Devastating Tornadoes: How They Form

ABC News' Ginger Zee explains why there was tornado activity in Midwest, South.
1:11 | 03/02/12

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Transcript for Devastating Tornadoes: How They Form
So I'm looking at radar right now on -- updating with all the warnings tornado -- severe thunderstorm warnings this is exactly what -- neatly talking about severe weather you need this break all the storms that happened earlier this morning in Huntsville and under ousted Tennessee. That was all warm front. Now it's cold front and the cold front is kicking off the more an unstable air you can feel it just started getting sunny -- -- Just started getting sunny here and what will happen is not the warm front is through. The atmosphere will become very unstable starts even feel it as we drive to Evansville the winds will shift. And that's where the tornadoes develop you have that really warm moist -- at the ground and the super cold dry air up above it. And it creates this twist and it's called wind -- -- like if you had a pencil in your hand and you're twisting it one way and twisting in another you get that. Rotation. And then it stands about this is going to be. Just a very dangerous day and they have already issued a part particularly dangerous situation -- this is something. They don't do very often called PE DS. Statements for the public. Just means danger today.

This transcript has been automatically generated and may not be 100% accurate.

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