Weather ensemble forecasts from multiple models.
Open-Meteo Ensemble API is a free Weather API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Ensemble weather forecasts from ICON, GFS, ECMWF, GEM and more. Access individual ensemble members for probabilistic forecasting via a free JSON API.
Details from open-meteo.com.

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Data from Personal Weather Stations called senseBoxes
The Open-Meteo Ensemble API is provided by Open-Meteo.com (open-meteo.com). Ensemble weather forecasts from ICON, GFS, ECMWF, GEM and more. Access individual ensemble members for probabilistic forecasting via a free JSON API.
Yes. The Open-Meteo Ensemble API is listed in the Weather category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Open-Meteo Ensemble API requires no authentication, so you can start making requests without signing up.
Yes. The Open-Meteo Ensemble API supports CORS, so front-end JavaScript can call it directly.
Yes. The Open-Meteo Ensemble API is served over HTTPS, so it's safe to use in production.