Heat Index - Formula

Formula

The formula below approximates the heat index in degrees Fahrenheit, to within ±1.3 °F. It is the result of a multivariate fit (temperature equal to or greater than 80°F and relative humidity equal to or greater than 40%) to a model of the human body. This equation reproduces the above NOAA National Weather Service table (except the values at 90°F & 45%/70% relative humidity vary unrounded by less than -1/+1, respectively).

where

= heat index (in degrees Fahrenheit)
= ambient dry-bulb temperature (in degrees Fahrenheit)
= relative humidity (decimal fraction of 1.00, i.e. percentage/100)

An alternative set of constants for this equation that is within 3 degrees of the NWS master table for all humidities from 0 to 80% and all temperatures between 70 and 115 °F and all heat indexes < 150 °F is

A further alternate is this:

where

For example, using this last formula, with temperature 90 °F (32 °C) and relative humidity (RH) of 85%, the result would be: Heat index for 90 °F, RH 85% =114.9.

Read more about this topic:  Heat Index

Famous quotes containing the word formula:

    Every formula which expresses a law of nature is a hymn of praise to God.
    Maria Mitchell (1818–1889)

    Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective positions of the beings which compose it, if moreover this intelligence were vast enough to submit these data to analysis, it would embrace in the same formula both the movements of the largest bodies in the universe and those of the lightest atom; to it nothing would be uncertain, and the future as the past would be present to its eyes.
    Pierre Simon De Laplace (1749–1827)

    I take it that what all men are really after is some form or perhaps only some formula of peace.
    Joseph Conrad (1857–1924)