AccuWeather's Bernie Rayno explains the speed, direction and significance of wind shear.

In a recent WeatherWise segment, AccuWeather's Bernie Rayno delved into the complexities of wind shear, explaining its significant role in meteorology and severe weather conditions. Wind shear involves changes in wind speed and direction with height, impacting weather patterns greatly. According to Rayno, there are two primary types of wind shear: speed wind shear and directional wind shear.

Speed wind shear occurs when wind speed increases with height while maintaining the same direction across the atmosphere. This type mainly leads to straight-line winds rather than tornadoes. In such scenarios, thunderstorms can lead to intense wind gusts due to the energy driven by the increased wind speeds. The process begins with rain cooled by evaporation that forces air downward, accelerating upon reaching the surface, which can result in extremely strong winds.

On the other hand, directional wind shear is characterized by a change in wind direction as altitude increases. Rayno highlights that when wind direction shifts from southeast at ground level to west at 9,000 feet, it creates a spin or vorticity in the atmosphere. This spin, when aligned vertically, facilitates tornado formation due to the atmospheric conditions that allow for the necessary rotational dynamics.



What is wind shear?

Alright, in today's WeatherWise segment, where we take something difficult in the world of meteorology and make it easy to understand, we're going to talk about wind shear. Pretty complex definition, but I'm going to make it easy. It's the changing of wind speed and wind direction, or both, with height, and it's one of the main ingredients for severe weather. And depending on whether you have directional wind shear or just speed wind shear, that determines whether you're going to get damaging wind gusts or you'll get tornadoes. Let's talk about when you have the former. That is, you have an increasing wind speed with height, but the direction is the same from the surface through the upper part of the atmosphere, in this case, out of the west-southwest. When you have this set of criteria, you're generally not going to get tornadoes, you're going to get straight-line winds. Because what happens? Thunderstorms build, all that increasing wind with height allows for some energy. You start getting rain, the rain is cooled by some evaporation, and then that air is forced south, or not south, but downward, and it accelerates as it comes down to the surface. And that's where you can get some really, really strong winds, and that's where you tend to get the gust front, which is the lowering of the thunderstorm. It always looks very dangerous, wind gusts with that, and it can actually spawn additional thunderstorms here. Now, let's talk about the directional wind shear, when the wind direction changes with height, in this case, from the southeast of the surface all the way to the west at 9,000 feet. That imparts a spin in the atmosphere, right? And that spin in the atmosphere is what allows tornadoes to form, because you start getting some directional, or a little vorticity there, a little spinning in the horizontal, and that becomes vertical, and that produces the tornado.

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