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How Twisters Develop From Funnel Clouds

Twisters, also known as tornadoes, are powerful and destructive forces of nature. They have the ability to uproot trees, destroy well-made structures and hurl objects through the air like deadly missiles, according to the American Red Cross. They are associated with powerful thunderstorms and are common throughout the United States, particularly in Plains states.

What is a Twister
- A twister is a rotating column of air that extends from the base of a thunderstorm to the ground. The average forward speed of a twister is around 30 miles per hour although, according to the National Oceanic and Atmospheric Administration, they can vary from almost stationary to 70 miles per hour. The severity of a twister is classified on the Fujita Scale, ranging from F0, weakest, to F5, strongest. The strongest twisters can have wind speeds of up to 250 miles per hour.
How Twisters are Formed
- Twisters are produced by powerful storms called supercells. Supercell thunderstorms last longer than a normal storm and form when cold dry polar air meets moist tropical air in an unstable atmosphere, according to Windows to the Universe. The wind entering the supercell begins to swirl and forms a funnel. As the wind speeds increase, the pressure within the cloud drops, causing moisture to condense, while sucking more air in. Oracle Thinkquest demonstrates how this action occurs down the funnel, giving the impression that the funnel is descending from the cloud base. The twister may appear transparent until debris and dust are picked up.
Common Occurrences
- Twisters occur across the world, however, they are most frequently found in the United States, east of the Rocky Mountains, during the spring and summer months. According to the NOAA, in an average year, 800 twisters are reported across the U.S., resulting in 80 deaths and more than 1,500 injuries. Although twisters predominantly occur on land, they can also occur over warm water and are called waterspouts. Waterspouts are most common along the Gulf Coast and southeastern states. They can occasionally move onshore and impact upon coastal areas.
Potential Impact of Global Warming
- A climate model developed by the NASA/Goddard Space Flight Center in 2007 projects that, for the United States, more extreme storms and twisters will occur more often in a warmer climate. This is because warming temperatures provide more energy to the climate system, fueling more powerful storms. The potential intensification and increased occurrence of twisters under global warming will place more people and properties at greater risk from the devastating effects of twisters.

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