Understanding Wind Shear

Air – it is all around. It can move slow or fast. It can gust past as a storm approaches or as the storm rages its magnificent fury. Air is a huge component in tornados and sandstorms. Slow moving air cools people on a hot, humid summer day. In the winter the air can freeze their faces, hands and toes, especially if it is moving fast.

Wind shear is a part of the constantly moving air. According to the Merriam-Webster Dictionary, Wind shear is defined as “a radical shift in wind speed and direction over a very short distance.” It is sometimes called wind gradient. It can be classified as being vertical or horizontal in motion.

Vertical wind shear is usually seen near the earth’s surface, though it can be found at higher levels of the atmosphere as well. It is needed for the formation of storms. Vertical wind shear determines the severity of the storm and length of time that the storm will last.

An example of vertical wind shear is a hurricane. The air moves in an upward motion carrying heat and water vapor which turns to liquid water as it reaches the upper atmosphere. The constant upward movement of the heat and water feed the hurricane. Vertical wind shear can be seen as the gusts that accompany the strong winds.

Horizontal wind shear is typically seen across storm fronts (the line of clouds at the front of a thunderstorm), squall lines, cold fronts and along the coast. Horizontal wind shear can weaken a tropical system such as a hurricane by “shearing” the top of it off. Wind shear can also “tilt” the hurricane’s eye where the heat and water vapor are rising and feeding the storm, starving the storm of what it needs to keep powering up and becoming more destructive.

Another example of wind shear is turbulence. Ever had a “bumpy” ride when traveling by airplane? Turbulence is the up and down motion of air in the troposphere which is section of our atmosphere where active weather is confined to. The rapid change in the wind causes a lift and raises the altitude of the airplane. The wind shear comes in waves and the airplane “rides” these waves much like a surfer rides the waves in the ocean. This is known as clear air turbulence.

Microbursts and downbursts create wind shear at a low altitude. These tend to be strong or violent yet short-lived downdrafts that fan out in all directions upon making contact with the ground.

Tornados form when instability in the air and wind shear mix together forming the downward motion that lowers the funnel to the ground. Air instability happens when warm and humid conditions are present in the lower atmosphere and the upper atmosphere contains a cooler environment.