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Weather

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  1. Weather Part 5: Weather Patterns

  2. Air Masses • Large bodies of air • Movement of them causes changes in weather • Cover thousands of square kilometers • Properties fairly uniform • Classified by where they form • Continental – form over continents; relatively dry • Maritime – form over oceans; relatively humid • Polar – cold • Tropical - warm

  3. 4 Major Air Mass Types in USA 1. Maritime tropical – • Forms over ocean near the equator • Warm, moist air • Most commonly affects Eastern states • In summer brings hot, humid weather • In winter brings rain or snow if it encounters a cold air mass

  4. 4 Major Air Mass Types in USA 2. Maritime polar – • Forms over northern Atlantic and northern Pacific oceans • Cool, moist air • Bring cloudy, damp weather to Northeast and Pacific Northwest

  5. 4 Major Air Mass Types in USA 3. Continental tropical – • Hot and very dry • Forms over the desert southwest and Mexico usually during summer • Affects southwest states, plains, and Mississippi valley and can bring record high temperatures

  6. 4 Major Air Mass Types in USA 4. Continental polar – • Cold and dry • Forms over Canada • Often dominant weather in winter • Brings very cold weather • Can also bring clear, pleasant weather to the North in summer

  7. Major Air Mass Types • mT = Maritime Tropical • mP = Maritime Polar • cT = Continental Tropical • cP = Continental Polar cA = Continental Arctic (5th type) Brings extremely cold temperatures with very little moisture, originate north of the arctic circle in winter

  8. Fronts • A front is a boundary that forms when two air masses with different properties meet • Weather is usually unsettled and stormy along a front. 4 types of fronts: • Cold • Warm • Occluded • Stationary

  9. Cold Front • Cold air mass meets and pushes under a warm air mass • Pushes warm air up • Can cause violent storms • Fair, cool weather usually follows a cold front • Generally move northwest to southeast • Can cause a rapid drop in temperature of more than 15° in one hour

  10. Cold Front • Weather symbol: blue triangles point in the direction the cold front is moving http://commons.wikimedia.org/wiki/File:Example_of_a_cold_front.svg

  11. Warm Front • Warm air overtakes cold air and goes over it • Showers followed by hot, humid weather • Noticeably warmer after the front passes • Generally move southwest to northeast

  12. Warm Front • Weather symbol: Red, semicircles pointing in the direction the warm front is moving http://commons.wikimedia.org/wiki/File:Example_of_a_warm_front.svg

  13. Occluded Front • A cold front moves faster than a warm front • When a cold front overtakes a warm front an occluded front forms • Usually form around low pressure areas • At the occluded front the cold air mass meets the cool air mass that was ahead of the warm front • Warm air rises to form cumulonimbus or nimbostratus clouds bringing precipitation

  14. Occluded Front • Weather symbol: purple, alternating triangles and semicircles pointing in the direction the front is moving https://commons.wikimedia.org/wiki/File:Occluded_cyclone.svg http://commons.wikimedia.org/wiki/File:Occlusiefront.png

  15. Stationary Front • When warm air meets cold air and no movement occurs • Rain may fall for many days • Weather Symbol: Alternating blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air