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Chapter 20. Weather Patterns. This Week’s Weather – 5/4/14. Section 1: Air Masses. Changes in weather patterns are caused by the movement of air masses An air mass is a large body of air with similar temperatures and amounts of moisture at a given altitude

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Chapter 20

Chapter 20

Weather Patterns



Section 1 air masses
Section 1: Air Masses

  • Changes in weather patterns are caused by the movement of air masses

    • An air mass is a large body of air with similar temperatures and amounts of moisture at a given altitude

    • Weather inside the area with the air mass will be different from weather outside of the air mass

    • As it moves, the characteristics of the air mass change and so does the weather in the area that the mass moves over


Types of air masses
Types of air masses

  • Air masses are classified by their temperature and the area where they form

    • Polar air masses are cold

    • Tropical air masses are warm

    • Continental air masses form over land

    • Maritime air masses form over water


Types of air masses1
Types of Air Masses

  • There are 4 basic types of air masses

    • Continental polar air mass is dry and cool

    • Continental tropical air mass is dry and warm

    • Maritime polar air mass is wet and very cold

    • Maritime tropical air mass is wet and hot

  • Most of the weather in the eastern United States is affected by continental polar and maritime tropical air masses


Section 2 fronts
Section 2: Fronts

  • A front is a boundary that forms when two air masses meet

    • A warm front forms when warm air moves into an area formerly covered by cool air

      • Brings precipitation and warmer weather

    • A cold from forms when cold air moves into an area formerly covered by warm air

      • Cold fronts bring more violent, windy weather and leave clear skies when they pass

    • Stationary fronts form when cold and warm air masses move next to each other

      • Stationary fronts bring light precipitation

    • Occluded fronts form when a cold air mass over takes a warm air mass

      • Precipitation forms when warm air is forced upward






Cyclones
Cyclones

  • Middle latitude cyclones are large centers of low pressure that travel from west to east and cause stormy weather

    • A cold front moves toward a warm front, forcing warm air up

    • The cold front merges with the warm front forming an occluded front that drops heavy rains

    • Occluded fronts move slowly causing several days of light rain



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