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    Weather Weather

    Weather and our world.

    What is weather?
    The weather is just the state of the atmosphere at any time, including things such as temperature, precipitation, air pressure and cloud cover. Daily changes in the weather are due to winds and storms. Seasonal changes are due to the Earth revolving around the sun.

    Rain

    What causes weather?
    Because the Earth is round and not flat, the Sun's rays don't fall evenly on the land and oceans. The Sun shines more directly near the equator bringing these areas more warmth. However, the polar regions are at such an angle to the Sun that they get little or no sunlight during the winter, causing colder temperatures. These differences in temperature create a restless movement of air and water in great swirling currents to distribute heat energy from the Sun across the planet. When air in one region is warmer than the surrounding air, it becomes less dense and begins to rise, drawing more air in underneath. Elsewhere, cooler denser air sinks, pushing air outward to flow along the surface and complete the cycle.

    weather

    Meteorologists use modern technology to predict the weather all over the world. In ancient times, people could only use the power of observation to tell when seasons changed and what the weather would bring. They could observe the changing patterns of the seasons. This taught them when to plant and when the crops would grow.

    People also observed animals and the growing cycles of plants to predict changes in the weather. They could tell when a rainy season was coming and when it would get cold. They learned to prepare themselves in advance for the winter. People used their senses to see and smell changes in the wather. The migration of animals was also a sign of change. Animals sense changes in weather. They change their behavior according to the weather and can sense when a storm is coming.   Nature gives signs, and humans have to know how to read them (even today!).

    What is a front?
    A front is a boundary between two different air masses, resulting in stormy weather. A front usually is a line of separation between warm and cold air masses.
    front

    http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=20
    How do you identify a front on a surface weather map or by your own weather observations?
    Look for: Sharp temperature changes over a relatively short distance, change in moisture content, rapid shifts in wind direction, pressure changes, clouds and precipitation patterns.

    What is a cold front?
    A cold front is a boundary between two air masses, one cold and the other warm, moving so that the colder air replaces the warmer air. A cold front is represented as a blue line with the teeth pointing toward the direction on movement.

    cold What is a warm front?
    A warm front is a boundary between two air masses, one cool and the other warm, moving so that the warmer air replaces the cooler air. A warm front is represented as a red line with half circles pointing toward the direction on movement.
    warm
    What is a stationary front?
    A stationary front is a boundary between two air masses that more or less doesn’t move, but some stationary fronts can wobble back and forth for several hundred miles a day. A stationary front is represented as an alternating warm and cold front symbol.

    stationary What is a occluded front?
    An occluded front is a combination of two fronts that form when a cold front catches up and overtakes a warm front. An occluded front is represented as a purple line with teeth and half circles.

    occluded What is a trough?
    A trough on a weather map is an elongated area of relatively low pressure. Troughs bring cloudy and rainy weather. A trough is represented by a hash mark line.
    trough