My API key is also working. However, the station info from Weather Underground shows that my Netatmo station is not connected for more than 11 days now.
The Azure link looks very interesting. However, the Azure cloud service will only be free for the first trials and it’s another cloud service that may fail and needs to be maintained.
Netatmo is a widespread affortable weather station and I would prefer a direct OpenSprinkler interface to it. In my opinion there is no really need for a weather service if somebody owns a weather station with an API interface. The Zimmerman algorithm does not rely on weather forecasts! From the Netatmo web interface it is known that all the actual and historic weather data is stored by Netatmo. I think the same data is also available via their API interface.
It may be some effort to provide such an interface, but it may be also a unique selling point for OpenSprinkler.