Refer to figures.
WIND SHEAR is a sudden change in wind direction and/or speed over a very short distance. We can think of wind shear as a gradient in wind velocity that can be interpreted in the same way as a pressure or temperature gradient. Wind shear can be broken up into two parts:

• Vertical wind shear is defined as a change of horizontal wind direction and/or speed with height, as would be determined utilizing two or more anemometers mounted at different heights on a single mast.
• Horizontal wind shear is defined as a change of horizontal wind direction and/or speed with horizontal distance, as would be determined by two or more anemometers mounted at the same height along a runway.

There can be several causes of low-level wind shear:

• The passage of the front in which the isobars change direction;
• A marked temperature inversion;
• Sea breeze;
• Topography and large buildings;
• Surface friction; and
• Cumulonimbus clouds, and their associated weather of heavy rain and hail, which can give rise to the phenomenon known as Microburst.