They further incorporate expected heat transfer rates across an average sized human body with an average metabolism. Their model includes heat index and windchill, but also other weather factors like cloud cover or UV index, sun intensity, visibility, and ground cover. A more complex estimate comes from the metric established in the 1990s and patented by Accuweather called the RealFeel Temperature. When a weather service makes a prediction about what a temperature will feel like, they typically include these basic measurements of the heat index and the windchill factor. How do you estimate a “feels like” temperature? Thus, for example, a temperature of 75 degrees can feel more like 65 degrees with windspeeds of 60 miles per hour. Wind can cause sweat from our bodies to evaporate faster and can carry heat away from us quickly to make us feel colder. On the other end of the temperature spectrum is the windchill factor. You can find the heat index in your city without actually doing any math thanks to online heat index calculators like those from the opens in a new windowNational Weather Service and the opens in a new windowThe Washington Post. So 85 degrees at 10% humidity, the temperature feels closer to 79 degrees, but at 90% humidity, it will feel closer to 100 degrees outside. That relative humidity, combined with the temperature, then determines the heat index or an estimate of how hot the air actually feels. The temperature and the dewpoint together give the relative humidity, a measure of how much moisture is in the air relative to how much moisture the air could potentially hold. Since water vapor can no longer remain in the air as humidity, it instead begins to condense on surfaces. The heat index combines the temperature and a measure of the relative humidity to give a better indication of how hot that temperature will actually feel.Ĭold air can hold less water vapor so as temperatures decrease, eventually a temperature called the dewpoint is reached when the air is too cold to hold anymore moisture. In humid locales, the air is already full of moisture and so our sweat evaporates more slowly (or not at all), leaving us feeling hotter. In a low humidity, dry environment, that sweat is quickly evaporated into the air leaving us feeling effectively cooled. On a hot day, our bodies sweat to cool down. The heat index combines the temperature and a measure of the relative humidity to give a better indication of how hot that temperature will actually feel. A simple measure of how a temperature of 85 degrees Fahrenheit, for example, will likely feel different in Houston, Texas versus Los Angeles, California is the heat index.
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