1. Chapter 12 Section 8 What is a front?
Objective:
Describe the different kinds of fronts and the weather they cause.

2. Key Terms front: boundary between air masses of different densities
cold front: forward edge of a cold air mass, formed when a cold air mass pushes under a warm air mass
warm front: forward edge of a warm air mass, formed when a warm air mass pushes over a cold air mass

3. Boundaries of Air
In the United States air masses usually travel west to east.
As they move they meet up with other air masses
Individual air masses do not usually mix
A front forms between them
Can be hundreds of kilometers long
Brings changes in weather

4. EXPLAIN:
What do fronts bring?

5. Cold Fronts Cold air is denser than warm air
As a cold front moves through an area, the warm air over a region is pushed upward
Gustly winds are formed
Cold fronts usually bring rain and cloudy skies
Once the cold front passes, the cold air masses move in

6. 2. DESCRIBE:
What kind of weather does a cold front bring?

7. Warm Fronts Warm air: moves more slowly than cold air
rises above cold air
As the warm air rises, it cools
cirrus clouds form high up
precipitation may follow

8. 3. DEFINE:
What is a warm front?

9. Stationary Fronts
Sometimes cold and warm air masses stay put for a while
they do not move
they remain stationary
brings very little change in the weather

10. 4. DEFINE:
What is a stationary front?

11. Occluded Fronts
occluded front: a warm air mass is between two cooler air masses
cooler air masses move beneath the warm air mass and push it up
they come together in the middle and may mix
makes the temperature near the ground cooler
The warm air mass is cut off, or occluded, from the ground
as the warm air cools and its water vapor condenses, the weather often turns cloudy, rainy, or snowy

12. 5. DESCRIBE:
What happens to the weather with an occluded front?

13. 12-8 Classwork What are four kinds of fronts?
How does a cold front form?
What kinds of clouds form when a warm front approaches?
Which kind of front causes very little change in weather?
What kind of weather is common with an occluded front?

14. 12-8 Classwork
6. INFER: A city gets a day of rain and on the next day skies clear. The temperature rises. Which kind of front has passed?
7. INFER: If a city has clear skies and warm temperatures for three days, which kind of front might be keeping the weather the same?