(Adopted by AMS Council 14 February 2000)
Bull. Amer. Met.Soc., 81, 1061—1065
Tornadoes are among the most violent natural atmospheric phenomena. The risk of death and injury from tornadoes can be minimized by learning more about them, planning for them, understanding the warning process, and following basic safety rules.
On average, 1200 tornadoes are reported in the United States each year. While statistics appear to indicate an increase in the occurrence of tornadoes since the 1950s, that trend is more likely due to advances in the observing, reporting, and documentation process. Most of the increase in tornadoes since the 1950s has been in the weak to moderate categories. The number of violent tornadoes has remained relatively steady. Less than two percent of all tornadoes reach the violent category (wind speeds in excess of 206 mph), but they account for at least two-thirds of all fatalities.
Tornado related fatalities and injuries decreased during the last half of the 20th century, especially in the 1980s and 1990s, when the average annual death toll dropped to 55, half of what it was in the 1950s through 1970s. Studies point to a number of factors which have contributed to this decrease, but prominent among them are improvements in detection and warning, increased public awareness, and advances in the delivery of information, especially through electronic media. A policy statement on tornado forecasting and warning was published in the AMS Bulletin in November, 1997.
In spite of the overall downward trend in fatalities, several events during the late 1990s demonstrated significant vulnerability in certain high risk situations. When strong or violent tornadoes impact densely populated areas, especially when they pass through mobile home communities or along heavily-traveled roads, or when they occur late at night, numerous fatalities and injuries can occur. In 1998, tornado related deaths in the U.S. totaled 130, including 42 in one Central Florida outbreak and 34 in one tornado which struck Birmingham, AL. In 1999, one tornado killed 38 in the Oklahoma City metropolitan area. There are lessons to be learned from these events for further mitigation of damage and reduction in casualties.
The primary dangers for humans associated with tornadoes are those produced by extremely high wind, the impact of debris propelled by high wind, destruction of mobile homes, collapse of buildings, and overturning or tossing of vehicles. Statistics continue to show a disproportionate number of tornado related fatalities (as high as 45 percent) in mobile homes. A policy statement on mobile homes and severe windstorms was published in the AMS Bulletinin May, 1997.
While tornadoes can occur almost anywhere in the United States at anytime of the year, geographical and climatological factors contribute to an increase in tornado frequency and higher risks in the southeast in late winter and early spring, followed by the southern and central Plains into the Ohio Valley in spring, and finally the upper Midwest into the Great Lakes during summer. Parts of the Plains and Midwest sometimes experience a limited recurrence in the fall.
2. Fundamentals for Reducing the Risk
Education, planning, awareness, prompt application of basic safety rules, and correct choice of shelter are critical elements by which individuals can reduce the risk of death or injury from tornadoes. Experience has demonstrated the importance of understanding the dangers associated with thunderstorms and tornadoes. It is also important to know the local geography, to develop contingency plans for protection, to keep up to date on the weather situation, especially on severe weather outlooks and watches, and to act promptly on warnings or reports of severe weather. Quick access to current warning information, especially during fast breaking events, is essential.
Government and community leaders at all levels, even down to the local neighborhood association, can reduce risks by upgrading and enforcing building codes, establishing contingency plans, requiring and providing shelters in mobile home communities and other areas where they are needed, and establishing or upgrading local warning dissemination systems. A particularly effective element in the warning dissemination process at almost any level of jurisdiction is the emergency operations center (EOC), the focal point for receiving critical information and making timely local warning dissemination decisions.
Owners, managers, directors, and staffs of public and private facilities where large numbers of people are housed or gathered can also play key roles in reducing the risk of tornado- related deaths and injuries. Each facility should have an up-to-date action plan, adequate shelter, an efficient means of receiving warning information, and an effective internal dissemination system. The EOC analogy can be followed by implementing the "designated weather watcher" concept, whereby an individual is directed to monitor the weather situation and activate the internal warning dissemination system when necessary.
Building designers, contractors, and manufacturers can reduce risk by promoting and following upgraded building codes, adhering to sound construction principles recommended by wind engineering experts, and incorporating hardened "safe rooms" or shelters into new and remodeled buildings. Going beyond minimum requirements and using documented techniques for withstanding high wind loads provides an extra measure of safety for the occupants of a building and reduces the chance that parts of a building will become debris that could impact other buildings or individuals. Consumers should demand higher standards from their contractors and specify shelter or safe room space when designing, purchasing, or leasing a home or building.
3. Specific Elements for Reducing Risks
The more a person understands about thunderstorms and their behavior, knows about his or her local geography (e.g. county names, surrounding cities, etc.), and is familiar with severe weather warnings and where to find them, the more likely that person is to survive a tornado.
Much can be learned from qualified meteorologists, weathercasters, and writers in the media who have done so much during the 1980s and 1990s to upgrade the level of basic weather knowledge among the public. There are many excellent weather education sources containing detailed information on thunderstorms and tornadoes. In most areas, the web site for the nearest National Weather Service office (available through http://www.noaa.gov ) contains useful information and links to a variety of other sources.
Basic weather knowledge, combined with an understanding of severe weather terminology and dissemination services, can help a person determine the level of threat and the urgency of a situation. For example, someone with a minimal understanding of severe thunderstorms could recognize that a tornado warning stating "...radar indicates a severe storm capable of producing a tornado..." means that a rotating severe thunderstorm has been detected on Doppler radar, that a tornado could occur in the storm at any time, and that safety precautions should be taken.
Knowing the local geography is also helpful when severe weather outlooks, watches, and warnings are issued. Reference maps can be posted or kept near the television, NOAA Weather Radio (NWR), scanner, etc. Many local officials and media offer severe storm plotting maps indicating county names and boundaries. Individuals should learn the names of their surrounding counties and some of the key cities and other landmarks. Knowing that a tornado warning has been issued for the "upstream" county can provide valuable extra lead time for residents in the "downstream" county.
During threatening weather conditions, travelers need to know the county in which they are located, and the names of nearby towns and other geographical references. National Weather Service warning forecasters and those disseminating warning information should incorporate highways and other well known references helpful to travelers.
Developing action plans for tornado emergencies is critical to minimizing the risk of injury or death. General safety rules need to be understood, but site specific plans will promote efficient communication and allow for quick action. Families and individuals should develop contingency plans for potential tornado events at home and away from home, and for all times of the day and night. Managers, supervisors, owners, clergy, superintendents, etc. should direct the development of plans for the facilities and institutions for which they are responsible. This includes schools, churches, hospitals, nursing homes, factories, office buildings, stores, theaters, stadiums, parks, etc.
Each plan should start with redundant means to access timely weather information and identify the individuals responsible for monitoring these sources and initiating local warning dissemination. The "designated weather watcher" concept can be an extremely useful part of any severe weather action plan. Shelters and safe areas should be identified, readily accessible, and equipped with basic supplies, such as flashlights, batteries, etc. Part of any severe weather plan should focus on operations without phones and electricity, including internal and external backup communication systems. Plans should also include contingencies for initial operations and recovery efforts immediately following a tornado event.
Plans should be made for times when a person is caught in a vehicle and other times when not at work, home, school, or in places occupied routinely. These must be flexible and tied closely to basic safety rules.
Plans should be reviewed thoroughly by all participants so they can be followed quickly in an emergency. Families should exercise their tornado plans just as they do fire safety plans. Managers of workplaces should oversee the exercise of tornado plans in their areas of responsibility. Those responsible for other public places should ensure that all employees exercise the local plans and are prepared to deal with the public who are gathered in their areas of responsibility.
Those responsible for developing emergency action plans will find useful information and assistance at local Red Cross chapters, FEMA district offices, state and local emergency management agencies, and at related web sites.
Part of the daily routine of checking the local weather forecast should include attention to any severe weather potential, especially during climatologically favored seasons. There are many excellent sources of weather information which highlight severe weather outlooks. These include NOAA Weather Radio, local and cable television programs, local radio programs, web sites, etc. The national and local severe weather outlooks issued by the National Weather Service and disseminated through various government and commercial services are extremely valuable sources of information and should be sought out, especially during the favored seasons. During days with potential for severe weather, forecasts should be monitored frequently for updated information. When severe weather develops, persons in the threatened area should monitor a reliable source of up to date information until the threat subsides.
Redundant "first warning" systems help ensure that timely warning information is received. For example, a family at home might rely both on a Weather Radio and a nearby siren. Devices such as NOAA Weather Radio, sirens, pagers, cell phones, the emergency activation system (EAS), etc. can provide critical early warning. After the initial warning, additional information can be found through television, radio, NOAA Weather Radio, etc. The effectiveness of all of these systems depends on local availability and broadcast range. Residents in areas where none of these types of systems or services are available should work with local officials to establish some type of first-warning system. Providers of "first warning" services should also consider the special requirements of hearing and sight impaired persons and those who do not speak English.
Many people have been killed or injured in the relative safety of their home because they were unaware of warnings or an approaching tornado. Some of the classic scenarios involve people sleeping, listening to music on a tape or CD, watching cable TV programs, watching a movie video or CD, etc. Others have been caught outdoors, without access to traditional media systems, or in vehicles. In many of these cases, prior awareness of a tornado threat and the presence of a first-warning device would make the difference. Motorists should not assume that all public and commercial radio stations will carry warning information. During threatening weather situations, a NOAA Weather Radio or the "seek" button on the vehicle's radio should be actively employed.
d. Basic Safety Rules
Since the primary hazards associated with tornadoes are extremely high wind and debris propelled by the wind, the most fundamental rule is to avoid the wind and debris. Go to the lowest place available in a shelter or sturdy building, away from windows, and get behind as many walls or other obstacles as possible.
If an immediate tornado threat is determined, either through warnings or observation, the safest place is a specially built tornado shelter. However, conventional homes and many other buildings, especially those with basements, usually provide at least some degree of shelter. Basic safety rules include going to the basement or other lowest level of the building. The particular part of the basement used is not as important as getting under a sturdy object, away from windows and exterior doors. If there is no basement, a small room at the interior of the lowest floor is usually the safest location, away from windows, exterior walls, and garage doors. Interior bathrooms, closets, and store rooms on the lowest floor are usually the best choices. If there is not time to get to the lowest floor, the middle of the building is usually safer than near exterior walls, especially those with windows. Hallways can provide more protection than rooms with windows or exterior walls, but under certain circumstances wind flow in hallways that have exterior doors at each end can be enhanced by the wind tunnel effect. Closing interior doors can help impede wind flow through a structure in some cases.
Additional protection in buildings can be provided by getting inside or under some structure or sturdy object such as stairs, a bathtub, a workbench, etc., and by covering oneself with blankets, mattresses, or coats, and even wearing head protection such as bicycle helmets.
While the primary rule in a building without a shelter or basement is to go to the lowest floor, away from outside walls, often the "downstream" portion of a building will be somewhat safer than the "upstream," relative to the approaching tornado. This means that if a tornado moves from southwest to northeast, there will often be less damage to the north section of the building, and more to the south section.
Buildings with large, expansive roofs and walls, such as gymnasiums, auditoriums, churches, factories, supermarkets, large stores, etc. can be dangerous, especially if large numbers of people are present and unable to fit into the few small rooms available. These types of buildings should be avoided if a tornado is imminent. If there is time, a more substantial structure should be sought. If caught inside one of these large buildings with no time to evacuate, small interior rooms should be used as shelter, if they are available. Otherwise, some protection should be found away from exterior walls and windows, under something sturdy.
Mobile homes and campers should be evacuated for more sturdy shelter if a tornado is imminent. Even the non-tornadic high winds accompanying the parent thunderstorm could be strong enough to overturn or destroy a mobile home. The decision about where to go should be based on how much time there is to act and what type of shelters are available. Certainly, underground shelters are best and should be in place in every mobile home community. If there is no shelter, and there is enough warning lead time, it might be best to evacuate in a vehicle to avoid an approaching tornado or to reach a sturdy shelter. Otherwise, it is best to have a sturdy building already in mind for quick access.
Those who are outdoors, in stores, at church, at a movie, in vehicles, or in any other situation outside of the home or workplace are under particular risk during a tornado. In these situations, awareness, access to timely warning information, and shelter options become even more critical. Being aware of a tornado threat might help a person decide to adjust activities in order to avoid such situations in the first place. However, a fundamental understanding of tornado hazards, timely access to warning information, and knowledge of basic safety rules will often contribute to quick and correct decisions and actions for personal safety.
Anyone caught outdoors near an approaching tornado should evacuate the area quickly for shelter inside a building. In severe weather situations, motorists should be extremely cautious about driving into threatening conditions, since tornadoes can be hard to distinguish when very close and can sometimes be hidden in rain. Motorists should use all available information to try to avoid an approaching tornado. Otherwise, the safest action is to abandon the vehicle for a sturdy building.
The basic rule of avoiding tornado driven debris should keep motorists, pedestrians, etc. from placing themselves in harm's way under highway overpasses. In spite of what many people might have seen in videos and photos, highway overpasses do not offer reliable protection from tornado winds and wind-driven debris. In fact, an overpass can produce a wind tunnel effect, depending on its configuration relative to the tornado. In addition, congregating under overpasses during threatening weather conditions creates an extremely dangerous traffic hazard.
The traditional advice given to those outdoors or in mobile homes and vehicles to lie in a ditch or culvert should be considered as a last resort, to be used only when a tornado cannot be avoided and when quick access to a sturdy building or shelter is impossible.
Every building, especially in areas of the country with higher frequency of tornadoes, should have a shelter, safe room, or at least some type of tornado resistant space. It should be kept uncluttered and be accessible to all occupants of the building. Shelters in public buildings should be clearly identified and easily accessible.
A great deal of information is available regarding shelter and safe room construction and modification, and there are many techniques for raising the level of safety or "hardening" appropriate rooms in existing homes and other buildings. One general source of information is the Federal Emergency Management Agency (FEMA) and its web site (www.fema.gov). The FEMA publication, "Design and Construction Guidance for Tornado and Hurricane Community Shelters" is especially useful.
Anyone building a new home should certainly include a shelter or safe room. Any company or group responsible for constructing a new commercial or public building should include shelters or at least tornado resistant areas. A few simple construction upgrades, such as bolting walls to foundations, using hurricane clips, etc. can make an entire building more tornado resistant.
New shelters, or those added to buildings through remodeling, should be constructed according to the latest standards which include the use of reinforced concrete, metal doors with multiple hinges and dead bolts, etc. Persons in the market for a shelter, safe room, or the upgrade of existing construction should seek out reputable contractors and ask for references.
4. A Call to Action
Government agencies at all levels and the media need to continue the outreach and education efforts which have already contributed to a significant reduction in tornado related fatalities and injuries. Specific plans should address the higher risk regions of the country and higher risk groups, such as mobile home residents, motorists, persons with disabilities, etc. Those involved in educational outreach should be aware of updated information and research results which might lead to new or modified preparedness and safety recommendations and to new systems or techniques related to awareness and warning dissemination.
Government and community leaders and the insurance industry should work swiftly toward upgraded building codes and construction standards within their jurisdictions that will raise the level of tornado resistance in homes and other buildings. Community wide standards and actions are needed to prevent sub-standard buildings from becoming tornado debris that would affect even those buildings constructed to higher standards.
Government leaders should coordinate with and obtain guidance from experts regarding the need for and operation of community shelters. They should adopt shelter requirements where they are needed, such as in mobile home communities, near frequently crowded outdoor facilities, etc., but avoid adopting policies that encourage residents to leave the relative safety of sturdy, site-built homes to travel to a community shelter when a tornado is approaching.
Beyond government requirements, those involved in the building industry and the manufactured housing industry should adopt and follow the standards and practices that are known to add high wind resistance to the structures they build. Most of these are common-sense techniques which are simply the right thing to do. Anyone purchasing a new home should require this higher level of building standard.
Finally, efforts need to continue at all levels of government, in the media, in the private sector, and among the public to take advantage of new and enhanced communication techniques to improve the dissemination of weather forecasts and warnings. There should be an emphasis in every community on reliable first-warning systems. Every school, church, hospital, nursing home, shopping mall, supermarket, store, office building, home, and apartment within range of a NOAA Weather Radio transmitter should have at least one receiver with warning alarm capability. Vehicle manufacturers should work swiftly toward integrating NOAA Weather Radio technology in all vehicles.
5. Final Comments
This policy statement addresses risks associated with tornadoes and recommendations for reducing those risks. It is based on research and experience during the last few decades of the twentieth century. Written from the meteorologist's perspective, t