Extract from the weather journal

Reading a weather map

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Weather maps are the assemblage of weather information gathered by observers. The first to be published in an Australian newspaper appeared in 1877 in the Sydney Morning Herald. Today they are ubiquitous, appearing in newspapers, on the internet and on television.

Isobars - often the only notation on weather maps - are lines of equal air pressure at sea level. Wind flow is closely related to the orientation and spacing of the isobars. Winds blow anticlockwise around high-pressure centres and clockwise around low-pressure centres. The closer the isobars are together, the higher the wind speed. Wind flows around low-pressure systems tend to converge, causing the air to rise. Wind flows around high-pressure systems tend to diverge, causing the air to fall.