General circulation models of all kinds are also applied operationally to the day-to-day prediction of weather at centres around the world. Modern weather forecasting did not become possible until weather information could be collected, assembled and processed rapidly. The first development came in the mid-nineteenth century with the invention of telegraphy, which permitted immediate analysis of weather data by the drawing of synoptic charts. These were first displayed in Britain at the Great Exhibition of 1851. Severe storm events and loss of life and property prompted the development of weather forecasting in Britain and North America in the 1860s to 1870s. Sequences of weather change were correlated with barometric pressure patterns in both space and time by such workers as Fitzroy and Abercromby, but it was not until later that theoretical models of weather systems were devised, notably the Bjerknes' depression model (see Figure 9.7).
Forecasts are usually referred to as short-range (up to approximately three days), medium-range (up to approximately fourteen days) and long-range (monthly or seasonal) outlooks. For present purposes, the first two can be considered together as their methodology is similar, and because of increasing computing power they are becoming less distinguishable as separate types of forecast.
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