The time since 1940 has changed a lot. We finally have a time machine to see it on an interactive map

I was born on a Monday in September at noon and, obeying the tradition of the San Miguel summer, the weather was mild and sunny even though October was just around the corner. I know this because my mother has told me a lot of times, but today I also just confirmed it. And be careful, finding out the weather of a day in the 80s was not a priori as easy as knowing what it was last year: it normally involved resorting to scientific databases or finding paper records, which are already old.

The good news is that there is a free tool, accessible from any browser and moderately intuitive so that anyone can know what the weather was like on any day (and any time!) from today until 1940, from your date of birth to your wedding or a trip. The not so good news is that it is the best test to see how time is changing due to climate change.

His name is Weather Replay and in a few words it works like a meteorological time machine in the form of a weather visualization web application. Behind this website there are two top-level European projects: on the one hand Copernicus Climate Change Serviceintegrated into the EU space program and with the aim of offering rigorous climate data available to everyone. On the other hand, ECMWF, the European Center for Medium-Range Weather Forecasting, the world reference body for numerical weather prediction.

Weather Replay Home Screen

The climate time machine starts in 1940

The first screen says roughly what it does: you choose a date and time, use the box at the bottom left to write a location and from there you can see a 48-hour animation where the atmospheric conditions of that specific moment are reproduced: temperature, wind, precipitation, pressure and a few other variables. Everything is very visual and available in a few seconds, without installing anything or registering.

Layers are a key element to learn more information. Weather Replay

Although there is an initial tutorial that may be interesting to follow, the buttons and their function and the legend are easy to understand and despite its simple appearance, it is quite powerful and with practical options to only have what interests us such as zooming, modifying colors and levels or layers. An especially interesting function is being able to compare the time on two specific dates.

Swipe left and right to see what the weather was like on two days from 1940 to today. Weather Replay

Under the hood of this comprehensive interactive map is ERA5, the ECMWF global atmospheric reanalysis that continuously reconstructs the state of the atmosphere using real data from satellites, sounding balloons, ocean buoys and weather stations with high-resolution numerical models. Thus, it covers the entire Earth with a mesh of about 31 kilometers and 137 vertical layers up to 80 kilometers in altitude. Despite the huge amount of data it handles, the simulations and management are agile thanks to the fact that it is in the cloud

DANA Floods of 2024. Weather Replay

Beyond tinkering and satisfying curiosity, this tool means that anyone has access to 80 years of atmospheric data in an intuitive and graphic way to see with your own eyes how phenomena have evolved such as heat waves, extreme rain events or wind patterns in the regions you know best. In short: that everyone can see climate change. At a teaching or journalistic level, it constitutes a magnificent resource to contextualize meteorology. For example, reproducing how the tragic Valencia DANA of 2024 began.

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Cover | Weather Replay