This is an update of the previously announced plans in relation to the changes to the C3S operational seasonal forecast systems.
- April 2025: The integration of a new forecast system version from DWD (GCFS2.2) has been succesful and this is now the operational contribution to C3S from DWD.
- May 2025: As announced earlier this year, with the release of May 2025 C3S seasonal forecasts we will have one new contributor to C3S seasonal, Australian Bureau of Meteorology, BOM, witht their ACCESS-S2 forecast system, and a new forecast system from one of the current contributors Météo-France System9
The documentation for these forecast systems can be found in the corresponding Knowledge Base pages linked in the previous paragraphs. The hindcast data for these forecast systems will be progressively processed by C3S and made available via the Climate Data Store. The evolution of the available start dates from each forecast system can be monitored in the table “Hindcasts” of our “Summary of available data”
Note that during the processing and archival of the hindcast data for these systems the CDS download forms won’t be updated as frequently as new data is made available. That means some dates can temporarily appear as unavailable in the CDS forms. In those cases, marked with a * close to the 
icon in the “Summary of available data”, data will be temporarily only available via the CDS API.
- July 2025: CMCC contribution will be upgraded to a new forecast system version (SPS4)
The availability of documentation pages and hindcast data for this forecast system will be communicated closer to the switchover date. At least on the 10th of the month prior to that release date, the initial set of hindcast (re-forecast) data will be released in the C3S seasonal forecast datasets on the Climate Data Store.