What is Wind Shear?

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Today’s video topic is wind shear.

You often hear the words instability, wind shear, and lift during severe storm season and if you are like a lot of the people I talk to, you may not actually know what those things are.

So what is Wind Shear?

Wind shear refers to a change in wind speed OR direction with height in the atmosphere.

It isn’t an advanced way to cut your hair…sorry.

Wind shear is an essential ingredient for supercell thunderstorms to form during the Spring storm season. Wind shear also contributes to severe weather in non-supercell storms as well.

The two types of wind shear we’re going to spend a bit talking about are speed shear and directional shear.

These are exactly what they sound like, hey sometimes this weather stuff is somewhat straightforward…but lets start with speed shear.

Speed shear is important for storm’s sustaining themselves for a long time and will also determine the speed at which storms might move.

What we look for with thunderstorms is winds which increase with height. Why is that you ask? Because these gradually stronger winds will allow for a storms updraft to tilt over, which puts the rain and hail away from the updraft.

The updraft of a storm is a pretty sensitive process, and rain falling back through it will weaken the storm overall. When winds are stronger above than they are below, storms will tend to rain well away from the updraft. This process of venting allows for the downdraft to reinforce the updraft, which could help sustain supercell storms for hours at a time.

Directional wind shear, on the other hand, is the change in wind direction with height. This impacts a storm’s ability to rotate faster to produce tornadoes. Ultimately, you want 90 degrees or so of gradual turning of winds with height from the surface to a storm’s mid-levels for the ideal tornado environment.

The exact relationship here is way more complex but we only have a few minutes.

Directional shear in the lower levels is extremely important for tornado formation, the exact reasons are not fully understood but this shear does increase the spin in the atmosphere which contributes to tornado formation.

An ideal environment for supercell thunderstorms, the biggest and baddest storms on the planet, consists of strong winds at the surface gradually increasing and turning with height.

For us, as storm chasers, strong surface winds of south or southeast turning to stronger West-Southwest or West winds aloft is a signal that an environment is ripe for supercell formation if instability and lift are also present.