The atmosphere, being invisible to the human eye, makes it is difficult to visualize the motions of the air without the aid of some object. Because of this most people have the idea that the wind blows in a relatively straight line from point A to point B. But when you can ?see? the wind because of blowing dust, pollution or this time of year exhaust or blowing snow, you begin to realize that wind blows in a very chaotic pattern.
Both natural and human made objects will accelerate and/or decelerate the air as it blows across the terrain, plus thermals generated by the sun or again, by humans will cause areas of upward and downward motions in the air that further adds to the complexity to the movement of the wind.
My graduate advisor in college frequently reminded me of this famous weather quote ?Big whirls have little whirls which feed on their velocity. Little whirls have lesser whirls, and so on to viscosity?. In fact, that quotation is on my coffee mug I am using right now.