Weather and climate data.
Meteorologisk Institutt API is a free Weather API that requires User-Agent authentication, is served over HTTPS and has unconfirmed CORS support.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Multi-model weather: GFS, ECMWF AIFS/IFS and a 31-member GEFS ensemble, keyless point forecasts
US coastal tides, water levels, currents and meteorological observations
Yes. The Meteorologisk Institutt 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 Meteorologisk Institutt API uses User-Agent authentication, so you need to register for credentials before making requests.
CORS support for the Meteorologisk Institutt API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Meteorologisk Institutt API is served over HTTPS, so it's safe to use in production.