Paula McGlamery, age 12, of Tulsa, Okla., for her question:
HOW DO THEY PREDICT THE WEATHER?
A century or so ago, most weather forecasting was based on fairly well educated guesswork. Long range predictions were based on what happened during previous years. Short range predictions were based on what the sky above was like or on signs that may or may not have something to do with the weather. Now we do the job on a more scientific basis. The results are more reliable though still not perfect.
The weather is an airy turmoil, operating on a global scale. And thousands of persons around the world work to keep tabs on its present and possible future behavior. Weather prediction is possible because, as a rule though by no means always, one thing leads to another.
For example, there are general patterns of weather behavior that operate on global and seasonal scale These include the prevailing planetary winds that circle the globe in six fairly orderly belts between the poles and the equator. The behavior of the gaseous air also can be depended upon to obey certain basic rules, governed by density, moisture and temperature.
If this were the whole story, global and local weather predictions would be no trouble at all. However, this neat planetary pattern is constantly upset by the smiling sun in co operation with the earth's geography. The air gets its warmth from the surface, and the sun warms the surface in uneven patches. Mountains, glaciers and oceans share different proportions of their precious warmth with the air.
Hence the large global patterns are continually upset by local disturbances. For example, storm fronts are born locally when conflicting masses of damp or dry, warm or cool air collide in weathery warfare. Such a storm front may be carried by the prevailing winds clear around the globe or challenged by another weather pocket.
Today with the use of pictures and data obtained by weather satellites the weatherman is able to predict weather more accurately. Weather satellites in earth orbit can beam down photographs of storms as they form and predict their path many hours in advance.
Since the weather ignores such items as national boundaries, forecasting relies on reports from thousands of far flung points around the world. Several times a day their reports are sent to centralized bureaus where data from far and near are computed. For example, reports of newborn storms are reported from polar regions and tropical seas. Their paths are watched to predict the possible arrival of blizzards and howling hurricanes.
Forecasting accuracy depends on the co operation of different countries around the world. Nowadays a lot of helpful information also comes from weather satellites that photograph the paths and progress of sunny and stormy events on a global scale.