
Finnish weather, sea, climate and radar observations via open WFS.
FMI Open Data 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.
The majority of the Finnish Meteorological Institute's data is available as open data. The data is in a machine-readable, digital format.
Details from en.ilmatieteenlaitos.fi.

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Weather
Radar-detected hail history for any US address from NOAA NEXRAD Level-III hail detections, by year
The FMI Open Data API is provided by Finnish Meteorological Institute (en.ilmatieteenlaitos.fi). The majority of the Finnish Meteorological Institute's data is available as open data. The data is in a machine-readable, digital format.
Yes. The FMI Open Data 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 FMI Open Data API requires no authentication, so you can start making requests without signing up.
Yes. The FMI Open Data API supports CORS, so front-end JavaScript can call it directly.
Yes. The FMI Open Data API is served over HTTPS, so it's safe to use in production.