Atmospheric conditions typical during tornado formation.
How a Tornado Forms
A tornado begins in a severe
thunderstorm called a
supercell. Scientists aren't exactly sure why, but air coming into the
storm begins to swirl and forms a funnel. The air inside the funnel spins
so fast it pulls in more air--and objects! The funnel is kind of like a
big vacuum cleaner.
The air pressure is very low inside the funnel, just like pressure is low
inside the
eye of a
hurricane. Only in a tornado, the pressure is a lot lower--lower than any
other place on earth.
Tornadoes can form when the atmosphere is
unstable. One other
thing that's needed is a
front, a place where warm moist
air meets cold dry air. This happens a lot in the Great Plains of the
United States which is why it's called
Tornado Alley.
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