NOAA aviation weather forecasts and observations.
AviationWeather API is a free Weather API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
How can the Aviation Weather Center help you? AWC provides comprehensive user-friendly aviation weather information.
Details from aviationweather.gov.

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Weather and forecast data from Spain
The AviationWeather API is provided by Aviation Weather Center (aviationweather.gov). How can the Aviation Weather Center help you? AWC provides comprehensive user-friendly aviation weather information.
Yes. The AviationWeather 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 AviationWeather API requires no authentication, so you can start making requests without signing up.
CORS support for the AviationWeather API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The AviationWeather API is served over HTTPS, so it's safe to use in production.