heat index

noun

plural heat indexes or heat indices

: a value that indicates what the ambient temperature feels like to the human body and that is derived from a calculation using air temperature and relative humidity

The most likely chances for a heat advisory are Thursday and Friday, when the heat index could approach at least 100 degrees, according to National Weather Service meteorologists …

—Julie E. Greene

The heat index is defined as a function of temperature and relative humidity. The combination of the two results in an apparent temperature that gives an idea of what the hot and humid air feels like to the average person.

—Neil MacFarquhar

Examples of heat index in a Sentence

Recent Examples on the Web

With a 110-degree heat index, there was no world in which this game was going to be well attended. — Ryan Kartje, Los Angeles Times, 31 Aug. 2026

Instead, humid and stormy weather is in the forecast for the next few days, with heat indices expected to reach the mid-90s. — Hope Karnopp, jsonline.com, 30 Aug. 2026

After a cooler and rainy weekend, things are going to heat up for central Iowa, with heat indices in Des Moines reaching as high as 102 degrees over the next week, according to the National Weather Service. — Isabelle Foland, Des Moines Register, 30 Aug. 2026

At that time, the temperature recorded at Larned—Pawnee County Airport, about 18 miles east of Pawnee Heights High School, was 84 degrees, with a heat index of 87. — Laura Bauer, Kansas City Star, 30 Aug. 2026

Word History

First Known Use

1984, in the meaning defined above