| Many of the most damaging and
life-threatening types of weather--torrential rains, severe thunderstorms, and
tornadoes--begin quickly, strike suddenly, and dissipate rapidly, devastating
small regions while leaving neighboring areas untouched. One such event, a
tornado, struck the northeastern section of Edmonton, Alberta, in July 1987.
Total damages from the tornado exceeded ＄ 250 million, the highest ever for any
Canadian storm. Conventional computer models of the atmosphere have limited
value in predicting short-lived local storms like the Edmonton tornado, because
the available weather data are generally not detailed enough to allow computers
to discern the subtle atmospheric changes that precede these storms. In most
nations, for example, weather-balloon observations are taken just once every
twelve hours at locations typically separated by hundreds of miles. With such
limited data, conventional forecasting models do a much better job predicting
general weather conditions over larger regions than they do forecasting specific
local events. Until recently, the observation--intensive approach needed for accurate, very short-range forecasts, or "Nowcasts", was not feasible. The cost of equipping and operating many thousands of conventional weather stations was prohibitively high, and the difficulties involved in rapidly collecting and processing the raw weather data from such a network were insurmountable. Fortunately, scientific and technological advances have overcome most of these problems. Radar systems, automated weather instruments, and satellites are all capable of making detailed, nearly continuous observation over large regions at a relatively low cost. Communications satellites can transmit data around the world cheaply and instantaneously, and modern computers can quickly compile and analyzing this large volume of weather information. Meteorologists and computer scientists now work together to design computer programs and video equipment capable of transforming raw weather data into words, symbols, and vivid graphic displays that forecasters can interpret easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, Nowcasting is becoming a reality. |