Implications of maintenance of the High-Performance Computer on the HARMONIE datasets from 1st of September to 15th of September

News item | 15-08-2025 | 10:14

KNMI uses and co-develops the weather model HARMONIE. This model is used by European meteorological services such as KNMI, for high-resolution short-range numerical weather forecasts. Since 2024, the new version HARMONIE Cy43 has been in use, produced by the United Weather Centres-West (UWC-West) partnership on a High-Performance Computer (HPC) located in Iceland.

The UWC West HPC will be subject to maintenance from Monday 2025-09-01 until Monday September 2025-09-15. On 5 days between 1 September and 15 September the availability of model data will be reduced during an expected maximum of 8 hours per day. That means on these days there will only be a 3-hourly deterministic run available for a significant partof the day. The exact timing of downtime during these days cannot be determined beforehand and will also depend on the dataset.

Expected impact of the maintenance

Expected impact per type of dataset

Type of dataset	Datasets	Expected impact
Deterministic European domain harmonie_arome_cy43 datasets	harmonie_arome_cy43_l20  harmonie_arome_cy43_p1  harmonie_arome_cy43_p3  harmonie_arome_cy43_p5  uwcw_extra_lv_ha43_nl_2km	During maintenance, every three hours the datasets will be updated with the deterministic model run, instead of every hour.
Ensemble and Caribbean domain harmonie_arome_cy43 datasets	harmonie_arome_cy43_bes  harmonie_arome_cy43_p2a  harmonie_arome_cy43_p2b  harmonie_arome_cy43_p4a  harmonie_arome_cy43_p4b  uwcw_extra_ha43_bess_0p05deg	There will be no data updates during the maintenance.
Datasets that use deterministic HARMONIE-model data as input *	residential_wood_burning_alert  hoogtewinden  QRF-RT-SSh	The datasets will be updated every three hours, as usual.
Datasets that use ensemble HARMONIE-model data as input *	seamless_precipitation_  ensemble_forecast_members	There will be no data updates during the maintenance.

* The list of datasets that use HARMONIE model data as input may be incomplete.

After the maintenance window has finished, the datasets will return to the regular hourly updates.

Expected period of the maintenance

The updates will be on the following dates: 

• Monday 1 September

• Wednesday 3 September

• Monday 8 September

• Wednesday 10 September

• Monday 15 September

Back-up dates planned in case more time is needed: 

• Thursday 4 September

• Thursday 11 September

Important note on the maintenance period

The maintenance will be postponed if weather conditions do not allow for it. Because the HPC is shared between Denmark, Iceland, Ireland and the Netherlands, this means if the weather situation in one of these countries does not allow for downtime, the maintenance will be performed on a later date. This will only be communicated via the developer portal news page and the KDP Community Slack (join the KDP Community Slack).