At its 50th session (June 1999), the ECMWF Council approved the implementation of the Boundary Condition Optional Project (BC). The Boundary Conditions Suite was set up in June 2000. It was set up as a separate operational suite to limit the impact on the core ECMWF activities. A data cut-off time of 4 hours was used and 3D-Var analysis and forecasts ran to 90 hours at 00, 06, 12 and 18 UTC , with 3-hourly post-processing.

Dissemination of BC products is to a schedule as defined below. If there are problems for cycles 06 and 18 UTC based and dissemination data are not available six and a half hours after analysis base time, that cycle will be abondoned.

Since the 14. March 2006 Boundary Condition project has been merged with the main deterministic operational forecast suite. In the new configuration, only the 06 and 18 UTC runs are part of the BC suite. For the 00 and 12 UTC runs data are provided from the main deterministic forecast suite. This new configuration has incorporated the following changes:

- All four data assimilation cycles are based on 4D-Var, combining the boundary value forecasts with ECMWF core forecast runs for 00 and 12 UTC, and replacing the 3D-Var (FGAT) analysis cycles for 06 and 18 UTC;

- The data for 00 and 12 UTC are sent with STREAM DA instead of SCDA in the GRIB description; 06 and 18 UTC data have continued to be sent with stream SCDA in the GRIB description.

Even though the input data come from different data streams, DA and SCDA, ECMWF has continued to provide users of BC data with separate dissemination files for all four cycles 00, 06 12 and 18 UTC. Data from the 00 and 12 UTC runs requested for the BC project (specifying USE=BC in the requirements, see bellow) have continued to be delivered in dissemination files with the data stream id 'S'.

16-04-2012