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Study Guide
Clouds and Precipitation
Some clouds look like puffs of smoke. Others look like big cotton balls.
However, clouds are really masses of tiny water droplets or ice
crystals. This water may fall to Earth as rain, snow, sleet or hail.
How Clouds Form
 Clouds form when water vapor in the air condenses.
 To condense means to change from a gas to a liquid, so when water vapor condenses, it
changes to liquid water.
Here’s what makes this happen.
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Clouds start with warm air near Earth’s surface and this warm air rises.
The warm air holds some water vapor.
As the air rises, it moves into a cooler part of the atmosphere.
The atmosphere is the blanket of gases that surrounds the Earth. Cool air cannot hold
as much water vapor as warm air. Some of the water vapor condenses around tiny dust
particles in the air. It forms tiny droplets of liquid water. If the air is very cold, the
water vapor forms ice crystals, or sometimes both.
 Cloud droplets form around tiny particles, such as specks of dust or soot. The droplets
cannot form without these particles. The particles are sometimes called cloud seeds.
Types of Clouds
There are many types of clouds. Each type is likely to bring different kind of weather. Weather is the
condition of the atmosphere at a certain time and place.
Stratus clouds
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Stratus clouds are low sheets of gray clouds.
They spread out and look like gray blanket covering the sky.
Some stratus clouds bring rain.
Cumulus clouds
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Usually puffy and white
You see them in nice weather
They are usually higher in the sky than stratus clouds.
They are often spread out, with big spaces of blue sky between them.
They can grow tall on a hot, sunny day.
Sometimes they are dark which bring rain, lightning and thunder.
Cirrus Clouds
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The highest clouds
They are wispy and look a little like feathers in the sky.
They form where the air is cold.
They are made up of ice crystals.
You see thin clouds in fair weather, but rainy weather often follows in a day or two.
At any time, clouds cover about one-half of Earth. Not all clouds are high in the sky. Fog is a cloud that is on or near the ground. If
you have been outside on a foggy day, you have been inside a cloud .
Precipitation
Precipitation is the water that falls from the atmosphere. The water can take the form of
rain, snow, sleet or hail.
Rain
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Falls in drops- cloud droplets are too tiny to fall to Earth.
For rain to fall, larger, heavier drops of water must form in clouds.
Some raindrops form when droplets bump into each other and stick together.
It takes millions of droplets to make one raindrop
Other raindrops come from ice crystals that form in cold clouds.
As the ice crystals grow, they become heavier and fall toward Earth. They melt into raindrops as they fall
through warmer parts of the atmosphere.
Snow
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Falls from cold clouds when ice crystals stay frozen as they fall.
The falling ice crystals stick together to form snowflakes of different sizes
Depending on the temperature, snow may be light and powdery or heavy and wet.
Sleet
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Frozen or partly frozen rain.
Forms when raindrops fall through very cold air near the ground.
Hail
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Precipitation in the form of balls or chunks of ice.
Dark cumulus clouds often produce hail
Hailstones start as tiny pellets of ice inside these clouds.
The ice pellets get caught in strong up and down movements of air called updrafts and downdrafts.
The pellets collect a new layer of ice each time they are bounced up and down.
In time, they get so heavy that the updrafts cannot hold them up.
Then the hailstones fall to the ground.
Most hailstones are small, but some are as big as softballs.
Discussion Question: What other form of precipitation is sleet
most like?
Lesson Review
1. Which of these must happen to form a cloud?
a. Water vapor condensing
b. Rain falling
c. Snow falling
d. Ice melting
2. What is fog?
a. Frozen precipitation
b. a cloud high in the sky.
c. A cloud on or near the ground
d. Rain
3. Which kind of cloud looks like feathers high in the sky?
a. Stratus
b. Cirrus
c. Cumulus
d. Fog
4. Which one forms when raindrops freeze?
a. Snow
b. Sleet
c. Hail
d. Dew
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Georgia CRCT Coach, GPS Edition, Science, Grade 4
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