Back in early 2026, we announced that we intended to transition from Harmonie 43 (HA43) to Harmonie 46 (HA46) in November. Due to technical challenges and at the request of several major users, we are postponing the transition to a date from mid-January 2027. This will also give users even more time to test the system. It also means that the data stream from Harmonie 43 will remain available for longer.
Retrieving test data
The introduction of HA46 involves a new data format. Some of the test data is now available, and various parties have retrieved this test data from the KNMI Data Platform (KDP). The P1 (NL domain), P3 (EU domain) and P5 packages are available there to help you prepare your systems for and test them with the new GRIB2 data format.
The data streams for packages P1, P3 and P5 can be accessed via these links from the KDP:
Packages P2 and P4 are not yet available.
Technical documentation
We also provide technical documentation. This includes, amongst other things, an explanation of the GRIB2 data format and a description of the contents of the data packages (specifying which parameters are included). In addition, there is an overview of the differences between the GRIB codes used in Harmonie Cy43 (GRIB1) and Harmonie Cy46 (GRIB2).
The verification report for Harmonie Cy46, which describes the model’s performance and the key differences in content compared with the current model version (HA43), can also be found here.
Support available
The testing phase is now in full swing. Many organisations are preparing their systems for the new model output, testing technical interfaces and sharing any findings with us. KNMI is still happy to offer support with any questions you may have about the data, data formats and implementation. To get in touch, please contact your account manager, or alternatively email opendata@knmi.nl or join the KDP Community Slack.
Revised timetable
The timetable has been revised and the transition and aftercare phases have been rescheduled.
The timetable is now as follows:
| Phase | Period | What is happening |
|---|---|---|
| Testing phase | April - December 2026 | You can prepare and test your systems using HA46 test data and provide feedback. |
| Transition phase | Mid. Jan. 2027 | Operational transition to Harmonie 46. Everyone will start using HA46. HA43 will be phased out one month after the transition phase. |
| Follow-up phase | Jan. 2027 – March 2027 | We collect feedback and evaluate the process, internally and with you. |