Each morning, millions of us turn on our radios and televisions for the weather forecast. Do the cloudy skies mean rain? Will rising temperatures bring a  spell  to melt snow and ice? Once we hear the forecast, we decide what clothes to wear and  weather to carry an umbrella or not.
 From time to time ,though, weather forecasts are obviously incorrect. Yes, though the accuracy of forecasts has improved in recent years, predicting（预测）the weather is a fascinating mixture of art and science.
Predicting the weather is not all hard science. The computers can only give some descriptions of the behavior of the atmosphere（大气） Furthermore, even an accurate forecast for a large area may not take into consideration the effect of local area on the weather. So some degree of art is also necessary.

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