1. Section 1: Thunderstorms
The intensity and duration of thunderstorms depend on the local conditions that create them. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions How do thunderstorms form?
What are the different types of thunderstorms?
What is the life cycle of a thunderstorm?
Thunderstorms
Copyright © McGraw-Hill Education

3. Vocabulary Review New latent heat air-mass thunderstorm
mountain thunderstorm
sea-breeze thunderstorm
frontal thunderstorm
stepped leader
return stroke
Thunderstorms
Copyright © McGraw-Hill Education

4. Overview of Thunderstorms
At any given moment, nearly 2000 thunderstorms are in progress around the world.
Both geography and air mass movements make thunderstorms most common in the southeastern United States.
Copyright © McGraw-Hill Education
Thunderstorms

5. Overview of Thunderstorms
How thunderstorms form
For a thunderstorm to form, three conditions must exist: a source of moisture, lifting of the air mass, and an unstable atmosphere.
Thunderstorms
Copyright © McGraw-Hill Education

6. Overview of Thunderstorms
How thunderstorms form
First, there must be an abundant source of moisture in the lower levels of the atmosphere.
Second, there must be some mechanism for moisture to condense and release its latent heat. This occurs when a warm air mass is lifted into a cooler region of the atmosphere.
Third, if the surrounding air remains cooler than the rising air mass, the unstable conditions can produce clouds that grow upward. This releases more latent heat and allows continued lifting.
Thunderstorms
Copyright © McGraw-Hill Education

7. Overview of Thunderstorms
Limits to thunderstorm growth
Because the rate of condensation diminishes with height, most cumulonimbus clouds are limited to about 12,000 m.
Thunderstorms are also limited by duration and size.
Thunderstorms
Copyright © McGraw-Hill Education

8. Types of Thunderstorms
Thunderstorms are often classified according to the mechanism that causes the air mass that formed them to rise.
There are two main types of thunderstorms: air-mass and frontal.
Thunderstorms
Copyright © McGraw-Hill Education

9. Types of Thunderstorms
Air-mass thunderstorms
When air rises because of unequal heating of Earth’s surface beneath one air mass, the thunderstorm is called an air-mass thunderstorm.
There are two kinds of air-mass thunderstorms.
Thunderstorms
Copyright © McGraw-Hill Education

10. Types of Thunderstorms
Air-mass thunderstorms
Mountain thunderstorms occur when an air mass rises by orographic lifting, which involves air moving up the side of a mountain.
Thunderstorms
Copyright © McGraw-Hill Education

11. Types of Thunderstorms
Air-mass thunderstorms
Sea-breeze thunderstorms are local air-mass thunderstorms that occur because land and water store and release thermal energy differently.
Thunderstorms
Copyright © McGraw-Hill Education

12. Types of Thunderstorms
Air-mass thunderstorms
During the day, the temperature of land increases faster than the temperature of water. At night, conditions are reversed.
Thunderstorms
Copyright © McGraw-Hill Education

13. Types of Thunderstorms
Frontal thunderstorms
Frontal thunderstorms are produced by advancing cold fronts and, more rarely, warm fronts.
Thunderstorms
Copyright © McGraw-Hill Education

14. Thunderstorm Development
A thunderstorm usually has three stages: the cumulus stage, the mature stage, and the dissipation stage. The stages are classified according to the direction the air is moving.
Thunderstorms
Copyright © McGraw-Hill Education

15. Thunderstorm Development
Cumulus stage
In the cumulus stage of a thunderstorm, air starts to rise vertically. This creates updrafts.
Thunderstorms
Copyright © McGraw-Hill Education

16. Thunderstorm Development
Mature stage
In the mature stage, updrafts and downdrafts exist side by side in the cumulonimbus cloud. The updrafts and downdrafts form a convection cell which produces the surface winds associated with thunderstorms.
Thunderstorms
Copyright © McGraw-Hill Education

17. Thunderstorm Development
Dissipation stage
In a thunderstorm, the cool downdrafts spread in all directions when they reach Earth’s surface. This cools the areas from which the storm draws its energy, the updrafts cease, and clouds can no longer form. The storm is then in the dissipation stage.
Thunderstorms
Copyright © McGraw-Hill Education

18. Add link to Animation from p. 347 here.
Thunderstorm Development
Concepts In Motion
FPO
Add link to Animation from p. 347 here.
Thunderstorms
Copyright © McGraw-Hill Education

19. Lightning
Lightning is the transfer of electrical charge caused by the rapid rushes of air in a cumulonimbus cloud.
Friction between the updrafts and downdrafts within a cumulonimbus cloud removes electrons from some of the atoms in the cloud. Atoms that lose electrons become positively charged ions, and atoms that receive the extra electrons become negatively charged ions.
Thunderstorms
Copyright © McGraw-Hill Education

20. Lightning
Friction between the updrafts and downdrafts within a cumulonimbus cloud removes electrons from some of the atoms in the cloud. Atoms that lose electrons become positively charged ions, and atoms that receive the extra electrons become negatively charged ions.
Eventually, the differences in charges break down, and a branched channel of partially charged air, called a stepped leader, is formed between the positive and negative regions.
Thunderstorms
Copyright © McGraw-Hill Education

21. Lightning
When the stepped leader nears the ground, a branched channel of positively charged particles, called the return stroke, rushes upward to meet it and illuminates the connecting channel with about 100 million volts of electricity.
Thunderstorms
Copyright © McGraw-Hill Education

22. Lightning
Thunder
A lightning bolt heats the surrounding air to about 30,000°C, about five times hotter than the surface of the Sun.
The thunder you hear is the sound produced as this superheated air rapidly expands and contracts.
Thunderstorms
Copyright © McGraw-Hill Education

23. Lightning Lightning variations
There are several names given to lightning effects: sheet lightning, heat lightning, spider lightning, ball lightning, blue jets, and red sprites.
Thunderstorms
Copyright © McGraw-Hill Education

24. Lightning Thunderstorm and lightning safety
Each year in the United States, lightning causes about 12,000 wildfires and an average of 300 injuries and 58 deaths to humans.
Thunderstorms
Copyright © McGraw-Hill Education

25. Review Essential Questions Vocabulary How do thunderstorms form?
What are the different types of thunderstorms?
What is the life cycle of a thunderstorm?
Vocabulary
air-mass thunderstorm
mountain thunderstorm
sea-breeze thunderstorm
frontal thunderstorm
stepped leader
return stroke
Thunderstorms
Copyright © McGraw-Hill Education