#13 Precipitation & Weather Patterns


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Movement of heat through moisture.

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#13 Precipitation & Weather Patterns

  1. 1. Precipitation Precipitation moves heat vertically within the Atmosphere (more specifically, within the Troposphere) When water evaporates , it becomes part of the surrounding air parcel. All air has water content ( humidity ) in the form of water vapor (droplets so tiny that they are not visible) due to the process of evaporation . As air is heated at the Earth’s surface, parcels of it become less dense and begin to rise (through convection , right?). As this air parcel rises, it encounters colder temperatures. As the air parcel cools, the water vapor begins to condense and turn into water droplets that collect as clouds. When enough water is present, it becomes heavier than the wind currents that hold it up, and it falls as precipitation . Depending on the temperature, precipitation falls as either RAIN, SNOW, SLEET, or HAIL.
  2. 2. 3 Processes Drive Precipitation: #1 Convection (once again) creates the Water Cycle... This process tends to produce precipitation in a given area.
  3. 3. Convection drives weather in TROPICAL REGIONS
  4. 4. #2 Orographic Weather relies on Earth formations to provide lift that moves moisture-laden air upward and eventually producing precipitation. MOUNTAINS are the mechanism that provide LIFT in Orographic weather patterns
  5. 5. OROGRAPHIC weather patterns in areas with which you are familiar... The Cascades in the Pacific Northwest The Sierra Nevada Range in California Notice how a RAIN SHADOW is created...
  6. 6. #3 Frontal Boundaries Warmer air is forced up and over cooler, denser air at the surface, again cooling, condensing and causing precipitation
  7. 7. Masses of Air settle in locations and in a short time take on the qualities of the region -- Cold, Wet, Hot or Dry These air masses are set into motion by pressure differences that build up in the atmosphere. Air piling up in one area creates high pressure, pulling air from another area, leaving low pressure. Air then begins to circulate around pressure centers, setting these air masses into motion.
  8. 8. When an air mass of a certain temperature and moisture content comes into contact with an air mass of differing quality, a Frontal Boundary is formed and surface air is lifted -- without the aid of convection or orography . Warm air that overrides cold air already in place produces different layers of clouds and varying levels of precipitation over a relatively longer period of time. When cold air advances on warmer air in place, the warmer air is bulldozed up into the atmosphere rather quickly, causing more intense showers and storms.
  9. 9. Air Masses, Pressure Systems and Frontal Boundaries cause the greatest effect on Weather in Temperate Zones
  10. 10. Other Influences on Climate and the Distribution of Heat Additional influences Large desert areas Lakes Forests Coastal vs continental mountain ranges Tall buildings and concrete Nearby Bodies of Water – large bodies of water absorb and disperse heat much differently than land areas with can dramatically affect temperatures over land in proximity to water. Coastal areas are also affected by nearby oceans, generally having warm and humid climates. In contrast, in deep continental regions , not much water is available to warm or cool so climates are generally cold and snowy in winter and hot and dry in summer. Elevation – air temperature decreases at a rate of 3.5 degrees per 1000 rise in elevation. Therefore, areas in mid latitudes at high altitude can be cold and snowy.
  11. 11. Climate Change Increasing rapidly because of human/environment interaction Causes ice caps to melt and sea levels to rise Causes more precipitation and flooding in some areas, and prolonged drought in other areas