What is a tornado?
A tornado—also known as a twister—is a violently rotating column of air that extends from a thunderstorm and comes into contact with the ground. Tornado intensity is measured by the Enhanced Fujita (EF) scale, which rates tornadoes from 0 through 5, based on the amount and type of wind damage.
How common are tornadoes?
An average of about 1,000 tornadoes are reported nationwide each year. Twisters are more common in the central United States, though they can occur almost anywhere in North America, including in large cities.
Tornadoes can happen at any time of year or at any time of the day or night, though they happen most frequently between early spring and July, and between the hours of 4pm and 9pm.
What are the warning signs of a tornado?
Signs that a twister is coming include:
- Dark greenish skies
- Large hail
- Dark, rotating, low-altitude cloud
- Loud roar, like a train
In communities with a history of tornado activity, there may be a tornado warning siren and/or a digital messaging system to alert residents that there is a twister coming and that they should seek proper shelter immediately.
What's the difference between a tornado watch and a tornado warning?
Both tornado watches and tornado warnings are issued by the National Oceanic and Atmospheric Administration (NOAA)/ National Weather Service. However, there are critical differences between the two alerts.
- A tornado watch means that conditions are favorable for tornadoes to develop. Be alert to changes in the weather, account for all family members, and listen to local radio and TV stations for updated storm information. Move cars inside and keep car and house keys with you. If time permits, move lawn furniture and equipment inside to minimize flying debris. If a tornado siren sounds, stay inside and take cover.
- A tornado warning means a tornado has actually been spotted or is indicated on weather radar in your area. This means danger is imminent and you may only have seconds to take cover.