WCI = 35.74 + 0.6215T - 35.75V(**0.16) + 0.4275TV(**0.16) where T is the air temperature in degrees Fahrenheit and V is the wind velocity in miles per hour. The twin asterisks ** mean “to the power of” because the way this is traditionally written in mathematics does not correspond well to typed newspaper copy. This, of course, is the formula for the Wind Chill Index.

However, the reality of “wind chill” is not nearly as precise as this equation looks. Sunshine is left out of the equation and so, too, is the fact that wind is officially measured at ten meters above the ground (33 feet) which is not where most of us encounter the wind. Wind does not actually make the air colder; it merely causes things to cool down to the air temperature more quickly. The system is far from perfect, but it does at least offer a numerical guide for people to easily quantify the combined cooling effect of wind and cold.

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