Many of the most damaging and life threatening types of
weather--torrential rains, severe thunderstorms, and tornadoes--begin quickly,
strike suddenly, and disappear rapidly, destroying small regions while leaving
neighboring areas untouched. Such event as 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
study carefully the subtle atmospheric changes that come before 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 large 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 extremely high, and the
difficulties involved in rapidly collecting and processing the raw weather data
from such a network were hard to overcome. 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 modem computers can quickly compile and analyze this large
volume of weather reformation. Meteorologists (气象学者) 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. According to the passage, what makes "Nowcasting" a reality