1. Science ~ chapter 8 weather
Miss Nelson

2. Water in the Atmosphere
Section 1
Water in the Atmosphere

3. Anticipatory set
What happens to the mirror in your bathroom when you take a hot shower?

4. Anticipatory set
What happens to the mirror in your bathroom when you take a hot shower? Warm, moist air from the shower comes in contact with cool surface of the mirror. The air cools and can hold less water vapor. As a result, water vapor condenses on the mirror. Clouds form in the same way!

5. standards
S 6.4.e – Students know differences in pressure, heat, air movement, and humidity result in change in weather

6. The big idea
What is humidity and how is it measured? How do clouds form? What are the three main types of clouds?

7. Key terms
Water cycle – the continual movement of water among Earth’s atmosphere, oceans, and land through evaporation, condensation, and precipitation
Evaporation – the process by which water molecules in liquid water escape into the air as water vapor
Humidity – the amount of water vapor in a given volume of air
Relative humidity - the percentage of water vapor in the air compressed to the maximum amount of water vapor that air can contain at a given temperature
Psychrometer – an instrument used to measure relative humidity, consisting of a wet-bulb thermometer and a dry-bulb thermometer

8. Key terms
Condensation – the process by which molecules of water vapor in the air become liquid water
Dew point – the temperature at which condensation begins
Cirrus – wispy, feathery clouds made mostly of ice crystals that form at high levels
Cumulus – fluffy, white clouds, usually with flat bottoms that look like rounded piles of cotton
Stratus – clouds that form in flat layers and often cover much of the sky

9. The Water cycle
View the diagram on page 301 of your textbook Read Water in the Atmosphere on page 300 of your textbook

10. humidity
Humidity is a measure of the amount of water vapor in the air Air’s ability to hold water vapor depends on its temperature Warm air = more water vapor than cool air

11. Relative humidity
Weather reports usually refer to the water vapor in the air as relative humidity
Relative humidity is the percentage of water vapor that is actually in the air compared to the maximum amount of water vapor the air can hold at a particular temperature
Air with a relative humidity of 100 percent is said to be saturated

12. Measuring relative humidity
Relative humidity can be measured with an instrument called a psychrometer

13. Read Humidity on pages 301-302 of your textbook

14. How clouds form
Clouds form when water vapor in the air condenses to form liquid water or ice crystals Process is called condensation

15. How clouds form
Two conditions are required for condensation:
Cooling of the air
Presence of particles in the air

16. The role of cooling
As air cools, the amount of water vapor it can hold decreases
The water vapor condenses into tiny droplets of water or ice crystals
The temperature at which condensation begins is called the dew point
Dew point above freezing = water droplets
Dew point below freezing = ice crystals

17. The role of particles
For water vapor to condense, tiny particles must be present
The water vapor needs a surface on which to condense
In cloud formation, most of these particles are:
Salt crystals
Dust from soil
Smoke

18. Scientists classify clouds into three main types based on their shape:
Types of clouds
Scientists classify clouds into three main types based on their shape:
Cirrus
Cumulus
Status
Clouds are further classified by their altitude

19. Cirrus clouds Wispy, feathery clouds
Comes from the word meaning “a curl of hair”
Form only at high levels where temperatures are very low
As a result, are made of ice crystals
Have feathery “hooked” ends
Look like the scales of a fish

20. Cumulus clouds Look like fluffy, rounded piles of cotton
Word means “heap” or “mass” in Latin
Usually indicate fair weather
When you add the suffix –nimbus, which means “rain,” you get clouds that produce thunderstorms

21. Stratus clouds Form in flat layers Strato means “spread out”
Usually cover most of the sky
Are a uniform, dull, gray color
As they thicken they produce
rain or snow
Called nimbostratus clouds

22. Altocumulus and altostratus
Part of a cloud’s name may be based on its height
Clouds that form between 2-6 kilometers above the surface have the prefix alto- (means high)
Altocumulus and altostratus are the two main types of these clouds

23. fog
Clouds that form near the ground are called fog
Often forms when the ground cools at night after a warm, humid day
More common near bodies of water or low-lying marshy areas

24. Read Types of Clouds on pages 304 – 306 of your textbook

25. Check for understanding
What is humidity? How is it measured?

26. Check for understanding
What is humidity? Humidity is a measure of the amount of water vapor in the air. How is it measured? Humidity is measured using “relative humidity,” which is the percentage of water vapor that is actually in the air compared to the amount of water vapor the air can hold at a particular temperature. Relative humidity can be measured using a psychrometer.

27. How do clouds form? What are the three main types of clouds?
Guided practice
How do clouds form? What are the three main types of clouds?

28. Guided practice
How do clouds form? Clouds form when water vapor in the air condenses to form liquid water or ice crystals. What are the three main types of clouds? The three main types of clouds are cirrus, cumulus, and stratus.

29. Complete Weather 8-1 Independent Practice