously with relative humidity.

Q: I often hear the dew point mentioned when describing the heat index. What is it?

A: Dew point is a measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation, assuming air pressure and moisture content are constant. A higher dew point indicates more moisture present in the air. It is sometimes referred to as Dew Point Temperature.


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