What are thunderstorms, hurricanes and tornadoes?

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Lesson 29 What are thunderstorms, hurricanes and
tornadoes?
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A thunderstorm is a storm with thunder,
lightning, heavy rain, and strong winds.
Thunderstorms usually happen when a cold front
and warm front meet.
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They start when huge cumulus clouds form giant
storm clouds.
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Lightning is caused when giant storm clouds give
off electricity.
The electricity causes the air to warm and expand
quickly.
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Thunder is caused by the expanding and
contracting air.
Did you ever notice that you see lightning before
you hear thunder?
That is because light moves faster than sound.
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Sometimes, a very low pressure area forms over
the ocean near the equator.
A tropical air mass picks up a lot of moisture
from the warm waters.
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Such low pressure causes very strong winds and
heavy rain.
When such a powerful storm forms over an ocean,
it is called a hurricane.
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A hurricane moves in a wide circular path.
From an airplane, it looks like bands of spinning
clouds.
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The winds spiral toward the center of the storm,
which is called the eye of the storm.
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Does it surprise you that the eye of the storm is
calm and clear?
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Sometimes hurricanes reach land and cause much
destruction.
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Hurricane winds can reach close to 325 kilometers
per hour, or 200 mph.
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Their rains cause much flooding.
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In 1969, hurricane Camille killed almost 300
people in the southern United States. It caused
about half a billion dollars worth of damage.
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The most violent kind of storm is a tornado. It
looks like a dark, curving funnel reaching down
from a black cloud.
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It is a small storm and only lasts a short time,
but in its path it causes tremendous destruction.
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Its low pressure causes winds up to 800 km per
hour, or 500 miles per hour.
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It blows down buildings and trees.
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It tumbles automobiles and trucks.
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It can pick up trees and carry them hundreds of
feet.
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One of the worst tornados in history happened on
March 18, 1925. This twister was much larger
and faster than most.
It killed 689 people as it roared across parts of
Missouri, Illinois, and Indiana.
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