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

Afternoon dew points are expected to reach the mid-70s across areas south of Kansas City, which could push heat index values to around 105 degrees. — Kansas City Star, 31 July 2026

Friday temperatures are predicted to have a high of 105 with a low of 82, with a heat index that reaches 110. — Ella Gonzales, Fort Worth Star-Telegram, 31 July 2026

Heat advisories earlier this week warned of heat indexes above 100 degrees Fahrenheit. — Irene Wright, USA Today, 31 July 2026

Temperatures will remain in the triple digits through the start of the weekend, with heat index values between 105-110°. — Michael Autovino, CBS News, 29 July 2026

Word History

First Known Use

1984, in the meaning defined above