Many of the most damaging types of weather begin quickly, strike suddenly, and disappear rapidly, destroying small areas while leaving neighboring areas untouched. Such event as a tornado(龙卷风) struck the northeastern part of Edmonton, Alberta, in July 1987. Total damages from the tornado went beyond $250 million, the highest ever for any Canadian storm.
Traditional 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 slight atmospheric changes that come before these storms. In most nations, for example, weather-balloon observations are taken just once every twelve hours at places separated by hundreds of miles. With such limited data, traditional forecasting models do a much better job predicting general weather conditions over large areas than they do forecasting specific local events.
Until recently, the observation intensive (十分细致) method needed for exact, very short-range forecasts, or “Nowcasts,” was not possible. The cost of equipping and operating many thousands of conventional weather stations was extremely high, and the difficulties concerned in rapidly collecting and processing the weather data from such a network were hard to overcome.
Fortunately, scientific and technological advances have overcome most of these problems. Radar(雷达) systems and satellites are all able to make detailed, nearly continuous observation over large areas at a lower cost. Communications satellites can send out data around the world cheaply and immediately, and modern computers can quickly collect and analyze this large amount of weather information.
Meteorologists(气象学者) and computer scientists now work together to design computer programs and video equipment able to change weather data into words and graphic displays(图解) that forecasters can understand easily and quickly. As meteorologists have begun using these new technologies in weather forecasting offices, nowcasting is becoming a reality.
Why can’t traditional computer models predict short-lived local storms?

A．The weather data people collect are often wrong.

B．Detailed weather data in some small areas are not available.

C．The computers are not advanced enough to predict them.

D．The computers are not used to forecast specific local events.

The word “Nowcast” in Paragraph 3 means       .

A．a network to collect storm data

B．a way of collecting weather data

C．a more advanced system of weather observation

D．a forecast which can predict weather in the small area

What can make “Nowcasts” a reality according to the passage?

A．Scientific and technological advances.	B．Advanced computer programs.
C．Computer scientists.	D．Meteorologists.

What does the passage mainly talk about?
A.The advantages of “Nowcatsts”.              
B.A tornado in Edmonton, A1bertA.
C.The difficulty in predicting tornado.
D.A great development in weather forecast.