Weather Forecasting

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Printed: June 19, 2013

www.ck12.org Concept 1. Weather Forecasting

CONCEPT 1 Weather Forecasting

Lesson Objectives

• State how meteorologists predict the weather.• Outline how technology and computers are used to forecast the weather.• Describe what weather maps show.

Vocabulary

• anemometer• barometer• hygrometer• meteorologist• rain gauge• snow gauge• thermometer• weather balloon• weather map• weather satellite• weather station• wind vane

Introduction

Did you ever have a picnic ruined by a surprise rainstorm? People often complain when the weather forecast iswrong. But in fact, weather forecasts today are much more accurate than they were just 20 years ago. Scientists whostudy and forecast the weather are called meteorologists. How do they predict the weather?

Predicting the Weather

Weather is very difficult to predict. That’s because it’s very complex and many factors are involved. Slight changesin even one factor can cause a big change in the weather. Still, certain “rules of thumb” generally apply. These“rules” help meteorologists forecast the weather. For example, low pressure is likely to bring stormy weather. So ifa center of low pressure is moving your way, you can expect a storm.

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Technology and Computers

Predicting the weather requires a lot of weather data. Technology is used to gather the data and computers are usedto analyze the data. Using this information gives meteorologists the best chance of predicting the weather.

Weather Instruments

Weather instruments measure weather conditions. One of the most important conditions is air pressure, which ismeasured with a barometer. Figure 1.1 shows how a barometer works. There are also a number of other commonlyused weather instruments (see Figure 1.2):

• A thermometer measures temperature.• An anemometer measures wind speed.• A rain gauge measures the amount of rain.• A hygrometer measures humidity.• A wind vane shows wind direction.• A snow gauge measures the amount of snow.

FIGURE 1.1The greater the air pressure outside the tube, the higher the mercuryrises inside the tube. Mercury can rise in the tube because there’s noair pressing down on it.

Collecting Data

Weather instruments collect data from all over the world at thousands of weather stations. Many are on land butsome float in the oceans on buoys. You can see what a weather station looks like in Figure 1.3. There’s probably atleast one weather station near you.

Other weather devices are needed to collect weather data in the atmosphere. They include weather balloons,satellites, and radar. You can read about them in Figure 1.3.

Weather stations contain many instruments for measuring weather conditions. The weather balloon in Figure 1.3will rise into the atmosphere until it bursts. As it rises, it will gather weather data and send it to the surface. Many

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FIGURE 1.2Some of the most commonly usedweather instruments. (a) Thermome-ter: temperature, (b) Anemometer: windspeed, (c) Rain gauge: amount of rain,(d) Hygrometer: humidity, (e) Wind vane:wind direction, (f) Snow gauge: amount ofsnow.

FIGURE 1.3Weather stations collect data on land andsea. Weather balloons, satellites, andradar collect data in the atmosphere.

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weather satellites orbit Earth. They constantly collect and transmit weather data from high above the surface. Aradar device sends out radio waves in all directions. The waves bounce off water in the atmosphere and then return tothe sender. The radar data shows where precipitation is falling. It’s raining in the orange-shaded area shown above.

Using Computers

What do meteorologists do with all that weather data? They use it in weather models. The models analyze the dataand predict the weather. The models require computers. That’s because so many measurements and calculations areinvolved.

Weather Maps

You may have seen weather maps like the one in Figure 1.4. A weather map shows weather conditions for a certainarea. The map may show the actual weather on a given day or it may show the predicted weather for some time inthe future. Some weather maps show many weather conditions. Others show a single condition.

FIGURE 1.4This weather map shows air pressurecontours. Which state has the lowest airpressure shown on the map?

Air Pressure Maps

The weather map in Figure 1.4 shows air pressure. The lines on the map connect places that have the same airpressure. Air pressure is measured in a unit called the millibar. Isobars are the lines that connect the points withthe same air pressure. The map also shows low- and high-pressure centers and fronts. Find the cold front on themap. This cold front is likely to move toward the northeast over the next couple of days. How could you use thisinformation to predict what the weather will be on the East Coast?

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Other Weather Maps

Instead of air pressure, weather maps may show other weather conditions. For example, a temperature map mightshow the high and low temperatures of major cities. The map may have isotherms, lines that connect places with thesame temperature.

Lesson Summary

• Weather is very complex. This makes it hard to predict. Certain “rules” can help. For example, low pressurebrings stormy weather.

• Weather instruments measure weather factors. Weather stations collect data on Earth’s surface. Weatherballoons, satellites, and radar collect data in the atmosphere. Computer models analyze the data and helppredict the weather.

• A weather map shows the weather for a certain area. It can show actual or predicted weather. It may show asingle weather condition or more than one.

Lesson Review Questions

Recall

1. Why is weather difficult to predict?

2. List three weather instruments, and state what they measure.

3. What is the role of weather balloons and weather satellites?

4. What does a weather map show?

5. Define isobars and isotherms.

Apply Concepts

6. What concepts explain how a barometer works?

7. In the weather map in Figure 1.4, where is the weather most likely to be clear and dry? How do you know?

Think Critically

8. Explain how radar could be used to track an approaching thunderstorm.

Points to Consider

In this chapter you learned about weather. Weather is sometimes confused with climate. The two are related but notthe same.

• What is climate?• How does climate differ from weather?

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Opening image copyright Zastol‘skiy Victor Leonidovich, 2010. Used under license from Shutterstock.com.

References

1. CK-12. . CC-BY-NC-SA2. (a) Brainless Christian, (b) Pearson Scott Foresman, (c) Dirtfoto, (d) Bidgee, (e) Stephen Aaron Rees, (f)

CambridgeBayWeather. (a) http://www.shutterstock.com/results.mhtml#searchterm=48665401 (b) http://commons.wikimedia.org/wiki/File:Anemometer_(PSF).png (c) http://www.shutterstock.com/pic.mhtml?id=51447562 (d) http://commons.wikimedia.org/wiki/File:Rain_recorded_in_a_rain_gauge.jpg(e)http://www.shutterstock.com/pic.mhtml?id=24166237 (f) http://commons.wikimedia.org/wiki/File:Snow_guage_graduate.JPG. (a) Im-age Copyright Brainless Christian, 2010 Used under license from Shutterstock.com; (b) Public domain;(c) Image Copyright Dirtfoto, 2010 Used under license from Shutterstock.com; (d) CC-SA-2.5; (e) ImageCopyright Stephen Aaron Rees, 2010 Used under license from Shutterstock.com; (f) Public domain

3. . Weather station url:http://upload.wikimedia.org/wikipedia/commons/1/16/Weather_Station_USDA.jpg; weather balloon url: http://commons.wikimedia.org/wiki/File:Ballon_radiosonde_f.jpg; weather satelliteurl: http://en.wikipedia.org/wiki/File:GOES_8_Spac0255.jpg;weatherradar url: http://en.wikipedia.org/wiki/Image:Sturmfront_auf_Doppler-Radar-Schirm.jpg;. Weather station: public domain; weather balloon: public domain;weather satellite: public domain; weather radar: public domain

4. . http://www.dnr.sc.gov/climate/sco/Education/wxmap/wxmap.php. Public domain

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