Annoyingly not very well in my experience - they said it was going to rain for the Tomb Sweeping Festival so I stayed at home for the three days - turned out it was sunny and clear for the last two.

In my experience, I would say less reliable.

if the weather forecast says sunshine, bring an umbrella.

I find it not that reliable. Still worth paying attention to for typhoons. One can be sure the weather will suck if a typhoon is near. 

in search for an app, the country of origin of an app does not matter, it is the origin of the data they use. I'll bet you that no american weather forecast providers have actual observations from China, so they rely on data from some government place. E.g. the US has NOAA which many forecasts rely on, there are other sources of US weather data too, but not that many.

About as accurate as their territorial claims on historical precedents.

I would always just type "Urumqi weather" into google each evening and see the result that came at the top of the screen, which, I've just checked, came from the weather channel. It was always pretty accurate, and I'm sure they have details for all medium-or-large Chinese cities.

Also, people would always tell us when rain or snow was expected - especially rain, like we were going to get excited about it. One of the best bits about living in the desert was getting away from bloody rain.

I wouldn't trust local forecasts.

Until they include pollution reports in the weather reports, they have no validity, let alone credibility