The prediction of Ice SuperSaturated Regions and persistent contrail formation using the modified ARPEGE weather forecast and comparison with in-flight measurements and observations.

Aviation emissions contribute to climate change, one of the key contributors being contrail cirrus clouds. The importance of the impact is strongly influenced by the conditions in which they form and evolve. 

A condensation trail - or contrail - is composed of ice crystals which form behind the aircraft engine exhaust at high altitudes when local weather conditions are favorable. The formation is also influenced by the engine technology and operating conditions, and by the fuel type. The contrail persists and evolves as long as it remains in an ice supersaturated region - or ISSR-, a local atmospheric air mass characterized by a low temperature and a humidity level that is saturated versus ice. Only persistent contrails are considered as having a potential climate effect.

As part of the SESAR CICONIA project and in order to help the forecasting of ISSRs and hence persistent contrail regions, Météo France has implemented a modification to the cloud scheme of the ARPEGE (Action de Recherche Petite Echelle Grande Echelle) operational numerical weather prediction (NWP) model to enable the representation of ISSRs at cruise altitude. As part of the CICONIA project, Météo France provided Airbus with access to this modified version of ARPEGE to use operationally in forecasting areas where persistent contrails could be formed in flight tests.

During October and November 2025 the temperature and humidity from the modified ARPEGE model was used to forecast areas of potential persistent contrail formation and the test flights were performed in these identified areas. In previous test flights the Global Forecast System (GFS) had been used and was again used for these flight tests as a comparison. 

In-flight humidity and temperature measurements are compared to the ARPEGE forecast by interpolating the weather data along the flight trajectories.  The observation of persistent contrails is compared to their simulation along the trajectories using the Airbus in house model. These results support the verification and validation of the data from the modified ARPEGE model. 

In addition, for a particular day, time and area where persistent contrail coverage was forecast, the in-flight measurements from IAGOS aircraft have also been analysed to confirm where the flights were in ISSRs and if persistent contrails were formed. These results and the associated meteorological parameters were compared to the ARPEGE and GFS forecasts and the ERA5 reanalysis datasets.

The stability of the forecast, which was provided as an hourly forecast for the first 48 hours and then 3 hourly up to 72 hours will be discussed. 

The changes to the ARPEGE model to improve the ISSR forecasts, a short description of the studies and analyses of the results for the selected flights will be presented.