Thanks Weok!
Meanwhile, I got it working by following this post: Getting warned when it's going to freeze
It utilizes OpenWeatherMap, which I had as a sensor already, so appreciated that.
But I see that yours is much easier to setup with no need of Python! If I wouldn´t have it up and running already I would definitely now have gone for this one even though I would have to get another weather service up and running for it. It is also able to be used with metric / European values (i.e. Celsius instead of Fahrenheit)?
BR, Jochen