Wind speed can vary quite dramatically, depending upon the height at which it is measured. Wind measurements closer to the ground show the effect of friction on air movement, and are generally slower. The higher the anemometer is positioned, generally the faster the wind speed readings. Agricultural weather stations usually have the anemometers placed about 10 feet above the ground. Many stations in the Kansas Mesonet measure winds at approximately 7 feet and 30 feet. Measurements for pan evaporation are usually much closer to the ground, about 2 feet above the surface. On the other hand, companies evaluating the wind energy at a particular location will have anemometers placed at several different heights, the highest of which might be over 120 feet.
Mary Knapp, Weather Data Library