Directional wind shear is the change in wind direction with
height. In the image (right), the view is looking north. The
wind near the surface is blowing from the southeast to the
northwest. As the elevation increases the direction veers
(changes direction in a clock-wise motion) becoming south, then
southwest, and finally, west. Speed shear is the change in wind
speed with height. In the illustration below, the wind is
increasing with height. This tends to create a rolling affect to
the atmosphere and is believed to be a key component in the
formation of mesocyclones which can lead to tornadoes. Strong
vertical shear is the combination of a veering directional shear
and strong speed shear and is the condition that is most
supportive of supercells.