1. Source Regions and Pressure Systems

2. Air Mass
A large body air where temperature and moisture content are similar throughout.
Air masses form over large land or water masses.

3. Source Region
Moisture content and temperature are determined by the area over which the air mass is formed called a source region.

4. Air masses are designate by a two letter system.

5. The first letter indicates the moisture content.
-Continental forms over continents
- Maritime forms over oceans

6. Continental -
Means land.
A Continental air mass forms over land.

7. Maritime -
Means water.
Maritime air masses form over water.

8. The second letter represents temperature.
- Polar - Cold air masses
- Tropical - Warm air masses

9. Polar
Polar means it forms over the poles.
COLD!

10. Tropical
Form over the tropics (near the equator)
WARM!!

11. Whether an air mass is warm or cold depends on the temperature of the source region.
4 types of air masses.
Tropical – warm air masses that form over the tropics.
Polar – cold air masses that form over the poles.
Maritime – air masses that form over the ocean (very humid)
Continental – form over land – (are dry)

12. Cold Air Mass
There are three polar air masses that influence the weather in the United States.
Continental polar
Maritime polar: over the North Pacific Ocean
Maritime polar: over the North Atlantic ocean

13. Warm Air Masses
There are three warm air masses that influence the weather in the United States.
Maritime tropical: that develops over the Gulf of Mexico
Maritime tropical: that develops over the South Pacific Ocean
Continental tropical

14. Complete the Source Region Map
You have every vocabulary word you need to complete the source region map.
ON YOUR OWN, put the words into practice and complete the map.

16. Pressure Systems

17. High Pressure vs. Low Pressure
Think about your ears popping!
Why do our ears pop?
When do our ears pop?

18. To release pressure!
Air moves in pressure systems very similarly to how the air moves when our ears “pop”!

19. Cold Vs. Warm
Cold air
Warm air

20. Pressure Systems
Go back and think about the convection cells we created for Global Winds…..

22. How does air move?!?
Air moves from an area of high pressure to an area of low pressure .
High Low

23. High Vs. Low Pressure
How will the air move?
How will the air move?

25. Low pressure causes LIFTING
High pressure causes SINKING

26. Low pressure is caused by WARM RISING AIR
High pressure is caused by COLD SINKING AIR
Low pressure is caused by WARM RISING AIR

27. So now we can put it all together!

29. Weather Fronts

30. High and Low Pressure Systems

31. Pressure Systems and Weather
What weather is associated with each pressure system?
Think about high pressure and low pressure and discuss with your neighbor as to what type of weather you may see with each system.

32. High and Low Pressure Systems

33. Pressure System Diagram
On the next page we will put in an illustration.

34. Weather Fronts

35. Weather happens when…
air masses meet but do not mix due to different temperatures and moisture content becomes a front.

36. Fronts
Fronts are the boundary between air masses of different temperature and moisture content.

37. Fronts 4 kinds of fronts: Cold front Warm front Occluded front
Stationary front

38. Cold Front A cold air mass is replacing a warmer air mass.
Shown on a weather map by a blue line with triangles pointing the direction the cool air is moving.

39. Cold Front
Rapidly moving cold air mass runs into a slowly moving warm air mass.
The denser cold air slides under the lighter warm air pushing it upward.
The rising air cools and condenses, forming clouds.
Heavy rain or snow may fall.
If the warm air mass contains only a little water vapor, there may be only cloudy skies.
MAP TAP
Weather Fronts

40. Air gets drier after a cold front moves through
Fronts: Five Types of Fronts
1. Cold Front: The zone where cold air is replacing warmer air
Air gets drier after a cold front moves through
NSF North Mississippi GK-8

41. Cold Front
Cold fronts move quickly and can cause abrupt weather changes including violent thunderstorms
After a cold front passes through, cool, dry air moves in.
Clear skies and cooler temperatures often follow.
MAP TAP
Weather Fronts

42. Warm Front
Warm air mass collides with a slowly moving cooler air mass.
Shown on a weather map by a red line with half circles pointing the direction the warm air is moving.
MAP TAP
Weather Fronts

43. Warm Front
Moving warm air mass collides with a slowly moving cold air mass.
The warm air moves over the denser cold air.
If the warm air is humid, showers and light rain fall along the front where the warm and cold air meet.
If the warm air is dry scattered clouds form.
MAP TAP
Weather Fronts

44. Air gets more humid after a warm front moves through
Fronts: Five Types of Fronts
2. Warm Front: The zone where warm air is replacing colder air
Air gets more humid after a warm front moves through
NSF North Mississippi GK-8

45. Warm Front
Because warm fronts move more slowly than cold fronts, the weather may be rainy or foggy for several days.
After the warm front passes, the weather is likely to be warm and humid.
In winter, warm fronts bring snow.
MAP TAP
Weather Fronts

46. Comparing Warm and Cold Fronts
Cold fronts move faster than warm fronts.
The weather activity in a cold front is often violent and happens directly at the front.
Cold fronts have sudden gusty winds high in the air creating turbulence.
The weather activity in a warm front generally happens before the front passes.
In a warm front the cloud formation is very low often creating situations of poor visibility.
MAP TAP
Weather Fronts

47. Occluded Fronts When a warm front is trapped by 2 cold fronts.
Shown on a weather map by a purple line with alternating triangles and semicircles pointing the direction the front is moving.
MAP TAP
Weather Fronts

48. Occluded Fronts
A warm air mass is caught between two cooler air masses.
The denser cool air masses move underneath the less dense warm air and push it upward.
The temperature near the ground becomes cooler.
MAP TAP
Weather Fronts

49. Occluded Fronts
The warm air mass is cut off, or occluded, from the ground.
As the warm air cools and its water vapor condenses, the weather may turn cloudy and rainy or snowy.
MAP TAP
Weather Fronts

50. Fronts: Five Types of Fronts
4. Occluded Front: Formed when a cold front overtakes a warm front
This occurrence usually results in storms over an area
In U.S., the colder air usually lies to the west
NSF North Mississippi GK-8

51. Stationary Fronts A front that stops moving or is moving very slowly.
Shown on a weather map with alternating red semicircles pointing away from the warm air and blue triangles pointing away from the cold air.
MAP TAP

52. Stationary Fronts
Sometime cold and warm air masses meet, but neither has enough force to move the other.
They meet in a “standoff”
MAP TAP
Weather Fronts

53. Stationary Fronts
Where the warm and cool air meet, water vapor in the air condenses into rain, snow, fog, or clouds.
It may stall over an area and bring many days of clouds and precipitation.
MAP TAP
Weather Fronts

54. Fronts: Five Types of Fronts
3. Stationary Front: When either a cold or warm front stops moving
When the front starts moving again it returns to either being a cold or warm front
NSF North Mississippi GK-8

55. Locate the 4 types of fronts on this weather map.

56. Cold Fronts

57. Warm Front

58. Stationary Front

59. Occluded Front

60. Be a Weather Forecaster
You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F.
Use the map to help you predict whether the temperature in Alabama will increase, decrease, or stay the same. Explain why you think so.
Weather Fronts

61. Be a Weather Forecaster
There is a cold front approaching. The temperatures will probably be cooler behind the front.

62. Be a Weather Forecaster
Of course, meteorologists (weather forecasters) use much more data than fronts and air masses to help them forecast the weather more accurately. But any forecast is just a prediction of what might happen. Even with the best data, weather forecasts can be wrong.
MAP TAP
Weather Fronts