Important: ERA5 data from July to October 2024 will differ from ERA5T – with July 2024 updated now

To the attention of windPRO online-data user

EMCWF has notified us of an issue with the preliminary ERA5T data from July to October 2024. For the second time since late 2019, the final validated ERA5 data will differ from the preliminary ERA5T data.

The issue is caused by non-representative snow depth observations over the Alps region which have triggered a correction of snow data followed by a re-run of the ERA5/ERA5T reanalysis models by ECMWF. The updated datasets will differ for the months of July to October 2024. Our findings show, that the final ERA5 100m wind data typically differs less than 0.1 m/s as monthly average – with largest differences in the tropics. Differences in individual, instantaneous timestamps are much larger, even up to 10 m/s. Read more in the notification from ECMWF and an analysis from EMD.

EMD will handle this issue by replacing ERA5T data with ERA5 data when it becomes available, and update derived datasets and services relying on ERA5. For windPRO users, ERA5T data for July 2024 has been updated with ERA5 data on 2024-10-23. For users who have already downloaded and used ERA5T data from July to October 2024 – or intend to use ERA5T data for August to October 2024, we recommend the following actions:

• Use proper caution when using the preliminary ERA5T data from July to October 2024, especially if your analysis relies on individual sample values (hourly values)
• Update the preliminary ERA5T data with the final, validated ERA5 data when it becomes available (2-3 months after current date)
• Given updated ERA5 data: Redo any calculations for your project, site or application and analyse any differences between results obtained from the preliminary ERA5T data and the final ERA5 data
• Take action in the event that results for your project/site/application are affected

Data Status as of 2024-10-25:
As of October 25, 2024, the following datasets and services have been updated with new ERA5 July 2024 data:
• ERA5(T) Rectangular Grid
• ERA5 Gaussian (Native) Grid
• EMD Global Wind Energy Index
• EMD Global Solar Energy Index

Please note that the update of the EMD-WRF Mesoscale Datasets for Europe and South Korea will be delayed until approximately November 1, 2024, due to processing time at the EMD “Thor” Supercomputer.

Read more:
• EMD memo on “2024 July to October Wind Speed and Solar Radiation Differences from the ERA5T-ERA5 Alps-Region Snow Depth Issue“
• Follow the status at the ECMWF homepage
• windPRO wiki on ERA5T

Figure: Relative deviation [%] between ERA5 and ERA5T for monthly average wind speeds at 100m (July 2024)