2. Air Masses
Air masses are large bodies of air where temperature and moisture content are constant throughout.
Moisture content and temperature of a mass are determined by the area over which the air mass forms.
These areas are called source regions.

3. Air Masses that Affect weather in North America

4. Cold Air Masses
Continental polar (cP) forms over northern Canada; brings extremely cold weather during winter; brings cool dry weather during summer
Maritime polar (mP) forms over North Pacific Ocean; cool, very wet; rain and snow during winter; foggy during summer

5. Warm Air Masses There are three warm air masses that affect the U.S.
Maritime tropical (mT) forms over warm water in the Pacific Ocean
Maritime tropical (mT) forms over the Gulf of Mexico and the Atlantic Ocean; brings hot, humid weather and hurricanes and thunderstorms during the summer; In winter, brings mild, cloudy weather
Continental Tropical (cT) forms deserts of Mexico and Southwestern U.S.; brings clear, hot, dry weather during summer

6. Fronts
The boundary between air masses of different densities and different temperatures are called Fronts
There are four different fronts that you need to know : Cold, warm, occluded, and stationary

7. Cold Front Cold Front – cold air moves under warm air
Cold fronts can move quickly and bring thunderstorms, heavy rain, or snow
Cooler weather usually follows a cold front because the air mass behind the cold front is cooler and drier than the air mass replacing it

8. Warm Front Warm Front – warm air moves over cold air
In a warm front, the warm air gradually replaces the cold air
Warm fronts generally brings drizzly rain followed by clear and warm weather.

9. Occluded Front
Occluded Front – warm air mass is caught between two colder air masses. Brings cool temperature and large amounts of rain and snow.

10. Stationary Front
Stationary Front – cold air mass meets warm air mass; remain separate; not enough energy to move warm air above cold air mass; can bring many days of cloudy, wet weather.

11. Front Illustrations
Front Illustrations

12. Air Pressure and Weather
Cyclones
areas in the atmosphere that has lower pressure
Air masses come together ( converge) and rise
Spiral
Causes Stormy weather
Anticyclones
Areas that have high pressure
Air masses move apart ( diverge)
Sinking air denser then surrounding air and pressure is higher
Brings dry, clear weather.

13. Cyclone and Anticylone

14. Quick Check
Air that has similar characteristics and covers a large region is called
a cloud
a(n) air mass
a storm
weather

15. Quick Check Continental Polar air masses form over Canada
the Caribbean Sea
the gulf of Mexico

16. Quick Check Maritime Polar masses form over Canada the Gulf of Mexico
Canada
the Gulf of Mexico
the North Atlantic Ocean  

17. Quick Check Maritime Tropical air masses form over Canada
the North Pacific Ocean
the ocean near the equator

18. Quick Check
Air masses usually move __________ across the United States. a. east b. west c. southwest d. northwest

19. Quick Check
A front forms a. inside an air mass. b. on the surface of an air mass. c. around an air mass. d. between two air masses.

20. Quick Check A cold air mass forces a warm air mass to move downward.
upward.
to the side.
to the back.