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 confidence¹ 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 degrees today, the persistence method predicts that it will be sunny and 87 degrees tomorrow. If two inches of rain fell today, the persistence method would predict two inches of rain for tomorrow. However, if weather conditions change significantly² from day to day, the persistence method usually breaks down³ and is not the best forecasting method to use.

The trends method involves determining⁴ the speed and direction of movement for fronts⁵, high and low pressure centers, and areas of clouds and precipitation. Using this information, the forecaster can predict where he or she expects those features⁶ 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 systems⁷ 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 direction⁸, 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 analog⁹). 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 virtually¹⁰ impossible to find a predict analog. Various weather features rarely align themselves in the same locations as they were in the previous time¹¹. Even small differences between the current time and the analog can lead to very different results.

词汇:

forecaster /5fC:kB:stE/n.(天气)预报员    下:降水量 ;降雨量

climatology /klaimE5tClEdVi/n.气候学    

scenario /si5nB:riEu/n.某事物（件）的模式，状况

precipitation /pri7sipi5teiFEn/n.(雨、雪、冰雹等的 )降      

注释：  

1. the degree of accuracy or confidence: cnedifnoc指的是“置信度”，所以该词之前用 or说明与 the degree of accuracy有意义上的联系，不能解释为“信心”。

2. significantly:意为“ greatly, considerably”(显著地 )。

3. break down:意为“ fail”(出问题，出故障 )。

4. determining: determine (确定)的动名词形式，其后跟三个宾语 : the speed and direction of movement for front high and low pressure centers, and areas of clouds and precipitation.

5. front:铮(锋面:不同温度和密度的两大气团交界处 )，如: cold front冷锋 warm front热锋

6. features:指上句中 determining的三个宾语所涉及的内容。见注释 4。

7. system:意为“a group of naturally occurring phenomena”(一组自然现象 )。这里指风暴等自然现象。见前句 : … if a storm system is 1,000 miles west of …

8. If they slow down, speed up, change intensity, or change direction,…：如果他们减速，或加速，或强度发生变化，或方向改变……

9. analog:相似物

10. virtually:事实上

It will be impossible to make weather forecast using the analog method

A:when the current weather scenario differs from the analog B:when the current weather scenario is the same as the analog C:when the analog is over ten years old D:when the analog is a simple repetition of the current weather scenario

Now satellites are helping to forecast the weather. They are in space, and they can reach any part of the world. The satellites take pictures of the atmosphere, because this is where the weather form. They send these pictures to the weather stations. So meteorologists can see the weather of any part of the world. From the pictures, the scientists can often say how the weather will change.
Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteorologists compare them with earlier ones. Perhaps they may find that the clouds have changed during the last few hours. This may mean that the weather on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.
So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for three or five days. Soon, perhaps, they may be able to forecast the weather for a week or more ahead.

A:the weather satellites can do it easily B:clouds form there C:the weather forms there D:the pictures can forecast the weather

A special feature of the weather in England is that

A:you can experience four seasons every day throughout the year. B:it does not have four seasons as other countries do. C:winter there is the coldest in the world. D:you may experience different types of weather in a single day.

A Now satellites are helping to forecast the weather．They are in space，and they can reach any part of the world．The satellites take pictures of the atmosphere(大气)，because this is where the weather form．They send these pictures to the weather stations．So meteorologists(气象学家)can see the weather of any part of the world．From the pictures，the scientists can often say how the weather will change． Today，nearly five hundred weather stations in sixty countries receive satellite pictures．When they receive new pictures，the meteorologists compare them with earlier ones．Perhaps they may find that the clouds have changed during the last few hours．This may mean that the weather on the ground may soon change，too．In their next weather forecast，the meteorologists can say this． So the weather satellites are a great help to the meteorologists．Before satellites were invented，the scientists could forecast the weather for about 24 0r 48 hours．Now they can make good forecasts for three or five days．Soon，perhaps，they may be able to forecast the weather for a week or more ahead． Why do we use the weather satellites to take pictures of the atmosphereBecause ．

A:the weather satellites can do it easily B:clouds form there C:the weather forms there D:the pictures can forecast the weather

A Now satellites are helping to forecast the weather．They are in space，and they can reach any part of the world．The satellites take pictures of the atmosphere(大气)，because this is where the weather form．They send these pictures to the weather stations．So meteorologists(气象学家)can see the weather of any part of the world．From the pictures，the scientists can often say how the weather will change． Today，nearly five hundred weather stations in sixty countries receive satellite pictures．When they receive new pictures，the meteorologists compare them with earlier ones．Perhaps they may find that the clouds have changed during the last few hours．This may mean that the weather on the ground may soon change，too．In their next weather forecast，the meteorologists can say this． So the weather satellites are a great help to the meteorologists．Before satellites were invented，the scientists could forecast the weather for about 24 0r 48 hours．Now they can make good forecasts for three or five days．Soon，perhaps，they may be able to forecast the weather for a week or more ahead． Why do we use the weather satellites to take pictures of the atmosphereBecause ．

A:the weather satellites can do it easily B:clouds form there C:the weather forms there D:the pictures can forecast the weather

Now satellites are helping to forecast the weather. They are in space, and they can reach any part of the world. The satellites take pictures of the atmosphere, because this is where the weather form. They send these pictures to the weather stations. So meteorologists can see the weather of any part of the world. From the pictures, the scientists can often say how the weather will change.
Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteorologists compare them with earlier ones. Perhaps they may find that the clouds have changed during the last few hours. This may mean that the weather on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.
So the weather satellites are a great help to the meteorologists. Before satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for three or five days. Soon, perhaps, they may be able to forecast the weather for a week or more ahead.

A:the weather satellites can do it easily B:clouds form there C:the weather forms there D:the pictures can forecast the weather