obtained by multiple regression analysis carried out by Lans P. Rothfusz The heat index formula is a long and kind of scary-looking equation, but the process of calculating it is pretty easy because it’s just a series of coefficients (factors you multiply by) attached to either temperature or relative humidity. This sets it apart from the more objective measure of temperature, but most people will be familiar with the impact of a very humid environment on your perception of heat. The formula below approximates the heat index in degrees Fahrenheit, to within ±1.3 °F (0.7 °C). The Rothfusz regression is not valid for extreme temperature and Heat index is often referred to as humiture, and is similar to wind chill in its attempt to measure perceived, rather than actual temperature. Most of the time in science, you want to deal with “objective” quantities. This is undoubtedly more convenient than calculating it by hand, and you might prefer it to Excel if you’re always going to have access to the internet when you need to perform the calculation. Estimating each of these individually would make the formula difficult to use, but the values generally used are based on well-founded assumptions and averages, and so give a result that’s broadly applicable to everyone.
He's written about science for several websites including eHow UK and WiseGeek, mainly covering physics and astronomy. The full heat index (HI) formula is: T is temperature and R is relative humidity. You can put the heat index formula in Excel if you want a re-usable version of it, with cell references in place of the T and R values, so you can input the values for a specific day or location and get an automatic result. The “heat index” is designed as a measure of the “feeling” of a certain combination of temperature and humidity to the human body. Alternatively, there are many online calculators (see Resources) you can use to calculate the heat index for your chosen location. The regression equation of Rothfusz is, National Centers for Environmental Prediction, Page last modified: Wednesday, 28-May-2014 17:15:11 UTC. The heat index formula is based upon the temperature and relative humidity to indicate the air temperature perceived by the body. These coefficients account for a few different things that would make it a very complicated equation, but they’re distilled into numerical values, so all you need to do is plug in your values for relative humidity and temperature and calculate. There isn’t a trick to this, and it’s just a long calculation where you have to be sure you’re entering the right values for the many coefficients and squaring the temperatures and humidity values where indicated. relative humidity conditions beyond the range of data considered by Steadman. For instance, if the temperature is 32°C and 70% relative humidity, the heat index is 41°C.
For example, an air temperature of 83°F with a relative humidity of 70% would result in an estimated 88°F perceived temperature. The Rothfusz regression is not appropriate when conditions of temperature and humidity warrant a heat index value below about 80 degrees F. In those cases, a simpler formula is applied to calculate values consistent with Steadman's results: HI = 0.5 * {T + 61.0 + [(T-68.0)*1.2] + (RH*0.094)}
WPC Heat Index Forecasts More Meteorological Conversions and … Heat Index = * Please note: The Heat Index calculation may produce meaningless results for temperatures and dew points outside of the range depicted on the Heat Index Chart linked below. (SR 90-23). The heat index formula is a long and kind of scary-looking equation, but the process of calculating it is pretty easy because it’s just a series of coefficients (factors you multiply by) attached to either temperature or relative humidity. This heat index has an implied humidity of 20%. Copyright 2020 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. This equation reproduces the above NO… It is the result of a multivariate fit (temperature equal to or greater than 80 °F (27 °C) and relative humidity equal to or greater than 40%) to a model of the human body. He was also a science blogger for Elements Behavioral Health's blog network for five years. You can now use the formula to calculate the heat index. Search by city or zip code. In fact, in some cases it’s more useful to know the heat index than the temperature, and it’s used in weather reporting for that reason.
Press enter or select the go button to submit request, The computation of the heat index is a refinement of a result and described in a 1990 National Weather Service (NWS) Technical Attachment Temperature is the same, starting from 0 degrees Kelvin (which is the coldest possible temperature) and increasing in a consistent way from that point onward. You don’t want the mass of a textbook to depend on who’s holding it, for example; it should just be the mass of the textbook by itself, as an objective measure of the amount of matter it contains. Additionally, use a whole-integer percentage for the value of the relative humidity. The factors the formula takes into account include the surface area of the average human, how well skin radiates and absorbs heat, clothing cover and its resistance to heat and moisture transfer, sweating rate, core body temperature and much more. It’s important to note that you should use Fahrenheit with this formula, so if you have a temperature in Celsius (or Kelvin), convert it first. Lee Johnson is a freelance writer and science enthusiast, with a passion for distilling complex concepts into simple, digestible language. Heat Index Chart and Explanation. thermometer image by Alfonso d'Agostino from, Brown Math: It’s Not the Heat … Humidity, Dew Point, and Heat Index. But human perception of temperature is also important, and that’s why in some circumstances you might need to look at a heat index forecast or calculate it to get an idea of how hot it’s going to be. It’s important to remember that this isn’t as “scientific” as just listing the temperature and relative humidity, but that doesn’t mean that it isn’t a useful measure. He studied physics at the Open University and graduated in 2018.
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