How do tornadoes form?

Thumbnail for Patrick Powell tornado development story
Thumbnail for Patrick Powell tornado development story

Tornadoes can develop quickly. But what does it take to make such a storm? FOX 11’s Severe Weather Expert, Patrick Powell, pulls apart the storm to show us how a tornado develops.

Much more than just the typical hot and cold air colliding, you need some specific keys for tornado development.

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You need humidity near the surface, a lot of instability - which mean cold air at the mid and upper levels. You need wind shear and you need a forcing mechanism to help the tornado develop.

In a typical severe weather setup, you have an area of low pressure coming out into the plains. This helps draw humid air northward from the Gulf of Mexico. It also creates wind shear because you have dry air coming in from the west and southwest. That causes rotation in the wind fields in the atmosphere. Also, you get the forcing mechanism with the cold and warm fronts and even the area of low pressure.

More specifically, though, inside an individual thunderstorm, tornado development occurs when you have a warm rotating column of air rushing upward. On the backside of the thunderstorm, you have cold air falling in behind the storm. What happens is, if that air is too cold it chokes off the thunderstorm, but if that air is just the right temperature it spreads out near the ground. That helps restrict the inflow a little, kind of like pressing on a garden hose. This makes the air flowing into the storm increase in speed. That helps in tornado development, in addition to the air being stretched out between the rising and falling and the air rotating upward.

What we end up with is a tornado that covers many different levels of the atmosphere driving toward the east.

Something that we have learned in the last few years is that with tornado development, especially in strong tornadoes, we can see what is called a "debris ball." That, basically, is the radar picking up flying objects inside that tornado.