Atmospheric conditions typical during tornado formation.
How a Tornado Forms
A tornado begins in a severe
thunderstorm called a
supercell. A supercell
can last longer than a regular thunderstorm. The same property that keeps
the storm going also produces most tornadoes. The wind coming into the
storm starts to swirl and forms a funnel. The air in the funnel spins
faster and faster and creates a very low pressure area which sucks more
air (and possibly objects) into it.
The severe thunderstorms which produce tornadoes form where cold dry polar
air meets warm moist tropical air. This is most common in a section of
the United States called
Tornado Alley. Also, the
atmosphere needs to be very
unstable.
Tornadoes can form any time during the year, but most form in May. But,
more severe ones form earlier because the most damge is caused in April.
The more north you go, the later the peak tornado season is. This is
because it takes longer to warm the northern parts of the plains so
tornadoes form later.
Most tornadoes spin
cyclonically but a few spin
anticyclonically.
Because there are records of anticyclonic tornadoes, scientists don't
think that the Coriolis Effect causes the rotations.
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