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Unit: Weather
Pt. 3 – Water in the Atmosphere
4c. Examine weather forecasting and
describe how meteorologists use
atmospheric features and technology
to predict the weather. (DOK 2)
Introduction
• Key Concept: Water is always moving
between the atmosphere and Earth’s surface.
• The water cycle is the movement of water
between the atmosphere and Earth’s surface.
• Water vapor enters
the air through
evaporation.
• Evaporation is when
a liquid becomes a
gas. Liquid water
evaporates to
become water
vapor.
• The water cycle includes all forms of
precipitation, including rain and snow. Water
moves from the atmosphere to Earth’s surface
by precipitation.
Is the following sentence true or false?
1. Water moves between the atmosphere and
Earth’s surface through the water cycle.
2. Circle the letter of the way that water enters
the atmosphere.
a. evaporation
b. precipitation
c. condensation
Humidity
Key Concept: Relative humidity can be
measured with an instrument called a
psychrometer.
• Humidity is a measure
of how much water
vapor is in the air.
• Warm air can hold more
water vapor than cold
air.
• Relative humidity is a
percentage
measurement.
• Relative humidity is the
percentage of water
vapor in the air
compared to how much
humidity the air can
hold.
A psychrometer (sy KRAHM uh tur) is an
instrument that measures relative humidity.
A psychrometer has two thermometers. One
thermometer has a wet cloth covering it. You
can tell the relative humidity of the air by
comparing the temperatures on the two
thermometers.
Read each word in the box. In each sentence below, fill
in the correct word or words.
a. An instrument that measures relative humidity is
a(an) ___________________.
b. The percentage of water vapor in the air compared
to how much humidity the air can hold is
called ________________.
c. A measure of how much water vapor is in the
air is called _____________________.
Circle the letter of each sentence that is true
about a psychrometer.
a. A psychrometer has two thermometers.
b. One thermometer has a wet cloth covering
it.
c. You compare the two thermometers to find
out the relative humidity.
- Water in the Atmosphere
How Clouds Form
• Clouds form when warm, moist air rises and
cools. Water vapor condenses on tiny particles
to form liquid water or ice crystals.
• Condensation is when a gas becomes a liquid.
For example, water vapor condenses to form
liquid water.
• This happens in the atmosphere when clouds
form.
• There are two things needed for condensation
to occur in the atmosphere:
1. There must be cooling of the air.
2. There must be particles—tiny solids—in the
air.
Cold air holds less water vapor than warm air.
When air cools, water vapor condenses into
little drops of water or ice crystals. The
temperature at which this happens is
called the dew point.
• Tiny particles must be in the air for
condensation of water to take place. Water
needs something to condense onto.
The process in which a gas becomes a liquid is
called ________________.
condensation
evaporation
precipitation
sublimation
Circle the letter of each thing needed for
condensation to occur in the atmosphere.
a. There must be particles in the air.
b. There must be cooling of the air.
c. There must be precipitation in the air.
Is the following sentence true or false?
The temperature at which water vapor
condenses into little drops of water is called
the dew point.
- Water in the Atmosphere
Types of Clouds
• Scientists classify
clouds into three
main types based on
their shape: cirrus,
cumulus, and
stratus. Clouds are
further classified by
their altitude.
• Cirrus (SEER us) clouds
are the wispy clouds
that look like feathers
in the sky. Cirrus clouds
only form high in the
sky.
• Cumulus (KYOO myuh
lus) clouds look like
fluffy, rounded piles of
cotton. Cumulus clouds
can produce
thunderstorms.
Thunderstorm clouds
are called
cumulonimbus clouds.
• Stratus (STRAT us)
clouds are flat layers of
clouds.
• Stratus clouds usually
cover most of the sky.
Stratus clouds that
produce rain are called
nimbostratus clouds.
• Clouds that form near
the ground are called
fog.
• Fog often forms when
the ground cools at
night.
• Fog is common near
bodies of water, such as
a lake.
Draw a line from each type of cloud
to its description.
Type of Cloud
cirrus clouds
cumulus clouds
stratus clouds
fog
Description
a. flat layers of clouds
b. clouds that form at or
near the ground
c. clouds that look like
fluffy,
rounded piles of cotton
d. wispy clouds that look
like feathers in the sky
- Water in the Atmosphere
The water cycle is the movement of
water between the atmosphere and
Earth’s surface.
Water Cycle Activity
- Water in the Atmosphere
Determining Relative Humidity
• Relative humidity is affected by
temperature. Use the data table
to answer the following
questions. First, find the drybulb temperature in the left
column of the table. Then find
the difference between the wetand dry-bulb temperatures
across the top of the table. The
number in the table where these
two readings intersect indicates
the relative humidity in percent.
- Water in the Atmosphere
Determining Relative Humidity
• Interpreting Data:
– At noon, the reading on a
sling psychrometer are 18ºC
for the dry-bulb
thermometer and 14ºC for
the wet-bulb thermometer.
What is the relative
humidity?
– 64%
- Water in the Atmosphere
Determining Relative Humidity
• Interpreting Data:
– At 5 p.m., the psychrometer
is used again. The reading on
the dry-bulb thermometer is
12ºC and the reading on the
wet-bulb thermometer is
11ºC. Determine the new
relative humidity.
– 88%
- Water in the Atmosphere
Determining Relative Humidity
• Interpreting Data:
– How did the temperature
change between noon and
5 P.M.?
– It decreased from 18 degrees
to 12 degrees.
- Water in the Atmosphere
Determining Relative Humidity
• Interpreting Data:
– How did the relative
humidity change during the
course of the day?
– It increased.
- Water in the Atmosphere
Determining Relative Humidity
• Drawing Conclusions:
– How was the relative
humidity affected by air
temperature? Explain your
answer.
– For the same amount of
water in the air, as the
temperature decreases, the
relative humidity increases.
Warm air can hold more
moisture than cool air can.
- Water in the Atmosphere
Asking Questions
Question
How does the water cycle work?
Answer
Water evaporates from the surface,
condenses to form clouds, and falls to Earth
as rain or snow.
What is relative humidity?
The percentage of water vapor in the air
compared to the maximum amount air can
hold at that temperature
How do clouds form?
Water in the air condenses on tiny particles in
the air to form liquid water or crystals.
Can you determine weather conditions by
looking at clouds?
Yes; each type of cloud is associated with a
particular type of weather.