Description of the upgrade

The IFS Cycle 50r1, will bring  major changes to the IFS model and data assimilation system, including among many others:

• New ocean and sea ice models based on NEMO4-SI ³
• Updates of the wave model including: new wave interaction with sea ice and ocean currents and revised wave model bathymetry
• Modified Stochastically Perturbed Parametrisation (SPP) configuration to reduce 10-metre wind spread in the ensemble
• New ocean and sea ice ensemble analysis system & outer loop coupling of ocean/sea-ice
• Reintroduction of stratospheric humidity assimilation from radiosondes up to 60 hPa
• Weak constraint formulation extended to the boundary layer allowing the increased use of T2m observations 

After making the former High-Resolution forecast (ex-HRES) and 'control' member of medium range ensemble forecast (ENS Control) identical in IFS Cycle 49r1, with this model upgrade we will stop running both separately, and produce only one which we refer as the ENS Control.
This change is planned only for IFS medium range forecast and includes both Atmospheric and wave Component of the IFS.

More detailed information will be made available in the coming weeks.

For  any questions, please contact us via the ECMWF Support Portal.

#IFS50r1 #newfcsystem @ECMWF

News

Datasets affected

• ENS Control and ex-HRES (day 1-15)

• ENS (day 1-15)

• ENS Sub-seasonal (day 1-46)

• Control-WAM and ex-HRES-WAM (day 1-15)

• ENS-WAM (day 1-15)

• ENS-WAM Sub-seasonal (day 1-46)

Resolution

There will be no resolution changes in this cycle.

Dissemination schedule

ENS control forecast will be disseminated earlier than currently, in the same schedule of the ex-HRES.

Meteorological content

Assimilation

• New ocean and sea ice ensemble analysis system
• Outer-loop coupled Data Assimilation of ocean and sea-ice
• A weak constraint formulation is extended to the boundary layer which allows for assimilation of many more T2m observations than in previous cycles
• Coupled ocean-atmosphere assimilation of microwave imagers and geostationary infrared data giving increments to ocean and sea-ice as well as upper air
• Unified moisture and temperature analysis in the land data assimilation system
• EDA configuration change: perturbed members' resolution reduction (TL399 to TL255)
• Single precision trajectories in 4DVar
• Introduction of time-varying correction in Weak Constraint 4D-Var with extension to the troposphere
• Reintroduction of stratospheric humidity assimilation from radiosondes up to 60 hPa
• An upgrade of the Radiative Transfer for TOVS (RTTOV) model to version 14, improving the simulation of satellite radiances for assimilation
• Increased number of wave observations being assimilated

Observations

• Upper air observations
  • Allowing specific humidity increments above the tropopause constrained by high quality radiosondes
  • The length of the observation timeslots has been reduced from 30 minutes to 15 minutes, allowing for a more accurate comparison between the model and the observations.  
  • Introduction of wind tracing with-ozone sensitive data
• Ocean observations
  • Activation of in situ temperature/salinity profiles (e.g. ARGO, moored buoy, ship subsurface, mammal, gliders, AXBTs etc)
  • Activation of Sea Level Anomaly (SLA) along-track products from Altika/Cryosat-2/Jason-3/Sentinel-3a/Sentinel-3b

Model

• New ocean and sea ice model  based on NEMO4-SI³ (see more  here), with the updates including:

  • Improved numerical schemes and physical parametrisation
  • Introduction of multi-category sea ice model with prognostic salinity and melt pond dynamics
  • Replacement of the LIM2 sea ice model with the more advanced SI ³   model
  • Climatological sea ice albedo replaced with albedo diagnosed by sea ice model SI³
  • Introduction of the Generic Length Scale (GLS) turbulence scheme for better vertical mixing processes
  • Use of the extended tripolar ORCA grid (eORCA025) (grid extends further towards the South Pole) 
• New ensemble analysis system for ocean and sea ice based on  ORAS6 reanalysis  (see more  here).
  This is used for initialising both the forecasts and the re-forecasts.
  The updates include:
  • Hourly surface forcing  from ERA5 atmospheric reanalysis. This allows much more accurate representation of short-term variability, such as diurnal cycle of sea surface temperature, which is not captured with daily forcing used in earlier systems.
  • Introduction of a flow-dependent background error covariance using ensemble of data assimilations
  • First-time use of variational assimilation of sea surface temperature (SST) with flow-dependent errors.
• Wave model:  
  • New waves and sea ice interaction
    Wave-current interaction (refraction, Dopler shift)
  • Revised wave model bathymetry  
• New glacier parametrisation scheme for ecLand component replaces the previous binary glacier mask with one that accounts for how much of the grid area is covered by ice and uses a four-layer land-ice scheme
• Snow (single layer representation) on sea ice tile – in NWP, reduces the warm bias seen in winter over the ice surface especially in cloud free situations
• Modified Stochastically Perturbed Parametrisation (SPP) configuration to reduce 10-metre wind spread in the ensemble, and related misalignment of wind speed and wave height in perturbed members
• Scale-selective EDA re-centring for ENS perturbed initial conditions to address issues with tropical cyclone initialisation arising from high-resolution EDA outer loop
• The IFS has been modified to account for the effects of solar eclipses using accurate astronomical computations of the sun’s and of the moon’s position
• Model physics:
  • Convection and microphysics changes to improve the propagation of precipitation from ocean across land
  • Physics call reordering with vertical diffusion now called last
  • Reduced vertical diffusion in stable conditions in the stratosphere
• Coupling:
  • Coupling of snow depth and sea ice thickness from the sea ice model to the atmosphere, to allow snow over sea ice and variable ice thickness to be represented in the atmospheric forecast model
  • Partial coupling is switched off to enable fully coupled ocean-atmosphere forecasts, meaning the atmosphere now uses sea surface temperatures (SSTs) directly from the ocean model

Meteorological impact

Medium range

• Better representation of convective precipitation: the revised convection / cloud-microphysics scheme reduces “stationary” convective precipitation, improving inland propagation of rainfall
• Improved tropical upper-air temperature and wind forecasts (at 850 hPa and 250 hPa) by up to ~7%, thanks to updates in aerosol climatology, convection, and physics ordering
• Improvement of temperature and humidity forecasts around the tropopause due to assimilation of stratospheric humidity from radiosondes up to 60 hPa
• Reduction of the known SST warm bias in the Southern Ocean  
• Improved Western Boundary Currents (e.g. Gulf Stream), and related large SST biases. 
• Dynamic evolution of marine variables (e.g. SST/SIC) in the analysis consistent with validity time
• Forecasts of total cloud cover, dewpoint temperature and 10-metre winds over sea improved by 1-2%, largely due to changes in the physics of the model
• Reduced ensemble wind spread at 10 m: the revised Stochastically Perturbed Parametrisation (SPP) scheme yields more realistic ensemble spread, particularly reducing excessive near-surface wind extremes 
• More realistic representation of tropical cyclones at initial and early lead times: the scale-dependent EDA re-centring reduces the appearance of spuriously deformed tropical cyclones, in e.g. mean sea level pressure fields, in individual ENS members

Sub-seasonal range

• Increased forecast skill for quasi-biennial oscillation (QBO) in tropical stratospheric winds — stronger amplitude and more realistic vertical descent
• More realistic stratospheric dynamics 

Evaluation

Interactive scorecards presenting the new cycle performance have been updated: 

• ENS scorecard
• Control (Former HRES) scorecard

Key configuration changes

Atmospheric model

• Starting at IFS Cycle 50r1, ENS Control forecasts will be disseminated and archived in MARS with class=od, stream=oper, type=fc rather than class=od, stream=enfo, type=cf

• There will be  no change  in vertical or  horizontal resolution nor steps of the   Atmospheric mode l
• The 06UTC and 18UTC runs will be archived in MARS with stream=oper instead of stream=scda.

Wave model

• Starting at IFS Cycle 50r1, ENS-WAM Control forecasts will be disseminated and archived in MARS with class=od, stream=wave, type=fc rather than class=od, stream=waef, type=cf
• There will be  no change  in vertical or  horizontal resolution nor steps of the   Wave mode l
• The 06UTC and 18UTC runs will be archived in MARS with stream=wave instead of stream=scwv.

New and changed parameters

New parameters

The table contains the list of parameters expected to be available with the new cycle implementation.

They will be available as part of the test data.
With implementation the parameters will be available in MARS and dissemination.  

Changes to existing parameters 

Additions to 06/18 UTC runs

With the implementation of the IFS Cycle 50r1 we will add parameters currently available only from 00 UTC and 12 UTC runs to the 06 UTC and 18 UTC forecast runs. This includes the following groups of parameters:

• Heat and cold indices, mean radiant temperature and globe temperature, introduced in the IFS Cycle 49r1
• Simulated Satellite Data (all parameters under (parameters under stream=oper, type=ssd)
• Medium range EFI and SOT forecast products (all parameters under stream=enfo, type=efi and stream=enfo, type=sot )
• Ensemble mean parameters (all parameters under stream=enfo, type=em)
• Ensemble spread parameters (all parameters under stream=enfo, type=es)
• Event probabilities parameters (all parameters under stream=enfo, type=ep)
• Cluster means parameters (all parameters under stream=enfo, type=cm)
• Cluster representative parameters (all parameters under stream=enfo, type=cr)

Currently these parameters are available from 00 UTC and 12 UTC runs only.

Tropical cyclone tracks

Tropical cyclone track forecast will be extended to the step 360 for 00 UTC and 12 UTC runs, and to step 144 for the 06 UTC and 18 UTC runs.

Tropical cyclone ensemble products currently contain 52 members (50 perturbed members, 1 control member and 1 ex-HRES).
After the upgrade 51 will remain (50 perturbed members and control forecast).

Ensemble Control forecast

Ensemble forecast

Harmonisation between Control forecast and Ensemble members

Snowmelt was available in Control forecast (ex-HRES), and it will be added to all the ensemble members (stream=enfo, type=pf).

Three hourly accumulated parameters including: 

• Maximum temperature at 2 metres in the last 3 hours
• Minimum temperature at 2 metres in the last 3 hours
• Maximum 10 metre wind gust in the last 3 hours
• Averaged total lightning flash density in the last 3 hours
• Precipitation type (most frequent) in the last 3 hours
• Precipitation type (most severe) in the last 3 hours
• Minimum total precipitation rate in the last 3 hours
• Maximum total precipitation rate in the last 3 hours

are available for every 1-hourly step in the IFS ensemble members (stream=enfo, type=pf) up to step 90, and every 3-hourly step in the Control forecast (stream=oper, type=fc). 
There will be no change for these parameters with the IFS Cycle 50r1 upgrade.

Discontinued parameters

Vegetation fraction difference (vegdiff) will be discontinued, and replaced by the Urban cover.

Technical content

Changes to GRIB encoding

The GRIB model identifiers (generating process identification number) for cycle 50r1 will be changed as follows:

For all parameters in GRIB 2 the Master Tables Version Number will be changed as follows:

Software

To handle the data of Cycle 49r1 we recommend to use the ECMWF software packages 

ecCodes 2.46.0 (minimum version 2.44.2)

On the ATOS HPC, this corresponds to ecmwf-toolbox/2026.02.0.0

Availability of 50r1 test data

Currently the following products are being regularly produced (table is being updated.)

Datasets	MARS	Test ECPDS	Test PREd	Completeness
CTRL (ex HRES)/HRES-WAM 00/06/12/18 UTC				Simulated Satellite Data available in dissemination, but not in MARS archive Tropical Cyclone tracks available in dissemination, but not in MARS archive
ENS/ENS-WAM 00/06/12/18 UTC				EFI/SOT available from 11 Mar 2026  Weather Parameter time series not available yet Tropical Cyclone tracks available in dissemination, but not in MARS archive
ENS/ENS-WAM re-forecast (hindcast) 00 UTC				Available in MARS archive from 21 Feb 2026
ENS/ENS-WAM re-forecast (hindcast) statistics 00 UTC				Available in MARS archive from 13 Mar 2026
ENS/ENS-WAM sub-seasonal 00 UTC				Available in MARS archive from 17 Mar 2026
ENS/ENS-WAM sub-seasonal re-forecast (hindcast) 00 UTC				Available in MARS archive from 09 Mar 2026
ENS sub-seasonal re-forecast (hindcast) statistics 00 UTC				Available in MARS archive from 19 Mar 2026
Open data 00/06/12/18 UTC
WMO Essential and Additional

As usual, any test data provided may not be complete and should not be used commercially or in service provision until the cycle is operational. Test data is provided for technical testing, evaluation and planning purposes only.

Test data in MARS archive

IFS Cycle 50r1 beta test data is available from MARS with E-suite experiment version (expver) 0080 (MARS keywords EXPVER=0080, CLASS=OD): 

Medium range forecast

Atmospheric model

• Control forecast (stream = oper)
• ENS (stream = enfo)
• ENS hindcast (stream = enfh)
• ENS hindcast statistics (stream=efhs)

Wave model

• HRES-WAM (stream = wave)

• ENS-WAM (stream = waef)

• ENS-WAM hindcast (stream = enwh)
• ENS-WAM hindcast statistics (stream = wehs)

Sub-seasonal range forecast

Atmospheric model

• ENS sub-seasonal (stream = eefo) 
• ENS Sub-seasonal hindcasts (stream = eefh)
• ENS Sub-seasonal hindcast statistics (stream = eehs)

Wave model

• ENS_WAM Sub-seasonal (former 'extended') (stream = weef)
• ENS-WAM Sub-seasonal (former 'extended') hindcasts (stream = weeh)

Only users registered with access to MARS are able to access these test data sets. The data should not be used for operational forecasting. 
Please report any problems you find with this data via the ECMWF Support Portal.

Test data in dissemination

We encourage all real-time users to test the IFS 50r1 test data, as the cycle upgrade will bring substantial changes to the data.  IFS Cycle 50r1 test data from the release candidate phase (RCP)   is available through the test dissemination system, starting from the 12Z run on  18 Feb 2026 . Users with access to ECPDS and the Products Requirements Editor (PREd) can login to the test systems here: 

• Test ECPDS:  https://xdiss-monitor.ecmwf.int/

• Test PREd (TPREd):  https://products.ecmwf.int/esuite/requirements/

Users can then trigger the transmission of test products in the usual manner. To receive the test products, users have to have their firewall open to the relevant ECPDS Data Movers:

INTERNET:

• • 136.156.192.0/26
  • 136.156.193.0/26

RMDCN:

• • 136.156.196.0/26
  • 136.156.197.0/26

The IFS Cycle 50r1 test products are available as version number 80 (file names including '*80' as expver) and are intended to be generated shortly behind near real-time. 

If you wish to receive 50r1 test data automatically (regularly), please contact Data Support via the Support Portal . 

Users are strongly advised to check that their software applications and data processing chain can handle the test data.

The new parameters of Cycle 50r1 listed above will become available in dissemination after the implementation date.

If you don't have access to the ECPDS system or (T)PREd or should require any assistance with IFS Cycle 50r1 test dissemination products, please contact us via the Support Portal .

Test data in Open Data Portal

For the users of the open data, test data can be accessed using the following link: https://data.ecmwf.int/forecasts/testdata/