A quarter of a century ago, forecasting the weather by computer had progressed to a stage where it could not only rival the skills of human forecasters, but could also produce accurate predictions for several days ahead. There was, however, one big snag: individual weather services had neither computers big enough to cope with the huge computations nor the scientific expertise to develop the predictive models. The solution was to pool resources.
By 1976, 18 European countries had established the European Centre for Medium Range Weather Forecasts in Reading, England. The centre employs a team of meteorological scientists and runs its mathematical model of the atmosphere on one of the largest computer systems in the world. The forecasts are transmitted daily to the weather services of all the member states
As meteorology progressed into the '90s, it became obvious that computers also held the key to short-range weather forecasting, but the same solution was not ideal. Firstly the model had to be run at regular intervals throughout the day, preferably in each country's central forecasting office, so that "fresh" forecasts for the near future would always be available. And secondly, each country needed to focus on its own vicinity.
The latter constraint arose because, to improve accuracy, the model needed to be run on a much finer grid-scale; the points for which the future state of the atmosphere was to be calculated had to be much closer together. To reduce the total computing power required, therefore, the calculations would be performed only over a relatively small area in each country - a so-called limited area model.
Co-operation of a different kind provided the solution. The weather services of Germany, Switzerland, Italy and Greece combined to form COSMO, the Consortium for Small-Scale Modelling, to produce a short-range forecasting model which could be used by each locally, but developed co-operatively by their combined scientific resources. Likewise France and several other countries produced the Aladin model (Aire Limitee Adaptation Dynamique Developement International). Britain developed its own model, but most of the remaining countries of Europe - the Scandinavian countries, Spain, the Netherlands and Ireland - produced HIRLAM, the High Resolution Limited Area Model. Used in the individual countries, these short-range forecast models incorporate an accurate computer representation of the local topography, which has a very significant effect on local weather.