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  3. Forecasting Methods There are several different methods that can be used to create a forecast. The method forecaster chooses

Forecasting Methods There are several different methods that can be used to create a forecast. The method forecaster chooses

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问题                         Forecasting Methods
    There are several different methods that can be used to create a forecast. The method forecaster chooses depends upon the experience of the forecaster, the amount of information available to the forecaster, the level of difficulty that the forecast situation presents, and the degree of accuracy or confidence needed in the forecast.
    The first of these methods is the persistence method; the simplest way of producing a forecast. The persistence method assumes that the conditions at the time of the forecast will not change. For example, if it is sunny and 87 degree today, the persistence method predicts that it will be sunny and 87 degree tomorrow. If two inches of rain fell today, the persistence method would predict two inches of rain for tomorrow. However, if weather conditions change significantly from day to day, the persistence method usually breaks down and is not the best forecasting method to use.
    The trends method involves determining the speed and direction of movement for fronts, high and low pressure centers, and areas of clouds and precipitation. Using this information, the forecaster can predict where he or she expects those features to be at some future time. For example, if a storm system is 1,000 miles west of your location and moving to the east at 250 miles per day, using the trends method you would predict it to arrive in your area in 4 days. The trends method works well when systems continue to move at the same speed in the same direction for a long period of time. If they slow down, speed up, change intensity, or change direction, the trends forecast will probably not work as well.
    The climatology method is another simple way of producing a forecast. This method involves averaging weather statistics accumulated over many years to make the forecast. For example, if you were using the climatology method to predict the weather for New York City on July 4th, you would go through all the weather data that has been recorded for every July 4th and take an average. The climatology method only works well when the weather pattern is similar to that expected for the chosen time of year. If the pattern is quite unusual for the given time of year, the climatology method will often fail.
    The analog method is a slightly more complicated method of producing a forecast. It involves examining today’s forecast scenario and remembering a day in the past when the weather scenario looked very similar(an analog). The forecaster would predict that the weather in this forecast will behave the same as it did in the past.
    The analog method is difficult to use because it is virtually impossible to find a predict analog. Various weather features rarely align themselves in the same locations they were in the previous time. Even small differences between the current time and the analog can lead to very different results.
The trends method works well when
选项 A、weather features are defined well enough.
B、predictions on precipitation are accurate.
C、weather features are constant for a long period of time.
D、the speed and direction of movement are predictable.
答案C
解析 根据第三段倒数第二句话“The trends method wi3rks well when systems continue to move atthe same speed in the same direction for a long period of time．”可知，当某一大气现象长时期以同一速度向同一方向运动时，趋势性方法很有效。
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