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Weather patterns
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Weather patterns


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  • 1. Weather Patterns
  • 2. Weather Patterns
    • Constant movement of air and moisture change the atmosphere
    • This is related to the development and movement of air masses
      • Air Mass: large body of air with the same properties as the surface it develops over
  • 3. Air Masses
    • Where the air mass develops will give it it’s characteristics.
    • Over water, the air will be moist and over land it will be dry
  • 4. Pressure Systems
    • Molecules push down from above, creating atmospheric pressure
  • 5. Pressure Systems
      • Variation in atmospheric pressure determines the weather
        • Areas of high pressure = descending colder air
          • Sinking high pressure air makes it more difficult for air to rise and clouds to form
          • High pressure = good weather
          • Low pressure = clouds
  • 6. Pressure Systems
  • 7. Fronts
    • Front: a boundary between two different air masses
      • Storms and precipitation occur here
      • Air in a front will move from high pressure to low pressure
        • When two air masses with different characterizations meet, they do not blend
  • 8. When Air Masses Have Different Characteristics
    • The cold air mass will move under the warm air mass and the warm air will rise and winds begin
    • Winds blow from high pressured air to low pressured air
  • 9. Four Types Of Fronts
    • Warm
      • Develop when a less dense warm air mass slides over departing cold air mass
    • Cold
      • Cold air mass moves under a warm air mass and pushes it along a steep front
      • Move at twice the speed of a warm front
      • Creates a narrow band of violent storms
    • Occluded
      • Result of two cool air masses merging, and forcing warm air between them to rise
      • May cause strong winds and heavy precipitation
    • Stationary
      • Pressure differences cause a warm or cold front to stop moving
        • May stay in the same place for several days
        • Causes light wind and precipitation
  • 10. Severe Weather
    • These types of weather pose a danger to people and animals
      • They include:
        • Blizzards
        • Thunderstorms
        • Tornadoes
        • Hurricanes
  • 11. A Thunderstorm
    • Air speed can reach 89km per hour
    • Occurs inside warm moist air masses and at fronts
    • Downdrafts-
      • Raindrops collide with other droplets and grow larger
      • Heavy raindrops fall, dragging down air
      • This causes downdrafts, which make strong winds
  • 12.
      • Lightning
        • Rapid uplift of air builds electric charge in clouds
        • Currents of opposite electric charge flowing in between regions makes lightning flash
        • Can leap cloud to cloud or cloud to earth
      • Thunder
        • Lightning rapidly heats air around it, the air expands and molecules crash into eachother
          • Can reach 5x the temperature of the surface of the sun
  • 13. Tornadoes
    • Tornado – violent, whirling wind, which moves in a narrow path over land.
    • Wind shear- difference in wind direction and speed
      • Strong updraft will tilt wind shear and produce rotation inside
        • Funnel cloud will appear
        • Can go up to 500km per hour
        • Most occur in United States
  • 14. Hurricane
    • Most powerful storm
    • Hurricane – large, swirling, low pressure system that forms over tropical oceans
      • Turns heat energy in ocean into wind
        • Must be 120km per hour to be classified as hurricane
        • Similar to low pressure systems on land but stronger
  • 15. Section Wrap Up
    • Why do high pressure areas usually have clear skies?
    • Explain how a tornado develops from a thunder storm.
    • How do two fronts form at a low pressure area? Which would bring the most severe weather?