The European Centre for Medium-Range Weather Forecasts (ECMWF) is an independent intergovernmental organisation supported by 21 European Member States and 13 cooperating States. At its headquarters in Reading, England, one of the largest supercomputer complexes in Europe is linked by high-speed telecommunication lines to the computer systems of the national weather services of its supporting states. The Centre's computer system contains the world's largest archive of numerical weather prediction data.