Integrated Forecast System

The Integrated Forecast System (IFS) is a global numerical weather prediction system jointly developed and maintained by the European Centre for Medium-Range Weather Forecasts (ECMWF) based in Reading, England, and Météo-France based in Toulouse. It comprises a spectral atmospheric model with a terrain-following vertical coordinate system coupled to a 4D-Var data assimilation system. In 1997, the IFS became the first operational forecasting system to use 4D-Var. Both ECMWF and Météo-France use the IFS to make operational weather forecasts, but using a different configuration and resolution (the Météo-France configuration is referred to as ARPEGE). It is one of the predominant global medium-range models in general use worldwide; its most prominent rivals in the 6–10 day medium range include the American Global Forecast System (GFS), the Canadian Global Environmental Multiscale Model (GEM and GDPS) and the UK Met Office Unified Model.

The version of the IFS run at ECMWF is often referred to as the "ECMWF" or the "European model" in North America, to distinguish it from the American GFS. ECMWF runs the IFS in several configurations. The highest resolution "HRES" configuration is run every twelve hours out to ten days with a horizontal resolution of 9 km using 137 layers in the vertical. The 51-member ensemble system "ENS" is also run every twelve hours out to 15 days with a horizontal resolution of 18 km and 91 layers in the vertical. Lower resolution versions are run out to 6 weeks and 1 year. All model versions except HRES are coupled to the ocean model NEMO. Many ECMWF member states use ECMWF global forecasts to provide boundary conditions for their own higher resolution, limited domain forecasts. ECMWF forecasts are free to the national weather services of its member states, but a fee is charged to commercial users, while limited operational data (select variables from the HRES and ENS out ten days) is available direct to consumers under the noncommercial Creative Commons license prohibiting derivative works (CC-BY ND NC). In contrast, output from the GFS and GEM/GDPS is freely licensed to all users.

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