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1. Introduction
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 2% 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 twentieth 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 that 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 Bulletin of the American Meteorological Society 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 United States totaled 130, including 42 in one central Florida outbreak and 34 in one tornado that struck Birmingham, Alabama. 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...