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An air mass is a large body of air that has similar


									An air mass is a large body of air
that has similar temperature and
moisture properties throughout.
For example, continental polar air masses ,
which originate over the northern plains of
  Canada, transport colder and drier air
     Maritime Tropical Air Masses
              warm temperatures and rich in moisture

•   Maritime tropical air masses originate over the warm waters of the
    tropics and Gulf of Mexico. The northward movement of tropical air
    masses transports warm moist air into the United States, increasing the
    potential for precipitation.
- the boundaries between air
•   Cold Front -a transition zone from warm
       air to cold air
•   The air behind a cold front is noticeably
    colder and drier than the air ahead of it.
•   When a cold front passes through,
    temperatures can drop more than 15 degrees
    within the first hour.
                     Warm Front

•   The frontal zone slopes up and over the colder air mass
    ahead of it. Warm air rides along the front (up and over the
    cold air mass), cooling as it rises, producing clouds and
    precipitation in advance of the surface warm front.
•   Because the lifting is very gradual and steady, generally
    wide spread and light intensity precipitation develops
    ahead of a warm front.
    Think of high pressure air (like in a
    balloon) escaping to a low pressure
          area (like a classroom).

•   Differences in pressure lead to winds.
    Winds change direction due to the
          rotation of the Earth
•   The coriolis effect:
•   A demonstration
          Air Pressure on Earth
•   We don’t feel air pressing on us because the
    pressure in our bodies is about the same as
    the surrounding air.
Air pressure is related to temperature

•   Hot air has lower air pressure
•   Its molecules are moving quickly,
    so they aren’t packed in together
•   The air weighs less and exerts less
•   Cold air has higher pressure
•   Its molecules are packed closely
    together and move more slowly.
•   This also explains why cold air
    tends to sink.
    The biggest influence on the
       Earth’s weather is…

•   …the sun
    The sun doesn’t heat much air

•   Most of the sun’s heat passes through the
    atmosphere and reaches the earth.
•   The earth absorbs the heat and it “radiates”
    back into the atmosphere.
•   That’s one reason why it’s colder at higher
    Cirrus Clouds

              Cirrus Clouds
•   Thin, wispy clouds that usually form above
    18,000 feet
•   Thin because they form in the higher levels
    of the atmosphere where little water vapor
    is present
•   Made of ice crystals
Cirrus Clouds
Cirrus Clouds
Cumulus Clouds
              Cumulus Clouds

•   Form as water vapor condenses in strong, upward
    air currents above the earth's surface
•   These clouds usually have flat bases and lumpy
•   Usually very isolated with large areas of blue sky
    in between the clouds
•   Most cumulus clouds form below 6,000 feet and
    are relatively thin and associated with fair weather
                     Cold Front

•   As the front advances, the colder air lifts the
    warmer air ahead of it (red arrows).
•   The air cools as it rises and the moisture condenses
    to produce clouds and precipitation ahead of and
    along the cold front.
•   Upward motions along a cold front are typically
    more vigorous, producing deeper clouds and more
                     Cumulus Clouds



Cumulus Clouds
Stratus Clouds
             Stratus Clouds:

•   Are thin-layered clouds
•   Are low to the earth’s surface
•   Look like stripes or streaks in the sky
•   Look like a layer of fog that never reaches
    the ground
Cumulonimbus Clouds
       Cumulonimbus Clouds:

•   Are much larger and more vertically
    developed than fair weather cumulus
•   Can easily reach 39,000 feet or higher
•   Are associated with powerful thunderstorms
Cumulonimbus Clouds








Surface Map   Monday 9:00
Rain Gauge

     (inches or

        wind speed
(miles – or kilometers –
                per hour

•   Barometers
    measure air
A modern barometer

 (degrees Celsius
   or Fahrenheit)
    Weathervane or wind vane

•   Show the direction of the wind



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