Tornado Guide: How To Protect Your Home from Disaster
Do you feel safe from tornadoes just because you live outside "Tornado Alley?" More of these unpredictable and dangerous storms touch down in Kansas, Oklahoma and Texas than other states, but twisters destroy homes and lives across vast swaths of the country. You may be at risk.
Tornadoes are nature’s most violent storms. Spawned from powerful thunderstorms, tornadoes can uproot trees, demolish buildings and turn harmless objects into deadly missiles. They can obliterate a neighborhood in seconds. A tornado appears as a rotating, funnel-shaped cloud that extends to the ground with whirling winds that can reach 300 miles per hour. Tornadoes cause damage along paths can be more than a mile wide and fifty miles long. Every state is at some risk from this hazard.
You can reduce tornado damage by planning and acting before it's too late. You can prepare for a tornado to protect your home and family from disaster by following the steps we list below. In this guide, we have provided some basic information about tornadoes, lists of specific actions you can take to get ready, and a section on frequently asked questions about tornadoes. Throughout the guide are links to additional resources for more information.
1. A tornado is a violently rotating column of air extending from a thunderstorm to the ground.
2. Tornadoes are capable of destroying homes and vehicles and can cause fatalities.
3. Tornadoes may strike quickly, with little or no warning.
4. Tornadoes may appear nearly transparent until dust and debris are picked up or a cloud forms in the funnel.
5. The average tornado moves SW to NE but tornadoes have been known to move in any direction.
6. The average forward speed is 30 mph but may vary from stationary to 70 mph with rotating winds that can reach 300 miles per hour.
7. Tornadoes can accompany tropical storms and hurricanes as they move onto land.
8. Waterspouts are tornadoes that form over water.
9. Tornadoes are most frequently reported east of the Rocky Mountains during spring and summer months but can occur in any state at any time of year.
10. In the southern states, peak tornado season is March through May, while peak months in the northern states are during the late spring and early summer.
11. Tornadoes are most likely to occur between 3 p.m. and 9 p.m., but can occur at any time of the day or night.
Although no home can withstand a direct hit from a severe tornado, solid construction will help your home survive if it's to the side of the tornado's path. Structures built to meet or exceed current model building codes for high-wind regions have a much better chance of surviving violent windstorms. The International Building Code, issued by the International Code Council, is one source for guidance on fortifying your home against fierce winds.
When inspecting your home, pay particular attention to the windows, doors, roof, gables and connections (roof-to-wall, wall-to-foundation). Residences in inland areas are typically not built to withstand high wind forces, and weaknesses in these elements of your home make it more vulnerable to significant damage.
If you're handy with a hammer and saw, you can do much of the work yourself. Work involving your home's structure may require a building contractor, however, or even a registered design professional such as an architect or engineer.
WHEN WORKING OUTSIDE:
- Replace gravel/rock landscaping material with shredded bark.
- Keep trees and shrubbery trimmed. Cut weak branches and trees that could fall on your house.
WHEN BUILDING OR REMODELING:
Windows: If you are replacing your existing windows, install impact-resistant window systems, which have a much better chance of surviving a major windstorm. These window systems are commonly available in hurricane-prone areas. If you are unable to find them locally, you can order them from manufacturers or home improvement stores in coastal areas.
Entry doors: Make certain your doors have at least three hinges and a dead-bolt security lock, with a bolt at least one inch long. Anchor door frames securely to wall framing.
Patio doors: Sliding glass doors are more vulnerable to wind damage than most other doors. If you are replacing your patio doors or building a new home, consider installing impact-resistant door systems made of laminated glass, plastic glazing or a combination of plastic and glass.
Garage doors: Because of their size and construction, garage doors are highly susceptible to wind damage. A qualified inspector can determine if both the door and the track system can resist high winds and, if necessary, replace them with a stronger system.
Garage doors more than 8 feet wide are most vulnerable. Install permanent wood or metal stiffeners. Or contact the door manufacturer's technical staff for recommendations about temporary center supports you can attach and remove easily when severe weather threatens.
Roofs: If you are replacing your roof, take steps to ensure that both the new roof covering and the sheathing will resist high winds. Your roofing contractor should:
- Remove old coverings down to the bare wood sheathing.
- Remove sheathing to confirm that rafters and trusses are securely connected to the walls.
- Replace damaged sheathing.
- Refasten existing sheathing according to the proper fastening schedule outlined in the current model building code for high-wind regions.
- Install a roof covering designed to resist high winds.
- Seal all roof sheathing joints with self-stick rubberized asphalt tape to provide a secondary moisture barrier.
If you want to give your roof sheathing added protection, but it's not time to re-roof, glue the sheathing to the rafters and the trusses. Use an adhesive that conforms to Performance Specification AFG-01 developed by APA - The Engineered Wood Association, which you can find at any hardware store or home improvement center.
Gables: Brace the end wall of a gable roof properly to resist high winds. Check the current model building code for high-wind regions for appropriate guidance, or consult a qualified engineer or architect.
Connections: The points where the roof and the foundation meet the walls of your house are extremely important if your home is to resist high winds and the pressures they place on the entire structure.
- Anchor the roof to the walls with metal clips and straps (most easily added when you replace your roof).
- Make certain the walls are properly anchored to the foundation. A registered design professional can determine if these joints need retrofitting, and a qualified contractor can perform the work the design professional identifies.
- If your house has more than one story, make certain the upper story wall framing is firmly connected to the lower framing. The best time to do this is when you remodel.
WHEN A TORNADO THREATENS:
While no home can ever be made "tornado-proof," you can improve the odds of your home surviving high winds by taking these precautions. Take these additional steps to protect yourself and your family:
- Decide in advance where you will take shelter (a local community shelter, perhaps, or your own underground storm cellar or in-residence "safe" room). When a tornado approaches, go there immediately. If your home has no storm cellar or in-residence "safe" room and you have no time to get to a community shelter, head to the centermost part of your basement or home - away from windows and preferably under something sturdy like a workbench or staircase. The more walls between you and the outside, the better.
- Become familiar with your community's severe weather warning system and make certain every adult and teenager in your family knows what to do when a tornado watch or warning sounds. Learn about your workplace's disaster safety plans and similar measures at your children's schools or day care centers.
- Study your community's disaster preparedness plans and create a family plan in case you are able to move to a community shelter. Identify escape routes from your home and neighborhood and designate an emergency meeting place for your family to reunite if you become separated. Also establish a contact point to communicate with concerned relatives.
- Put together an emergency kit that includes a three-day supply of drinking water and food you don't have to refrigerate or cook; first aid supplies; a portable NOAA weather radio; a wrench and other basic tools; a flashlight; work gloves; emergency cooking equipment; portable lanterns; fresh batteries for each piece of equipment; clothing; blankets; baby items; prescription medications; extra car and house keys; extra eyeglasses; credit cards and cash; important documents, including insurance policies.
- Move anything in your yard that can become flying debris inside your house or garage before a storm strikes. Do this only if authorities have announced a tornado watch, however. If authorities have announced a tornado warning, leave it all alone.
- Don't open your windows. You won't save the house, as once thought, and you may actually make things worse by giving wind and rain a chance to get inside.
- Don't try to ride out a tornado in a manufactured home. Even manufactured homes with tie-downs overturn in these storms because they have light frames and offer winds a large surface area to push against. In addition, their exteriors are vulnerable to high winds and wind-borne debris.
Finally, review your homeowners insurance policy periodically with your insurance agent or company representative to make sure you have sufficient coverage to rebuild your life and home after a tornado. Report any property damage to your insurance agent or company representative immediately after a natural disaster and make temporary repairs to prevent further damage.
For information about filing an insurance claim after a natural disaster, contact your insurance agent or insurance company.
- Q. Where do tornadoes come from?
- A. Tornadoes come from the energy released in a thunderstorm. As powerful as they are, tornadoes account for only a tiny fraction of the energy in a thunderstorm. What makes them dangerous is that their energy is concentrated in a small area, as little as a hundred yards across. Not all tornadoes are the same, of course, and science does not yet completely understand how part of a thunderstorm's energy sometimes gets focused into something as small as a tornado, but keep reading...
- Q. Where do tornadoes occur?
- A. Whenever and wherever conditions are right, tornadoes are possible, but they are most common in the central plains of North America, east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer; the tornado season comes early in the south and later in the north because spring comes later in the year as one moves northward. They usually occur during the late afternoon and early evening. However, they have been known to occur in every state in the United States, on any day of the year, and at any hour. They also occur in many other parts of the world, including Australia, Europe, Africa, Asia, and South America.
If you'd like to plot tornado tracks, download "Severe Plot" and the associated data from the NOAA Storm Prediction Center.
- Q. What type of damage can tornadoes do?
- A. The damage from tornadoes comes from the strong winds they contain. It is generally believed that tornadic wind speeds can be as high as 300 mph in the most violent tornadoes. Wind speeds that high can cause automobiles to become airborne, rip ordinary homes to shreds, and turn broken glass and other debris into lethal missiles. The biggest threat to living creatures (including humans) from tornadoes is from flying debris and from being tossed about in the wind. It used to be believed that the low pressure in a tornado contributed to the damage by making buildings "explode" but this is no longer believed to be true.
- Q. How are tornadoes detected?
- A. Today, the development of Doppler radar has made it possible, under certain circumstances, to detect a tornado's winds with a radar. However, human beings remain an important part of the system to detect tornadoes, because not all tornadoes occur in situations where the radar can "see" them. Ordinary citizen volunteers make up what is called the SKYWARN network of storm spotters, who work with their local communities to watch out for approaching tornadoes, so that those communities can take appropriate action in the event of a tornado. Spotter information is relayed to the National Weather Service, which operates the Doppler radars and which issues warnings (usually relayed to the public by radio and TV) for communities ahead of the storms, using all the information they can obtain from weather maps, modern weather radars, storm spotters, monitoring power line breaks, and so on.
- Q. Can tornadoes be predicted?
- A. Yes, but only to a limited extent. Although the process by which tornadoes form is not completely understood, scientific research has revealed that tornadoes usually form under certain types of atmospheric conditions. Those conditions can be predicted, but not perfectly. When forecasters see those conditions, they can predict that tornadoes are likely to occur. However, it is not yet possible to predict in advance exactly when and where they will develop, how strong they will be, or precisely what path they will follow. There are some "surprises" every year, when tornadoes form in situations that do not look like the right conditions in advance, but these are becoming less frequent. Once a tornado is formed and has been detected, warnings can be issued based on the path of the storm producing the tornado, but even these cannot be perfectly precise about who will or will not be struck.
- Q. How can I keep myself safe from a tornado?
- A. A complete list of tornado safety rules can be found at the FEMA Tornado Safety Website. The main point is to protect yourself from flying and falling debris, specifically:
- A storm shelter is your best choice, if you have one. If you have a basement, go there and get under something sturdy to shelter you from falling debris (for instance, a strong workbench, or a staircase).
- If you have no basement or storm shelter, go to an interior room without windows on the first floor of your home. Bathrooms are a good choice because the plumbing reinforces the walls. Closets are also a good choice since they normally have no windows. The idea is to put as many walls between you and an approaching tornado as possible; flying debris can penetrate exterior walls.
- Stay away from windows entirely! It used to be thought that opening windows would reduce a tornado's damage to a home. This is no longer considered to be good advice: leave windows alone completely and get to a safe place immediately.
- If you live in a mobile home, it should be abandoned; seek shelter in a neighboring frame home or, better yet, a storm shelter. If you are in a motor vehicle in an populated area, do not try to drive away from a tornado; abandon your vehicle and seek shelter nearby.
- If you are traveling in a rural area, drive away from the tornado at a right angle to its path. If caught in the open, get down in a sheltered low spot, and cover your head with your arms; hang on to something if it is available.
- If you are at school or work, your school or workplace should have an approved tornado safety plan, which you should follow. If no such plan exists, speak with the appropriate person about getting a plan developed! Knowing what to do in a specific situation means you are less likely to panic and do something dangerous without realizing it. Have a plan within your family about what you would do, and follow it exactly, including where you will go if you are separated.
- If you hear a tornado warning, you should seek immediate shelter and not waste precious seconds to see if it is true for you; wasting a few minutes in a safe place once in awhile is better than becoming another tornado statistic!
- Q. Should I seek shelter under a bridge over-pass during a tornado?
- A. It is not advisable to seek shelter under a bridge. This is due to increased wind speeds that result from a phenomenon known as Bernoulli's principle, which states that air moving through a constriction or over a curved surface will undergo a pressure drop and an increase in wind speed. This translates to higher potential for injury from flying tornado debris. To illustrate this principle, think of what happens when you constrict the flow of water through a garden hose. The water speeds up. Likewise, the air speeds up when forced through a narrow overpass.
For more information on overpasses and safety in your car, NOAA developed a slideshow: Highway Overpasses as Tornado Shelters.
- Q. What is the smallest, largest, average size of a tornado?
- A. The answer to this depends on what is being measured. The easiest way to answer this is by the size of the damage path. Also, it is important to note that the "average" can be misleading, since most tornadoes are small ... a simple average puts too much emphasis on the infrequent large events. A way around this is to use what is called the "median" to represent what is typical. The typical tornado damage path is about one or two miles long with a width of about 50 yards. The largest tornado path widths can exceed one mile, and the smallest widths can be less than 10 yards. Widths can vary considerably during a single tornado, because the size of the tornado can change considerably during its lifetime. Path lengths can vary from what is basically a single point to more than 100 miles. Note that tornado intensity (the peak wind speeds) is not necessarily related to the tornado size ... bigger is not necessarily stronger!
- Q. How long is a tornado usually on the ground?
- A. Detailed statistics about the time a tornado is on the ground are not available. This time can range from an instant to several hours ... roughly 5 minutes is typical.
- Q. How fast do tornadoes move?
- A. As with tornado duration, detailed statistics about forward speed are not available. Movement can range from virtually stationary to more than 60 miles per hour ... roughly 10-20 miles per hour is typical.
- Q. How do I know if it is a tornado or just a funnel?
- A. The definition of a tornado means that the vortex of rapidly rotating air must be in contact with the ground. This means that to be a tornado, the swirling winds must be at the surface, capable of doing damage. If you see debris (dust and other objects swirling in the winds), it is definitely a tornado, even if there is no visible funnel cloud. If you can't see debris with a funnel cloud, then it might be a tornado but you can not be certain that it is (or is not). A tornado can move over a surface with few objects to be picked up and swirled about, or you may not be able to see all the way to the surface beneath a funnel cloud because of intervening hills, trees, or buildings. All funnel clouds should be treated as if they are tornadoes, unless you can be certain that they will not touch down...and being certain about such things is difficult. Even if the funnel is not in contact with the surface when you first see it, that situation can change quite rapidly!
- Q. Does a tornado always come from a wall cloud?
- A. A wall cloud is not always present, or will not always appear to be present, when there is a tornado. You may not be able to see a wall cloud because of your viewing angle.
As the storm intensifies, the updraft draws in low-level air from several miles around. Some low-level air is pulled into the updraft from the rain area. This rain-cooled air is very humid; the moisture in the rain-cooled air quickly condenses (at a lower altitude than the rain-free base) to form the wall cloud. If you are interested to learn more about how to identify a wall cloud, contact your local NOAA National Weather Service to learn when storm spotter training is offered in your area. You do not have to be a storm spotter to attend free storm spotter training.
- Q. Does NSSL do things like they showed in the movie Twister?
- A. The movie Twister was based upon work National Severe Storms Laboratory (NSSL) did in the mid-1980's using a 55-gallon drum filed with various meteorological sensors. It was called TOTO (TOtable Tornado Observatory). NSSL tried for several years to put it in the path of an oncoming tornado, but had minimal success. It did not have the sensors that fly up into the tornado, like in the movie. However, that is not a bad idea and with the advances being made in computer technology, we might be able to do that someday.
For additional information and links to other sites check the tornado section of the NSSL Web Guide. The latest on NSSL efforts in tornado education is included in the Severe Weather 101 Series: Tornadoes, and on Dr. Erik Rasmussen's Severe Storms and Tornadoes Research Paper.