Currently the interactive CDS forms doesn't allow users to perform a regional subselection or an interpolation of the selected data. Regardless of that, both action can be performed using the CDS API keywords area and grid with the same syntax used by ECMWF MARS and Web API, as explained here.

Despite that feature being available via CDS API, users must be aware of the following:


Currently the interactive CDS forms doesn't allow users to select NetCDF as data format for their retrievals. Regardless of that, the value of format keyword in CDS API scripts can be set to "netcdf" to obtain a netCDF version of the archived GRIB data.

Despite that feature being available via CDS API, users must be aware of the following:


The C3S seasonal forecast dataset is currently based on GRIB files archived at ECMWF's MARS archive. This implies in some situations accessing data not available online (on disk) but archived in the tape library.

The way the user combines the data they want to retrieve in one single request can make a huge difference in the performance of the retrieval.