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  • Hi, this is Duane Friend with University of Illinois Extension.

  • In the summer you'll often hear weather reports give you an actual temperature

  • and then a feels like temperature. This feels like temperature is always much

  • higher than what the actual temperature is.

  • This feels like temperature is what's known as a heat index.

  • The heat index is mainly based on two things:

  • the actual temperature and humidity.

  • What is humidity? Well humidity is a general term that's used for the amount of moisture in the air.

  • This is usually expressed in terms of relative humidity or as a percentage.

  • Relative humidity is the percentage of moisture in the air

  • compared to the maximum amount of moisture the air can hold at that temperature.

  • Warmer air can hold more moisture.

  • Therefore in the summertime, the air is holding much more moisture than it would

  • be in the winter.

  • How does this relate to humans? Well more moisture in the air

  • slows the amount of the evaporation. Evaporation removes moisture or sweat

  • from our skin

  • which also removes heat, which cools our body. With high temperatures and high

  • moisture, we can sweat but were not able to remove the heat from our bodies.

  • Our internal body temperature increases, which can lead to such things as heat cramps,

  • exhaustion or heat stroke.

  • The heat index was developed from a mathematical formula.

  • We usually see this as a chart.

  • For example: with that actual temperature at 90 degrees Fahrenheit,

  • coupled with a relative humidity of sixty percent this creates a heat index

  • of 100 degrees.

  • The National Weather Service issues alerts when the heat index is expected to

  • exceed 105 degrees for two consecutive days.

  • The index should be used as a guide when planning an outdoor summer activities.

Hi, this is Duane Friend with University of Illinois Extension.

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什麼是熱指數? (What is the Heat Index?)

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