Localized storms

The previous chapter was mainly concerned with the effects of strong winds generated by secondary features of general air circulation. These winds were associated with the development of low-pressure cells spanning areas of 10,000–100,000 km−2. While tropical cyclones and extra-tropical depressions produce some of the strongest winds and highest amounts of precipitation over the widest areas, they are by no means the only source of high winds or heavy precipitation. These values can be matched by thunderstorms, which cover no more than 500 km2 in area and rarely travel more than 100–200 km before dissipating. They can produce high-magnitude, short-period rainfalls leading to flash flooding. Thunderstorms are also associated with a wide range of climatic phenomena such as lightning, hail and tornadoes that bring death and destruction. Tornadoes generate the highest wind speeds and can produce localized wind damage just as severe as that produced by a tropical cyclone. This chapter will examine first the development and structure of thunderstorms resulting in lightning and hail. This is followed by a description of tornadoes and the major disasters associated with them. The chapter concludes with a discussion of warning and response to the tornado threat, an aspect that has been responsible for decreasing death tolls throughout the twentieth century.