Excerpt from medium-range high-resolution forecast for 500 hPa geopotential height and 850 hPa temperature.
With the upgrade of the Integrated Forecasting System (IFS) to Cycle 48r1 in June 2023, the horizontal resolution of medium-range ensemble forecasts (ENS) increased from 18 to 9 km, bringing it to the same resolution as the high-resolution forecast (HRES).
The HRES is still produced and disseminated. It is meteorologically equivalent to the ENS 'control', but due to some technical and configuration differences, it does not provide completely identical outputs. The HRES runs for 10 days, while the ENS control runs for 15, and the HRES is disseminated earlier than the full ensemble forecast.
Our aim is to stop using the term ‘high-resolution forecast’, or HRES, as all members of the ensemble are now also at 9 km horizontal resolution.
For the next IFS upgrade, Cycle 49r1, planned for October 2024, the HRES and the ENS control are being made bit identical. Both will run to 15 days for 00 and 12 UTC.
From IFS Cycle 50r1, planned for October 2025, we will stop producing the current ENS control, and the data stream that is currently called the HRES will be called ‘ENS control’ instead. This single, unperturbed forecast will continue to be made available earlier than the ensemble perturbed members, in line with the agreed dissemination schedule.
Implications for users
IFS Cycle 49r1: no necessary changes for users are expected relating to the HRES/ENS control naming. Information will be provided in the coming months on the implementation of this upgrade.
IFS Cycle 50r1: some action will be required on the part of users. Detailed information will be provided with adequate time before the upgrade.