heat index

[ heet-in-deks ]

/ ˈhit ˌɪn dɛks /

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noun Meteorology.

a formulaically calculated approximation of how hot it feels given the temperature of the air combined with the relative humidity, based on the fact that an actual temperature will feel warmer as the relative humidity rises and causes a decrease in the natural evaporative cooling from perspiration. Abbreviations: HI, H.I.

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THINGAMABOB OR THINGUMMY: CAN YOU DISTINGUISH BETWEEN THE US AND UK TERMS IN THIS QUIZ?

Do you know the difference between everyday US and UK terminology? Test yourself with this quiz on words that differ across the Atlantic.

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In the UK, COTTON CANDY is more commonly known as…

candystring

candyfloss

candypuff

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Also called ap·par·ent tem·per·a·ture

[uh-pair-uhnt tem-per-uh-cher, -choor, -pruh-, -per-cher, -choor, uh-par-uhnt] /əˈpɛər ənt ˈtɛm pər ə tʃər, -ˌtʃʊər, -prə-, -pər tʃər, -ˌtʃʊər, əˈpær ənt/ .

Compare temperature-humidity index.

Origin of heat index

First recorded in 1975–80

Words nearby heat index

heath grass, heath hen, Heath Robinson, heath wren, heathy, heat index, heating, heating degree-day, heating element, heating pad, heat island

How to use heat index in a sentence

Humidity remains high, so a heat index around 100 is possible at times during peak heating.
PM Update: Downpours wane this evening ahead of a steamy Friday with more storm chances|Ian Livingston|August 26, 2021|Washington Post
High heat indexes are often the reason esteemed athletes have to change their plans, says Schimelpfenig.
What Parents Need to Know About Kids and Heat Waves|smurguia|August 26, 2021|Outside Online
Highs are mainly in the mid-90s, with heat index values around 100.
PM Update: Scattered storms this evening, then more high heat and humidity tomorrow|Ian Livingston|August 25, 2021|Washington Post
Humidity was down a little today, just enough for heat indexes to struggle to hit 100.
PM Update: Relatively pleasant this evening. Well into the 90s again Wednesday.|Ian Livingston|August 24, 2021|Washington Post

Dew points rise into the low 70s meaning high humidity and heat index values up to the upper 90s to about 100.
D.C.-area forecast: A series of hot sunny days; storm chances return this weekend|Matt Rogers|August 24, 2021|Washington Post
Large sweat stains were visible on his shirt and jacket as the heat index approached 95 degrees.
Eliot Spitzer Mobbed by Press, Heckled at First Campaign Stop|David Freedlander|July 9, 2013|DAILY BEAST
The tourmaline has a light-refractive index of 1.63, with a heat index of none, being to heat-rays completely opaque.
The Chemistry, Properties and Tests of Precious Stones|John Mastin

Scientific definitions for heat index

heat index

A measurement of the air temperature in relation to the relative humidity, used as an indicator of discomfort. The heat index is higher when high air temperatures occur with high humidity, and lower when they occur with low humidity. The heat index is based on studies of skin cooling caused by the evaporation of sweat. Also called apparent temperature