Weather Replay: the new European app is like a digital “time machine” for exploring the climate of the past

Brussels – The EU is giving citizens the keys to access Earth’s climate memory and relive every atmospheric change over the last eighty years.  The Copernicus Climate Change Service (C3S), the European Union’s monitoring service managed by the European Centre for Medium-Range Weather Forecasts (ECMWF), has officially launched Weather Replay, a new application that allows users to relive weather conditions from anywhere in the world. The tool allows users to browse hourly weather data from January 1940 up to a few days prior to the present. Furthermore, the application is not just a data archive, but an advanced visualisation tool: thanks to a curated selection of case studies, users can explore significant historical events such as Hurricane Katrina of 2005 or Cyclone Nargis, which struck Myanmar in 2008. In addition to major events, the app allows for personalised searches: for example, you can find out what the weather was like on the day you were born. 

According to Chiara Cagnazzo, Principal Scientist at C3S, the app represents a crucial step towards making climate information more accessible to the media and the general public: “It could be a game-changer for people to explore and understand our data.” 

Weather Replay utilises innovative tools such as the ERA5 reanalysis dataset and the ECMWF’s new ARCO data archive system, enabling complex visualisations to be generated in a matter of seconds. In addition to surface temperatures, experienced users can monitor upper-atmosphere variables, such as the jet stream (the high-altitude wind) at 10 km altitude or geopotential height (the meteorological parameter indicating the altitude at which a given atmospheric pressure value is found) up to 500 hPa. 

The app is not just for contemplation, but for practical use. Among its most advanced features is a comparison tool that allows users to compare two different events side-by-side, such as the historic Scandinavian heatwave of 2018 and the unprecedented one of 2025, to analyse the differences. In addition, the app allows users to download detailed time series and share them via links or images, thereby facilitating the dissemination of verified data in reports and on social media. 

“This technological initiative aims to transform the vast amount of data from the Copernicus programme into intuitive tools for European citizens,” the service’s experts emphasise, adding that “a picture is worth a thousand words, and the best way to understand how our climate is changing is to explore it for yourself.”