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Forecasts are computed by several numerical weather models: the European ICON from Germany's DWD, down to a few kilometres of resolution over Europe; the American GFS from NOAA, global but coarser; and the ECMWF IFS, the European Centre's reference model, the most reliable beyond 5 days. Each one splits the atmosphere into a grid and recomputes its state several times a day.
For every town, at its exact coordinates and elevation, Open-Meteo picks the source judged most reliable at that moment — usually the finest model available locally for the first few days, then the ECMWF IFS beyond that. The figure shown is therefore not an average of all models, but the best estimate for that place and that time.
The first 48 hours are the most reliable: accurate enough to plan a day around. Beyond 5 days, the forecast becomes a trend — warmer or cooler, wetter or drier — rather than an exact figure. By day 10 and beyond, let's be honest: it's a general direction, not a precise forecast; the models themselves already disagree significantly at that range.
Near 0°C, the line between rain and snow depends on the exact elevation, the air's humidity and the depth of the cold layer: a difference of a hundred metres can be enough to turn a shower from rain into snow. We show the forecast at each town's actual elevation, but this line remains one of the hardest details to call with certainty, even for official weather services.
The alerts shown on the site come from the official Meteoalarm feed, the European platform that gathers each country's warnings, fed in Canada by Environment Canada. There are three levels — yellow (be aware), orange (be very vigilant) and red (acute danger) — and in case of dangerous weather, Environment Canada always has the final word, never weather-canada.com.
The 'warmer or colder than normal' comparison relies on the 1991–2020 climate normals, computed from the ERA5 reanalysis via Open-Meteo's archive API, for each town individually. These normals are computed once and then updated periodically; a gap of more than 2°C from the month's normal is flagged as notable.
All forecasts are recalculated three times a day, the live block every hour. Data comes from Open-Meteo, published under the open CC BY 4.0 licence; alerts come from Meteoalarm, and normals from the ERA5 reanalysis of Europe's Copernicus programme. We don't alter any of these sources: we simply turn them into a page for every town.