I don't think that there is SE site for your question.
Web Applications could be the closest site, as the question iscould be about a Google web app(web search), but the scope of this site is about using a web application, not about the data sources per se.
As pointed out on a comment, also a similar question could be on topic on Android Enthusiasts as there are several Android apps that return weather results.
Maybe you could make a related question like where to check the data source of an specific query / result as Google could use several data sources as they love to "personalize" results, i.e. they could use different data sources for different cities due to any criteria that they want to use, like relevance, user rating, costs, A/B testing, etc.
Earth Science has a some way related questions:
- From where do weather radar maps get their data?
- What is the status of meteorological data exchange standards?
Internet of Things also has a some way related question:
- How to ask Multiple questions to Google Home (several of the sample questions are about weather)