The windchill index tells you

A. how wind and temperature affect your body in winter.

B. the temperature of the water during winter.

C. how wind speed affects heating needs for structures.

D. the amount of moisture in the air.

The windchill index tells you A. how wind and temperature affect your body in winter. This is how you perceive the temperature outside due to the flow of air. The windchill index is always lower than the measured temperature outside. This is because wind increases the rate at which your body loses heat. For example, if it is 25 degrees outside, but there is a strong wind, the perceived temperature on your skin may be closer to 15 degrees.