3. Learning Goals SStudents will: learn what air masses are explain what happens when air masses meet learn how pressure systems affect the weather

4. 3-Minute Warm Up  Are these statements true? If not, correct them. 1. Air pressure pushes only in a downward motion. 2. The Coriolis effect influences air motion across Earth’s surface. 3. The changing of a gas to a liquid is evaporation.

5. 3-Minute Warm Up  Are these statements true? If not, correct them. 1. Air pressure pushes only in a downward motion. False-Air pressure pushes in all directions 2. The Coriolis effect influences air motion across the Earth’s surface. True 3. The changing of a gas to a liquid is evaporation. False-The changing of a gas to a liquid is condensation

6. Air masses are large bodies of air  air mass—a large body of air, in which temperature and humidity are nearly the same at different locations but the same altitude.  Covers a large area—thousands of kilometers  Takes on characteristics of land or water below it  Classified (described) by 2 characteristics: moisture temperature

7. Characteristics of air masses  Air masses are named by their characteristics Moisture: ○ continental—dry air, forms over land ○ maritime—moist air, forms over water Temperature: ○ Tropical—warm air from the equator ○ Polar—cool air from the poles Ex: continental tropical air mass—dry and warm air mass maritime polar—moist and cool air mass

8. Weather changes where air masses meet  Air masses move due to global winds and jet streams.  When a new air mass meets and moves into another air mass, the weather changes  front—a boundary between air masses

9. Fronts and Weather  Different fronts produce different types of weather.  3 types of fronts Cold front Warm front Stationary front

10. Cold Fronts  cold front—cold air mass pushes a warm air mass and forces warm air to rise quickly to form tall clouds (cumulonimbus). It brings brief heavy storms. Cold Front

11. Warm Fronts  warm front—warm air mass moves over a mass of denser, colder air. It brings many hours of steady rain or snow. Warm Front

12. Stationary Fronts  stationary front—cold and warm air mass pushes against each other without moving. Stationary Front

13. Weather Systems: High and Low

14. Weather Systems: High and Low  high-pressure system— formed when air sinks down in a high pressure center and spreads out toward low pressure areas in a clockwise motion.  It brings clear skies and calm or gentle breezes.  low-pressure system— formed when air moves counterclockwise around into a low pressure center, then it moves up to higher altitudes.  It brings stormy weather. www.bom.gov.au/lam/Students _Teachers/pressure.shtml