TIL the Heat Index (aka "feels-like" temperature) is only accurate for healthy and well-hydrated adults of average size and weight who are sitting in the shade with a breeze of 5 knots. These and other assumptions are parameterized as constants in the formula and any deviations result in inaccuracy.

en.wikipedia.org/wiki/Heat_ind…
reddit.com/r/todayilearned/com…

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