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    This does give meteorologists an advantage ,because they can track weather patterns as they move

    from west to east across the country.

    But you have an advantage,too.You can look at the sky and get your data directly.A meteorologist

    uses a computer forecast that's several hours old to make a local forecast .

    What are you seeing when you look at a cloud？“A picture of what moisture is doing in the ”

    atmosphere“says meteorologist Peter Leavit .There's moisture throughout the atmosphere.Most of the ”

    time you don't see it ,because it's in the form of an invisible gas called water vapor .

    Sometimes,the temperature of the air gets cold enough to cause the water vapor to change to

    liquid water.That's called condensation ,and we see it happen all the time(for example ,when humid

    air from the hower hits the cold glass of a mirror)。When enough water vapor condenses,droplets form

    in the air.These droplets scatter light.A cloud is seen.

    Watching clouds over a day or two tells you a lot more than a single cloud about the weather to

    come.Changes in clouds show changes in the atmosphere.