Tornado warning dissemination since 1948 has advanced from outdoor sirens, through radio and television, NOAA Weather Radio, and lately GPS-based systems.
Despite promising research on the conditions that are favorable for tornadoes in the 1880s by John P. Finley, a general consensus was reached among scientists in the 1880s and 1890s that tornado forecasts and warnings would cause more harm than good. A ban was placed on the issuance of tornado warnings from 1887, when the U.S. Army Signal Corps handled weather forecasts, until 1938, when the civilian U.S. Weather Bureau (USWB) finally lifted the ban. The beginning of modern tornado warnings was primarily a result of the success of Fawbush and Miller in forecasting a tornado at Tinker Air Force Base in 1948 (e.g., Bradford 1999; Galway 1985; Bradford 2001).
The science of tornado warning, and the subsequent dissemination of those warnings to the public, has continued to expand rapidly since 1950. The development of spotter networks, and the conversion of radar to use for the detection of tornadoes, made tornado warning programs much more successful. However, as stated in the policy statement of the American Meteorological Society on tornado detection, tracking, and warning (AMS 1975), "One of the most crucial steps in the tornado warning process is communication of the danger to the public." During the 1950s and 1960s, tornado warnings were disseminated to the public primarily by commercial television and radio stations. The TV and radio stations received these warnings from the USWB by telephone or teletype. Radio and television stations continue today as a primary source of warning information. The methods of television warning dissemination have advanced considerably in the past 20 years. Outdoor "air raid" sirens have been used for tornado warnings since about 1970. After the Super Outbreak of tornadoes in 1974, a large expansion of the National Oceanic and Atmospheric Administration's (NOAA) Weather Radio was ordered (NOAA 1999), allowing millions of Americans to receive tornado warnings in their homes directly from the National Weather Service (NWS), formerly the USWB.
Today, in addition to commercial broadcasting, NOAA Weather Radio (NWR), and outdoor sirens, other innovative methods of warning dissemination are being developed as technology advances. Warnings are delivered via the Internet to people's computers or mobile telephones. Since the NWS transitioned from county-based warnings to "storm based" warnings in 2007, where warnings are defined by latitude-longitude coordinates of a polygon (e.g., NWS 2010c), new GPS-based warning dissemination systems have appeared. These include sectorized tornado warning siren systems and automatic telephone-based warnings to homes for the areas actually in the warning area. The new warning system reduces "overwarning" by significant amounts in area and population.
Clearly, the efforts of the NWS, in coordination with emergency managers, broadcasters, and others, have been successful in saving many lives. Since organized tornado warning efforts began in the 1950s, tornado deaths per capita have decreased significantly (e.g., Brooks and Doswell 2002).
EARLY RESEARCH AND WARNING IDEAS. Research was performed during the 1880s by Sgt. John P. Finley, of the U.S. Signal Corps, on tornadoes and the conditions that accompanied them (e.g., Finley 1883; 1884b,a,c, 1886, 1888c,b,a; Galway 1985). Using his observations, Finley began to issue long-period, large-area "tornado alerts" (similar to today's tornado watches) (e.g., Bradford 1999; Schaefer 1986). Based on Finley's work, Edward S. Holden developed a plan for a short-term, local tornado warning system, consisting of telegraph wires around the southwest side of a town that would break in high winds. The broken telegraph circuit would alert the town by automatically triggering alarm bells and firing a cannon (Holden 1883; Bradford 1999; Coleman and Pence 2009). However, there was a general feeling that publicly issued tornado forecasts would induce panic and cause more harm than good; therefore, local tornado warnings were rejected by many scientists of the time (e.g., U.S. Army 1887; Hazen 1890; Abbe 1899a,b; Galway 1985). Therefore, the official forecasting of, or warning for, tornadoes ended in 1887 and was reaffirmed by the U.S. Weather Bureau, created in 1890, in regulations in 1905, 1915, and 1934 (Bradford 1999). The very use of the word tornado was banned in official releases (Galway 1985; Schaefer 1986). The USWB removed the ban on the word tornado in warnings, but not in forecasts, in 1938 (Bates 1962; Doswell et al. 1999). Therefore, despite some research on tornadoes during the first half of the twentieth century (e.g., Durand-Greville 1914; Varney 1926; Lloyd 1942; Showalter and Fulks 1943), tornado warnings were not issued for numerous significant tornadoes.
THE BEGINNINGS OF THE MODERN TORNADO WARNING SYSTEM. The primary event that forced the civilian USWB to change its position was the successful short-term forecast of a tornado at Tinker Air Force Base (AFB) in Oklahoma in 1948 by Major E. J. Fawbush and Captain R. C. Miller (Maddox and Crisp 1999; Doswell et al. 1993). A tornado had struck Tinker AFB on 20 March 1948 without warning, causing $10 million in damage (AMS 1948; Maddox and Crisp 1999). Fawbush and Miller, who had examined the weather conditions that produced the 20 March tornado, as well as recent research on tornadoes, issued a forecast for a tornado at Tinker AFB only five days later on 25 March 1948. The tornado forecast was issued at 1450 CST , and contained a warning for Tinker AFB for 1600-1800 CST, prompting a tornado plan, involving damage mitigation and personnel safety, to go into effect on the base (see Fig. 1). A tornado struck the base around 1800 CST, meaning that Fawbush and Miller's warning was verified, beginning the modern era of tornado warnings (R. C. Miller c.1977, unpublished manuscript; Newton et al. 1978; Maddox and Crisp 1999).
News of the successful tornado warning quickly spread, and the general public began to wonder why the government could not also provide them tornado warnings, especially since military tornado forecasts were sometimes "leaked to the public" (R. G. Beebe 1984, unpublished manuscript; Galway 1992), and J. R. Lloyd, meteorologist-in-charge of the Kansas City office of the USWB, reworded U. S. Air Force tornado forecasts and released them to the press (Galway 1992). In response, the U.S. Weather Bureau completely removed the ban on tornado forecasting in a memo from its chief on 12 July 1950 (see Fig. 2). An article was written in the Saturday Evening Post about Fawbush and Miller's success and its applications to public tornado warnings. It stated
The Fawbush-Miller system will not cut into the big business of selling storm cellars . . . But the Oklahoma farmer who said he always depended upon flying cornstalks and bed quilts to warn him of an approaching twister will now have ample time to walk-not run-to his "scarehole." (Saturday Evening Post, 28 July 1951).
It was also very fortuitous that two of the most important aspects of a tornado warning program- weather radar and storm spotter networks-were being developed around this time. Storm spotter networks were developed at least as early as 1942, by the USWB and the military (Doswell et al. 1999; Galway 1992; Bates 1962). The early spotter networks were primarily used to warn military bases of approaching tornadoes during and after World War II, but they were expanded for civilian protection in the 1950s, especially in Texas (Doswell et al. 1999). Radar was being converted from military to meteorological use in the late 1940s and the 1950s (e.g., Whiton et al. 1998; Bigler 1981), and it was shown in the early 1950s to be a tool for detecting tornadoes. A "hook echo" was photographed on the radar display at the Illinois State Water Survey on 9 April 1953 and was associated with a tornado (Whiton et al. 1998; Stout and Huff 1953). On 11 May 1953, a devastating tornado caused 110 fatalities in Waco, Texas (Winston 1953), and a 10-cm wavelength radar at Texas A&M University, being used to determine if radar data could be used in weather analysis, showed another hook-shaped echo associated with this storm (Kahan 1953; Whiton et al. 1998). These events, along with radar detection of another hook echo associated with a tornado near Worcester, Massachusetts, in 1953, showed that radar could be used to identify tornadoes or at least the storms that produce them (Whiton et al. 1998). Other authors performed studies on radar indications of possible tornadoes (e.g., Donaldson 1961). Also, the event in Waco showed that if communications had taken place between Texas A&M, the USWB, and the public, tornado warnings could have been issued and would have saved lives (Kahan 1953).
The result was a series of tornado warning conferences in Texas in 1953 and the development of the "Texas Radar Tornado Warning Network." The details of converting radars for use in detecting tornadoes were discussed. Communications between USWB offices and public officials were greatly enhanced. This allowed not only improved "ground truth" spotter information related to the weather associated with radar echoes to the USWB but also a more efficient method of dissemination of warning information from USWB to local officials (e.g., Whiton et al. 1998; AMS 1955; Kahan 1953). As stated in a NWS technical attachment on the Tornado warning conference, "it can be fairly said that those aspects of today's NWS severe weather operations are rooted in the June 1953 gathering" (NWS 2003).
Starting in 1952, the Severe Local Storms unit (SELS) of the USWB issued "tornado forecasts," which were large-area (up to 100,000 km2), longperiod (up to seven hours) forecasts indicating that the large-scale atmospheric conditions for tornadoes were present (Edwards and Ostby 2009). The name "tornado forecast" was officially changed to "tornado watch" in 1965 (e.g., NOAA 2005). The modern "tornado warning," designed for short periods and small areas (typically counties), was officially adopted by the USWB in 1965, in response to public confusion during the Palm Sunday tornado outbreak of 11 April 1965 (NOAA 2005), even though some USWB offices had issued tornado warnings at least as early as 1956. Today, a tornado warning is issued by the NWS when a tornado has been spotted or when a strong likelihood of a tornado is indicated by radar. It communicates "imminent danger, or the high probability of imminent danger" (AMS 1975). At least until the 1970s, there was also the use of a "tornado alert" by the USWB and then the NWS. There are conflicting reports as to the use of this message. Apparently, in some areas, the tornado alert was the most urgent form of issuance by the USWB until official tornado warnings began in 1965 (e.g., NOAA 2005). The use of tornado alerts continued, somewhat, for several years after 1965, likely as an intermediate bulletin with urgency between that of a watch and a warning.
COMMERCIAL RADIO AND TELEVISION . From NWS to broadcasters. Even the most accurate tornado warnings are of no real use if they are not disseminated to the people who are in danger. One of the most widely utilized, and longest running, methods of warning dissemination is through broadcast on commercial radio and television stations. For example, 85% of the survivors of the F5 tornado in Birmingham, Alabama, on 8 April 1998 stated that they were warned by television (Legates and Biddle 1999). From the 1950s through much of the 1960s, unofficial and official tornado warnings were disseminated from the USWB/NWS to local radio and television stations through local teletype circuits (see Figs. 3a,b,c), often also connected to some newspapers and civil defense offices. Telephone calls, through regular or "hotline" telephone lines, were also used (e.g., Mogil and Groper 1977). In some cases, local civil defense offices, upon receipt of the warning, would then pass it along to radio and television stations. From the late 1960s through the early 1970s, likely also in response to the 1965 Palm Sunday tornado outbreak, the National Weather Wire Service (NWWS), which was eventually renamed the NOAA Weather Wire Service, was developed and implemented across the United States (e.g., White 1972). This system provided teletype-based warning delivery to any radio station, television station, or other news outlet within the warning area of a NWS office. This system became well established in the 1970s and eventually transitioned from teletype communication to satellite communication. This occurred after the computer system Automation of Field Operations and Services (AFOS; see Fig. 3d) came online in National Weather Service offices in the early 1980s, allowing computer dissemination of tornado warnings (e.g., Johnson and Giraytys 1975; NWS 2009a). Warnings are distributed to broadcasters today through NWWS, the Emergency Managers Weather Information Network (EMWIN), and other sources and are issued via the modern NWS system Advanced Weather Interactive Processing System (AWIPS).
The Emergency Alert System (EAS), launched in 1997, is a national public warning system that requires broadcasters to provide a direct line of communication between the president of the United States and the American public during a national emergency. The system is also used more often by local authorities to disseminate weather information, including tornado warnings (FCC 2010). The FCC regulates local EAS plans to ensure that these plans conform to FCC rules (FCC 2010). While there is no specific federal law requiring local broadcasters to provide tornado warnings, the FCC requires a broadcaster to operate in the public interest, providing programming that is necessary or important to its local area. Therefore, most television and radio stations do provide severe weather information, to varying degrees, depending on the importance of severe weather in that station's geographic area.
Early cut-ins. Beginning in the 1950s, tornado alerts and warnings were broadcast, typically as cut-ins (interruption of normal programming for a short period, often 30-60 s), on commercial radio stations. Similar cut-ins began on commercial television stations in the 1950s and continued to be one of the primary methods of warning dissemination on television well into the 1990s. Many stations still use cut-ins.
These cut-ins were sometimes simply a full-screen graphic indicating that a tornado warning was in effect, with a broadcaster providing more specific information via audio only. The warning information was sometimes preceded by some sound that heightens the attention of viewers, such as a beeping sound or the Emergency Broadcast System (EBS) tone alert. Occasionally, full-screen tornado warnings were used to begin a more in-depth video cut-in.
In-depth video cut-ins began at least as early as 1964, when a tornado was captured by a camera at a television station in Wichita Falls, Texas, and broadcast live (Fig. 4). Typically, video cut-ins featured a broadcaster/meteorologist reading the tornado warning information received from the NWS, with some additional insight, and various visual aids. The most common of these visual aids, especially in the 1970s and later, was a weather radar display, either connected to a TV-station-owned radar or to a local NWS radar. (Interestingly, the station that broadcast the Wichita Falls, Texas, tornado of 1964 also owned and displayed a weather radar, showing the hook echo that is often observed with tornadoes.) Examples of these types of cut-ins are shown in Fig. 5. Other visual aids included maps showing the counties under tornado warnings, other weather maps, and video from the scenes of tornadoes or tornado damage when available. For example, during the late 1970s, WSFA-TV in Montgomery, Alabama, showed a map with light bulbs in each county in their viewing areas; a lighted bulb indicated a watch and a flashing bulb indicated a warning. Nationwide cable TV channel The Weather Channel also linked into NWWS and broadcast tornado warnings, in the form of cut-ins showing the NWS warning text on a red screen and starting with several distinctive beeps, in the local cable markets affected by the warning starting in the early 1980s (see Fig. 6).
Crawls and bugs. Around 1980, some television stations began using "crawls" and "bugs" to disseminate tornado warning information or updates without the necessity of interrupting programming or to supplement warning information between cut-ins. A crawl is simply a stream of text that moves from right to left, usually across the bottom of the television screen. The crawl may be superimposed over the program, or the program may be reduced to a smaller box and the crawl displayed below it (Fig. 7). A series of audio tones is often broadcast at the beginning of the crawl to heighten viewer attention.
The use of bugs by television stations became a popular method for informing viewers that a tornado watch or warning was in effect for some part of a station's viewing area and is still commonly used today. Bugs are typically placed over regular programming but only in one corner of the screen. Early bugs were simple slides, indicating the most urgent type of watch or warning in effect (with a tornado warning being the most urgent). Some contained the name or channel of the television station (Figs. 8a,b). Around 1991, bugs became much more sophisticated and were run by computers linked into NWWS. These new bugs showed a map of the television station's viewing area, along with a color legend, and highlighted counties in different colors to indicate which counties were under different types of watches and warnings (Fig. 8c). Eventually, some stations' bugs began to include radar images, either of the entire viewing area or even zoomed into each individual county.
Links between cable TV providers and EAS. As early as the 1980s, some cable television providers set aside a channel devoted to weather. These channels typically displayed the image from the closest NWS radar and audio from the local NOAA Weather Radio station (Fig. 9a). In some markets, local civil defense and/or emergency management officials were, and in some markets still are, given the ability in many areas to break in on the radar channel or on several or all channels to provide warning information (Fig. 9b). This information is sometimes provided by voice directly from someone at the local Emergency Management Agency (EMA) or through NOAA Weather Radio. Much of the system is now automated and is part of the EAS.
Wall-to-wall coverage. Since the 1990s, some television stations in markets with active severe weather began broadcasting continuous weather coverage during tornado warnings, eliminating all normal programming and advertisements, sometimes for periods of many hours. The coverage typically consists of one or more meteorologists discussing the specific areas in danger due to tornadoes, with information updated continuously. Broadcasters provide viewers with specific storm information using radar and storm reports. An early instance of the use of this technique occurred when a television station in Birmingham, Alabama, went to continuous or "wall to wall" severe weather coverage during the central Alabama tornado outbreak of 8 April 1998. That evening, an F5 tornado struck the western suburbs of Birmingham, causing 32 fatalities and 258 injuries (NCDC 1998). However, considering the path of the large tornado through some of the Birmingham metropolitan area, the number of fatalities may be considered low. A billboard was erected along a highway in the area after the event thanking the television meteorologist involved in the coverage.
This type of continuous coverage began to evolve further slightly more than one week later, as a tornado was shown live on television to viewers in Nashville, Tennessee, as a tornado hit the downtown area on 16 April 1998 (Fig. 10a). Similar coverage was provided on 3 May 1999, with wall-towall coverage of the F5 tornado just south of Oklahoma City, Oklahoma. Not only were meteorologists on the air covering the storm long before it entered the Oklahoma City metropolitan area, but they were able to show the viewers live video of the tornado on the ground from both mobile storm chasers and from a helicopter (Fig. 10b). This situation occurred again when an F4 tornado struck Tuscaloosa, Alabama, on 16 December 2000 (Fig. 10c), and another example occurred when a tornado struck Panama City Beach, Florida, on 15 September 2004 (Fig. 10d). By 2000, wall-to-wall coverage became common during tornado warnings in many television markets, especially in the plains and the southeastern United States. It should also be noted that many commercial radio stations also began to provide wall-to-wall coverage during tornado warnings.
There is some debate over television stations' policies regarding wall-to-wall weather coverage during tornado warnings. Some television viewers find the interruption of regularly scheduled programming to be problematic, especially when sporting events or other largely viewed shows are preempted. However, this type of coverage often brings more up-to-date storm location information than other dissemination methods. It also produces a visual component to the tornado warning that, along with the analysis provided by television meteorologists, may be more convincing to some people who may otherwise ignore tornado warnings (especially when the tornado is shown live on television). NWSChat, a new instant messaging system that allows broadcasters (and emergency managers) to communicate more directly with NWS forecasters, has made live coverage even more beneficial, as NWS warning decisions are sometimes announced before the warning is formally issued and the reasoning behind warning decisions is sometimes communicated. With the rapid proliferation of remote cameras ("towercams" and "webcams," among others) that are controlled by television stations and may be pointed in any direction, the number of tornadoes being shown live on television should continue to increase. Finally, since the switch from analog to digital television broadcasts nationwide in 2009, some television stations now broadcast continuous weather information during severe weather events only on their "secondary" channels. Some stations also use these extra channels to broadcast continuous weather information 24 hours per day.
NOAA WEATHER RADIO . Beginnings. The USWB began operating a very small number of radio stations in the early 1950s to provide weather information for aviation; two of these radio stations were LaGuardia Airport in New York and O'Hare Airport in Chicago. During the 1950s and 1960s, a small network of 50-60 radio stations was put in place, providing weather forecasts mainly for aviation and marine interests; however, some stations provided weather information for the general public (e.g., Coleman and Pence 2009; NWS 2005). The network grew to approximately 125 stations by 1974.
Widespread broadcasts and tone alerts. After the Super Outbreak of tornadoes across the central and eastern United States in April 1974, a survey indicated that the lack of warning dissemination was one of the problems in the outbreak (NOAA 2007). Congress then appropriated money to expand the network to cover 70% of the country's population with more than 300 weather radio stations (NOAA 1999). It was around this time that the network was named "NOAA Weather Radio." A 1975 White House policy statement declared NWR the official direct government source of information on weather hazards to the public (NOAA 2007). The weather broadcasts were 24 hours a day, 7 days a week, and originated from local National Weather Service offices. Most NWR stations, through the early 1990s, were programmed using a series of one-track tapes, or "carts," that played in a continuous loop (Fig. 11a). Forecasts were updated 4 times or more per day, while area weather observations were updated hourly and weather summaries and updates were updated as needed, depending on the weather conditions. During severe weather, normal programming was interrupted to provide watches and warnings. Typically, NWS offices broadcast on 2-4 NWR stations located in their warning area. The broadcasts could only be heard on special receivers, since they were broadcast at frequencies between 162.40 and 162.55 MHz, well above the upper end of most commercial FM radios (near 108 MHz).
One of the primary features of NOAA Weather Radio, since the 1960s, has always been the "alert" feature. When the NWS office issued a tornado warning, a 1,050-Hz tone, known as the "warning alarm tone" (WAT) was broadcast (NWS 1999), and specially equipped receivers would activate upon the broadcast of the tone when a tornado warning was issued, allowing the NWR receiver to alert or wake people even when the receiver was in standby mode, eliminating the need for a person to listen to the broadcast constantly during a period of severe weather. Some receivers would automatically turn the audio on, so people nearby would hear the NWR audio when the WAT was broadcast. Other receivers sounded a loud alarm or siren when the WAT was received, alerting people to turn on the NWR audio. This feature made NWR invaluable in disseminating warning information directly to the public. NWR was also designated for use in disseminating attack warnings in the event of a nuclear attack on the United States. NWR warnings were also rebroadcast over commercial radio and television broadcasts in some areas as part of the Emergency Broadcast System (e.g., NWS 1999); this practice continues today in some areas through the EAS.
The typical broadcast area for a single NWR transmitter that was part of the first 300-400 stations (comprising the post-1974 network) was more than 1,000 square miles, with some approaching 10,000 square miles. This often encompassed multiple counties, and since warnings were issued on a county basis, a single NWR receiver would be activated for warnings in counties that were sometimes 50 miles away. Therefore, only 10%-25% of the warning activations for a typical NWR receiver were even relevant to the county where the receiver was located. Therefore, some people thought that NWR's tone alert activated their receiver too often, waking them for distant warnings and prompting some to turn the NWR receivers off completely, especially at night, when NWR is perhaps most valuable in warning dissemination. This is a good example of the "cry wolf" syndrome, in this case involving perceived overwarning by the public.
SAME technology and expansion. In response to the "cry wolf " syndrome discussed above, the NWS began in 1985 to examine the use of a digital code at the beginning of each warning broadcast (NWS 1999). These codes would eventually become the Specific Area Message Encoding system that is still in use today. The codes contain the type of warning, its duration, and the county or counties the warning affects. These codes are added to the audio in tornado warnings, in addition to the original 1,050-Hz tone. This system was fully implemented in 1996 and was adopted as part of the new EAS that replaced the Emergency Broadcast System in 1997 (NWS 1999). Around the same time, the analog tape transmitter systems were being replaced by digital voice recording consoles (Fig. 11b). These consoles were updated to include buttons that allowed the broadcaster to select the warning type/county/duration for SAME encoding. The SAME information is contained in audio bursts that are played 3 times at the beginning of the warning. New SAME-equipped NOAA Weather Radio receivers (Fig. 12) became available and allowed people to program their receivers to only alert them for warnings affecting their counties. This greatly reduced the number of alerts for an individual receiver, making NWR more popular.
Just prior to SAME technology, NWR had begun another expansion in response to the Palm Sunday tornado outbreak in Alabama, Georgia, and the Carolinas on 27 March 1994. There were 42 fatalities in this outbreak (NWS 1994). Twenty of these fatalities occurred in a church near Piedmont, Alabama. Despite the issuance of an official tornado warning 11 min prior to the tornado and the sounding of the 1,050-Hz alarm tone and dissemination of the warning on NWR 13 min prior to the tornado, many did not receive the warning. A campaign was begun to expand the NWR network. Numerous, typically lower-power NWR transmitters were added, with the broadcast originating from local NWS offices and the funding for the transmitter provided jointly by NWS and local entities. As of April 2010, 1,012 NWR stations provide NWR coverage to about 97% of the U.S. population (NOAA 2010).
Beginning in the late 1990s, the digital voice recorders were replaced by computers that automatically receive warnings inside the NWS and broadcast those warnings, along with the necessary 1,050 Hz and SAME codes, on NWR (Fig. 11c). These computers were known as Console Replacement Systems (CRS). A computerized voice reads the warning information. This voice was also used for regular NWR programming and was initially of low quality, generating complaints from the public (e.g., NWS 2001b,a). The voice has been improved over the past few years. In addition, some broadcasters and private companies are disseminating warnings directly to individual users through e-mail, telephone, and social media, as an alternative to NOAA Weather Radio (see later in article).
OUTDOOR WARNING SIRENS . In response to the threat of an enemy attack on the United States with atomic bombs, President Harry S. Truman issued an executive order creating the Federal Civil Defense Administration (FCDA) in 1950, and Congress passed the Federal Civil Defense Act of 1950 (e.g., Green 2003; Delaney 2010). Part of this legislation provided federal support to states for defense equipment. The federal government required public warning systems, and large outdoor sirens could reach large numbers of people (VictorySiren Foundation 2003). Several significant natural disasters occurred during the administration of President Richard M. Nixon, including Hurricane Camille in 1969. This, in addition to political pressure to move away from large-scale civil defense against nuclear attack, prompted the government to allow the "dual use" of civil defense funds for natural disaster preparedness (USDHS 2006). This effectively paved the way for civil defense sirens to be used for tornado warnings.
The use of outdoor sirens for tornado warnings is documented as early as 1970 (Kessler 1970) and varied in use and method in different communities (e.g., AMS 1975). The NWS had direct access to civil defense sirens in limited areas in 1971 (Cressman 1971); however, the warnings were disseminated to local emergency management/ civil defense officials through teletype, telephone, and NOAA Weather Radio. A very effective means of communication of tornado warnings to local officials for dissemination and siren activation is the National Warning System (NAWAS), originally implemented in the 1950s for use during enemy attack. Today, NAWAS is a tiered national telephone system that connects federal officials, NWS offices, and many state and local warning points (FAS 1998; Mogil and Groper 1977).
Initially, a long single note, or tone alert, was emitted from these sirens to indicate tornado warnings, while an oscillating frequency, or "wail," was used to indicate enemy attack. Today, different sirens use various tones, alerts, and wails in the event of tornado warnings. Early sirens were mechanical; some were powered by automobile engines (Fig. 13a), while most were powered by electric motors (Fig. 13b). In both cases, air was blown through a horn to produce the siren's sound. Modern sirens are made up of speakers, similar to those in baseball parks (Fig. 13c). Early sirens were controlled remotely from civil defense or emergency management offices through analog telephone circuits (Fig. 13d) or at the site of the siren by a control panel (Fig. 13e). Sirens are now activated remotely by radio transmission from emergency management agencies or other local public service agencies (Fig. 13f). (It should be noted that outdoor siren policies vary considerably in some parts of the country. Some communities sound sirens for severe thunderstorm warnings in addition to tornado warnings, while others may only do so when a tornado has been confirmed by a spotter.)
A typical outdoor warning siren produces at least 70 dB (equivalent to normal radio volume) at 1-km range outdoors. Some are more powerful. Therefore, outdoor warning sirens are a unique part of the tornado warning dissemination process, since one siren may alert thousands of people, even if they are not watching or listening to any type of commercial broadcast. However, there are weaknesses in the outdoor tornado siren system. First, many communities, especially small towns and rural areas, do not have outdoor sirens. Second, there is variability in the sound level of a siren for any person. This may depend on a person's distance from the siren, whether he is indoors, weather conditions, and even whether the windows in a room face the direction of the siren location. Currently, a better option for in-home warning is NOAA Weather Radio.
STORM-BASED WARNINGS AND THE FUTURE OF WARNING DISSEMINATION. Based on research and testing, the NWS determined in 2007 that the tornado warning system could be improved (NWS 2007b). Beginning on 1 October 2007, the National Weather Service implemented "storm-based warnings," which replaced the decadesold tornado warnings that were based on geopolitical boundaries, typically counties (e.g., NWS 2008). The new warnings' areas are defined by polygons in the specific area of threat of a tornado, reducing the overall area warned (see example in Fig. 14). The polygon's area of coverage is disseminated in the warning by the latitude and longitude of its vertices.
According to a study by Sutter and Erickson (2010), the time spent under tornado warnings annually for people in the United States averaged 234 million person-hours from 1996 to 2004. Stormbased warnings would reduce that time significantly, at least to about 175 million person-hours. This would have the economic impact of saving between $500 million and $1.9 billion annually (Sutter and Erickson 2010).
The Common Alerting Protocol (CAP) is a nonproprietary data format for the dissemination of various types of warnings through various technologies (e.g., Churchill 2010; Jones and Botterell 2005). CAP was officially adopted by the Federal Emergency Management Agency (FEMA) on 30 September 2010 (FEMA 2010a). CAP will allow multiple agencies, such as NWS (tornadoes), the U.S. Geological Survey (earthquakes, tsunamis), and the Department of Homeland Security (enemy or terrorist attack) to disseminate warnings for various hazards, and these warnings will be decoded by many different receivers and programs (e.g., FEMA 2010b). CAP will streamline the process of warning the public of multiple hazards through multiple methods. CAP is backward compatible with the current SAME codes for NWR and the Emergency Alert System. In the near future, it is likely that NWR will continue to broadcast only county-specific warnings. However, NWR may eventually be able to broadcast the specific area of a tornado warning using CAP, along with NWR receivers with GPS capability or a user-entered ZIP code or address could then be activated more precisely using polygon warnings. CAP, along with the new NWS storm-based warnings, will also allow area-specific issuance of tornado warnings through many other devices, including digital television, traditional and cellular telephones, car radios and navigation systems, and electronic highway signs (Churchill 2010; Rhodes 2008). Technologies are also being developed and implemented that allow county EMA officials to either manually or automatically sound outdoor sirens only in the warned area, greatly reducing the number of siren activations.
However, many private entities have already begun to modernize the dissemination of warnings. Many local news media outlets, and other private companies, now disseminate tornado warnings through e-mail, cellular telephone, and social media (e.g., Facebook and Twitter). Some companies call people's homes when their home is within the polygon area of a tornado warning, based on home address.
Also, over the past decade, a higher-urgency type of tornado warning is being used by the NWS, known as a "tornado emergency." This wording was first used by the NWS office in Norman, Oklahoma, when a large tornado struck Moore, Oklahoma, on 3 May 1999. These tornado emergencies are typically issued by NWS as part of a severe weather statement that follows the tornado warning, but they may be included in the warning itself. According to NWS Instruction 10-511, "They are only issued when reliable sources confirm a tornado, or there is clear radar evidence of the existence of a damaging tornado such as the observation of debris" (NWS 2009b, 2010b,d).
SUMMARY AND CONCLUSIONS. Since the first successful tornado forecast at Tinker AFB in 1948, the development of tornado spotters in the 1940s, and the discovery that radar could detect tornadoes in the 1950s, the science of tornado warnings has developed rapidly. However, a tornado warning is not effective if it is not disseminated to the people in the tornado's path. The Texas tornado warning conferences in 1953 began to develop the framework for a modern tornado warning system, including the conversion of radars for use in tornado detection, and to improve communication between the USWB, spotters, and public officials.
Several methods of tornado warning dissemination have evolved over the past 50 years. Commercial radio and television continue to be one of the main sources of tornado warning information for the public. Early radio and television warnings were composed of cut-ins that interrupted regular programming occasionally to provide weather information. "Crawls" and "bugs" were developed in the 1970s and 1980s, to provide constant on-screen warning information without interrupting programming. Today, many radio and television stations, especially in the plains and southeastern U.S. states, use live wall-to-wall coverage during some or all tornado warnings affecting their viewing area, with meteorologists and journalists providing continuous weather updates using Doppler radar, spotter reports, and remote cameras.
After the Super Outbreak of tornadoes in April 1974, a small network of government-operated weather radio stations was greatly expanded to include 70% of the U.S. population. It was given the name "NOAA Weather Radio." Local NWS offices were able to broadcast weather information 24 hours per day, 7 days per week on NWR, and broadcast a tone alert during a tornado warning that would activate specially equipped receivers to alert people even when the radio broadcast was turned off, allowing for people to be alerted of severe weather without the need to listen to a broadcast continuously. This also provided the ability to wake people when storms approach. NWR was expanded again after the 1994 Palm Sunday tornado outbreak in Alabama, and 97% of the U.S. population is able to receive these broadcasts today. SAME technology allows receivers to be activated only when the warning affects the county a person is located in, and CRS has made the process of broadcasting tornado warnings on NWR automatic.
Outdoor warning sirens were placed in many parts of the country as part of civil defense activities because of the threat of enemy attack during the Cold War era. However, the sirens began to be used for tornado warnings also around 1970, and networks of outdoor tornado sirens are in place in large areas of the United States, especially where tornadoes are most common.
Tornado warnings have been technologically improved since 2007, when "storm based" warnings replaced county-based warnings. These warnings are issued only for the area in danger, and they may reduce the number of warned person-hours by 30%- 50%. Along with the implementation of the CAP by FEMA, tornado warnings will become more targeted to the area in the storm-based warning, through the use of GPS technology in cellular telephones and possibly NWR receivers, location information in digital television broadcasts and e-mails, and the sounding of outdoor sirens only in the warning area. This will represent the next advance in tornado warnings and their dissemination.
ACKNOWLEDGMENTS. Funding for this article was provided the National Oceanic and Atmospheric Administration (Grant NA07OAR4600493). The authors wish to thank Jay Shelley and Bob Deitlein (NWS, retired), George Wilcox, Ron Gird, and Wayne Hart (NOAA). We also thank the television stations, film production operations, and newspapers that produced some of the video, photographs, and screen captures in this paper, including Tinker AFB, The Calvin Company, the USDA, KXASTV, WAVE-TV, WAAY-TV, KAUZ-TV, WBRC-TV, The Weather Channel, WLKY-TV, WAVY-TV, WVTM-TV, KETV-TV, WSMV-TV, KWTV-TV, WBMA-TV, WJHGTV, John Baker, and the Civil Defense Museum. We also wish to thank YouTube and its subscribers for making much of the video available publicly online.
[Reference]
REFERENCES
Abbe, C., 1899a: The prediction of tornadoes and thunderstorms. Mon. Wea. Rev., 27, 159-60.
_____, 1899b: Unnecessary tornado alarms. Mon. Wea. Rev., 27, 255.
AMS, 1948: Severe local storms for March 1948. Mon. Wea. Rev., 76, 61-62.
_____, 1955: Texas radar tornado warning network. Bull. Amer. Meteor. Soc., 36, 234.
_____, 1975: Policy statement of the American Meteorological Society on tornado detection, tracking, and warning. Bull. Amer. Meteor. Soc., 56, 464-466.
Bates, F. C., 1962: Severe local storm forecasts and warnings and the general public. Bull. Amer. Meteor. Soc., 43, 288-291.
Bigler, S. G., 1981: Radar: A short history. Weatherwise, 34, 158-163.
Bradford, M., 1999: Historical roots of modern tornado forecasts and warnings. Wea. Forecasting, 14, 484-491.
_____, 2001: Scanning the Skies: A History of Tornado Forecasting. University of Oklahoma Press, 220 pp.
Brooks, H. E., and C. A. Doswell, 2002: Deaths in the 3 May 1999 Oklahoma City tornado from a historical perspective. Wea. Forecasting, 17, 354-361.
Churchill, S., cited 2010: Common alerting protocol. [Available online at www.dailywireless.org/2010/03/25/common-alerting-protocol.]
Coleman, T. A., and K. J. Pence, 2009: The proposed 1883 Holden tornado warning system: Its genius and its applications today. Bull. Amer. Meteor. Soc., 90, 1789-1796.
Cressman, G. P., 1971: Uses of public weather services. Bull. Amer. Meteor. Soc., 52, 544-546.
Delaney, D. G., cited, 2010: Major acts of Congress: Federal Civil Defense Act of 1950. [Available online at www.enotes.com/major-acts-congress/federalcivil-defense-act.]
Donaldson, R. J., 1961: Radar reflectivity profiles in thunderstorms. J. Meteor., 18, 292-305.
Doswell, C. A., III., S. J. Weiss, and R. H. Johns, 1993: Tornado forecasting: A review. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr., Vol. 79, Amer. Geophys. Union, 557-571.
_____, A. R. Moller, and H. E. Brooks, 1999: Storm spotting and public awareness since the first tornado forecasts of 1948. Wea. Forecasting, 14, 544-557.
Durand-Greville, E., 1914: Squalls and the prediction of tornadoes. Mon. Wea. Rev., 42, 97-99.
Edwards, R., cited 2009: The online tornado FAQ: Frequently asked questions about tornadoes. [Availableonline at www.spc.ncep.noaa.gov/faq/tornado.]
_____, and F. Ostby, cited 2009: Time line of SELS and SPC. [Available online at www.spc.noaa.gov/history/timeline.html.]
FAS, cited 1998: National Warning System (NAWAS). [Available online at www.fas.org/nuke/guide/usa/c3i/nawas.htm.]
FCC, cited 2010: Emergency alert system. [Available online at www.fcc.gov/pshs/services/eas.]
FEMA, cited 2010a: FEMA announces adoption of new standard for emergency alerts. [Available online at www.fema.gov/news/newsrelease.fema?id=52880.]
_____, cited 2010b: Standards: Common alerting protocol (EXDL-CAP). [Available online at www.fema.gov/about/programs/disastermanagement/standards/cap.shtm.]
Finley, J. P., 1883: The special characteristics of tornadoes, with practical directions for the protection of life and property. Signal Service Notes, U.S. Army Signal Corps 12, 19 pp.
_____, 1884a: Intelligence from American scientific stations. Science, 3, 767-68.
_____, 1884b: The character of six hundred tornadoes. Professional Papers of the Signal Service, U.S. War Department Paper 7, 28 pp.
_____, 1884c: Tornado predictions. Amer. Meteor. J., 1, 85-88.
_____, 1886: Tornado study-Its past, present, and future. J. Franklin Inst., 71, 241-62.
_____, 1888a: The relation of tornado regions to areas of low pressure. Amer. Meteor. J., 5, 83-87.
_____, 1888b: Tornadoes. Amer. Meteor. J., 5, 165-179.
_____, 1888c: Tornadoes: What They Are and How to Escape Them. J. H. Soul�, 90 pp.
Galway, J. G., 1985: J.P. Finley: The first severe storms forecaster. Bull. Amer. Meteor. Soc., 66, 1389-1395.
_____, 1992: Early severe thunderstorm forecasting and research by the United States Weather Bureau. Wea. Forecasting, 7, 564-587.
Green, W. G., III, cited 2003: Civil defense: The Truman administration. [Available online at https://facultystaff.richmond.edu/~wgreen/Ecdtruman.htm.]
Hazen, H. A., 1890: The Tornado, N. D. C. Hodges, 143 pp.
Holden, E. S., 1883: A system of local warnings against tornadoes. Science, 2, 521-522.
Johnson, R. E., and J. Giraytys, 1975: The AFOS experimental system. WMO Bull., 24, 86-92.
Jones, E., and A. Botterell, Eds., cited 2005: Common Alerting Protocol, v 1.1. [Available online at www.oasis-open.org/committees/download.php/15135/emergency-CAPv1.1-Corrected_DOM.pdf.]
Kahan, A. M., 1953: The first Texas tornado warning conference. Preprints, Conf. on Radio Meteorology, Austin, TX, Amer. Meteor. Soc., 4 pp.
Kessler, E., 1970: Tornadoes. Bull. Amer. Meteor. Soc., 51, 926-936.
Legates, D. R., and M. D. Biddle, cited 1999: Warning response and risk behavior in the Oak Grove- Birmingham, Alabama, tornado of 08 April 1998. Quick Response Rep. 116, Natural Hazards Center. [Available online at www.colorado.edu/hazards/research/qr/qr116/qr116.html.]
Lloyd, J. R., 1942: The development and trajectories of tornadoes. Mon. Wea. Rev., 70, 65-75.
Maddox, R. A., and C. A. Crisp, 1999: The Tinker AFB tornadoes of March 1948. Wea. Forecasting, 14, 492-499.
Mogil, H. M., and H. S. Groper, 1977: NWS's severe local storm warning and disaster preparedness programs. Bull. Amer. Meteor. Soc., 58, 318-324.
NCDC, 1998: Storm Data. Vol. 40. [Available from NCDC, 151 Patton Ave., Asheville, NC 28801-5001.]
Newton, C. W., R. C. Miller, E. R. Fosse, D. R. Booker, and P. McManamon, 1978: Severe thunderstorms: Their nature and their effects on society. Interdiscip. Sci. Rev., 3, 71-85.
NOAA, cited 1999: 1974 tornado outbreak showed need for NOAA Weather Radio. [Available online at www.publicaffairs.noaa.gov/storms/wxradio.html.]
_____, cited 2005: NOAA remembers the Midwest's deadly 1965 Palm Sunday tornado outbreak. [Available online at www.noaanews.noaa.gov/stories2005/s2418.htm.]
_____, cited 2007: Transforming the weather business. [Available online at http://celebrating200years.noaa.gov/transformations/weather.]
_____, cited 2010: NOAA Weather Radio all hazards (NWR). [Available online at www.nws.noaa.gov/nwr/resources/poster.pdf.]
NSSL, cited 1998: The first operational tornado forecast. [Available online at www.nssl.noaa.gov/goldenanniversary/millerposter.pdf.]
NWS, 1994: Natural disaster survey report: Southeastern United States Palm Sunday tornado outbreak of March 27, 1994, NOAA Rep., 75 pp.
_____, 1999: National Weather Service/NOAA Weather Radio transmitters: NWR Specific Area Message Encoding (NWR SAME). NOAA/NWR Memo. Update 4.43, 30 pp.
_____, 2001a: New and improved NOAA Weather Radio voice. Carolina Sky Watcher, No. 8, National Weather Service, Newport, NC, 3 pp.
_____, cited 2001b: No-uh weh-thurr rah-deo weel suhn sahhnd bet-her. [Available online at www.nws.noaa.gov/com/nwsfocus/fs031401.htm#Topic6.]
_____, cited 2002: NOAA Weather Radio. [Available online at www.srh.noaa.gov/bmx.]
_____, 2003: The first Texas tornado warning conference. NOAA Tech. Attachment SR-SSD 2003-10. [Available online at www.srh.noaa.gov/topics/attach/pdf/ssd03-10.pdf.]
_____, cited 2005: History of NOAA Weather Radio KWO-39 in Chicago. [Available online at www.crh.noaa.gov/lot/nwr/nwrhistory.php.]
_____, cited 2007a: History of federal weather services in central Illinois. [Available online at www.crh.noaa.gov/ilx/nwshist.php.]
_____, 2007b: Storm-based warnings: Team report. NWS Rep., 45 pp. [Available online at www.weather.gov/sbwarnings/docs/Polygon_Report_Final.pdf.]
_____, cited 2008: Why storm-based warnings. [Available online at www.weather.gov/sbwarnings.]
_____, cited 2009a: AWIPS: Advanced Weather Interactive Processing System. [Available online at www.erh.noaa.gov/okx/tour/awips.html.]
_____, cited 2009b: Service assessment: Super Tuesday tornado outbreak of February 5-6, 2008. NWS Rep., 48 pp. [Available online at www.nws.noaa.gov/os/assessments/pdfs/super_tuesday.pdf.]
_____, cited 2010a: NWS Huntsville history. [Available online at www.srh.noaa.gov/hun/?n=stationhistory.]
_____, cited 2010b: The voice of the National Weather Service. [Available online at www.erh.noaa.gov/pbz/onlinetour/nwr.htm.]
_____, 2010c: WFO severe weather products specification. NWS Instruction 10-511, 32 pp.
Rhodes, C. W., cited, 2008: Improving a digital EAS with the new ATSC signal. [Available online at www.tvtechnology.com/article/68320.]
Schaefer, J. T., 1986: Severe thunderstorm forecasting: A historical perspective. Wea. Forecasting, 1, 164-189.
Showalter, A. K., and J. R. Fulks, 1943: Preliminary report on tornadoes. U.S. Weather Bureau Rep., 162 pp.
Stout, G. E., and F. A. Huff, 1953: Radar records Illinois tornadogenesis. Bull. Amer. Meteor. Soc., 34, 281-284.
Sutter, D., and S. Erickson, 2010: The time cost of tornado warnings and the savings with storm-based warnings. Wea. Climate Soc., 2, 103-112.
U.S. Army, 1887: Report of the chief signal officer of the Army (RCSO). U.S. Army Rep., 41 pp.
USDHS, 2006: Civil defense and homeland security: A short history of national preparedness efforts. Homeland Security, National Preparedness Task Force Rep., 36 pp. [Available online at http://training.fema.gov/EMIWeb/edu/docs/DHS%20Civil%20Defense-HS%20-%20Short%20History.pdf.]
Varney, B. M., 1926: Aerological evidence as to the causes of tornadoes. Mon. Wea. Rev., 54, 163-165.
VictorySiren Foundation, cited 2003: Chrysler air raid siren-History. [Available online at www.antiqueweekend.com/x/hist/h-cars.htm.]
White, R. M., 1972: The National Hurricane Warning Program. Bull. Amer. Meteor. Soc., 53, 631-633.
Whiton, R. C., P. L. Smith, S. G. Bigler, K. E. Wilk, and A. C. Harbuck, 1998: History of operational use of weather radar by U.S. weather services. Part I: The pre-NEXRAD era. Wea. Forecasting, 13, 219-243.
Winston, J. S., 1953: The weather and circulation of May 1953. Mon. Wea. Rev., 81, 135-140.
[Author Affiliation]
Affiliations: Coleman and Knupp-Department of Atmospheric Science, University of Alabama in Huntsville, Huntsville, Alabama; Spann-WBMA Television (ABC 33/40), Birmingham, Alabama; Elli ott-The Weather Company, Birmingham, Alabama; and Peters*-National Weather Service, Birmingham, Alabama
* Retired
Corresponding Author: Tim Coleman, Department of Atmospheric Science, University of Alabama in Huntsville, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805
E-mail: coleman@nsstc.uah.edu
The abstract for this article can be found in this issue, following the table of contents.
DOI:10.1175/2010BAMS3062.1
In final form 19 October 2010
�2011 American Meteorological Society
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