04 Extreme Weather

Severe storms happen in low-pressure weather systems. Warm, wet air begins rising. The higher it rises, the cooler it becomes. Water vapour in the air forms drops in a process called condensation. The drops join together to form clouds. Precipitation in the form of rain, snow, sleet, or hail falls down to Earth's surface.

Thunderstorms are the most common kind of extreme weather. Before a thunderstorm can happen, three conditions must be present. First of all, moisture must be present in the air. Next, there has to be an approaching cold front. Finally, the warm air that rises must stay warm enough to be warmer than the air it passes through. When all these conditions are present, the moisture in the air condenses. Clouds form, and a storm begins.

A cold front happens when cold air is moving near the surface of Earth, and it pushes warm air up very quickly. This is often the beginning of a thunderstorm. Clouds form, and heavy rains begin falling. Thunderstorms often bring disasters with them. This can be in the form of floods, fires caused by lightning, damage from hailstones or strong winds, and even tornadoes. A tornado is a spinning mass of air over land that can destroy almost everything in its path.

A blizzard is a combination of strong winds and extremely low temperatures. Snowfall increases until it is very diffi cult or impossible to see. People can become lost in the snow and freeze to death.

A hurricane is the most powerful kind of storm on Earth. It forms over warm ocean waters off the coast of the tropics, becoming a giant mixture of swirling air and water. Wind speeds can average 1 10 kilometres per hour. Hurricanes do the most damage to coastal cities because they very quickly lose strength as they move over land. Hurricanes are so large and powerful that their swirling clouds can be seen from space!

Word List

hail : balls of ice

extreme : strong and dangerous

swirling : moving very quickly in circles

You Practice

I. Answer the following questions.

1) What happens in low pressure weather systems?

2) How do thunderstorms happen?

3) Why are blizzards dangerous?

4) What is the most dangerous form of extreme weather? Why?

5) What are some different kinds of precipitation?

II. Word power—Use these words from the reading in sentences of your own.

1) extreme ______________________________________________

2) surface _______________________________________________

3) blizzard ______________________________________________

4) swirling ______________________________________________

5) coastal _______________________________________________

III. Read these sentences carefully. Write Yes or No for each one.

____ 1) Blizzards are the most common forms of extreme weather.

____ 2) Hurricanes have very heavy winds.

____ 3) Thunderstorms can cause fires

____ 4) All storms can be seen from space.

____ 5) Five different conditions must be present for a thunderstorm to happen.