like a hot-air baa log. the sun comes out to warm the ground and the air wants to rise. as the air rises into space it goes up higher and higher and gets into colder and colder air. so all the particles start to congeal down here. all the humidity comes in and then it goes straight up in the air. you can see the towering cumulus clouds, a lot like everything in the northern hemisphere that spins to the right and everything in the southern hemisphere that spins to the left. eventually if you move this stuff long enough on the way up, literally 60,000 feet in the sky, 12 miles from the surface to the top, you will get this spin and eventually the whole storm spins into the back half, we call it the mesocyclone, the conservation of mo pen tim momentum like an ice skater she skates faster and faster. at the bottom a tornado falls out and comes out of the storm. >> we'll have much more on the science of tornadoes and why this year has been so deadly