A tornado is a whirling, funnel-shaped cloud that forms during a thunderstorm when warm, moist air near the ground becomes trapped under cooler, drier air above it. If the warm air is able to break through, it will start to spiral upward. As it rises it begins to cool, and the moisture condenses to form clouds. An area of low pressure begins to form in the middle of this funnel-shaped cloud. When the air closer to the ground rushes in to fill the space, a tornado exists.
Tornadoes can be a mile wide and can reach 60,000 feet above the ground. They can move at a speed of 35 miles per hour, and their winds can reach 250 miles per hour or more.
When and Where Do Tornadoes Occur?
Tornadoes can occur in all regions of the United States. At least 1,000 tornadoes are reported each year. Although no area of the country is immune, some areas are more prone to tornadoes than others. For example, the area of land extending from the Dakotas south to Texas sees the formation of many tornadoes each year. It has become known as "Tornado Alley."
Tornadoes can occur at any time of day, but most form between 3 and 9 p.m. They may form any time of year, but the majority form during spring and summer ("tornado season").
What Are the Consequences of Tornadoes?
The spiraling winds of a tornado can cause great destruction. Property can be destroyed by the strength of the winds. Power lines may be knocked down, and damaged water, sewage and gas systems may result. People and animals may be injured or killed. Damage, injuries and deaths also result from flying debris.
After the tornado passes, secondary disasters such as fires and flooding can persist. The destruction caused by a tornado can lead to injuries and disease from contamination, hypothermia and unsanitary conditions.
Resources for Tornadoes