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Chapter 3-Lesson 3
Transcript of Chapter 3-Lesson 3
The temperature is how hot or cold the air is. The amount of water vapor in the air is called humidity. High humidity can make the air feel wet and sticky. Wind is the movement of air. As you know, air pressure is the wight of air as it presses down on Earth.
Each weather condition can be measured using a different tool.
1. Label each weather instrument. Tell what each measures.
Wind and Air Masses
What Causes Weather?
Chapter 3-Lesson 3
Weather is all the conditions of the atmosphere at a certain time and place. These conditions include temperature, amount of water vapor in the air, wind, and air pressure.
Weather is the conditions of the atmosphere at a certain time and place.
A rain gauge collects and measures the amount of precipitation that has fallen in an area.
A thermometer measures the temperature of the air.
An anemometer measures the speed of the wind.
A barometer measures air pressure.
Wind is moving air. Air flows from places of high pressure to places of low pressure.
During the day, Earth's surfaces take in heat from the Sun. The land becomes warm quickly. It warms the air above it. As the air warms, it rises. This causes a spot of low pressure.
Oceans warm slowly. During the day, air above the ocean is not as warm as air over land. This cooler air does not rise. It stays close to earth's surface. This causes a spot of high pressure.
As the warm air above the land rises, the cooler air above the ocean moves in to take its place. This flow of air, or wind, is called a sea breeze.
2. Look at the diagram on page 74 in your book. Circle the place on the diagram where air pressure is high. Put a star at the place where air pressure is low.
Circle the correct answer in your book.
3. Wind is caused by air that is moving
A. from areas of high pressure to areas of low pressure.
B. from areas of low pressure to areas of high pressure.
C. from dry areas to wet areas.
D. from warm areas to cool areas.
Each place on Earth warms or cools the air above it. This creates an air mass. An
is a large body of air that has about the same temperature, air pressure, and moisture.
4. The air in an air mass has about the same
Two conditions are used to describe air masses--temperature and humidity. Air masses are either warm or cold, and they are either moist or dry. Air masses that form in warm places are usually warm. Air masses that form near cold places are cold. Air masses that form over oceans are moist. Those over land are usually dry.
Most changes in weather happen when one air mass moves into a place and pushes out another air mass.
5. Look at the diagram. Put an X over the air masses that would be cold. Circle the air masses that would be warm.
Air masses do not stay in one place. As they move, they bump into each other.
The place where two air masses meet is called a front.
A front moves across earth's surface as one air mass pushes against the other. The weather can change suddenly when a front moves across an area. Most storms and precipitation take place along fronts.
A cold front forms as a cold air mass meets a warm air mass. The cold air moves under the warm air, pushing it up. As the warm air rises, clouds form and precipitation occurs. Thunderstorms often happen along a cold front.
A cold front can cause a line of powerful thunderstorms that move across the United States.
6. Define Front.
the place where two air masses meet.
7. Complete the diagram to describe a cold front.
a. A cold air mass meets a
warm air mass
b. The cold air moves under the warm air, pushing it up.
c. As the warm air rises
A warm front forms as a warm air mass pushes into a cold air mass. The warm air slowly moves up over the cold air. Layers of gray clouds and steady precipitation are seen when a warm front moves into an area.
8. Complete the diagram to describe a warm front.
a. A warm air mass pushes into a
cold air mass
b. The warm air moves
up and over
the cold air.
c. Layers of
The same types of air masses usually form over North America each year. The air masses usually move in the same direction, too. This creates weather patterns that repeat with the seasons. For example, a cold air mass moves down from Canada. A warm air mass moves up from Mexico. These air masses sometimes push against each other. The cold front can cause violent thunderstorms and tornadoes.
Analyzing Weather Data
A meteorologist is a scientist who studies weather. Studying weather involves measuring conditions near Earth's surface and high in the atmosphere.
Meteorologists use these measurements to identify the kinds of air masses over an area. They also predict what kind of front will form and where that front will move. This is used to create a weather map. Weather maps are often used as part of a weather forecast. A forecast is a prediction of what the weather will be for a certain day, week, or longer period of time.
9. What is a weather forecast?
A weather forecast is a prediction of what the weather will be for a certain day, week, or longer period of time.
10. Study the weather map. Along what kind of front is rain falling?
Rain is falling along the cold front.
Severe weather includes hurricanes, tornadoes, and snowstorms. Hurricanes often cause floods and strong winds. Severe storms, including hurricanes and blizzards, can destroy homes and put people in harm's way.
Meteorologists study storms using tools that are in space and on the ground. Forecasters give weather warnings when severe weather is likely to move into an area. These warnings can save lives. They give people time to prepare for the storm. Warnings also give people time to leave an area that is in the path of severe weather.
A hurricane is huge swirling storm that forms over the ocean.
Scientists gather data about temperature, humidity, wind, and air pressure. They use this information to make predictions about weather. List three kinds of severe weather that meteorologists try to predict.
snowstorms or blizzards
Main Idea and Details
Scientists gather data about temperature, humidity, wind, and air pressure. They use this information to make predictions about weather.
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