At the end of 2025, we announced the upcoming transition from Harmonie 43 (HA43) to Harmonie 46 (HA46). The preparation phase has taken more time than initially expected. We are now ready to start the testing phase, and you can begin working with the test data.
Test data
The introduction of HA46 includes a new data format, GRIB2. Therefore, we are providing test data that you can download using the button at the bottom of the article for the data packages P1 (NL domain) and P3 (EU domain). These data packages can be used to prepare your systems for and test with the new GRIB2 data format.
Technical documentation
Alongside the test data, you will also find technical documentation containing the following:
- An overview of the variables and products included in the different data packages can be found in the files HA46_P1_contents.txt and HA46_P3_contents.txt. For more information about the parameters, please refer to the parameter descriptions.
- A verification report of Harmonie Cy46 describing the model’s performance and the main content differences compared to the current model version (HA43).
Support available
By making these datasets available, we are starting the testing phase of the transition to Harmonie 46. During this period, you can prepare your systems for the new model output, test technical interfaces, and share any findings with us. KNMI will provide support during this phase for any questions regarding the data, data formats, and implementation. You can contact your account manager with question. Alternatively you can email us at opendata@knmi.nl or join the KDP-community Slack.
Revised schedule
Since the preparation phase took longer than expected, the schedule has been adjusted, and the transition and aftercare phases have been shifted. The operational transition will now take place in October instead of May 2026. The schedule is now as follows:
| Phase | Period | What is happening |
|---|---|---|
| Testing phase | April - September 2026 | You can prepare your systems, test with HA46 test data and provide feedback. Later in the testing phase a data stream will be provided for you to test with. |
| Transition phase | October 2026 | Operational transition to Harmonie 46. Everyone will start working with HA46. HA43 will be discontinued. |
| Aftercare phase | November - December 2026 | We collect feedback and evaluate the process, internally and with you. |