ABSTRACT
Beyond the predictions o f tribal rainm akers, the w eather can be forecast in two distinct ways. O ne is to look at the averages over the last couple o f years and to predict, for any day, cloudiness and rain on the basis o f the past history. A no th er m ethod is to use a large com pu ter that contains a m athem atical m odel o f the processes generating weather. T he
m odel advances from starting conditions, the situation in the world today, to the w eather a few days o r weeks hence. As sim ulation m odels have becom e better, forecasters have becom e bolder: W eather can now be forecast 5 days in advance.
