About a dozen computer models are available to modern weather forecasters, running the gamut from models that produce detailed local forecasts for just the next few hours to global models that forecast out two weeks. The National Weather Service runs several computer models daily, and weather bureaus from Canada and the United Kingdom, as well as some universities and private companies, have quality computer models too.

Meteorologists compare forecasts from the various models to see which are doing the best job in each situation, and then apply their experience to evaluate the usefulness of the computer guidance. The various models usually agree in a general sense, but differ in the details. Forecasters often disagree on which model to believe, if any, helping to explain why you sometimes hear different forecasts from different sources. So far, human forecasters have been able to improve on the accuracy of computer forecasts, and a forecaster who relies completely on computer guidance will never compensate for the times when the models perform poorly.

Check out some links to the various computer models. It's a great way to get a feel for what an operational meteorologist goes through every day trying to prepare a forecast.