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— In the winter we talk about wind chill and in the spring and summer, it is the heat index that is important, Storm Center 7 Meteorologist Kirstie Zontini said.
Both are apparent or “feels like” temperatures. The heat index is a “feels like” temperature that looks at the actual air temperature and how much moisture is in the air, either with relative humidity or dew point. When it is hot, it can be uncomfortable. When it is hot and muggy, it is a different level for our bodies.
The amount of moisture in the air affects how well our bodies can cool off. When you are hot, your body starts to sweat, that sweat is then evaporated from your body into the atmosphere. If the moisture content of the air is high, it is harder for that evaporation to take place, and harder then for your body to cool down.
Here is the actual equation for calculating heat index:
HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH