| 第四十三篇
Forecasting Methods
There are several different methods that can be used to create a forecast.The method a 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（可信度） needed in the forecast.
1.What factor is NOT mentioned in choosing a forecasting method?
A.Imagination of the forecaster
B.Necessary amount of information
C.Practical knowledge of the forecaster
D.Degree of difficulty involved in forecasting
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 rain fell today, the persistence method would predict two inches of rain for tomorrow.However, if weather conditions change significantly for day to day, the persistence method usually breaks down and is not the best forecasting method to use.
2.Persistence method will work well
A.if weather conditions change greatly from day to day.
B.if weather conditions do not change much.
C.on sunny days.
D.on rainy days.
The trends method involves determining the speed and direction of movement for fronts（锋）, high and low pressure center, and areas of clouds and precipitation（降水）.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（天气特征） 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 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 works as well.