With such a large amount of data coming from so many different sources, the operational forecaster must find a way to organize this information. This is done by the analysis. This might include drawing weather maps of high and low pressure systems and fronts, or examining satellite and radar information to look for organized cloud and precipitation patterns. Intimately linked to the analysis process is the diagnosis. At this step the forecaster uses a thorough knowledge of physics and meteorology to explain all weather elements over the entire area.
Diagnosis is a vital step toward deciding on the prognosis.
Beyond that time frame, the forecaster has additional tools, mostly in the form of sophisticated computer models, to use as guidance for the forecast. Often, the trick is to use the guidance wisely based on the forecaster's diagnosis. Once a decision has been made on how the weather is likely to evolve, a forecast is written. Forecasters use many different computer models to help them predict changes in the weather. The computer model is not a forecast but rather a guide to the forecaster.