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Weather Forecasting And Air Masses 1

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Weather Forecasting And Air Masses 1

  1. 1. Air Masses, Fronts and Global Wind Patterns Meteorology
  2. 2. Air Masses
  3. 3. Definition: <ul><li>Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. </li></ul><ul><li>Very similar to a balloon. </li></ul>
  4. 4. Continental Arctic (cA): <ul><li>Frigid – record low temperatures </li></ul><ul><li>Dry - very low dew points </li></ul><ul><li>Dense - very high barometric pressure </li></ul><ul><li>Usually originate north of the Arctic Circle </li></ul><ul><ul><li>Siberian Express </li></ul></ul><ul><li>Usually once or twice a winter </li></ul><ul><li>very rarely form during the summer </li></ul><ul><ul><li>because the sun warms the Arctic. </li></ul></ul>
  5. 5. Continental polar (cP): <ul><li>Cold and dry - stable </li></ul><ul><li>Usually originates in NW Territory of Canada </li></ul><ul><li>Influences mainly the northern USA </li></ul><ul><li>Responsible for clear and pleasant weather during the summer </li></ul><ul><li>Usually in winter </li></ul><ul><li>Creates troughs in the polar jet stream </li></ul><ul><li>Lake effect snow in Great Lakes areas </li></ul>
  6. 6. Maritime polar (mP): <ul><li>Cool and moist - unstable </li></ul><ul><li>Originate over N. Atlantic and N. Pacific </li></ul><ul><li>Main Influence - the Pacific Northwest and the Northeast. </li></ul><ul><li>can form any time of the year </li></ul><ul><li>Generally not as cold as cP air masses </li></ul>
  7. 7. Maritime tropical (mT): <ul><li>Warm and very moist – unstable </li></ul><ul><li>Originate in the Gulf of Mexico and the Southern Atlantic Ocean </li></ul><ul><li>Influences the eastern USA </li></ul><ul><li>Most prevalent during summer </li></ul><ul><li>Responsible for hot, humid summer days across the South and the East. </li></ul>
  8. 8. Continental Tropical (cT): <ul><li>Very Hot and very dry – stable aloft </li></ul><ul><li>Originates in Desert Southwest and northern Mexico </li></ul><ul><li>Occurs in the summer, rarely in winter </li></ul><ul><li>Usually keeps the Desert Southwest scorching above 100 o F during summer </li></ul><ul><li>Generally clear skies, hot, low humidity </li></ul>
  9. 9. Source Regions
  10. 11. Reasoning for Tornadoes <ul><li>Orographic Perfection </li></ul><ul><li>Meeting of </li></ul><ul><ul><li>Moist - mT </li></ul></ul><ul><ul><li>Hot - cT </li></ul></ul><ul><ul><li>Cool – cP </li></ul></ul>Rocky Mtn.
  11. 12. Tornado Alley <ul><li>http://www.britannica.com/thunderstorms_tornadoes/video/ocliwea124v4.mov </li></ul>
  12. 13. Fujita Scale (NationalAtlas.com)
  13. 14. Fronts and their symbols
  14. 15. Fronts: <ul><li>Boundary between two air masses </li></ul><ul><li>Characterized by shift in weather </li></ul><ul><ul><li>Cold </li></ul></ul><ul><ul><li>Warm </li></ul></ul><ul><ul><li>Stationary </li></ul></ul><ul><ul><li>Occluded </li></ul></ul>
  15. 16. 5 Characteristics of a Front <ul><li>Sharp temperature changes over a relatively short distance. </li></ul><ul><li>Changes in air moisture content </li></ul><ul><li>Shifts in wind direction </li></ul><ul><li>Pressure changes </li></ul><ul><li>Clouds and precipitation </li></ul>
  16. 18. Cold Fronts <ul><li>Temperature – drops rapidly </li></ul><ul><li>Pressure – rises steadily </li></ul><ul><li>Clouds – Vertical building </li></ul><ul><li>Precipitation – Heavy along front </li></ul><ul><li>Winds – Strong and shifting </li></ul><ul><li>Typically move faster than warm front </li></ul>
  17. 19. Cold Front
  18. 20. (Fozzy) Cold Front
  19. 21. Cold Front
  20. 22. In the summer, cold fronts can trigger: <ul><li>thunderstorms </li></ul><ul><li>large hail </li></ul><ul><li>dangerous winds </li></ul><ul><li>tornadoes </li></ul>
  21. 23. Graphic Depiction!
  22. 24. Warm Fronts <ul><li>Temperature – rises slowly </li></ul><ul><li>Pressure – slight rise, then fall </li></ul><ul><li>Clouds – strato- and cirro- </li></ul><ul><li>Precipitation – long, steady </li></ul><ul><li>Winds – variable and light </li></ul><ul><li>Typically will have affect for days </li></ul>
  23. 25. Warm Front
  24. 26. Warm Front
  25. 27. Warm Front
  26. 28. Effects of warm fronts <ul><li>Slow-moving warm front can mean days of wet weather before warm air </li></ul><ul><li>Sometimes water vapor in warm fronts condense to produce </li></ul><ul><ul><li>rain </li></ul></ul><ul><ul><li>snow </li></ul></ul><ul><ul><li>sleet </li></ul></ul><ul><ul><li>freezing rain </li></ul></ul>
  27. 29. Stationary Front
  28. 30. Stationary Fronts <ul><li>Temperature – stagnent </li></ul><ul><li>Pressure – slightly fluctuates </li></ul><ul><li>Clouds – altocumulus </li></ul><ul><li>Precipitation – none </li></ul><ul><li>Winds – variable and light </li></ul><ul><li>Can last for days weeks </li></ul>
  29. 31. Occluded Front
  30. 32. Occluded Fronts <ul><li>Temperature – </li></ul><ul><ul><li>Warm – gets milder </li></ul></ul><ul><ul><li>Cold – gets colder </li></ul></ul><ul><li>Pressure – </li></ul><ul><ul><li>Warm - slight drop </li></ul></ul><ul><ul><li>Cold – slight rise </li></ul></ul><ul><li>Clouds – cumulus </li></ul><ul><li>Precipitation – steady and light </li></ul><ul><li>Winds – variable and light </li></ul>
  31. 33. Occluded Front
  32. 35. Different Temperatures - Different Pressures Cool Air Warm Air Denser More Pressure Less Dense Less Pressure
  33. 36. Pressure and Air Movement
  34. 37. Pressure Gradient Force <ul><li>Difference in pressure over a given distance---between isobars </li></ul><ul><ul><li>Close together = step pressure gradient </li></ul></ul><ul><ul><ul><li>STRONG winds </li></ul></ul></ul><ul><ul><li>Far apart = gentle pressure gradient </li></ul></ul><ul><ul><ul><li>Light winds </li></ul></ul></ul><ul><li>Just like contour lines </li></ul>
  35. 38. Pressure Gradient Force
  36. 39. Isobaric Maps
  37. 40. Coriolis Effect <ul><li>Apparent force due to the rotation of the Earth (Think Merry-go-round) </li></ul><ul><ul><li>N. Hemisphere  wind turns right </li></ul></ul><ul><ul><li>S. Hemisphere  wind turns left </li></ul></ul><ul><li>Strength depends on latitude and wind speed </li></ul>
  38. 41. Coriolis Effect
  39. 44. Coriolis Effect
  40. 45. Centripetal Force <ul><li>In-ward directed force </li></ul><ul><li>Allows an object to remain in circular motion </li></ul><ul><li>Winds moving around high and low pressure areas </li></ul><ul><ul><li>Clockwise around Highs. </li></ul></ul><ul><ul><li>Counter-clockwise around Lows. </li></ul></ul>
  41. 46. Friction (What a Drag) <ul><li>The resistance to movement </li></ul><ul><li>Surface winds are affected by friction </li></ul><ul><li>Why? Ground resistance: </li></ul><ul><ul><li>trees, mountains, houses, buildings, etc. </li></ul></ul><ul><li>This drag causes winds to blow across pressure gradient at the surface. </li></ul>
  42. 47. Pressures All Together
  43. 48. General Planetary Circulation
  44. 50. Winds <ul><li>Horizontal movements at surface </li></ul><ul><li>Names from WHERE it came from…not where it is going!!! </li></ul>
  45. 51. Around Pressure Cells
  46. 52. Pressure Cells <ul><li>High – In and Up </li></ul><ul><ul><li>Converge at surface </li></ul></ul><ul><ul><li>Ascend in center </li></ul></ul><ul><ul><li>Diverge Aloft </li></ul></ul><ul><li>Low – Down and Out </li></ul><ul><ul><li>Converge aloft </li></ul></ul><ul><ul><li>Descend in center </li></ul></ul><ul><ul><li>Diverge at surface </li></ul></ul>
  47. 53. X-section of Planetary Circulation
  48. 54. January Global Pressure Map January
  49. 55. July Global Pressure Map July
  50. 56. Summer Highs

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