Aemet
Weather and forecast data from Spain

Weather.
APIXU API is a free Weather API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Get current weather information, historical data and forecasts using weatherstack - a free world weather REST API supporting millions of global locations.
Details from apixu.com.

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Weather and forecast data from Spain
Weather
The APIXU API is provided by Weatherstack (apixu.com). Get current weather information, historical data and forecasts using weatherstack - a free world weather REST API supporting millions of global locations.
Yes. The APIXU 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.
Yes. The APIXU API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the APIXU API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The APIXU API is served over HTTPS, so it's safe to use in production.