Wind is caused by a difference in air pressure. Air pressure changes develop due to heat absorption and are at their largest during the day. Wind speeds are determined by the rate of change in pressure between atmospheric areas.
As wind travels upward, it begins to cool, causing moisture to condense and form clouds. Developing storms also inhibit solar energy and can add to greater differences in pressure. These areas are marked on weather maps as L's and H's, surrounded by lines called isobars. The closer the bars are spaced together on a map, the higher wind speeds are expected to develop. Areas where the lines are farther apart have lower wind speeds and calmer weather. While wind can move in any direction, it travels horizontally with more intensity than in any other direction.
As thunderstorms develop, the front edge of the storm is pulled downward in a rush of wind called a gust front. The cooler wind that develops before a storm is caused by rain hitting dry air, causing it to evaporate and cool quickly. Due to colder air sinking, it creates a rush of wind toward the ground. A powerful gust front that is strong enough to do damage to structures and trees is called a downburst.