How is a "wind chill factor" calculated?

The calculation of the "wind chill factor" is based on combining wind speed with air temperature, which provides an estimate of how cold it feels on the skin due to the cooling effect of the wind. As wind blows over exposed skin, it removes heat from the body more rapidly than still air, leading to a lower perceived temperature. This is particularly important in cold conditions, where the wind can significantly enhance the chilling effect and increase the risk of frostbite and hypothermia.

In contrast, averaging the current temperature and wind speed does not accurately reflect the way the body loses heat in windy conditions, as it doesn't account for the nonlinear relationship between wind speed and temperature perception. Measuring how long the wind blows does not relate to how cold it feels, while determining humidity levels is more pertinent to heat index calculations rather than wind chill. Therefore, the option focusing on the interaction of wind speed and air temperature accurately captures the phenomenon of wind chill, making it the correct choice.