A tornado is a narrow, violently rotating column of air that extends from the base of a thunderstorm to the ground. It is hard to see a tornado until it forms condensation within the funnel made of water droplets, dust, or debris.
Tornadoes are the most violent of all atmospheric storms. While tornadoes occur throughout the world, the United States averages around 1,200 a year, one of the highest concentrations in the world.
Tornadoes form primarily from supercell thunderstorms, those with well-defined radar circulation. A rotating updraft is key to the development of the supercell and eventually the tornado itself. Often winds at ground level are slowed by friction while winds in the upper levels of the supercell move much faster.
Rising air, often warm and moist, begin to develop the "tube" which then creates a vertical rotation. This vertical updraft fed by the warm moist air can lead to the formation of the tornado.
Tornadoes can also form in non-supercell thunderstorms, hurricanes, and other coastal storms. The National Weather Service reports that on average only 20% of supercell storms will develop tornadic activity.
Damages & Danger
Damages caused by tornadoes are usually the result of high wind velocities and wind-blown debris. Lightning and hail usually accompany these storms and can also result in damage.
On average, tornadoes kill about 60 people per year, mostly from falling or flying debris.
Peak tornado season in the Southeast is March through May and in the northern states it runs from late spring through early summer. They can occur at any time of the day, but are most likely to occur between 3 and 9 p.m. Structures of light construction, such as mobile homes, are at the greatest risk for damage from tornadoes.
According to the National Oceanic and Atmospheric Administration, the Storm Prediction Center in Oklahoma City has the highest concentration of tornado activity for a city. North Carolina and Onslow County have approximately 1-6 tornadoes per average year.
The states with the highest concentration of tornados are:
A tornado is reported by its magnitude according to the Enhanced Fujita Scale (EF Scale). The EF Scale became operational on February 1, 2007, replacing the original Fujita Scale. The scale assigns a "rating" based on estimated wind speeds and related damage.
After a tornado occurs, field surveyors will compare a list of Damage Indicators (DI) and degrees of damage to help estimate the range of wind speeds that were likely produced. The highest radar motion detected was over 300 mph.
|EF Rating||3 Second Gust||Expected Types of Damages|
|EF0||65-85 mph||Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages to sign boards|
|EF1||86-110 mph||The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.|
|EF2||111-135 mph||Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated.|
|EF3||136-165 mph||Roof and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted.|
|EF4||166-200 mph||Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated.|
|EF5||200 mph +||Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel re-enforced concrete structures badly damaged.|
Waterspouts are weak tornadoes that form over the water and are most common along the Gulf Coast and the Southeastern United States. Waterspouts will occasionally move inland, becoming a tornado that can cause damage and injury.
Most waterspouts will dissipate over open water causing the highest threat to marine and boating interests. Typically, waterspouts are weak and short-lived and most go unreported unless they cause damage.
What to do before a tornado
- Listen to NOAA Weather Radio or radio or television newscasts for the latest updates. In any emergency, always listen to the orders given by local emergency management officials.
- Be alert to changing weather. Look for oncoming storms.
- Look for the following danger signs:
- Dark, often greenish sky.
- Large hail.
- A large, dark, low-lying cloud (particularly if rotating).
- Loud roar, much like a freight train.
- If you see oncoming storms or any of these danger signs, be ready to take shelter quickly.
- Know where to go. The safest place to be during a tornado is in a basement. If you have no basement, go to an inner hallway or smaller inner room without windows, such as a bathroom or closet. Go to the center of the room. Try to find something sturdy you can get under and hold onto to shield you from flying debris and/or a collapsed roof. Use your arms to protect your head and neck.
- Mobile homes, even those with tie-downs, are particularly open to damage from high winds. Go to a prearranged shelter when the weather turns bad.
- If no shelter is available, go outside and lie on the ground, if possible in a ditch or depression. Use your arms to protect your head and neck and wait for the storm to pass. While waiting, be alert for the flash floods that sometimes come with tornadoes.
- Never try to outrun a tornado in a car. A tornado can toss cars and trucks around like toys. If you see a funnel cloud or hear a tornado warning issued, get out of your vehicle and find safe shelter. If no shelter is available, lie down in a low area using your arms to cover the back of your head and neck. Be sure to stay alert for flooding.
Know the Terms
Familiarize yourself with these terms to help identify a tornado hazard:
Tornado Watch - Tornadoes are possible. Remain alert for approaching storms. Watch the sky and stay tuned to NOAA Weather Radio, commercial radio or television for information.
Tornado Warning - A tornado has been sighted or indicated by weather radar. Take shelter immediately.
During a Tornado
- At Home: Seek shelter on the lowest possible floor or in the basement. Under the stairs or in a bathroom or closet are good shelter spots. Do not open or close windows. Stay away from windows. Bend down on the floor in the egg position.
- At Work: Seek shelter on the lowest possible floor or a basement, if there is a basement. Stairwells, bathrooms and closets are good spots. Stay away from windows. As a last resort, crawl under your desk.
- At School: Seek shelter in inside hallways, small closets and bathrooms. Stay away from windows. Get out of mobile classrooms. Stay out of gymnasiums, auditoriums and other rooms with a large expanse of roof. Bus drivers should be alert for bad weather on their routes.
- At The Mall/Store: Seek shelter against an inside wall. An enclosed hallway or fire exit leading away from the main mall concourse is a good spot. Stay away from skylights and large open areas.
- Outside: Find the closest sturdy shelter. If no shelter is available, try to find a ditch or low-lying area. Cover your head with your hands. Do not get under an overpass or bridge. You are safer in a low, flat location. Watch out for flying debris. Flying debris from tornadoes causes most deaths and injuries.
After a Tornado
Injuries may result from the tornado or after a tornado when people walk among and clean up debris. Watch out for sharp objects, especially nails and glass. Look out for damaged power lines, gas lines or electrical systems. There may be a risk of fire, electrocution or an explosion.
Immediately after a tornado:
- Check for injuries. Do not try to move badly injured people unless they are in immediate danger of further injury. Get medical help quickly. If someone has stopped breathing, begin CPR if you are trained to do so. Stop a bleeding injury by putting direct pressure to the wound. Have any puncture wound looked at by a doctor. If you are trapped, try to get attention to where you are located.
To avoid injury after a tornado:
- Continue to use your battery-powered radio or television for emergency information.
- Be careful when entering any structure that has been damaged.
- Wear sturdy shoes/boots, long sleeves and gloves when walking or working near debris.
- Be aware of dangers from exposed nails and broken glass.
- Do not touch downed power lines or objects in contact with downed lines. Report electrical hazards to the police and utility company.
- Use battery-powered lanterns, if possible, rather than candles to light homes without electrical power. If you use candles, make sure they are in safe holders away from curtains, paper, wood or other flammable items. Never leave a candle burning when you are out of the room.
- Never use generators, pressure washers, grills, camp stoves or other gasoline, propane, natural gas or charcoal-burning devices inside your home, basement, garage or camper – or even outside near an open window, door or vent. Carbon monoxide is an odorless, colorless gas that can cause sudden illness and death if you breathe it. These fumes can build up in your home, garage or camper and poison the people and animals inside. Seek prompt medical help if you feel dizzy, light-headed or nauseated.
- Respond to requests for volunteer help by police, fire fighters, emergency management and relief groups. Just DO NOT GO into damaged areas unless help has been requested. You being there could slow down relief efforts.
- Be aware of possible structural, electrical or gas-leak hazards in your home. Call your local building inspectors for information on structural safety codes and standards. They may also offer tips on finding a trained contractor to do work for you.
- If you think there might be damage to your home, shut off electrical power, natural gas and propane tanks to stop any fires, electrocutions or explosions.
- If it is dark when you are checking your home, use a flashlight rather than a candle or torch to not have the risk of fire or explosion in a damaged home.
- If you see frayed wiring or sparks, or if there is an odor of something burning, quickly turn off the electrical system at the main circuit breaker.
- If you smell gas or suspect a leak, turn off the main gas valve, open all windows and leave the house quickly. Tell the gas company, the police or fire departments. DO NOT: turn on the lights, light matches, smoke or do anything that could cause a spark. Do not return to your house until you are told it is safe to do so.