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
Julie E. GreeneThe 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
Neil MacFarquharExamples of heat index in a Sentence
Recent Examples on the Web
The forecast high and max heat index for the Pittsburgh area from July 30, 2026, to July 4, 2026.
—
Ray Petelin,
CBS News,
30 June 2026
The effects for both will be worsened by humidity and cloud cover, with heat indices pushing 110.
—
Marc Ramirez,
USA Today,
29 June 2026
Hot conditions are expected this week into the holiday weekend with heat index values forecast above 100 degrees each day for most locations.
—
Kristi Swartz,
AJC.com,
29 June 2026
Much of the eastern half of the United States is about to endure a brutal heatwave with heat index temperatures potentially reaching 100 to 110 degrees Fahrenheit.
—
Marshall Shepherd,
Forbes.com,
29 June 2026
Temperatures are expected to hit a high of 96 degrees this week, with heat indexes falling between 105 and 110 degrees.
—
Jenna Ebbers,
Kansas City Star,
29 June 2026
Daytime highs in and around Chicago will be in the 90s with no cooling effect from the lake, and residents will experience little relief as heat indices remain in the 90s until well after sunset and overnight indices stay over 75 degrees.
—
Adriana Pérez,
Chicago Tribune,
29 June 2026
New York City is expected to record temperatures as high as 95 Friday, with a heat index of 106.
—
Mirna Alsharif,
NBC news,
29 June 2026
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Ray Petelin,
CBS News,
30 June 2026
The effects for both will be worsened by humidity and cloud cover, with heat indices pushing 110.
—
Marc Ramirez,
USA Today,
29 June 2026
Hot conditions are expected this week into the holiday weekend with heat index values forecast above 100 degrees each day for most locations.
—
Kristi Swartz,
AJC.com,
29 June 2026
Much of the eastern half of the United States is about to endure a brutal heatwave with heat index temperatures potentially reaching 100 to 110 degrees Fahrenheit.
—
Marshall Shepherd,
Forbes.com,
29 June 2026
Temperatures are expected to hit a high of 96 degrees this week, with heat indexes falling between 105 and 110 degrees.
—
Jenna Ebbers,
Kansas City Star,
29 June 2026
Daytime highs in and around Chicago will be in the 90s with no cooling effect from the lake, and residents will experience little relief as heat indices remain in the 90s until well after sunset and overnight indices stay over 75 degrees.
—
Adriana Pérez,
Chicago Tribune,
29 June 2026
New York City is expected to record temperatures as high as 95 Friday, with a heat index of 106.
—
Mirna Alsharif,
NBC news,
29 June 2026
Cite this Entry
“Heat index.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/heat%20index. Accessed 1 Jul. 2026.
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