1. Warm up

3. Poirier

4. Meteorology  The study of processes that govern Earth’s atmosphere to help make weather predictions  List as many things as you can think of that affect Earth’s atmosphere and the weather

5. Air Mass  A large body of air in the lower troposphere that has uniform characteristics  Similar temperature  Similar humidity  The interaction of air masses is what causes local weather.

6. North American Air Masses

7. What is a Weather Front?  A Front is the boundary that separates opposing air masses  Common in mid-latitudes (meeting place of polar and tropical air)  Movement – interaction of air based on density (temperature humidity)

8. Cold Front  Cold air mass moving in to replace warmer air  More dense so moves under warmer air  Pushes warmer air up (vertical flow)  Brings  Thunder storms in summer  Less humid air  Change in wind direction  Short period of precipitation  Moves about twice as fast as a warm front

9. Cold Front

10. Warm Front  Warm air moves in and displaces cold air  Less dense so rises up over the cold air  Shallow slope less abrupt weather change  Brings  ~24 hours of increasing clouds starting with cirrus  Overcast  Prolonged period of precipitation  After clearing warmer more humid conditions  Moves about half as fast as a cold front

11. Warm Front

12. Occluded front  When one cold front catches up with previous cold air mass  Push warm air up  Causes cloudiness and precipitation

13. Stationary Front  When a front is no longer moving forward  Warmer air rises, condenses, causes precipitation  Flooding can occur

14.  Materials  hand outs  Scissors  Blue and red crayons  Tape  Turn in question sheet when finished

15. Review Moving Masses Answers

16. Passing of a low-pressure system Low pressure systems can be up to 2,000 km across

17. Low pressure system  Warm front, then cold front  Approach of warm front, clouds increasing from cirrus to nimbostratus, steady rain  Warm front passes, temp and humidity increase, winds shift, skies clear  Approach of cold front, scattered showers or T- storms  Cold front passes, temp and humidity decrease, winds shift again, skies clear

18. Life cycle of a low-pressure system