Shop Windows to the Universe

Please help support Windows to the Universe, and our activities to help Earth and space science teachers, with a tax-exempt donation today!
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.

Shop Windows to the Universe Science Store!

The Fall 2009 issue of The Earth Scientist, which includes articles on student research into building design for earthquakes and a classroom lab on the composition of the Earth’s ancient atmosphere, is available in our online store.

Windows to the Universe Community



You might also be interested in:

Science, Evolution, and Creationism

How did life evolve on Earth? The answer to this question can help us understand our past and prepare for our future. Although evolution provides credible and reliable answers, polls show that many people turn away from science, seeking other explanations with which they are more comfortable....more


Tornadoes form from severe thunderstorms. They have a very high energy density which means that they affect a small area but are very destructive to that area. They also don't last very long which makes...more

Tornado Forecasts

It's hard to forecast tornadoes. They don't last very long and are also very complicated. Scientists don't really know how they form, but they do where they tend to form. Using what they know about the...more

Tornado Notification

Tornadoes are very dangerous so it's important to know when they may form so you can take shelter. Forecastors at the National Weather Service are always looking for possible storms. Even though nobody...more

Tornado Lookouts

Meteorologists use radar to forecast where tornadoes might form. But, the radar can't detect actual tornadoes. People are needed to do that. The National Weather Service can't rely on tornado reports from...more

Wave Beats

Sound travels in waves. You hear sound because waves hit your ear. Sound waves are similar to ocean waves. They both have a certain frequency. The frequency is measured in hertz, which is one cycle per...more

Chasing Tornadoes

Storm chasers are different than storm spotters. Chasers travel around Tornado Alley looking for severe storms and tornadoes. This area in the Great Plains is the best for chasing because of the frequency...more

Energy Density

A tornado is the most intense force in nature. That doesn't mean it's the most powerful. In fact, a thunderstorm can be 40,000 times more powerful than a tornado. Then why aren't thunderstorms as dangerous...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA