Friction or Boundary Layer
The lowest layer of the earth's atmosphere, usually up to 3,300 feet. Surface friction is effective in slowing down wind up to approximately 1,500 to 3,000 feet above the ground. Above this level, air tends to flow parallel to the isobars. Wind distribution within this layer is determined by vertical temperature gradient and the physical contours of the underlying surface features. This layer is sometimes called the boundary layer or surface boundary layer.
The Mississippi river valley has gently rolling plains that constitute only a minimal friction layer that permits frontal systems and air mass ingress in the Gulf coast region.