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Chapter 20: Weather

Chapter 20: Weather. 20.1: Air Masses & Weather 20.2: Fronts & Lows 20.3: Thunderstorms and Tornadoes 20.4: Hurricanes and Winter Storms 20.5: Forecasting Weather. 20.1: Air Masses & Weather.

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Chapter 20: Weather

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  1. Chapter 20: Weather • 20.1: Air Masses & Weather • 20.2: Fronts & Lows • 20.3: Thunderstorms and Tornadoes • 20.4: Hurricanes and Winter Storms • 20.5: Forecasting Weather Chapter 20 Notes

  2. 20.1: Air Masses & Weather Meteorology-The study of processes that govern Earth's atmosphere helps make weather predictions possible. Chapter 20 Notes

  3. 20.1: Air Masses & Weather A. Origin of an Air Mass • Air Mass- Large body of air in the lower troposphere that has similar characteristics throughout. (Can be Big) • Temperature and Humidity is dependant on where the mass comes from. Chapter 20 Notes

  4. 20.1: Air Masses & Weather B. Types of Air Masses • Continental Arctic- Very cold and Dry. Originate in arctic regions. • Continental Polar- Cold and Dry. Can produce some precipitation. Originate inland in Alaska and Canada. Chapter 20 Notes

  5. 20.1: Air Masses & Weather 3. Maritime Polar- Cold and Damp. Originate over the ocean in high latitudes. 4. Maritime Tropical- Warm and Moist. Originates over tropical oceans. 5. Continental Tropical- Hot and dry. Originates over deserts. • Air masses moving across North America. Chapter 20 Notes

  6. 20.1: Air Masses & Weather Chapter 20 Notes

  7. 20.1: Air Masses & Weather Chapter 20 Notes

  8. 20.2: Fronts & Lows • What is a Front? • Front- The boundary that separates opposing air masses. • Can be very large. Usually form at mid-latitudes. • At the front, the less dense air mass is forced to rise over the more dense air. P. 439 Chapter 20 Notes

  9. 20.2: Fronts & Lows B. Kinds of Fronts • Cold Front- The boundary between an advancing cold air mass and the warmer air mass it is displacing. Type of weather depends on type of air mass that is being displaced. • Warm Front- The boundary between warm air displacing cold air. Less dramatic weather changes. • Stationary Front- A front that is not moving forward. • Occluded Front- Cold fronts move twice as fast as warm fronts. If a cold front catches a warm front then precipitation and cloudiness result. Chapter 20 Notes

  10. 20.2: Fronts & Lows • Life Cycle of a Mid-Latitude Low • See page 442. It takes 12-24 hours to pass through the first 2 stages and 3 or more days for the final stage. Chapter 20 Notes

  11. 20.2: Fronts & Lows D. Weather Associated with Pressure Systems • Low pressure fronts indicate bad weather • High pressure usually indicates fair weather. • Warm and Cold Fronts. Chapter 20 Notes

  12. 20.3: Thunderstorms and Tornadoes A. Thunderstorms • Thunderstorm- storms with lightning, thunder, rain, and sometimes hail. • Form Cumulonimbus clouds from warm, moist, unstable air. • Often occur in the afternoon because the air has become unstable. See page 445. Chapter 20 Notes

  13. 20.3: Thunderstorms and Tornadoes 4. Squall Line- Lines ahead of the front. 5. Supercells- Very large single-cell thunderstorms with strong updrafts. Chapter 20 Notes

  14. 20.3: Thunderstorms and Tornadoes B. Lightning • Lightning- Is a discharge of electricity from a thundercloud to ground or another cloud. • Thunder- Is created by the heating of the air surrounding the lightning. Chapter 20 Notes

  15. 20.3: Thunderstorms and Tornadoes • Tornadoes • Tornado- Violently rotating column of air the usually touches the ground. • Tornadoes are unpredictable. • Intensity Scale on page 448. F0-F5 Chapter 20 Notes

  16. 20.3: Thunderstorms and Tornadoes 4. Appears on radar as a hooked shaped area of precipitation. 5. Doppler radar can tell direction of cloud movement. Can predict about 20 mins in advance. Chapter 20 Notes

  17. 20.3: Thunderstorms and Tornadoes D. Storm or Tornado Watches and Warnings • Thunderstorm watch means to watch for a storm. • Thunderstorm warning means that a storm is approaching. • Thunderstorm • Tornado Chapter 20 Notes

  18. 20.4: Hurricanes and Winter Storms A. Hurricane- A large rotating storm of tropical origin that has sustained winds of at least 119 kilometers per hour. • Air pressure in the center (eye) is very low. • Gets energy from the heat of surface ocean water. • The eye wall has the strongest winds and rain. Chapter 20 Notes

  19. 20.4: Hurricanes and Winter Storms B. Hurricane Formation • Needs a supply of warm, moist air for a long period of time. • The release of heat from condensation fuels the hurricane development. • They are usually born between 5° and 20° latitude. Chapter 20 Notes

  20. 20.4: Hurricanes and Winter Storms 4. Tropical Depression- Wind speeds up 61 kph 5. Tropical Storm- Wind speeds 61-119 kph 6. Hurricane-Winds speeds 119 kph and up 7. Hurricane season is June-November • Hurricane. Chapter 20 Notes

  21. 20.4: Hurricanes and Winter Storms • Storm Surge- Results from the strong winds of the eye wall, which blow water into a broad dome and flood coastlines. • The Saffir-Simpson Hurricane Scale rates a hurricane's strength. See page 452. Chapter 20 Notes

  22. 20.4: Hurricanes and Winter Storms D. Winter Storms • It is a mid-latitude-low pressure system occurring in winter. • Blizzard- A winter storm characterized by high winds, low temperatures and falling or blowing snow. Chapter 20 Notes

  23. 20.4: Hurricanes and Winter Storms 3. Winds must exceed 56 kph 4. The temperature must be -7°C or lower 5. The falling snow must reduce visibility. Chapter 20 Notes

  24. 20.5: Forecasting Weather A. Gathering Data • Weather forecasting is very difficult and requires cooperation of several stations around the country. • Satellites provide both visible and infrared images of the entire earth. • Visible satellites allow meteorologists to track wind speed, direction and movement of storms Chapter 20 Notes

  25. 20.5: Forecasting Weather 4. Infrared satellites provide information on storm temperature and precipitation. 5. Radiosondes- Measure temperature, pressure and humidity at different altitudes. (attached to a balloon) 6. Observations can also be made from the ground from weather stations like ours. Chapter 20 Notes

  26. 20.5: Forecasting Weather B. Station Model • See page 457. We will go over this together. Copy top half into notes • This information can be plotted onto a larger map and general trends can be observed. Chapter 20 Notes

  27. 20.5: Forecasting Weather C. Forecasting • Modern day forecasting is based on the data that is collected from weather stations and satellites and entered into computer where computer models are created using special formulas. Chapter 20 Notes

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