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

11. various weather features rarely align themselves in the same locations as they were in the previous time:不同的天气特征很少同时出现在与前次出现时一样的地点。

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

Yellowstone National Park is at high altitude. Most of the park is above 7,500 feet (2,275 meters).
Yellowstone’s weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70F. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings, especially if you are camping or hiking. When you leave your campsite, please leave it prepared for possible thundershowers and wind.
A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy hike or boat trip can turn into a battle for survival.
Seasonal Weather Information
Spring
Cold and snow continue into May, although temperatures gradually climb Early in spring, daytime temperatures average in the 40F to 50F; by late May and June, they may reach the 60F and 70F. Nighttime lows fall below freezing.
Summer
Daytime temperatures are usually in the 70F, occasionally reaching the 80F in the lower elevations (高度). Nights are cool, temperatures may drop in the 40F and 30F—sometimes even the 20F. June can be cool and rainy; July and August tend to be somewhat drier, although afternoon thundershowers are common.
Fall
Weather can be pleasant, although temperatures average 10-20 degrees lower than summer readings. Nighttime lows can fall into the teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.
Winter
Temperatures often stay near zero throughout the day, occasionally reaching high in the 20F. Subzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200 -400 inches of snow have been recorded.
Which of the following best describes Yellowstone’s weather

A:Yellowstone’s weather is generally changeable and it snows most of the year. B:It’s neither too hot in summer nor too cold in winter. C:Weather in fall is pleasant and temperatures never fall below freezing. D:It’s pretty warm in the day and very cool at night throughout the year.

Yellowstone National Park is at high altitude. Most of the park is above 7,500 feet (2,275 meters).
Yellowstone’s weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70F. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings, especially if you are camping or hiking. When you leave your campsite, please leave it prepared for possible thundershowers and wind.
A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy hike or boat trip can turn into a battle for survival.
Seasonal Weather Information
Spring
Cold and snow continue into May, although temperatures gradually climb Early in spring, daytime temperatures average in the 40F to 50F; by late May and June, they may reach the60F and 70F. Nighttime lows fall below freezing.
Summer
Daytime temperatures are usually in the 70F, occasionally reaching the 80F in the lower elevations (高度). Nights are cool, temperatures may drop in the 40F and 30F—sometimes even the 20F. June can be cool and rainy; July and August tend to be somewhat drier, although afternoon thundershowers are common.
Fall
Weather can be pleasant, although temperatures average 10-20 degrees lower than summer readings. Nighttime lows can fall into the teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.
Winter
Temperatures often stay near zero throughout the day, occasionally reaching high in the20F. Subzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200-400 inches of snow have been recorded.
Which of the following best describes Yellowstone’s weather

A:Yellowstone’s weather is generally changeable and it snows most of the year. B:It’s neither too hot in summer nor too cold in winter. C:Weather in fall is pleasant and temperatures never fall below freezing. D:It’s pretty warm in the day and very cool at night throughout the year.

Passage Five
In England, people often talk about the weather because they can experience four seasons in one day. In the morning the weather is warm just like in spring. An hour later’ black clouds come and then it rains hard. The weather gets a little cold. In the late afternoon the sky will be sunny, the sun will begin to shine, and it will be summer at this time of a day.
In England, people can also have summer in winter, or have winter in summer. So in winter they can swim sometimes, and in summer sometimes they should take warm clothes.
When you go to England, you will see that some English people usually take an umbrella or a raincoat with them in the sunny morning, but you should not laugh at them.
If you don’t take an umbrella or a raincoat, you will regret later in the day.

Why do people in England often talk about the weather（）

A:Because they may have four seasons in one day. B:Because they often have very good weather. C:Because the weather is warm just like in spring. D:Because the sky is sunny all day.

Why do people in England often talk about the weather

A:Because they may have four seasons in one day. B:Because they often have very good weather. C:Because the weather is warm just like in spring. D:Because the sky is sunny all day.

Yellowstone National Park is at high altitude. Most of the park is above 7,500 feet (2,275 meters).
Yellowstone’s weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70F. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings, especially if you are camping or hiking. When you leave your campsite, please leave it prepared for possible thundershowers and wind.
A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy hike or boat trip can turn into a battle for survival.
Seasonal Weather Information
Spring
Cold and snow continue into May, although temperatures gradually climb Early in spring, daytime temperatures average in the 40F to 50F; by late May and June, they may reach the 60F and 70F. Nighttime lows fall below freezing.
Summer
Daytime temperatures are usually in the 70F, occasionally reaching the 80F in the lower elevations (高度). Nights are cool, temperatures may drop in the 40F and 30F—sometimes even the 20F. June can be cool and rainy; July and August tend to be somewhat drier, although afternoon thundershowers are common.
Fall
Weather can be pleasant, although temperatures average 10-20 degrees lower than summer readings. Nighttime lows can fall into the teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.
Winter
Temperatures often stay near zero throughout the day, occasionally reaching high in the 20F. Subzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200 -400 inches of snow have been recorded.
Which of the following best describes Yellowstone’s weather

A:Yellowstone’s weather is generally changeable and it snows most of the year. B:It’s neither too hot in summer nor too cold in winter. C:Weather in fall is pleasant and temperatures never fall below freezing. D:It’s pretty warm in the day and very cool at night throughout the year.

D 　　Yellowstone Weather 　　Yellowstone National Park is at high altitude(海拔). Most of the park is above 7,500 feet (2,275 meters). 　　Yellowstone’s weather is unpredictable. In summer, it may be warm and sunny with temperatures in the high 70s. At night in any given month, the temperature may drop close to freezing. So it is best to come prepared for cold evenings and mornings, especially if you are camping or hiking. When you leave your campsite, please leave it prepared for possible thundershowers and wind. 　　A sunny warm day may become fiercely stormy with wind, rain, sleet and sometimes snow. Without enough clothing, an easy hike or boat trip can turn into a battle for survival. 　　Seasonal Weather InformationSpring 　　Cold and snow continue into May, although temperatures gradually climb.Early in spring, daytime temperatures average in the 40s to 50s; by late May and June, they may reach the 60s and 70s. Nighttime lows fall below freezing. 　　Summer 　　Daytime temperatures are usually in the 70s, occasionally reaching the 80s in the lower elevations (高度). Nights are cool, temperatures may drop in the 40s and 30s-sometimes even the 20s. June can be cool and rainy; July and August tend to be somewhat drier, although afternoon thundershowers are common.Fall 　　Weather can be pleasant, although temperatures average 10-20 degrees lower than summer readings. Nighttime lows can fall into the teens and lower. Snowstorms increase in frequency as the weeks go by or towards the end of the fall season.Winter 　　Temperatures often stay near zero throughout the day, occasionally reaching high in the 20s. Suhzero nighttime lows are common. Annual snowfall averages nearly 150 inches in most of the park. At higher places, 200-400 inches of snow have been recorded. Which of the following best describes Yellowston’s weather

A:Yellowstone’s weather is generally changeable and it snows most of the year. B:It’s neither too hot in summer nor too cold in winter. C:Weather in fall is pleasant and temperatures never fall below freezing. D:It’s pretty warm in the day and very cool at night throughout the year.