At The Old Farmer’s Almanac, readers often ask us about tornadoes. What causes them? Does the sky really turn green? Was Elvis ever in a tornado? Here are answers to common questions about nature’s most violent storms.
If a tornado warning is issued for your location, take shelter immediately. Don’t wait to see a funnel cloud.
What Is a Tornado?
A tornado is a violently rotating column of air extending from a thunderstorm to the ground. Its winds are invisible; the familiar funnel becomes visible when water droplets condense or the circulation picks up dust and debris. A tornado can be on the ground even when its visible funnel doesn’t reach the surface.
What Causes Tornadoes?
When conditions are right, a thunderstorm can produce one or more tornadoes. Warm, moist air supplies energy, rising air feeds the storm, and changes in wind speed or direction with height—called wind shear—can help create rotation.
The most destructive tornadoes usually develop from supercells, thunderstorms with rotating updrafts. However, not every supercell produces a tornado, and some tornadoes form within lines of thunderstorms or from other storm circulations. Scientists are still studying why one storm produces a tornado while another does not.
If There Is One Tornado, Are There Likely to Be More?
Tornadoes can come one at a time or as part of an outbreak. A storm may produce successive tornadoes, while a larger weather system can create favorable conditions across several states.
They vary greatly in width, direction of travel, speed, and duration. Some last only briefly; others remain on the ground much longer. Don’t assume the danger has passed because one tornado has moved away. Continue monitoring official warnings.
Is a Twister the Same as a Tornado?
Yes. Twister is an informal name for a tornado, not a separate category or a term reserved for smaller storms.
Where Do Tornadoes Occur?
Tornadoes have been reported in all 50 U.S. states. NOAA’s National Severe Storms Laboratory puts the U.S. total at about 1,200 a year, although numbers vary.
The central Plains are well known for tornadoes, but dangerous storms also occur in the Southeast, Midwest, and elsewhere. “Tornado Alley” has no official boundary, and living outside it does not mean you are outside tornado country.
Is There a Tornado Season?
Tornadoes can occur in any month. The greatest activity generally shifts northward as spring and summer progress: the Gulf Coast’s peak comes earlier, the southern Plains’ peak is generally in May and early June, and the northern Plains and upper Midwest often peak in June or July.
Tornadoes can also strike at any hour, including overnight.
How Are Tornadoes Rated?
In the United States, tornadoes are rated using the Enhanced Fujita Scale, or EF Scale, which became operational in 2007. It builds on the original Fujita Scale developed by Dr. T. Theodore Fujita.
Survey teams examine damage to buildings, trees, and other objects to estimate wind speeds and assign a rating from EF0 to EF5. These are damage-based estimates, not direct measurements of the tornado’s winds.
| EF Rating | Estimated 3-Second Wind Gust |
|---|
| EF0 | 65–85 mph |
| EF1 | 86–110 mph |
| EF2 | 111–135 mph |
| EF3 | 136–165 mph |
| EF4 | 166–200 mph |
| EF5 | More than 200 mph |
A tornado’s rating is assigned after the storm. Never wait for a rating before taking shelter.
Does the Sky Really Turn Green Before a Tornado?
Clouds in powerful thunderstorms sometimes take on a greenish hue. Scientists have proposed several explanations involving how sunlight interacts with the large amounts of water and ice inside a storm.
However, a green sky does not prove that a tornado is coming, and tornadoes can occur without one. Treat threatening weather seriously and rely on official alerts rather than sky color alone.
Why Do Tornadoes Seem to Hit Mobile Home Parks?
Tornadoes do not seek out mobile home parks. Mobile and manufactured homes are especially vulnerable to strong winds and flying debris, making the damage particularly severe.
Even a tied-down mobile home is not safe tornado shelter. Identify a nearby sturdy building or designated storm shelter before severe weather arrives, and allow time to reach it safely.
Where Should You Shelter During a Tornado?
Go to a designated tornado safe room or storm shelter, a basement, or a small, windowless interior room on the lowest floor of a sturdy building.
A closet, bathroom, or interior hallway may offer protection when no basement is available. Put as many walls as possible between yourself and the outdoors. Get beneath sturdy furniture if available, and protect your head and neck.
Stay away from windows and large, open rooms such as gymnasiums and auditoriums. At school or work, follow the building’s tornado shelter plan.
What If You’re Outside or in a Car?
Seek a sturdy building immediately. An open field, tent, shed, or highway overpass is not safe tornado shelter.
If you are driving and can safely reach a nearby sturdy building, go there. Don’t try to outrun a tornado.
If shelter is unreachable, the National Weather Service advises either getting down in your vehicle and covering your head, or leaving the vehicle for a low-lying area such as a ditch or ravine. Neither option is safe; a ditch is a last resort, and flooding is an additional danger.
What Is the Difference Between a Tornado Watch and Warning?
- Tornado watch: Conditions favor tornadoes. Review your shelter plan and stay alert.
- Tornado warning: A tornado has been observed or indicated by radar. Take shelter immediately if your location is included.
Don’t count on having a particular number of minutes to prepare. Know where you’ll go before a warning arrives.
Tornado Tales From the Almanac
Tornadoes have carried household belongings astonishing distances. The Old Farmer’s Almanac Book of Weather and Natural Disasters recounts one such story from the Great Tri-State Tornado of 1925, which struck Missouri, Illinois, and Indiana.
According to the account, Joe Boston, a policeman in Murphysboro, Illinois, lost a bond for a deed that had been locked inside a safe in his home. The document was reportedly found in Lawrenceville, about 125 miles away, and returned to him by mail.
The book also tells of a farmer near Robinson, Illinois, who watched a $10 bill and a $20 bill drop from the sky with other articles reportedly carried from Murphysboro.
Was Elvis Ever in a Tornado?
Yes! Elvis Presley and his parents survived the devastating tornado that struck his hometown of Tupelo, Mississippi, on April 5, 1936. Elvis was about 15 months old, not yet the performer who would become known around the world. His family escaped unharmed, while the storm destroyed much of the city and killed more than 200 people.
Learn More About Tornadoes
For more tornado science, visit NOAA’s National Severe Storms Laboratory. Review the National Weather Service’s tornado shelter guidance, and use weather.gov for local forecasts and warnings.
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