Wind Shear

Meteorological Spring is right around the corner! During the spring months, we generally see an uptick in severe weather across the area. Over the next few posts, I will be walking you through some of the terms to become familiar with over the course of this spring.

The first one I’m going to focus on is wind shear. This is primarily because the Thursday afternoon and evening thunderstorm event may be driven more by wind shear, rather than instability, which is another ingredient when looking for severe weather.

When we talk about wind shear, it is important to note that there are two types of wind shear.

The first type of wind shear is vertical speed shear. This simply means the speed of the wind changes with respect to height in the atmosphere. An increase of wind speed with height in the atmosphere will cause a storm’s updraft to tilt. This will help sustain thunderstorms because it keeps the updraft and downdraft of a thunderstorm separated.

Above is an illustration of a thunderstorm. Notice the red arrow indicating the updraft, and the blue arrow indicating the downdraft. The yellow arrows indicate wind speed aloft, with longer arrows depicting higher wind speeds. Higher wind speeds aloft than at the surface can tilt the updraft like in the above representation.

The second type of wind shear is called vertical directional shear. This simply means the wind changes direction with height. Directional shear can help develop rotating updrafts in thunderstorms. Rotating thunderstorms are responsible for most, if not all, tornadoes.

Above is a graph that we call a Skew-T. A Skew-T is a vertical profile of the atmosphere above a given point. Plotted is the temperature, dew point temperature, wet bulb temperature, and virtual temperature. However, what we’re more concerned with for this post is wind direction on the right side, circled in red.

This gives you an idea of what the wind profile is like over a certain area. I have highlighted surface winds will be out of the south, while winds aloft will be out of the southwest, and winds high in the atmosphere will be out of the west-southwest. This gives you an idea of the twisting of the winds with respect to height in the atmosphere.

Be sure to stay tuned for more severe weather terms in the coming days.