What is wind shear?

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

Transcript

00:00All right, in today's WeatherWise segment where we take something difficult in the world of

00:08meteorology and make it easy to understand, we're going to talk about wind shear. Pretty

00:13complex definition, but I'm going to make it easy. It's the changing of wind speed and wind

00:19direction or both with height, and it's one of the main ingredients for severe weather.

00:25And depending on whether you have directional wind shear or just speed wind shear,

00:29that determines whether you're going to get damaging wind gusts or you'll get tornadoes.

00:34Let's talk about when you have the former. That is, you have an increasing wind speed with height,

00:39but the direction is the same from the surface through the upper part of the atmosphere. In this

00:44case, out of the West Southwest. When you have this set of criteria, you're generally not going to get

00:51tornadoes. You're going to get straight line winds. Here's what happens. Thunderstorms build all that

00:57increasing wind with height allows for some energy. You start getting rain. The rain is cooled by some

01:03evaporation. And then that air is forced south or not south, but downward. And it accelerates as it

01:11comes down to the surface. And that's where you can get some really, really strong winds. And that's

01:16where you tend to get the gust front, which is the lowering of the thunderstorm. It always looks very

01:21dangerous wind gusts with that. And it can actually spawn additional thunderstorms here. Now, let's

01:27talk about the directional wind shear. When the wind direction changes with height, in this case,

01:32from the Southeast at the surface, all the way to the West at 9,000 feet, that imparts a spin in the

01:39atmosphere, right? And that spin in the atmosphere is what allows tornadoes to form because you start

01:45getting some directional or a little vorticity there, a little spinning in the horizontal. And that becomes

01:55vertical. And that produces the tornado.