23 March — World Meteorological Day
In a world of increasing weather and climate extremes, it is more important than ever for organisations to work together globally, to help make societies safer, better prepared, and more resilient.

On World Meteorological Day, run by the World Meteorological Organisation (WMO), the European Centre for Medium-Range Weather Forecasts (ECMWF) is joining forces with Météo-France and the Ballon Generali de Paris to highlight the essential role of weather prediction in protecting lives and strengthening climate resilience.

With the theme of this year’s World Meteorological Day being ‘Observing today, protecting tomorrow’, the organisations are uniting to demonstrate how international scientific excellence and national operational expertise benefit society.
It comes after the Ballon Generali de Paris invited the Copernicus Climate Change Service (C3S), and the Copernicus Atmosphere Monitoring Service (CAMS), implemented by ECMWF, to join as a scientific collaborator last spring.

ECMWF receives 800 million observations daily, and 60 million quality-controlled observations are available for use in its models and products every day, drawn from satellite measurements to sea-surface temperature monitoring. These observations are used to create initial conditions for modelling and to simulate how those conditions may play out in a range of scenarios. Using both traditional physics-based modelling and AI-driven models co-developed with Météo-France and other EU partners, this data, which includes temperature, wind and rainfall measurements, produces forecasts on a range of timescales from the medium range (four days to two weeks) through sub-seasonal (up to six weeks) to seasonal (six weeks to a year).

Observational data and modelling systems are essential for weather forecasting as well as understanding and analysing climate change from both a global and regional perspective, from the past to the future.

Meteorological and hydrological services and associated consortia in ECMWF’s Member States, such as Météo-France, use the data and modelling systems, combining them with their own observations and models to produce forecasts, enabling informed, authoritative decisions to be made locally about the best protective or mitigating action to take. Civil protection, aeronautics, agriculture, energy, and the transport and insurance sectors are among those to benefit from these forecasts, as well as the general public.

The new Ballon Generali de Paris highlights three indicators of climate change produced by ECMWF in the framework of the C3S, and it is hoped that the public will become even more interested in learning about the science, technology, and observations that enable us to develop them.

Météo-France has released new data on Ballon Generali: by 2025, the average temperature recorded in France was 2.5 °C above the average value of the pre-industrial era, due to the combined effects of global warming and natural year-to-year variability.
Météo-France analyses climate trends and helps predict the impacts of climate change on both a global and local scale using some of the world’s most advanced climate models. In economic and social sectors that are increasingly sensitive to weather and climate, Météo-France provides local authorities and businesses with meteorological and climate services to help them make the best decisions and develop tailored adaptation strategies.

A Shared Scientific Engine: IFS and ARPEGE
At the heart of the ECMWF–Météo-France collaboration is the Integrated Forecasting System (IFS - ARPEGE) a global numerical weather prediction system jointly developed and maintained by both institutions for the benefit of ECMWF’s 35 Member and Co-operating States.
The system combines advanced atmospheric dynamics, physical modelling, and cutting-edge data assimilation techniques to produce some of the world’s most accurate global forecasts. Because it is co-developed, the scientific innovations and software codebase reflect decades of shared expertise and continuous improvement.

At ECMWF, the operational global system is known as IFS.
IFS underpins the physics-based forecasting and analysis delivered operationally by ECMWF for medium-range, sub-seasonal and seasonal forecast, global atmospheric composition forecasts for CAMS and the global climate reanalysis, ERA5, for CAMS.

At Météo-France, the operational global configuration of the same system is called ARPEGE.
Despite the different names:

• IFS is ECMWF’s global forecasting configuration.
• ARPEGE is Météo-France’s global configuration built on the same IFS-ARPEGE codebase, optimised with a variable-resolution grid to enhance national performance, run quickly after observations are collected, and deliver tailored services.

In practical terms, the same fundamental meteorological engine drives forecasts at both centres, with each institution tailoring configurations to serve their respective missions; global medium-range forecasting at ECMWF and 4-day operational forecasting at Météo-France. Furthermore, the AROME regional weather forecasting model used operationally by Météo-France, uses the same code base in a specific configuration, jointly developed with the 26 partners of the ACCORD consortium.

Celebrating Scientific Cooperation
World Meteorological Day provides an opportunity to celebrate this long-standing partnership and recognise the generations of scientists whose work underpins today’s forecasting capability.

Forecasts That Save Lives
“The societal value of global forecasting is immense and profound in protecting life and property”, said Head of Forecasts Evaluation at ECMWF, Dr Matthieu Chevallier.
“ARPEGE and the IFS along with other regional models across Europe that have stemmed from it, are powerful examples of European scientific cooperation at its best and help ensure that cutting-edge science translates into timely, trusted warnings for our citizens. Our move earlier this month to make the portable version of our forecasting system fully open source, only serves to broaden the opportunity to use these shared assets for maximum benefit for all interested sectors from academia to industry.”

Virginie Schwarz, President and CEO of Météo-France, said:
“International cooperation is essential in meteorology, both for operational forecasting and for research and development. Météo-France works closely with the European Centre for Medium-Range Weather Forecasts (ECMWF), which coordinates European efforts in medium-range numerical weather prediction and supports national meteorological services.”

Both Météo-France and ECMWF are working with the support of a landmark partner, the Ballon Generali de Paris.
Through this platform, Generali supports the visibility and accessibility of high‑quality weather and climate data, helping to bridge scientific observation and public understanding. By illustrating how international scientific cooperation can be shared with society, the Ballon Generali de Paris highlights the role of observation and forecasting in improving the understanding of climate risks.

Simon Blaquière, Head of Generali Climate Lab concludes:
“By relying on the scientific excellence of organisations such as ECMWF and Météo‑France, weather and climate data can be transformed into actionable information, enabling more refined risk assessment at the most local scale and placing prevention at the forefront. This enhanced capacity to anticipate is essential to strengthening long‑term preparedness in the face of intensifying climate risks.”