1. 4.2 Weather Patterns
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2. Pressure Systems Air pressure is the force of air on the surface.
High pressure air always moves toward areas of Low Pressure
Hot Air Rises Cold Air Sinks

3. High Pressure System low pressure is on either side of the HP
cold air from above sinks and creates a high pressure system on the ground
low pressure is on either side of the HP
HP moves toward LP and creates wind circulating clockwise
Brings sunny fair weather with light winds.
High Pressure System

4. warm air on the ground forms a low pressure system with high pressure on either side
HP moves toward LP creating counter-clockwise winds
the warm air rises, condenses and forms clouds
Brings stormy weather with strong winds
Low Pressure System

5. Air Masses large bodies of air that have a similar humidity (moisture)
and temperature

6. the air must remain above a high pressure system, known as a “source region” for at least a couple of days
Ex. if an air mass forms over Canada, Canada is considered the source region

7. As the winds begin to move the air mass from it’s source region, it begins to bring the moisture and temperature to a new location

8. Air masses are given a two word name that describes it’s moisture and temperature
Naming Air Masses

10. Moisture/Humidity (1st word)
continental (c)
forms over land – dry
maritime (m)
forms over water –
wet/humid/moist

11. forms in warmer regions, hot Polar – (P) forms in cold regions – cold
Temperature (2nd word)
Tropical (T)
forms in warmer regions, hot
Polar – (P)
forms in cold regions – cold
Arctic – (A)
forms in arctic regions- bitterly cold and dry

13. Weather Fronts
A boundary between two different air masses, resulting in a change of weather
Temperature, humidity, clouds, precipitation, and winds

14. Cold Front
1. cold air mass approaches a warm air mass 2. dense cold air moves under the warm lighter air and forces the warm air to rise 3.tall vertical clouds form which result in stormy weather and colder temperatures

15. A cold front is represented as a blue line with the triangles pointing toward the direction on movement. 

16. Warm Front 1. a warm air mass approaches a cold air mass
2. less dense warm cannot move under the cold air so it slides over the top
3. produces clouds, precipitation, and warmer temperatures

17. A warm front is represented as a red line with half circles pointing toward the direction of movement.

18. Stationary Front
1. a cold and warm air mass meet and neither is strong enough to push ahead
2. it stalls over one location and brings days of precipitation along the front
3. it eventually moves and become a cold or warm front

19. A stationary front is represented as an alternating cold/warm front symbol pointing in the direction of each front.

20. Occluded Front Cold fronts move faster than warm fronts.
2. A fast moving cold front catches up with a slow moving warm front
3. Cold air pushes right through and
pushes warm air out of the way.
4. Usually brings precipitation.
Occluded Front

21. An occluded front is represented as cold and warm front symbols on the same side pointing in the direction of the front