Lesson 3
How Can You Track Severe Storms?
Fast Fact
The Big Ones In 2004, four hurricanes came ashore in Florida in less than six weeks. They
resulted in deaths, injuries, and property damage. Meteorologists track hurricanes and
predict their paths so they can warn people to evacuate or to prepare for these powerful
storms. In the Investigate, you will use data to plot the path of a hurricane.
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Investigate
Tracking Hurricanes
Materials
 hurricane tracking map
 history table for Hurricane Chase
 forecast/advisory for Hurricane Chase
 3 colored pencils
---see table
Procedure
1. On the hurricane tracking map, plot the path of Hurricane Chase, using the data from the
history table and the forecast/advisory. Use a regular pencil to draw a small circle on the
map for each location listed in the history table.
2. Your first circles should show Chase as a tropical depression. Fill in the tropical depression
circles with one color. When winds become stronger than 39 mi/hr, a tropical depression is
classified as a tropical storm and is given a name. Write Tropical Storm Chase under the
place where the tropical depression becomes a tropical storm. Fill in the tropical storm
circles with another color.
3. When winds become greater than 74 mi/hr, a tropical storm becomes a hurricane. Write
Hurricane Chase under the place where Chase reaches hurricane strength. Use your third
color to fill in the hurricane circles.
Draw Conclusions
1. Observe the track of the storm on the map. What is the general pattern of the storm's
direction and wind speed?
2. Inquiry Skill When and where do you predict the storm will hit land? Use the tracking map
and the latest data.
Investigate Further
Find out what happens when hurricanes cross islands in the Caribbean. Draw a
conclusion as to whether they will continue as hurricanes.
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VOCABULARY
thunderstorm p. 264
tornado p. 265
hurricane p. 266
blizzard p. 268
SCIENCE CONCEPTS
 how meteorologists study weather conditions
 how severe storms form
READING FOCUS SKILL
MAIN IDEA AND DETAILS Look for the details that describe each severe storm.
Weather Forecasts
Weather forecasts help people decide what to wear and how the weather will affect their plans.
A forecast is a prediction about the weather. Forecasts are accurate up to about three to
five days into the future.
Meteorologists are scientists who study weather conditions to provide forecasts.
Meteorologists use instruments developed to measure conditions in the atmosphere. You
already know that a thermometer measures temperatures. Meteorologists use barometers to
measure air pressure. They use anemometers to measure wind speed.
Meteorologists also use more complex equipment. Advances in technology have increased the
accuracy of forecasts. Weather
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balloons and weather satellites collect data high up in the troposphere. They provide
information on weather patterns and storms that can't be obtained at ground level.
Weather balloons and weather satellites carry instruments that record air pressure, temperature,
and humidity. Satellite images show how an area's weather is changing. The images, which
show clouds and storms, are sent to meteorological centers around the world. Doppler
radar uses radio waves to detect wind and the movements of rain, snow, and ice. It tracks
the movement of severe storms, such as tornadoes and hurricanes. The collected data is
analyzed by weather professionals, and updates are sent to local weather stations.
Meteorologists use weather data to make maps. A weather map is a map that shows recent
weather conditions across a large area. Symbols on the map indicate storms, regions of
high and low pressure, fronts, and other weather conditions. Meteorologists use weather
maps to make forecasts.
MAIN IDEA AND DETAILS What equipment is used to collect weather data beyond the
troposphere? What's the Weather?
Insta-Lab
What's the Weather?
Find a copy of yesterday's weather map in a local newspaper. Interpret the map. Compare the
three-day forecast with the weather that actually occurs in your area. Was the weather
forecast accurate? Why or why not?
Measuring Weather
---see pictures pgs. 262 & 263
Doppler Radar Tower
Doppler Radar Image
Anemometer
Weather Balloon
Weather Satellite
Barometer
English scientist Robert Hooke invented the anemometer in 1667.
In 1643, a student of the early Italian scientist Galileo invented the barometer.
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---see pictures
Thunderhead
A large mass of warm air moves up rapidly. Large amounts of water vapor condense to
form thick cumulonimbus clouds. Heavy rain falls, causing a downward movement of
air.
A Doppler radar image shows the size and location of a thunderstorm.
Thunderstorms and Tornadoes
At any time, about 2000 thunderstorms are occurring on Earth. A thunderstorm is a strong
storm with rain, lightning, and thunder.
A thunderstorm begins to form when warm, humid air moves upward rapidly. The sun heats a
place on Earth's surface, which, in turn, warms the air mass above it. Then a cold front may
push under the warm air mass, or wind may force it upward. The higher surrounding air is
colder than the rising air mass.
As the warm air cools, the water vapor in it condenses into water droplets, which form a
cumulonimbus cloud. Soon the water droplets become heavy enough to fall as rain. The
falling rain pulls in cool air with it. Winds blow both upward and downward in the cloud.
Negative electric charges build up in the bottom of the cloud. The charges travel through the air
in a lightning discharge. The air along the path of a lightning bolt is extremely hot. The
intense heat makes the air expand so fast that sound waves are produced. You hear the
sound as thunder. Most of the lightning occurs at the beginning and at the end of a
thunderstorm.
Most thunderstorms are over within an hour. The rain and cool air moving downward through
the clouds prevent more warm air from
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moving up into the cloud. Sometimes, however, the cool air rushing down to Earth's
surface pushes more warm air up, causing another cumulonimbus cloud to form.
Whenever forecasters detect a strong thunderstorm, they look for another severe weather event.
A tornado is a violently rotating column of air that extends downward from thunderclouds
and touches the ground. Tornadoes form in fewer than one percent of thunderstorms. A
tornado may also form from the severe thunderstorms spun off by a hurricane.
A tornado starts when winds spin a column of air that bulges from the bottom of a
cumulonimbus cloud. Strong updrafts, or rising air, are already present inside this bulge.
Next, warm, humid air is pulled into the often funnel-shaped column. The air spins so fast
that an area of very low pressure forms in the center. The swirling funnel starts to descend.
Because of the low pressure, nearby air on the ground rushes into the funnel. The air in the
funnel rotates upward around the center, joining the storm above.
The wind speed in a tornado can reach 400 km/hr (250 mi/hr) or more. The force of the
tornado's winds destroys houses, cars, and anything else in its path. The greatest danger is
flying debris, or wreckage.
These violent storms can last from a few minutes to a few hours. Their storm path is usually
quite narrow. They are more difficult to predict than other storms. However,
meteorologists can usually issue warnings that give people enough time to take cover.
MAIN IDEA AND DETAILS Why do most thunderstorms stop?
---see pictures
Compare the Doppler radar image of this tornado with the Doppler radar image of a
thunderstorm.
These photographs show how a tornado develops. The funnel cloud is called a tornado
when it touches the ground.
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Hurricanes
If you have seen pictures of hurricanes bending tall palm trees, then you have an idea of the
power of a hurricane. A hurricane is a large, rotating tropical storm system with wind
speeds of at least 119 km/hr (74 mi/hr).
A hurricane might start as a low-pressure area over the Atlantic Ocean off the coast of Africa.
The storm is first called a tropical depression, because the air pressure is low, or depressed.
As winds blow into the low-pressure area, Earth's rotation causes them to rotate, or spiral,
around that area.
If the winds reach a constant speed of 63 km/hr (39 mi/hr), the tropical depression is called a
tropical storm and given a name. About half of the tropical storms that form each year
develop into hurricanes.
The eye of a hurricane is a calm center. It is caused by dry, cool air pulled down from above.
Around the eye is the eye wall, the most intense part of the storm. The warm, wet air that
rushes to the center of a hurricane is pulled upward in the eye wall. As the air travels
upward, it causes low pressure at the surface. This pulls in more air. The water vapor that
is being pulled upward condenses into rain, releasing heat that strengthens the storm. Heat
and moisture from below increase the energy of both the upward- moving and the
downward-moving air.
Pushed ahead of the storm, the ocean's surface can rise up to 10 m (33 ft) high. These rises are
called storm surges. They can be as wide as 80 to 161 km (50 to 100 mi). Storm surges can
smash into the coast, causing great
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harm to people and property. Other hurricane dangers include high winds, flooding, and
tornadoes.
Large amounts of warm, humid air keep hurricanes in motion. A typical hurricane may be as
large as 483 km (300 mi) across. It can travel for thousands of kilometers and last for more
than a week. In time it will reach cooler seas or move across land. Because the air is cooler
and less humid there, the hurricane will at last die out.
Hurricane is the name given to a tropical cyclone in the North Atlantic Ocean, the North
Pacific Ocean (east of the international date line), and the South Pacific Ocean (east of
160°E). In the Northwest Pacific Ocean (west of the date line), a tropical cyclone is called
a typhoon. When you hear or read about a typhoon hitting Japan or Bangladesh, you will
know that it is the same kind of storm we call a hurricane in the United States.
Because meteorologists can track hurricanes from the time they form, people who may be in
the storm's path can be given plenty of warning. People living near the coasts may have to
evacuate their homes until the hurricane danger has passed. People must leave mobile
homes and manufactured housing, which can be severely damaged. Hurricane shelters are
opened for those who have no safe place in which to wait out the storm.
MAIN IDEA AND DETAILS What are three ways hurricanes cause damage?
---see pictures pgs. 266 & 267
Warm, wet air is pulled into the base and the sides of a hurricane.
The spiral is made up of cumulus clouds that can tower 12 km (7 mi) into the atmosphere.
In the hurricane's center, known as the eye, the winds are quiet and no rain falls.
The hurricane is pushed by winds at 15 to 40 km/hr (9 to 25 mi/hr).
The hurricane's fastest winds rotate around the eye in the eye wall.
This satellite photograph taken above the Gulf Coast shows how large a hurricane can
become.
Compare this Doppler radar image of a hurricane to the images of the thunderstorm and
the tornado.
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Other Natural Disasters
A winter storm with strong winds and large amounts of heavy, blowing snow is a blizzard.
Visibility, or the ability to see, is very low—usually less than 1/4 mile and often nearly
zero. During a blizzard, it is best to stay indoors. The cold temperatures can cause many
health problems. Frostbite is injury to the skin from freezing. Hypothermia is a condition
in which the body temperature falls dangerously low.
A drought is an extended period of time with very little rainfall. Crops and other vegetation can
die, and wildfires become more frequent during a drought. Water conservation is
particularly important in times of drought. Regulations are established to limit the use of
water. For example, you may not be allowed to water the lawn or wash the car when water
supplies are low.
Unlike a drought, a flood occurs when a body of water overflows onto land that is usually dry.
Floods happen when there has been too much rain or when snow melts quickly in the
spring. The moving water in a flooded river or stream is very dangerous. You should never
enter flood waters. People who live near rivers and streams may be evacuated to a shelter
during a flood.
MAIN IDEA AND DETAILS How do people respond to droughts and floods?
The blizzard record for amount of snow is held by Mount Shasta, California. In 1959 a
blizzard dropped more than 480 cm (189 in.) of snow there.
Severe blizzards have winds of at least 72 km/hr (45 mi/hr). They also have temperatures
of less than -12°C (I0°F).
This town has been flooded due to excess rain.
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Reading Review
1. MAIN IDEA AND DETAILS Copy and complete this graphic organizer.
---see organizer
2. SUMMARIZE Use the graphic organizer to write a summary that describes severe storms.
3. DRAW CONCLUSIONS Why is a mobile home an unsafe place to be during a tornado?
4. VOCABULARY Use forecast and weather map in a sentence that explains both.
Test Prep
5. Critical Thinking How have Doppler radar and satellites increased the accuracy of weather
forecasts?
6. Where do hurricanes form?
A. on shore
B. over land
C. over oceans
D. in the stratosphere
Writing
Expository Writing
Find out about waterspouts. Write and illustrate a short magazine article about them. Explain
what waterspouts are, tell how they form, and describe their effects.
Math
Use Decimals
Sound travels more slowly than light. If you see lightning and hear the thunder 5 seconds later,
the flash was about 1.6 km away. If you see a lightning flash and hear thunder 12 seconds
later, how far away is the storm? Show the formula you used.
Health
Storm Safety Steps
Research steps people can take to protect themselves in severe storms. Make a pamphlet of tips
for each type of storm, illustrate it, and share it with your family.
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