1. Bell work
How would you describe the air you are breathing right now? Is it warm or cool? Humid or dry? Is it stale, sweet, or salty? The air you are breathing right now was hundreds of miles away yesterday. Do you know how or why air moves from one place to another?

2. Fronts

3. Describe the four major types of fronts.
Objectives
Identify the four kinds of air masses that influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.

4. Air Masses
Changes in weather are caused by the movement and interaction of air masses.
An air mass is a large body of air where temperature and moisture content are similar throughout.
Air masses are characterized by their moisture content and temperature.

5. Air Masses
The moisture content and temperature of an air mass are determined by the area over which the air mass forms.
These areas are called source regions.
There are many types of air masses, each of which is associated with a particular source region.

6. The characteristics of these air masses are represented on maps by a two-letter symbol.
The first letter indicates the moisture content that is characteristic of the air mass.
The second letter represents the temperature that is characteristic of the air mass.
Air Masses

7. Air Mass Symbols M= Maritime, forms over the water; wet
C= Continental, forms over land; dry
T= Tropical, forms near the equator; warm
P= polar, forms near the poles; cold
mT=wet and warm
mP=wet and cold
cT=dry and warm
cP=dry and cold

8. Fronts
The area in which two types of air masses meet is called a front.
The four kinds of fronts—cold fronts, warm fronts, occluded fronts, and stationary fronts

9. Describe the four major types of fronts.
Objectives
Identify the four kinds of air masses that influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.

10. Cold Front Cold dense air pushes warm air out of the way
Cold fronts move very quickly and bring short periods of rain/thunderstorms
Lower temperatures are behind the front
SYMBOL – the direction of the “arrows” points towards the direction the front is MOVING

12. Cold Front:
Warm air is abruptly pushed upward, cooling, condensing moisture into cumulus or cumulonimbus clouds
                                                                              

13. Cold Front Notice how steep the angle is between the two air masses
Typically brings sudden, heavy rains and storms

15. Describe the four major types of fronts.
Objectives
Identify the four kinds of air masses that influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.

16. Warm Front
Warm air moves up the cold front as it slowly displaces the cold air
Warm fronts move slowly, and bring many days of steady precipitation
Higher temperatures are behind the front
SYMBOL – direction of “half-moons” is the direction the front is moving

18. Warm Front
WARM FRONT: when a warm air mass moves into a colder,denser air mass.
Warm air rides up and over the colder air
Notice the angle of slope between the two air masses.
                                                                              

19. Warm Front
The weather during a WARM FRONT starts with cirrus clouds about hours before the rain begins
Cirrus clouds are “at the front of the front”

20. Warm Front
As more warm air is pushed upward, more moisture condenses forming cirrostratus clouds

21. Warm Front
As warm more warm air is pushed up, heavier clouds form mid-way up over the cold air
Altostratus and stratus

22. Warm Front The final cloud type in a warm front is the nimbostratus
“nimbo” = “rain”

23. Warm front: rain or snow is steady over several hours or days

25. Describe the four major types of fronts.
Objectives
Identify the four kinds of air masses that influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.

26. Occluded Fronts
An occluded front forms when a warm air mass is caught between two colder air masses.
The coldest air mass moves under and pushes up the warm air mass.
The coldest air mass then moves forward until it meets a cold air mass that is warmer and less dense.

27. Occluded Fronts
The colder of these two air masses moves under and pushes up the warmer air mass.
Sometimes, though, the two colder air masses mix. An occluded front has cool temperatures and large amounts of rain and snow.

29. Stationary Front
The air from the warm front and cold front meet, but do not move
These fronts have the same weather as warm fronts
SYMBOL – warm and cold fronts are moving in opposite directions, thus making a stationary condition

30. Stationary front
A stationary front forms when a cold air mass meets a warm air mass.
Both air masses do not have enough force to lift the warm air mass over the cold air mass.
The two air masses remain separated.
A stationary front often brings many days of cloudy, wet weather.

32. Describe the four major types of fronts.
Objectives
Identify the four kinds of air masses that influence weather in the United States.
Describe the four major types of fronts.
Explain how fronts cause weather changes.