Producing a weather forecast

Before computers, the increasing volumes of data from the network of surface observing stations, radiosondes and radar, transmitted by teleprinter, telex and facsimile, were a mixed blessing to forecasters. Much information had to be plotted by hand, and it became difficult for forecasters to comprehend it all.

The final step, the prediction, became a major problem. It seemed that it would never be possible to predict accurately how current weather would evolve. Forecasters who analysed and tracked highs and lows and weather systems hoped that the history of the weather systems would provide a good guide to their future behaviour: yet weather systems movements are irregular-- they can speed up or slow down or change direction, as well as changing their shape, nature and intensity.

Forecasters faced particular challenges in the tropics, where the geostrophic relationship between wind and pressure breaks down and the conventional isobaric weather maps have very limited application. Apart from intense tropical cyclones with very low central pressures, pressure changes are relatively small and there are no well-defined highs and lows. Tropical weather forecasters use different maps, such as streamline charts that indicate wind directions and more readily define areas of convergence and divergence in low latitudes.

Today's forecasters increasingly depend on computer modelling of weather. They must have a thorough understanding of mathematics and physics so that they can understand the mathematical computer models and appreciate their strengths and weaknesses, when considering their forecast.

(above left) Computer plotting of southern hemisphere weather observations

(above right) Australian forecasters are able to choose and display massive amounts of weather data on specialised terminals.