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What Is Weather?
You have seen weather every day of your life, but do you
know what it is? Weather is what the air is like at a certain
place and time. Clouds and precipitation are part of weather.
Precipitation is water that falls from clouds to Earth. Rain,
snow, sleet, and hail are precipitation. How hot or cold it
is and the speed and direction of the wind are also part of
weather. Air pressure and humidity are part of weather, too.
Humidity is the amount of water vapor in the air.
Georgia receives much
more rain than snow.
Both rain and snow are
precipitation.
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Climate is different from weather. Climate is the pattern
of weather an area goes through over a long time. It might
be raining in your town today, but that does not mean that
your town is in an area where it rains a lot. You would have
to look at a record of the weather in your area over many
years to find out the climate of your town.
Georgia’s climate is not too hot and not too cold. Georgia
has hot, sticky summers. Summer days often are in the
mid-80s. Winter days often are nearly 50 degrees. Georgia
gets 45 to 55 inches of rain every year. It almost never snows
in Georgia, except in the Blue Ridge Mountains, in the
northern part of the state.
MAIN IDEA AND DETAILS What is the difference
between weather and climate?
The hottest temperature ever recorded in
Georgia was 112 degrees Fahrenheit
(44.4 degrees Celsius). That high
temperature happened on August 20,
1983, in Greenville, Georgia.
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The Sun
It’s a beautiful day. You feel the sunlight warm your skin.
You know that the sun is causing the nice weather. But did
you know that the sun affects weather in many ways?
On most days, it is cool in the morning. It gets warmer in
the afternoon. It cools off again in the evening. This
happens because the air warms up as the sun rises and heats
it. The air cools off as the sun sets. This is called a daily
weather pattern.
The sun also drives seasonal weather patterns. Spring and
summer in the United States are warm because the
Northern Hemisphere receives more direct sunlight for more
hours. Fall and winter are cool because the Northern
Hemisphere receives less direct sunlight for fewer hours.
The sun heats Earth unevenly. Places closer to the equator
get more sunlight than places closer to the poles. So places
closer to the equator have warm climates. Places closer to
the poles have cold climates.
Georgia
Northern Hemisphere
B
Southern Hemisphere
The United States is in the
Northern Hemisphere, which has
warm springs and summers and
cool falls and winters.
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Wind is caused by the sun’s uneven heating of Earth’s air.
Air moves when it is heated unevenly. Wind causes
precipitation and other kinds of
weather to move, instead of
staying in one spot.
The Northern Hemisphere
gets more direct sunlight
in the spring and summer
CAUSE AND EFFECT Why
because of the way that
are afternoons warm and
Earth is tilted on its axis.
evenings cool?
The equator runs through
Brazil. Places closer to the
equator have a much warmer
climate than places that are
closer to the poles.
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The Water Cycle
Have you ever made ice cubes or watched them melt in
a glass? Have you ever wondered why puddles disappear?
Water can change from a solid to a liquid to a gas and back
again. It goes through all three forms as part of the water
cycle. The water cycle happens when water moves from
the surface of Earth to the air and back again. The water
cycle affects weather.
The sun drives the water cycle. When the sun warms
water on Earth’s surface, some of the water changes from a
liquid to a gas. This is called evaporation. The gas form of
water is called water vapor. You can’t see it, but it is there
just the same.
The water that you drank today might be
the same water that a dinosaur drank
millions of years ago! The same amount
of water has always existed on Earth. It
moves around because of the water cycle.
CONDENSATION
EVAPORATION
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Water vapor becomes part of the air. The air carries it
high above Earth, where the air is cooler. The water vapor
cools and condenses into a liquid. This is called
condensation. When water vapor cools, it condenses on
tiny pieces of dust in the air. The condensed water and dust
form clouds or fog. Fog is a cloud that forms near the
ground. As more water vapor condenses, the clouds grow
heavy with water. Then the water falls from the clouds as
precipitation.
Precipitation can be rain, which is a liquid, or snow,
sleet, or hail, which are solids. Some precipitation soaks
into the ground. Some flows along the ground until it joins
a body of water such as an ocean. From there, the cycle
repeats again.
MAIN IDEA AND DETAILS Name and describe the
three parts of the water cycle.
PRECIPITATION
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The Oceans
If you live near a coast, you might already know that
oceans affect weather and climate. Oceans heat up and cool
down much more slowly than land does. Oceans take in a
lot of heat from the sun during the summer. The air over
oceans then stays cooler than it would be if the water did
not absorb the heat. During the winter, oceans slowly
release that heat into the air above them. This keeps
temperatures on Earth from getting too hot or too cold.
The sun heats different parts of the oceans unevenly.
Uneven heating makes the air temperature above the ocean
uneven. Remember that uneven air temperature causes
wind. Water on the surface of the oceans is pushed forward
by winds. This makes currents. A current is a stream of
water that flows like a river through the ocean.
In the summer,
Georgia’s beaches are
cooler than they would
otherwise be because
of the cool air coming
from the ocean.
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Ocean currents affect weather all
over the world. The Gulf Stream
current brings warm temperatures
to Georgia and the eastern coast of
the U.S. It then flows on to Europe.
Because it is near the
Atlantic Ocean, Georgia’s
coastline has warmer
weather than other parts
of the state.
Currents carry warm water a
long way. Warm currents cause the
climate of some places to be
warmer than it would otherwise be.
Currents also carry cold water a long way. Cold currents
cause the climate of some places to be colder than it would
otherwise be.
The oceans also affect where it rains and how much it
rains. Warm water evaporates faster than cold water does.
So, where the ocean is warmer, clouds form and it rains.
CAUSE AND EFFECT What keeps temperature on Earth
from getting too hot or too cold?
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Air Masses
Earlier we talked about how the sun affects weather. You
now know that winds are caused by the sun’s uneven
heating of Earth’s air. Uneven heating causes air to move. It
moves in large air masses. An air mass is a large body of air
that all has the same temperature and humidity.
An air mass can be warm or cold, humid or dry. It
depends on whether the air mass forms over an ocean or
land. It also depends on whether the air mass forms near the
equator or near the poles. An air mass that forms over the
Atlantic Ocean near the equator will be humid and warm.
This diagram shows how
a cold air mass pushes a
warm air mass upward to
form a cold front.
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When an air mass over a place changes, the weather in
that place changes. The line where two air masses meet is
called a front. Most weather changes happen along fronts.
There are two kinds of fronts. A cold front forms where a
cold air mass moves under a warm air mass and pushes it
up. The warm air mass cools, and the water vapor inside it
condenses very quickly. This causes short periods of heavy
rain, thunderstorms, or snow.
A warm front forms where a warm air mass moves over a
cold air mass. The warm air slowly slides up and over the
cold air. Clouds form ahead of the front. This causes rain or
snow that usually lasts a long time.
MAIN IDEA AND DETAILS Describe the two kinds of
fronts and how they form.
Cold fronts often cause
thunderstorms. In 2005,
Georgia had 279
thunderstorms.
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Predicting Weather
You might have seen people talking about the weather
on a TV news show. Meteorology is the study of weather.
Meteorologists are scientists who study weather. They use
different tools to measure weather. This helps them figure
out what the weather will be in the coming days or weeks.
A thermometer measures the air temperature. If the air
temperature drops during the day or rises at night, that
signals the weather will change soon.
A barometer measures air pressure. If a barometer rises,
it means heavier air is moving in, which means less
humidity and a lower chance of rain. If a barometer falls,
it means more humidity and a higher chance of rain.
Meteorologists use barometers to
measure air pressure. Changing air
pressure means changing weather.
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Meteorologists are people who study
and predict the weather. This
meteorologist is explaining weather
patterns in the United States.
An anemometer measures wind speed. A wind vane
measures wind direction. Wind often brings changes in
weather. If it is winter and a wind starts blowing from the
north, you can predict that the weather will be colder soon.
A hygrometer measures humidity.
If humidity goes up, it might rain soon.
Much of Georgia has
A rain gauge measures how much rain
very humid summers,
falls. Rain gauges help meteorologists
so meteorologists
figure out how much rain usually falls in
there use hygrometers
a certain place. That helps them figure
a lot!
out the climate of the place.
MAIN IDEA AND DETAILS Why do scientists measure
weather?
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Weather Maps
Meteorologists use weather maps in their work. Weather
maps show what the weather is like in a place. They use
pictures to show the weather.
A sun picture means it is sunny. A picture of a cloud with
rain means that it is rainy. The picture for a warm front is a
red line with half circles on the side of the direction in
which the front is moving. A blue line with triangles shows
a cold front.
Meteorologists might write temperatures on a weather
map or show them with certain colors. They use an H to
show a place that has high air pressure. They use an L to
show a place that has low air pressure.
MAIN IDEA AND DETAILS How do meteorologists show
cold and warm fronts on a weather map?
This map of the United States shows
warm and cold fronts and areas of high
and low pressure.
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Summary
Weather is the state of the air at a certain place and time.
Climate is the kind of weather a place goes through over a
long time. Several things affect the weather. The sun drives
daily and seasonal weather patterns. It also heats Earth
unevenly. That causes warm and cold climates and wind.
The water cycle is also driven by the sun. It carries water
through evaporation, condensation, and precipitation. The
oceans heat and cool the land near them. Ocean currents
carry warm or cool water all over the world. This affects
climate. The oceans also affect where and how much it
rains. Air masses form fronts, which bring precipitation.
Meteorologists use tools to measure the weather. This
helps them figure out what the weather will be like in the
future. They use weather maps with pictures to show what
the weather is like in a place.
The sun affects
weather in many ways.
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Glossary
air mass (air mas) A large body of air all of which has similar
temperature and humidity (10, 11, 15)
anemometer (an•uh•MAHM•uht•er) An instrument for measuring
wind speed (13)
barometer (buh•RAHM•uht•er) An instrument for measuring air
pressure (12)
climate (KLY•muht) The pattern of weather an area experiences over a
long period of time (3, 5, 8, 9, 13, 15)
condensation (kahn•duhn•SAY•shuhn) The process by which a gas
changes into a liquid (7, 15)
current (KUR•uhnt) A stream of water that flows like a river through
the ocean (8, 9, 15)
evaporation (ee•vap•uh•RAY•shuhn) The process by which a liquid
changes into a gas (6, 7, 15)
front (FRUHNT) The border where two air masses meet (10, 11, 14, 15)
humidity (hyoo•MID•uh•tee) A measurement of the amount of water
in the air (2, 10, 12, 13)
hygrometer (hy•GRAHM•uht•er) An instrument for measuring
humidity (13)
meteorology (meet•ee•uh•RAHL•uh•jee) The study of weather (12)
precipitation (pree•sip•uh•TAY•shuhn) Water that falls from clouds to
Earth (2, 3, 5, 7, 15)
water cycle (WAW•ter SY•kuhl) The constant movement of water
from the surface of Earth to the air and back again (6, 7, 15)
water vapor (WAW•ter VAY•per) The gas form of water (2, 7, 11)
weather (WETH•er) The condition of the atmosphere at a certain
place and time (2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15)
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Think and Write
1. How does the water cycle work? Describe the three
parts of the cycle.
2. MAIN IDEA AND DETAILS How do oceans affect
the weather?
3. CAUSE AND EFFECT What might happen to
weather if there is rising humidity?
4. Narrative Writing Pretend that you are a
meteorologist. Write a story about how you use
weather tools to predict what the weather will be
like the next day in your town. Make sure to include
all the tools described on pages 12-13 of the Reader.
Hands-On Activity
Find a weather map online or in a newspaper or a
magazine. Do not look at the box that tells you what the
picture means. See if you can figure out which pictures,
numbers, letters, or colors show warm and cold fronts,
temperatures, precipitation, and high or low pressure areas.
School-Home Connection
Talk with family members about Georgia’s climate and what
the weather is usually like in your part of the state. Then
make a prediction about what the weather will be like this
fall, this winter, next spring, and next summer. Make sure to
include predictions about temperatures and precipitation.
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