Class 4 and higher areas usually are found near the coasts, along ridges of mountain ranges and in a wide belt that stretches across the Great Plains. Class 1 and 2 winds dominate southeastern regions. Wind classification is, however, only one component of wind energy potential. Many windy sites are unsuitable for development because of rocky terrain, inaccessibility, environmental protection or population density. The strongest winds usually are found in well-exposed areas such as hilltops and ridges.
Wind is caused by uneven heating of the earth's surface by the sun.
When the heat is transferred to the air, differences in air temperature, density and pressure create wind. Temperature differences between the tropics and the poles also drive global trade winds that keep extreme temperatures in check in these areas. On a smaller scale, wind is created because of temperature differences between land and sea and mountains and valleys. The earth's rotation, local topographical features and the roughness of the terrain also cause air movement. Wind energy can be converted to electricity by using wind turbines.