full text of the classic FAA guide
Since early childhood, you have expressed the comfort of weather in degrees of temperature. Why, then, do we stress temperature in aviation weather? Look at your flight computer; temperature enters into the computation of most parameters on the computer. In fact, temperature can be critical to some flight operations. As a foundation for the study of temperature effects on aviation and weather, this chapter describes commonly used temperature scales, relates heat and temperature, and surveys temperature variations both at the surface and aloft.