Summary

To make a weather forecast, a computer needs a way of estimating the way all the different processes will affect things. These processes include forces (for wind), mixing, radiation (for temperature), advection, and condensation/evaporation (for water vapor). Because many of these processes depend on the horizontal and vertical distribution of things in the atmosphere, a forecast must be made over a wide area of the Earth. The arrangement of grid points and the combination of programs for computing everything are together called a "computer model".

In addition, the computer model must start with an accurate analysis of current conditions. Slight errors in the initial conditions eventually lead to large errors in the forecasts. Forecast errors can therefore be caused by inadequacies in the computer models or inaccuracies in the initial conditions.

In the next module, you will learn about the different types of computer models used by the National Weather Service to forecast the weather.

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