Download Barometer An instrument used by weather forecasters and scientists

Barometer
An instrument used by weather forecasters and scientists to measure air
pressure at any given moment for a particular place. Changes is pressure
in the atmosphere can be used to predict changes in the weather. (See
high and low pressure centers below.)
Dew
Atmospheric moisture that condenses after a warm day and appears
during the night on cool surfaces as small drops. The cool surfaces cause
the water vapor in the air to cool to the point where the water vapor
condenses.
Dew Point
The temperature to which air must be cooled for dew to begin forming,
and water vapor condenses into liquid. If air rises and cools enough to
reach the dew point, then clouds will form.
A high pressure center is represented on a weather map by a blue "H"
and air moves outward from a surface high. With air moving away from
this region, more air must sink from above to replace it. This sinking
motion leads to generally fair skies and no precipitation near the high.
Winds flow clockwise around a high pressure center in the northern
hemisphere (above).
A low pressure ce nte r is an area of low pressure around which the
winds flow counterclockwise in the northern hemisphere. Moving in any
direction away from the "Low" will result in increasing pressure. Air moves
into a low pressure center, which causes air to rise. The rising motion may
produce clouds and precipitation.
A low is represented on a weather map by a red "L". As a low pressure
mass of air approaches, the likelihood of clouds and precipitation
increases.
Evapora tion: The change of water from a liquid into a gas.
Condensation: The change of water from a gas into a liquid.
Precipi tation: The transfer of water from the atmosphere to land. Rain,
snow, hail, sleet, and freezing rain are examples.
Runoff is the movement of landwater to the oceans, mostly in the form
of rivers, lakes, and streams. Even the smallest streams are connected to
larger rivers that carry billions of gallons of water into oceans worldwide.